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[openldap] / libraries / liblmdb / mdb.c

/** @file mdb.c
 *      @brief Lightning memory-mapped database library
 *
 *      A Btree-based database management library modeled loosely on the
 *      BerkeleyDB API, but much simplified.
 */
/*
 * Copyright 2011-2014 Howard Chu, Symas Corp.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted only as authorized by the OpenLDAP
 * Public License.
 *
 * A copy of this license is available in the file LICENSE in the
 * top-level directory of the distribution or, alternatively, at
 * <http://www.OpenLDAP.org/license.html>.
 *
 * This code is derived from btree.c written by Martin Hedenfalk.
 *
 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
#ifndef _GNU_SOURCE
#define _GNU_SOURCE 1
#endif
#ifdef _WIN32
#include <malloc.h>
#include <windows.h>
/** getpid() returns int; MinGW defines pid_t but MinGW64 typedefs it
 *  as int64 which is wrong. MSVC doesn't define it at all, so just
 *  don't use it.
 */
#define MDB_PID_T       int
#define MDB_THR_T       DWORD
#include <sys/types.h>
#include <sys/stat.h>
#ifdef __GNUC__
# include <sys/param.h>
#else
# define LITTLE_ENDIAN  1234
# define BIG_ENDIAN     4321
# define BYTE_ORDER     LITTLE_ENDIAN
# ifndef SSIZE_MAX
#  define SSIZE_MAX     INT_MAX
# endif
#endif
#else
#include <sys/types.h>
#include <sys/stat.h>
#define MDB_PID_T       pid_t
#define MDB_THR_T       pthread_t
#include <sys/param.h>
#include <sys/uio.h>
#include <sys/mman.h>
#ifdef HAVE_SYS_FILE_H
#include <sys/file.h>
#endif
#include <fcntl.h>
#endif

#if defined(__mips) && defined(__linux)
/* MIPS has cache coherency issues, requires explicit cache control */
#include <asm/cachectl.h>
extern int cacheflush(char *addr, int nbytes, int cache);
#define CACHEFLUSH(addr, bytes, cache)  cacheflush(addr, bytes, cache)
#else
#define CACHEFLUSH(addr, bytes, cache)
#endif


#include <errno.h>
#include <limits.h>
#include <stddef.h>
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#if defined(__sun)
/* Most platforms have posix_memalign, older may only have memalign */
#define HAVE_MEMALIGN   1
#include <malloc.h>
#endif

#if !(defined(BYTE_ORDER) || defined(__BYTE_ORDER))
#include <netinet/in.h>
#include <resolv.h>     /* defines BYTE_ORDER on HPUX and Solaris */
#endif

#if defined(__APPLE__) || defined (BSD)
# define MDB_USE_POSIX_SEM      1
# define MDB_FDATASYNC          fsync
#elif defined(ANDROID)
# define MDB_FDATASYNC          fsync
#endif

#ifndef _WIN32
#include <pthread.h>
#ifdef MDB_USE_POSIX_SEM
# define MDB_USE_HASH           1
#include <semaphore.h>
#endif
#endif

#ifdef USE_VALGRIND
#include <valgrind/memcheck.h>
#define VGMEMP_CREATE(h,r,z)    VALGRIND_CREATE_MEMPOOL(h,r,z)
#define VGMEMP_ALLOC(h,a,s) VALGRIND_MEMPOOL_ALLOC(h,a,s)
#define VGMEMP_FREE(h,a) VALGRIND_MEMPOOL_FREE(h,a)
#define VGMEMP_DESTROY(h)       VALGRIND_DESTROY_MEMPOOL(h)
#define VGMEMP_DEFINED(a,s)     VALGRIND_MAKE_MEM_DEFINED(a,s)
#else
#define VGMEMP_CREATE(h,r,z)
#define VGMEMP_ALLOC(h,a,s)
#define VGMEMP_FREE(h,a)
#define VGMEMP_DESTROY(h)
#define VGMEMP_DEFINED(a,s)
#endif

#ifndef BYTE_ORDER
# if (defined(_LITTLE_ENDIAN) || defined(_BIG_ENDIAN)) && !(defined(_LITTLE_ENDIAN) && defined(_BIG_ENDIAN))
/* Solaris just defines one or the other */
#  define LITTLE_ENDIAN 1234
#  define BIG_ENDIAN    4321
#  ifdef _LITTLE_ENDIAN
#   define BYTE_ORDER  LITTLE_ENDIAN
#  else
#   define BYTE_ORDER  BIG_ENDIAN
#  endif
# else
#  define BYTE_ORDER   __BYTE_ORDER
# endif
#endif

#ifndef LITTLE_ENDIAN
#define LITTLE_ENDIAN   __LITTLE_ENDIAN
#endif
#ifndef BIG_ENDIAN
#define BIG_ENDIAN      __BIG_ENDIAN
#endif

#if defined(__i386) || defined(__x86_64) || defined(_M_IX86)
#define MISALIGNED_OK   1
#endif

#include "lmdb.h"
#include "midl.h"

#if (BYTE_ORDER == LITTLE_ENDIAN) == (BYTE_ORDER == BIG_ENDIAN)
# error "Unknown or unsupported endianness (BYTE_ORDER)"
#elif (-6 & 5) || CHAR_BIT != 8 || UINT_MAX < 0xffffffff || ULONG_MAX % 0xFFFF
# error "Two's complement, reasonably sized integer types, please"
#endif

#ifdef __GNUC__
/** Put infrequently used env functions in separate section */
# ifdef __APPLE__
#  define       ESECT   __attribute__ ((section("__TEXT,text_env")))
# else
#  define       ESECT   __attribute__ ((section("text_env")))
# endif
#else
#define ESECT
#endif

/** @defgroup internal  LMDB Internals
 *      @{
 */
/** @defgroup compat    Compatibility Macros
 *      A bunch of macros to minimize the amount of platform-specific ifdefs
 *      needed throughout the rest of the code. When the features this library
 *      needs are similar enough to POSIX to be hidden in a one-or-two line
 *      replacement, this macro approach is used.
 *      @{
 */

        /** Features under development */
#ifndef MDB_DEVEL
#define MDB_DEVEL 0
#endif

        /** Wrapper around __func__, which is a C99 feature */
#if __STDC_VERSION__ >= 199901L
# define mdb_func_      __func__
#elif __GNUC__ >= 2 || _MSC_VER >= 1300
# define mdb_func_      __FUNCTION__
#else
/* If a debug message says <mdb_unknown>(), update the #if statements above */
# define mdb_func_      "<mdb_unknown>"
#endif

#ifdef _WIN32
#define MDB_USE_HASH    1
#define MDB_PIDLOCK     0
#define THREAD_RET      DWORD
#define pthread_t       HANDLE
#define pthread_mutex_t HANDLE
#define pthread_cond_t  HANDLE
#define pthread_key_t   DWORD
#define pthread_self()  GetCurrentThreadId()
#define pthread_key_create(x,y) \
        ((*(x) = TlsAlloc()) == TLS_OUT_OF_INDEXES ? ErrCode() : 0)
#define pthread_key_delete(x)   TlsFree(x)
#define pthread_getspecific(x)  TlsGetValue(x)
#define pthread_setspecific(x,y)        (TlsSetValue(x,y) ? 0 : ErrCode())
#define pthread_mutex_unlock(x) ReleaseMutex(*x)
#define pthread_mutex_lock(x)   WaitForSingleObject(*x, INFINITE)
#define pthread_cond_signal(x)  SetEvent(*x)
#define pthread_cond_wait(cond,mutex)   do{SignalObjectAndWait(*mutex, *cond, INFINITE, FALSE); WaitForSingleObject(*mutex, INFINITE);}while(0)
#define THREAD_CREATE(thr,start,arg)    thr=CreateThread(NULL,0,start,arg,0,NULL)
#define THREAD_FINISH(thr)      WaitForSingleObject(thr, INFINITE)
#define LOCK_MUTEX_R(env)       pthread_mutex_lock(&(env)->me_rmutex)
#define UNLOCK_MUTEX_R(env)     pthread_mutex_unlock(&(env)->me_rmutex)
#define LOCK_MUTEX_W(env)       pthread_mutex_lock(&(env)->me_wmutex)
#define UNLOCK_MUTEX_W(env)     pthread_mutex_unlock(&(env)->me_wmutex)
#define getpid()        GetCurrentProcessId()
#define MDB_FDATASYNC(fd)       (!FlushFileBuffers(fd))
#define MDB_MSYNC(addr,len,flags)       (!FlushViewOfFile(addr,len))
#define ErrCode()       GetLastError()
#define GET_PAGESIZE(x) {SYSTEM_INFO si; GetSystemInfo(&si); (x) = si.dwPageSize;}
#define close(fd)       (CloseHandle(fd) ? 0 : -1)
#define munmap(ptr,len) UnmapViewOfFile(ptr)
#ifdef PROCESS_QUERY_LIMITED_INFORMATION
#define MDB_PROCESS_QUERY_LIMITED_INFORMATION PROCESS_QUERY_LIMITED_INFORMATION
#else
#define MDB_PROCESS_QUERY_LIMITED_INFORMATION 0x1000
#endif
#define Z       "I"
#else
#define THREAD_RET      void *
#define THREAD_CREATE(thr,start,arg)    pthread_create(&thr,NULL,start,arg)
#define THREAD_FINISH(thr)      pthread_join(thr,NULL)
#define Z       "z"                     /**< printf format modifier for size_t */

        /** For MDB_LOCK_FORMAT: True if readers take a pid lock in the lockfile */
#define MDB_PIDLOCK                     1

#ifdef MDB_USE_POSIX_SEM

#define LOCK_MUTEX_R(env)       mdb_sem_wait((env)->me_rmutex)
#define UNLOCK_MUTEX_R(env)     sem_post((env)->me_rmutex)
#define LOCK_MUTEX_W(env)       mdb_sem_wait((env)->me_wmutex)
#define UNLOCK_MUTEX_W(env)     sem_post((env)->me_wmutex)

static int
mdb_sem_wait(sem_t *sem)
{
   int rc;
   while ((rc = sem_wait(sem)) && (rc = errno) == EINTR) ;
   return rc;
}

#else
        /** Lock the reader mutex.
         */
#define LOCK_MUTEX_R(env)       pthread_mutex_lock(&(env)->me_txns->mti_mutex)
        /** Unlock the reader mutex.
         */
#define UNLOCK_MUTEX_R(env)     pthread_mutex_unlock(&(env)->me_txns->mti_mutex)

        /** Lock the writer mutex.
         *      Only a single write transaction is allowed at a time. Other writers
         *      will block waiting for this mutex.
         */
#define LOCK_MUTEX_W(env)       pthread_mutex_lock(&(env)->me_txns->mti_wmutex)
        /** Unlock the writer mutex.
         */
#define UNLOCK_MUTEX_W(env)     pthread_mutex_unlock(&(env)->me_txns->mti_wmutex)
#endif  /* MDB_USE_POSIX_SEM */

        /** Get the error code for the last failed system function.
         */
#define ErrCode()       errno

        /** An abstraction for a file handle.
         *      On POSIX systems file handles are small integers. On Windows
         *      they're opaque pointers.
         */
#define HANDLE  int

        /**     A value for an invalid file handle.
         *      Mainly used to initialize file variables and signify that they are
         *      unused.
         */
#define INVALID_HANDLE_VALUE    (-1)

        /** Get the size of a memory page for the system.
         *      This is the basic size that the platform's memory manager uses, and is
         *      fundamental to the use of memory-mapped files.
         */
#define GET_PAGESIZE(x) ((x) = sysconf(_SC_PAGE_SIZE))
#endif

#if defined(_WIN32) || defined(MDB_USE_POSIX_SEM)
#define MNAME_LEN       32
#else
#define MNAME_LEN       (sizeof(pthread_mutex_t))
#endif

/** @} */

#ifndef _WIN32
/**     A flag for opening a file and requesting synchronous data writes.
 *      This is only used when writing a meta page. It's not strictly needed;
 *      we could just do a normal write and then immediately perform a flush.
 *      But if this flag is available it saves us an extra system call.
 *
 *      @note If O_DSYNC is undefined but exists in /usr/include,
 * preferably set some compiler flag to get the definition.
 * Otherwise compile with the less efficient -DMDB_DSYNC=O_SYNC.
 */
#ifndef MDB_DSYNC
# define MDB_DSYNC      O_DSYNC
#endif
#endif

/** Function for flushing the data of a file. Define this to fsync
 *      if fdatasync() is not supported.
 */
#ifndef MDB_FDATASYNC
# define MDB_FDATASYNC  fdatasync
#endif

#ifndef MDB_MSYNC
# define MDB_MSYNC(addr,len,flags)      msync(addr,len,flags)
#endif

#ifndef MS_SYNC
#define MS_SYNC 1
#endif

#ifndef MS_ASYNC
#define MS_ASYNC        0
#endif

        /** A page number in the database.
         *      Note that 64 bit page numbers are overkill, since pages themselves
         *      already represent 12-13 bits of addressable memory, and the OS will
         *      always limit applications to a maximum of 63 bits of address space.
         *
         *      @note In the #MDB_node structure, we only store 48 bits of this value,
         *      which thus limits us to only 60 bits of addressable data.
         */
typedef MDB_ID  pgno_t;

        /** A transaction ID.
         *      See struct MDB_txn.mt_txnid for details.
         */
typedef MDB_ID  txnid_t;

/** @defgroup debug     Debug Macros
 *      @{
 */
#ifndef MDB_DEBUG
        /**     Enable debug output.  Needs variable argument macros (a C99 feature).
         *      Set this to 1 for copious tracing. Set to 2 to add dumps of all IDLs
         *      read from and written to the database (used for free space management).
         */
#define MDB_DEBUG 0
#endif

#if MDB_DEBUG
static int mdb_debug;
static txnid_t mdb_debug_start;

        /**     Print a debug message with printf formatting.
         *      Requires double parenthesis around 2 or more args.
         */
# define DPRINTF(args) ((void) ((mdb_debug) && DPRINTF0 args))
# define DPRINTF0(fmt, ...) \
        fprintf(stderr, "%s:%d " fmt "\n", mdb_func_, __LINE__, __VA_ARGS__)
#else
# define DPRINTF(args)  ((void) 0)
#endif
        /**     Print a debug string.
         *      The string is printed literally, with no format processing.
         */
#define DPUTS(arg)      DPRINTF(("%s", arg))
        /** Debuging output value of a cursor DBI: Negative in a sub-cursor. */
#define DDBI(mc) \
        (((mc)->mc_flags & C_SUB) ? -(int)(mc)->mc_dbi : (int)(mc)->mc_dbi)
/** @} */

        /**     @brief The maximum size of a database page.
         *
         *      It is 32k or 64k, since value-PAGEBASE must fit in
         *      #MDB_page.%mp_upper.
         *
         *      LMDB will use database pages < OS pages if needed.
         *      That causes more I/O in write transactions: The OS must
         *      know (read) the whole page before writing a partial page.
         *
         *      Note that we don't currently support Huge pages. On Linux,
         *      regular data files cannot use Huge pages, and in general
         *      Huge pages aren't actually pageable. We rely on the OS
         *      demand-pager to read our data and page it out when memory
         *      pressure from other processes is high. So until OSs have
         *      actual paging support for Huge pages, they're not viable.
         */
#define MAX_PAGESIZE     (PAGEBASE ? 0x10000 : 0x8000)

        /** The minimum number of keys required in a database page.
         *      Setting this to a larger value will place a smaller bound on the
         *      maximum size of a data item. Data items larger than this size will
         *      be pushed into overflow pages instead of being stored directly in
         *      the B-tree node. This value used to default to 4. With a page size
         *      of 4096 bytes that meant that any item larger than 1024 bytes would
         *      go into an overflow page. That also meant that on average 2-3KB of
         *      each overflow page was wasted space. The value cannot be lower than
         *      2 because then there would no longer be a tree structure. With this
         *      value, items larger than 2KB will go into overflow pages, and on
         *      average only 1KB will be wasted.
         */
#define MDB_MINKEYS      2

        /**     A stamp that identifies a file as an LMDB file.
         *      There's nothing special about this value other than that it is easily
         *      recognizable, and it will reflect any byte order mismatches.
         */
#define MDB_MAGIC        0xBEEFC0DE

        /**     The version number for a database's datafile format. */
#define MDB_DATA_VERSION         ((MDB_DEVEL) ? 999 : 1)
        /**     The version number for a database's lockfile format. */
#define MDB_LOCK_VERSION         1

        /**     @brief The max size of a key we can write, or 0 for dynamic max.
         *
         *      Define this as 0 to compute the max from the page size.  511
         *      is default for backwards compat: liblmdb <= 0.9.10 can break
         *      when modifying a DB with keys/dupsort data bigger than its max.
         *      #MDB_DEVEL sets the default to 0.
         *
         *      Data items in an #MDB_DUPSORT database are also limited to
         *      this size, since they're actually keys of a sub-DB.  Keys and
         *      #MDB_DUPSORT data items must fit on a node in a regular page.
         */
#ifndef MDB_MAXKEYSIZE
#define MDB_MAXKEYSIZE   ((MDB_DEVEL) ? 0 : 511)
#endif

        /**     The maximum size of a key we can write to the environment. */
#if MDB_MAXKEYSIZE
#define ENV_MAXKEY(env) (MDB_MAXKEYSIZE)
#else
#define ENV_MAXKEY(env) ((env)->me_maxkey)
#endif

        /**     @brief The maximum size of a data item.
         *
         *      We only store a 32 bit value for node sizes.
         */
#define MAXDATASIZE     0xffffffffUL

#if MDB_DEBUG
        /**     Key size which fits in a #DKBUF.
         *      @ingroup debug
         */
#define DKBUF_MAXKEYSIZE ((MDB_MAXKEYSIZE) > 0 ? (MDB_MAXKEYSIZE) : 511)
        /**     A key buffer.
         *      @ingroup debug
         *      This is used for printing a hex dump of a key's contents.
         */
#define DKBUF   char kbuf[DKBUF_MAXKEYSIZE*2+1]
        /**     Display a key in hex.
         *      @ingroup debug
         *      Invoke a function to display a key in hex.
         */
#define DKEY(x) mdb_dkey(x, kbuf)
#else
#define DKBUF
#define DKEY(x) 0
#endif

        /** An invalid page number.
         *      Mainly used to denote an empty tree.
         */
#define P_INVALID        (~(pgno_t)0)

        /** Test if the flags \b f are set in a flag word \b w. */
#define F_ISSET(w, f)    (((w) & (f)) == (f))

        /** Round \b n up to an even number. */
#define EVEN(n)         (((n) + 1U) & -2) /* sign-extending -2 to match n+1U */

        /**     Used for offsets within a single page.
         *      Since memory pages are typically 4 or 8KB in size, 12-13 bits,
         *      this is plenty.
         */
typedef uint16_t         indx_t;

        /**     Default size of memory map.
         *      This is certainly too small for any actual applications. Apps should always set
         *      the size explicitly using #mdb_env_set_mapsize().
         */
#define DEFAULT_MAPSIZE 1048576

/**     @defgroup readers       Reader Lock Table
 *      Readers don't acquire any locks for their data access. Instead, they
 *      simply record their transaction ID in the reader table. The reader
 *      mutex is needed just to find an empty slot in the reader table. The
 *      slot's address is saved in thread-specific data so that subsequent read
 *      transactions started by the same thread need no further locking to proceed.
 *
 *      If #MDB_NOTLS is set, the slot address is not saved in thread-specific data.
 *
 *      No reader table is used if the database is on a read-only filesystem, or
 *      if #MDB_NOLOCK is set.
 *
 *      Since the database uses multi-version concurrency control, readers don't
 *      actually need any locking. This table is used to keep track of which
 *      readers are using data from which old transactions, so that we'll know
 *      when a particular old transaction is no longer in use. Old transactions
 *      that have discarded any data pages can then have those pages reclaimed
 *      for use by a later write transaction.
 *
 *      The lock table is constructed such that reader slots are aligned with the
 *      processor's cache line size. Any slot is only ever used by one thread.
 *      This alignment guarantees that there will be no contention or cache
 *      thrashing as threads update their own slot info, and also eliminates
 *      any need for locking when accessing a slot.
 *
 *      A writer thread will scan every slot in the table to determine the oldest
 *      outstanding reader transaction. Any freed pages older than this will be
 *      reclaimed by the writer. The writer doesn't use any locks when scanning
 *      this table. This means that there's no guarantee that the writer will
 *      see the most up-to-date reader info, but that's not required for correct
 *      operation - all we need is to know the upper bound on the oldest reader,
 *      we don't care at all about the newest reader. So the only consequence of
 *      reading stale information here is that old pages might hang around a
 *      while longer before being reclaimed. That's actually good anyway, because
 *      the longer we delay reclaiming old pages, the more likely it is that a
 *      string of contiguous pages can be found after coalescing old pages from
 *      many old transactions together.
 *      @{
 */
        /**     Number of slots in the reader table.
         *      This value was chosen somewhat arbitrarily. 126 readers plus a
         *      couple mutexes fit exactly into 8KB on my development machine.
         *      Applications should set the table size using #mdb_env_set_maxreaders().
         */
#define DEFAULT_READERS 126

        /**     The size of a CPU cache line in bytes. We want our lock structures
         *      aligned to this size to avoid false cache line sharing in the
         *      lock table.
         *      This value works for most CPUs. For Itanium this should be 128.
         */
#ifndef CACHELINE
#define CACHELINE       64
#endif

        /**     The information we store in a single slot of the reader table.
         *      In addition to a transaction ID, we also record the process and
         *      thread ID that owns a slot, so that we can detect stale information,
         *      e.g. threads or processes that went away without cleaning up.
         *      @note We currently don't check for stale records. We simply re-init
         *      the table when we know that we're the only process opening the
         *      lock file.
         */
typedef struct MDB_rxbody {
        /**     Current Transaction ID when this transaction began, or (txnid_t)-1.
         *      Multiple readers that start at the same time will probably have the
         *      same ID here. Again, it's not important to exclude them from
         *      anything; all we need to know is which version of the DB they
         *      started from so we can avoid overwriting any data used in that
         *      particular version.
         */
        txnid_t         mrb_txnid;
        /** The process ID of the process owning this reader txn. */
        MDB_PID_T       mrb_pid;
        /** The thread ID of the thread owning this txn. */
        MDB_THR_T       mrb_tid;
} MDB_rxbody;

        /** The actual reader record, with cacheline padding. */
typedef struct MDB_reader {
        union {
                MDB_rxbody mrx;
                /** shorthand for mrb_txnid */
#define mr_txnid        mru.mrx.mrb_txnid
#define mr_pid  mru.mrx.mrb_pid
#define mr_tid  mru.mrx.mrb_tid
                /** cache line alignment */
                char pad[(sizeof(MDB_rxbody)+CACHELINE-1) & ~(CACHELINE-1)];
        } mru;
} MDB_reader;

        /** The header for the reader table.
         *      The table resides in a memory-mapped file. (This is a different file
         *      than is used for the main database.)
         *
         *      For POSIX the actual mutexes reside in the shared memory of this
         *      mapped file. On Windows, mutexes are named objects allocated by the
         *      kernel; we store the mutex names in this mapped file so that other
         *      processes can grab them. This same approach is also used on
         *      MacOSX/Darwin (using named semaphores) since MacOSX doesn't support
         *      process-shared POSIX mutexes. For these cases where a named object
         *      is used, the object name is derived from a 64 bit FNV hash of the
         *      environment pathname. As such, naming collisions are extremely
         *      unlikely. If a collision occurs, the results are unpredictable.
         */
typedef struct MDB_txbody {
                /** Stamp identifying this as an LMDB file. It must be set
                 *      to #MDB_MAGIC. */
        uint32_t        mtb_magic;
                /** Format of this lock file. Must be set to #MDB_LOCK_FORMAT. */
        uint32_t        mtb_format;
#if defined(_WIN32) || defined(MDB_USE_POSIX_SEM)
        char    mtb_rmname[MNAME_LEN];
#else
                /** Mutex protecting access to this table.
                 *      This is the reader lock that #LOCK_MUTEX_R acquires.
                 */
        pthread_mutex_t mtb_mutex;
#endif
                /**     The ID of the last transaction committed to the database.
                 *      This is recorded here only for convenience; the value can always
                 *      be determined by reading the main database meta pages.
                 */
        txnid_t         mtb_txnid;
                /** The number of slots that have been used in the reader table.
                 *      This always records the maximum count, it is not decremented
                 *      when readers release their slots.
                 */
        unsigned        mtb_numreaders;
} MDB_txbody;

        /** The actual reader table definition. */
typedef struct MDB_txninfo {
        union {
                MDB_txbody mtb;
#define mti_magic       mt1.mtb.mtb_magic
#define mti_format      mt1.mtb.mtb_format
#define mti_mutex       mt1.mtb.mtb_mutex
#define mti_rmname      mt1.mtb.mtb_rmname
#define mti_txnid       mt1.mtb.mtb_txnid
#define mti_numreaders  mt1.mtb.mtb_numreaders
                char pad[(sizeof(MDB_txbody)+CACHELINE-1) & ~(CACHELINE-1)];
        } mt1;
        union {
#if defined(_WIN32) || defined(MDB_USE_POSIX_SEM)
                char mt2_wmname[MNAME_LEN];
#define mti_wmname      mt2.mt2_wmname
#else
                pthread_mutex_t mt2_wmutex;
#define mti_wmutex      mt2.mt2_wmutex
#endif
                char pad[(MNAME_LEN+CACHELINE-1) & ~(CACHELINE-1)];
        } mt2;
        MDB_reader      mti_readers[1];
} MDB_txninfo;

        /** Lockfile format signature: version, features and field layout */
#define MDB_LOCK_FORMAT \
        ((uint32_t) \
         ((MDB_LOCK_VERSION) \
          /* Flags which describe functionality */ \
          + (((MDB_PIDLOCK) != 0) << 16)))
/** @} */

/** Common header for all page types.
 * Overflow records occupy a number of contiguous pages with no
 * headers on any page after the first.
 */
typedef struct MDB_page {
#define mp_pgno mp_p.p_pgno
#define mp_next mp_p.p_next
        union {
                pgno_t          p_pgno; /**< page number */
                struct MDB_page *p_next; /**< for in-memory list of freed pages */
        } mp_p;
        uint16_t        mp_pad;
/**     @defgroup mdb_page      Page Flags
 *      @ingroup internal
 *      Flags for the page headers.
 *      @{
 */
#define P_BRANCH         0x01           /**< branch page */
#define P_LEAF           0x02           /**< leaf page */
#define P_OVERFLOW       0x04           /**< overflow page */
#define P_META           0x08           /**< meta page */
#define P_DIRTY          0x10           /**< dirty page, also set for #P_SUBP pages */
#define P_LEAF2          0x20           /**< for #MDB_DUPFIXED records */
#define P_SUBP           0x40           /**< for #MDB_DUPSORT sub-pages */
#define P_LOOSE          0x4000         /**< page was dirtied then freed, can be reused */
#define P_KEEP           0x8000         /**< leave this page alone during spill */
/** @} */
        uint16_t        mp_flags;               /**< @ref mdb_page */
#define mp_lower        mp_pb.pb.pb_lower
#define mp_upper        mp_pb.pb.pb_upper
#define mp_pages        mp_pb.pb_pages
        union {
                struct {
                        indx_t          pb_lower;               /**< lower bound of free space */
                        indx_t          pb_upper;               /**< upper bound of free space */
                } pb;
                uint32_t        pb_pages;       /**< number of overflow pages */
        } mp_pb;
        indx_t          mp_ptrs[1];             /**< dynamic size */
} MDB_page;

        /** Size of the page header, excluding dynamic data at the end */
#define PAGEHDRSZ        ((unsigned) offsetof(MDB_page, mp_ptrs))

        /** Address of first usable data byte in a page, after the header */
#define METADATA(p)      ((void *)((char *)(p) + PAGEHDRSZ))

        /** ITS#7713, change PAGEBASE to handle 65536 byte pages */
#define PAGEBASE        ((MDB_DEVEL) ? PAGEHDRSZ : 0)

        /** Number of nodes on a page */
#define NUMKEYS(p)       (((p)->mp_lower - (PAGEHDRSZ-PAGEBASE)) >> 1)

        /** The amount of space remaining in the page */
#define SIZELEFT(p)      (indx_t)((p)->mp_upper - (p)->mp_lower)

        /** The percentage of space used in the page, in tenths of a percent. */
#define PAGEFILL(env, p) (1000L * ((env)->me_psize - PAGEHDRSZ - SIZELEFT(p)) / \
                                ((env)->me_psize - PAGEHDRSZ))
        /** The minimum page fill factor, in tenths of a percent.
         *      Pages emptier than this are candidates for merging.
         */
#define FILL_THRESHOLD   250

        /** Test if a page is a leaf page */
#define IS_LEAF(p)       F_ISSET((p)->mp_flags, P_LEAF)
        /** Test if a page is a LEAF2 page */
#define IS_LEAF2(p)      F_ISSET((p)->mp_flags, P_LEAF2)
        /** Test if a page is a branch page */
#define IS_BRANCH(p)     F_ISSET((p)->mp_flags, P_BRANCH)
        /** Test if a page is an overflow page */
#define IS_OVERFLOW(p)   F_ISSET((p)->mp_flags, P_OVERFLOW)
        /** Test if a page is a sub page */
#define IS_SUBP(p)       F_ISSET((p)->mp_flags, P_SUBP)

        /** The number of overflow pages needed to store the given size. */
#define OVPAGES(size, psize)    ((PAGEHDRSZ-1 + (size)) / (psize) + 1)

        /** Link in #MDB_txn.%mt_loose_pgs list */
#define NEXT_LOOSE_PAGE(p)              (*(MDB_page **)((p) + 2))

        /** Header for a single key/data pair within a page.
         * Used in pages of type #P_BRANCH and #P_LEAF without #P_LEAF2.
         * We guarantee 2-byte alignment for 'MDB_node's.
         */
typedef struct MDB_node {
        /** lo and hi are used for data size on leaf nodes and for
         * child pgno on branch nodes. On 64 bit platforms, flags
         * is also used for pgno. (Branch nodes have no flags).
         * They are in host byte order in case that lets some
         * accesses be optimized into a 32-bit word access.
         */
#if BYTE_ORDER == LITTLE_ENDIAN
        unsigned short  mn_lo, mn_hi;   /**< part of data size or pgno */
#else
        unsigned short  mn_hi, mn_lo;
#endif
/** @defgroup mdb_node Node Flags
 *      @ingroup internal
 *      Flags for node headers.
 *      @{
 */
#define F_BIGDATA        0x01                   /**< data put on overflow page */
#define F_SUBDATA        0x02                   /**< data is a sub-database */
#define F_DUPDATA        0x04                   /**< data has duplicates */

/** valid flags for #mdb_node_add() */
#define NODE_ADD_FLAGS  (F_DUPDATA|F_SUBDATA|MDB_RESERVE|MDB_APPEND)

/** @} */
        unsigned short  mn_flags;               /**< @ref mdb_node */
        unsigned short  mn_ksize;               /**< key size */
        char            mn_data[1];                     /**< key and data are appended here */
} MDB_node;

        /** Size of the node header, excluding dynamic data at the end */
#define NODESIZE         offsetof(MDB_node, mn_data)

        /** Bit position of top word in page number, for shifting mn_flags */
#define PGNO_TOPWORD ((pgno_t)-1 > 0xffffffffu ? 32 : 0)

        /** Size of a node in a branch page with a given key.
         *      This is just the node header plus the key, there is no data.
         */
#define INDXSIZE(k)      (NODESIZE + ((k) == NULL ? 0 : (k)->mv_size))

        /** Size of a node in a leaf page with a given key and data.
         *      This is node header plus key plus data size.
         */
#define LEAFSIZE(k, d)   (NODESIZE + (k)->mv_size + (d)->mv_size)

        /** Address of node \b i in page \b p */
#define NODEPTR(p, i)    ((MDB_node *)((char *)(p) + (p)->mp_ptrs[i] + PAGEBASE))

        /** Address of the key for the node */
#define NODEKEY(node)    (void *)((node)->mn_data)

        /** Address of the data for a node */
#define NODEDATA(node)   (void *)((char *)(node)->mn_data + (node)->mn_ksize)

        /** Get the page number pointed to by a branch node */
#define NODEPGNO(node) \
        ((node)->mn_lo | ((pgno_t) (node)->mn_hi << 16) | \
         (PGNO_TOPWORD ? ((pgno_t) (node)->mn_flags << PGNO_TOPWORD) : 0))
        /** Set the page number in a branch node */
#define SETPGNO(node,pgno)      do { \
        (node)->mn_lo = (pgno) & 0xffff; (node)->mn_hi = (pgno) >> 16; \
        if (PGNO_TOPWORD) (node)->mn_flags = (pgno) >> PGNO_TOPWORD; } while(0)

        /** Get the size of the data in a leaf node */
#define NODEDSZ(node)    ((node)->mn_lo | ((unsigned)(node)->mn_hi << 16))
        /** Set the size of the data for a leaf node */
#define SETDSZ(node,size)       do { \
        (node)->mn_lo = (size) & 0xffff; (node)->mn_hi = (size) >> 16;} while(0)
        /** The size of a key in a node */
#define NODEKSZ(node)    ((node)->mn_ksize)

        /** Copy a page number from src to dst */
#ifdef MISALIGNED_OK
#define COPY_PGNO(dst,src)      dst = src
#else
#if SIZE_MAX > 4294967295UL
#define COPY_PGNO(dst,src)      do { \
        unsigned short *s, *d;  \
        s = (unsigned short *)&(src);   \
        d = (unsigned short *)&(dst);   \
        *d++ = *s++;    \
        *d++ = *s++;    \
        *d++ = *s++;    \
        *d = *s;        \
} while (0)
#else
#define COPY_PGNO(dst,src)      do { \
        unsigned short *s, *d;  \
        s = (unsigned short *)&(src);   \
        d = (unsigned short *)&(dst);   \
        *d++ = *s++;    \
        *d = *s;        \
} while (0)
#endif
#endif
        /** The address of a key in a LEAF2 page.
         *      LEAF2 pages are used for #MDB_DUPFIXED sorted-duplicate sub-DBs.
         *      There are no node headers, keys are stored contiguously.
         */
#define LEAF2KEY(p, i, ks)      ((char *)(p) + PAGEHDRSZ + ((i)*(ks)))

        /** Set the \b node's key into \b keyptr, if requested. */
#define MDB_GET_KEY(node, keyptr)       { if ((keyptr) != NULL) { \
        (keyptr)->mv_size = NODEKSZ(node); (keyptr)->mv_data = NODEKEY(node); } }

        /** Set the \b node's key into \b key. */
#define MDB_GET_KEY2(node, key) { key.mv_size = NODEKSZ(node); key.mv_data = NODEKEY(node); }

        /** Information about a single database in the environment. */
typedef struct MDB_db {
        uint32_t        md_pad;         /**< also ksize for LEAF2 pages */
        uint16_t        md_flags;       /**< @ref mdb_dbi_open */
        uint16_t        md_depth;       /**< depth of this tree */
        pgno_t          md_branch_pages;        /**< number of internal pages */
        pgno_t          md_leaf_pages;          /**< number of leaf pages */
        pgno_t          md_overflow_pages;      /**< number of overflow pages */
        size_t          md_entries;             /**< number of data items */
        pgno_t          md_root;                /**< the root page of this tree */
} MDB_db;

        /** mdb_dbi_open flags */
#define MDB_VALID       0x8000          /**< DB handle is valid, for me_dbflags */
#define PERSISTENT_FLAGS        (0xffff & ~(MDB_VALID))
#define VALID_FLAGS     (MDB_REVERSEKEY|MDB_DUPSORT|MDB_INTEGERKEY|MDB_DUPFIXED|\
        MDB_INTEGERDUP|MDB_REVERSEDUP|MDB_CREATE)

        /** Handle for the DB used to track free pages. */
#define FREE_DBI        0
        /** Handle for the default DB. */
#define MAIN_DBI        1

        /** Meta page content.
         *      A meta page is the start point for accessing a database snapshot.
         *      Pages 0-1 are meta pages. Transaction N writes meta page #(N % 2).
         */
typedef struct MDB_meta {
                /** Stamp identifying this as an LMDB file. It must be set
                 *      to #MDB_MAGIC. */
        uint32_t        mm_magic;
                /** Version number of this lock file. Must be set to #MDB_DATA_VERSION. */
        uint32_t        mm_version;
        void            *mm_address;            /**< address for fixed mapping */
        size_t          mm_mapsize;                     /**< size of mmap region */
        MDB_db          mm_dbs[2];                      /**< first is free space, 2nd is main db */
        /** The size of pages used in this DB */
#define mm_psize        mm_dbs[0].md_pad
        /** Any persistent environment flags. @ref mdb_env */
#define mm_flags        mm_dbs[0].md_flags
        pgno_t          mm_last_pg;                     /**< last used page in file */
        txnid_t         mm_txnid;                       /**< txnid that committed this page */
} MDB_meta;

        /** Buffer for a stack-allocated meta page.
         *      The members define size and alignment, and silence type
         *      aliasing warnings.  They are not used directly; that could
         *      mean incorrectly using several union members in parallel.
         */
typedef union MDB_metabuf {
        MDB_page        mb_page;
        struct {
                char            mm_pad[PAGEHDRSZ];
                MDB_meta        mm_meta;
        } mb_metabuf;
} MDB_metabuf;

        /** Auxiliary DB info.
         *      The information here is mostly static/read-only. There is
         *      only a single copy of this record in the environment.
         */
typedef struct MDB_dbx {
        MDB_val         md_name;                /**< name of the database */
        MDB_cmp_func    *md_cmp;        /**< function for comparing keys */
        MDB_cmp_func    *md_dcmp;       /**< function for comparing data items */
        MDB_rel_func    *md_rel;        /**< user relocate function */
        void            *md_relctx;             /**< user-provided context for md_rel */
} MDB_dbx;

        /** A database transaction.
         *      Every operation requires a transaction handle.
         */
struct MDB_txn {
        MDB_txn         *mt_parent;             /**< parent of a nested txn */
        MDB_txn         *mt_child;              /**< nested txn under this txn */
        pgno_t          mt_next_pgno;   /**< next unallocated page */
        /** The ID of this transaction. IDs are integers incrementing from 1.
         *      Only committed write transactions increment the ID. If a transaction
         *      aborts, the ID may be re-used by the next writer.
         */
        txnid_t         mt_txnid;
        MDB_env         *mt_env;                /**< the DB environment */
        /** The list of pages that became unused during this transaction.
         */
        MDB_IDL         mt_free_pgs;
        /** The list of loose pages that became unused and may be reused
         *      in this transaction, linked through #NEXT_LOOSE_PAGE(page).
         */
        MDB_page        *mt_loose_pgs;
        /* #Number of loose pages (#mt_loose_pgs) */
        int                     mt_loose_count;
        /** The sorted list of dirty pages we temporarily wrote to disk
         *      because the dirty list was full. page numbers in here are
         *      shifted left by 1, deleted slots have the LSB set.
         */
        MDB_IDL         mt_spill_pgs;
        union {
                /** For write txns: Modified pages. Sorted when not MDB_WRITEMAP. */
                MDB_ID2L        dirty_list;
                /** For read txns: This thread/txn's reader table slot, or NULL. */
                MDB_reader      *reader;
        } mt_u;
        /** Array of records for each DB known in the environment. */
        MDB_dbx         *mt_dbxs;
        /** Array of MDB_db records for each known DB */
        MDB_db          *mt_dbs;
        /** Array of sequence numbers for each DB handle */
        unsigned int    *mt_dbiseqs;
/** @defgroup mt_dbflag Transaction DB Flags
 *      @ingroup internal
 * @{
 */
#define DB_DIRTY        0x01            /**< DB was modified or is DUPSORT data */
#define DB_STALE        0x02            /**< Named-DB record is older than txnID */
#define DB_NEW          0x04            /**< Named-DB handle opened in this txn */
#define DB_VALID        0x08            /**< DB handle is valid, see also #MDB_VALID */
/** @} */
        /** In write txns, array of cursors for each DB */
        MDB_cursor      **mt_cursors;
        /** Array of flags for each DB */
        unsigned char   *mt_dbflags;
        /**     Number of DB records in use. This number only ever increments;
         *      we don't decrement it when individual DB handles are closed.
         */
        MDB_dbi         mt_numdbs;

/** @defgroup mdb_txn   Transaction Flags
 *      @ingroup internal
 *      @{
 */
#define MDB_TXN_RDONLY          0x01            /**< read-only transaction */
#define MDB_TXN_ERROR           0x02            /**< txn is unusable after an error */
#define MDB_TXN_DIRTY           0x04            /**< must write, even if dirty list is empty */
#define MDB_TXN_SPILLS          0x08            /**< txn or a parent has spilled pages */
/** @} */
        unsigned int    mt_flags;               /**< @ref mdb_txn */
        /** #dirty_list room: Array size - \#dirty pages visible to this txn.
         *      Includes ancestor txns' dirty pages not hidden by other txns'
         *      dirty/spilled pages. Thus commit(nested txn) has room to merge
         *      dirty_list into mt_parent after freeing hidden mt_parent pages.
         */
        unsigned int    mt_dirty_room;
};

/** Enough space for 2^32 nodes with minimum of 2 keys per node. I.e., plenty.
 * At 4 keys per node, enough for 2^64 nodes, so there's probably no need to
 * raise this on a 64 bit machine.
 */
#define CURSOR_STACK             32

struct MDB_xcursor;

        /** Cursors are used for all DB operations.
         *      A cursor holds a path of (page pointer, key index) from the DB
         *      root to a position in the DB, plus other state. #MDB_DUPSORT
         *      cursors include an xcursor to the current data item. Write txns
         *      track their cursors and keep them up to date when data moves.
         *      Exception: An xcursor's pointer to a #P_SUBP page can be stale.
         *      (A node with #F_DUPDATA but no #F_SUBDATA contains a subpage).
         */
struct MDB_cursor {
        /** Next cursor on this DB in this txn */
        MDB_cursor      *mc_next;
        /** Backup of the original cursor if this cursor is a shadow */
        MDB_cursor      *mc_backup;
        /** Context used for databases with #MDB_DUPSORT, otherwise NULL */
        struct MDB_xcursor      *mc_xcursor;
        /** The transaction that owns this cursor */
        MDB_txn         *mc_txn;
        /** The database handle this cursor operates on */
        MDB_dbi         mc_dbi;
        /** The database record for this cursor */
        MDB_db          *mc_db;
        /** The database auxiliary record for this cursor */
        MDB_dbx         *mc_dbx;
        /** The @ref mt_dbflag for this database */
        unsigned char   *mc_dbflag;
        unsigned short  mc_snum;        /**< number of pushed pages */
        unsigned short  mc_top;         /**< index of top page, normally mc_snum-1 */
/** @defgroup mdb_cursor        Cursor Flags
 *      @ingroup internal
 *      Cursor state flags.
 *      @{
 */
#define C_INITIALIZED   0x01    /**< cursor has been initialized and is valid */
#define C_EOF   0x02                    /**< No more data */
#define C_SUB   0x04                    /**< Cursor is a sub-cursor */
#define C_DEL   0x08                    /**< last op was a cursor_del */
#define C_SPLITTING     0x20            /**< Cursor is in page_split */
#define C_UNTRACK       0x40            /**< Un-track cursor when closing */
/** @} */
        unsigned int    mc_flags;       /**< @ref mdb_cursor */
        MDB_page        *mc_pg[CURSOR_STACK];   /**< stack of pushed pages */
        indx_t          mc_ki[CURSOR_STACK];    /**< stack of page indices */
};

        /** Context for sorted-dup records.
         *      We could have gone to a fully recursive design, with arbitrarily
         *      deep nesting of sub-databases. But for now we only handle these
         *      levels - main DB, optional sub-DB, sorted-duplicate DB.
         */
typedef struct MDB_xcursor {
        /** A sub-cursor for traversing the Dup DB */
        MDB_cursor mx_cursor;
        /** The database record for this Dup DB */
        MDB_db  mx_db;
        /**     The auxiliary DB record for this Dup DB */
        MDB_dbx mx_dbx;
        /** The @ref mt_dbflag for this Dup DB */
        unsigned char mx_dbflag;
} MDB_xcursor;

        /** State of FreeDB old pages, stored in the MDB_env */
typedef struct MDB_pgstate {
        pgno_t          *mf_pghead;     /**< Reclaimed freeDB pages, or NULL before use */
        txnid_t         mf_pglast;      /**< ID of last used record, or 0 if !mf_pghead */
} MDB_pgstate;

        /** The database environment. */
struct MDB_env {
        HANDLE          me_fd;          /**< The main data file */
        HANDLE          me_lfd;         /**< The lock file */
        HANDLE          me_mfd;                 /**< just for writing the meta pages */
        /** Failed to update the meta page. Probably an I/O error. */
#define MDB_FATAL_ERROR 0x80000000U
        /** Some fields are initialized. */
#define MDB_ENV_ACTIVE  0x20000000U
        /** me_txkey is set */
#define MDB_ENV_TXKEY   0x10000000U
        uint32_t        me_flags;               /**< @ref mdb_env */
        unsigned int    me_psize;       /**< DB page size, inited from me_os_psize */
        unsigned int    me_os_psize;    /**< OS page size, from #GET_PAGESIZE */
        unsigned int    me_maxreaders;  /**< size of the reader table */
        unsigned int    me_numreaders;  /**< max numreaders set by this env */
        MDB_dbi         me_numdbs;              /**< number of DBs opened */
        MDB_dbi         me_maxdbs;              /**< size of the DB table */
        MDB_PID_T       me_pid;         /**< process ID of this env */
        char            *me_path;               /**< path to the DB files */
        char            *me_map;                /**< the memory map of the data file */
        MDB_txninfo     *me_txns;               /**< the memory map of the lock file or NULL */
        MDB_meta        *me_metas[2];   /**< pointers to the two meta pages */
        void            *me_pbuf;               /**< scratch area for DUPSORT put() */
        MDB_txn         *me_txn;                /**< current write transaction */
        size_t          me_mapsize;             /**< size of the data memory map */
        off_t           me_size;                /**< current file size */
        pgno_t          me_maxpg;               /**< me_mapsize / me_psize */
        MDB_dbx         *me_dbxs;               /**< array of static DB info */
        uint16_t        *me_dbflags;    /**< array of flags from MDB_db.md_flags */
        unsigned int    *me_dbiseqs;    /**< array of dbi sequence numbers */
        pthread_key_t   me_txkey;       /**< thread-key for readers */
        MDB_pgstate     me_pgstate;             /**< state of old pages from freeDB */
#       define          me_pglast       me_pgstate.mf_pglast
#       define          me_pghead       me_pgstate.mf_pghead
        MDB_page        *me_dpages;             /**< list of malloc'd blocks for re-use */
        /** IDL of pages that became unused in a write txn */
        MDB_IDL         me_free_pgs;
        /** ID2L of pages written during a write txn. Length MDB_IDL_UM_SIZE. */
        MDB_ID2L        me_dirty_list;
        /** Max number of freelist items that can fit in a single overflow page */
        int                     me_maxfree_1pg;
        /** Max size of a node on a page */
        unsigned int    me_nodemax;
#if !(MDB_MAXKEYSIZE)
        unsigned int    me_maxkey;      /**< max size of a key */
#endif
        int             me_live_reader;         /**< have liveness lock in reader table */
#ifdef _WIN32
        int             me_pidquery;            /**< Used in OpenProcess */
        HANDLE          me_rmutex;              /* Windows mutexes don't reside in shared mem */
        HANDLE          me_wmutex;
#elif defined(MDB_USE_POSIX_SEM)
        sem_t           *me_rmutex;             /* Shared mutexes are not supported */
        sem_t           *me_wmutex;
#endif
        void            *me_userctx;     /**< User-settable context */
        MDB_assert_func *me_assert_func; /**< Callback for assertion failures */
};

        /** Nested transaction */
typedef struct MDB_ntxn {
        MDB_txn         mnt_txn;                /**< the transaction */
        MDB_pgstate     mnt_pgstate;    /**< parent transaction's saved freestate */
} MDB_ntxn;

        /** max number of pages to commit in one writev() call */
#define MDB_COMMIT_PAGES         64
#if defined(IOV_MAX) && IOV_MAX < MDB_COMMIT_PAGES
#undef MDB_COMMIT_PAGES
#define MDB_COMMIT_PAGES        IOV_MAX
#endif

        /** max bytes to write in one call */
#define MAX_WRITE               (0x80000000U >> (sizeof(ssize_t) == 4))

        /** Check \b txn and \b dbi arguments to a function */
#define TXN_DBI_EXIST(txn, dbi) \
        ((txn) && (dbi) < (txn)->mt_numdbs && ((txn)->mt_dbflags[dbi] & DB_VALID))

        /** Check for misused \b dbi handles */
#define TXN_DBI_CHANGED(txn, dbi) \
        ((txn)->mt_dbiseqs[dbi] != (txn)->mt_env->me_dbiseqs[dbi])

static int  mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp);
static int  mdb_page_new(MDB_cursor *mc, uint32_t flags, int num, MDB_page **mp);
static int  mdb_page_touch(MDB_cursor *mc);

static int  mdb_page_get(MDB_txn *txn, pgno_t pgno, MDB_page **mp, int *lvl);
static int  mdb_page_search_root(MDB_cursor *mc,
                            MDB_val *key, int modify);
#define MDB_PS_MODIFY   1
#define MDB_PS_ROOTONLY 2
#define MDB_PS_FIRST    4
#define MDB_PS_LAST             8
static int  mdb_page_search(MDB_cursor *mc,
                            MDB_val *key, int flags);
static int      mdb_page_merge(MDB_cursor *csrc, MDB_cursor *cdst);

#define MDB_SPLIT_REPLACE       MDB_APPENDDUP   /**< newkey is not new */
static int      mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata,
                                pgno_t newpgno, unsigned int nflags);

static int  mdb_env_read_header(MDB_env *env, MDB_meta *meta);
static int  mdb_env_pick_meta(const MDB_env *env);
static int  mdb_env_write_meta(MDB_txn *txn);
#if !(defined(_WIN32) || defined(MDB_USE_POSIX_SEM)) /* Drop unused excl arg */
# define mdb_env_close0(env, excl) mdb_env_close1(env)
#endif
static void mdb_env_close0(MDB_env *env, int excl);

static MDB_node *mdb_node_search(MDB_cursor *mc, MDB_val *key, int *exactp);
static int  mdb_node_add(MDB_cursor *mc, indx_t indx,
                            MDB_val *key, MDB_val *data, pgno_t pgno, unsigned int flags);
static void mdb_node_del(MDB_cursor *mc, int ksize);
static void mdb_node_shrink(MDB_page *mp, indx_t indx);
static int      mdb_node_move(MDB_cursor *csrc, MDB_cursor *cdst);
static int  mdb_node_read(MDB_txn *txn, MDB_node *leaf, MDB_val *data);
static size_t   mdb_leaf_size(MDB_env *env, MDB_val *key, MDB_val *data);
static size_t   mdb_branch_size(MDB_env *env, MDB_val *key);

static int      mdb_rebalance(MDB_cursor *mc);
static int      mdb_update_key(MDB_cursor *mc, MDB_val *key);

static void     mdb_cursor_pop(MDB_cursor *mc);
static int      mdb_cursor_push(MDB_cursor *mc, MDB_page *mp);

static int      mdb_cursor_del0(MDB_cursor *mc);
static int      mdb_del0(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data, unsigned flags);
static int      mdb_cursor_sibling(MDB_cursor *mc, int move_right);
static int      mdb_cursor_next(MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op);
static int      mdb_cursor_prev(MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op);
static int      mdb_cursor_set(MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op,
                                int *exactp);
static int      mdb_cursor_first(MDB_cursor *mc, MDB_val *key, MDB_val *data);
static int      mdb_cursor_last(MDB_cursor *mc, MDB_val *key, MDB_val *data);

static void     mdb_cursor_init(MDB_cursor *mc, MDB_txn *txn, MDB_dbi dbi, MDB_xcursor *mx);
static void     mdb_xcursor_init0(MDB_cursor *mc);
static void     mdb_xcursor_init1(MDB_cursor *mc, MDB_node *node);

static int      mdb_drop0(MDB_cursor *mc, int subs);
static void mdb_default_cmp(MDB_txn *txn, MDB_dbi dbi);

/** @cond */
static MDB_cmp_func     mdb_cmp_memn, mdb_cmp_memnr, mdb_cmp_int, mdb_cmp_cint, mdb_cmp_long;
/** @endcond */

#ifdef _WIN32
static SECURITY_DESCRIPTOR mdb_null_sd;
static SECURITY_ATTRIBUTES mdb_all_sa;
static int mdb_sec_inited;
#endif

/** Return the library version info. */
char *
mdb_version(int *major, int *minor, int *patch)
{
        if (major) *major = MDB_VERSION_MAJOR;
        if (minor) *minor = MDB_VERSION_MINOR;
        if (patch) *patch = MDB_VERSION_PATCH;
        return MDB_VERSION_STRING;
}

/** Table of descriptions for LMDB @ref errors */
static char *const mdb_errstr[] = {
        "MDB_KEYEXIST: Key/data pair already exists",
        "MDB_NOTFOUND: No matching key/data pair found",
        "MDB_PAGE_NOTFOUND: Requested page not found",
        "MDB_CORRUPTED: Located page was wrong type",
        "MDB_PANIC: Update of meta page failed",
        "MDB_VERSION_MISMATCH: Database environment version mismatch",
        "MDB_INVALID: File is not an LMDB file",
        "MDB_MAP_FULL: Environment mapsize limit reached",
        "MDB_DBS_FULL: Environment maxdbs limit reached",
        "MDB_READERS_FULL: Environment maxreaders limit reached",
        "MDB_TLS_FULL: Thread-local storage keys full - too many environments open",
        "MDB_TXN_FULL: Transaction has too many dirty pages - transaction too big",
        "MDB_CURSOR_FULL: Internal error - cursor stack limit reached",
        "MDB_PAGE_FULL: Internal error - page has no more space",
        "MDB_MAP_RESIZED: Database contents grew beyond environment mapsize",
        "MDB_INCOMPATIBLE: Operation and DB incompatible, or DB flags changed",
        "MDB_BAD_RSLOT: Invalid reuse of reader locktable slot",
        "MDB_BAD_TXN: Transaction cannot recover - it must be aborted",
        "MDB_BAD_VALSIZE: Unsupported size of key/DB name/data, or wrong DUPFIXED size",
        "MDB_BAD_DBI: The specified DBI handle was closed/changed unexpectedly",
};

char *
mdb_strerror(int err)
{
#ifdef _WIN32
        /** HACK: pad 4KB on stack over the buf. Return system msgs in buf.
         *      This works as long as no function between the call to mdb_strerror
         *      and the actual use of the message uses more than 4K of stack.
         */
        char pad[4096];
        char buf[1024], *ptr = buf;
#endif
        int i;
        if (!err)
                return ("Successful return: 0");

        if (err >= MDB_KEYEXIST && err <= MDB_LAST_ERRCODE) {
                i = err - MDB_KEYEXIST;
                return mdb_errstr[i];
        }

#ifdef _WIN32
        /* These are the C-runtime error codes we use. The comment indicates
         * their numeric value, and the Win32 error they would correspond to
         * if the error actually came from a Win32 API. A major mess, we should
         * have used LMDB-specific error codes for everything.
         */
        switch(err) {
        case ENOENT:    /* 2, FILE_NOT_FOUND */
        case EIO:               /* 5, ACCESS_DENIED */
        case ENOMEM:    /* 12, INVALID_ACCESS */
        case EACCES:    /* 13, INVALID_DATA */
        case EBUSY:             /* 16, CURRENT_DIRECTORY */
        case EINVAL:    /* 22, BAD_COMMAND */
        case ENOSPC:    /* 28, OUT_OF_PAPER */
                return strerror(err);
        default:
                ;
        }
        buf[0] = 0;
        FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM |
                FORMAT_MESSAGE_IGNORE_INSERTS,
                NULL, err, 0, ptr, sizeof(buf), pad);
        return ptr;
#else
        return strerror(err);
#endif
}

/** assert(3) variant in cursor context */
#define mdb_cassert(mc, expr)   mdb_assert0((mc)->mc_txn->mt_env, expr, #expr)
/** assert(3) variant in transaction context */
#define mdb_tassert(mc, expr)   mdb_assert0((txn)->mt_env, expr, #expr)
/** assert(3) variant in environment context */
#define mdb_eassert(env, expr)  mdb_assert0(env, expr, #expr)

#ifndef NDEBUG
# define mdb_assert0(env, expr, expr_txt) ((expr) ? (void)0 : \
                mdb_assert_fail(env, expr_txt, mdb_func_, __FILE__, __LINE__))

static void
mdb_assert_fail(MDB_env *env, const char *expr_txt,
        const char *func, const char *file, int line)
{
        char buf[400];
        sprintf(buf, "%.100s:%d: Assertion '%.200s' failed in %.40s()",
                file, line, expr_txt, func);
        if (env->me_assert_func)
                env->me_assert_func(env, buf);
        fprintf(stderr, "%s\n", buf);
        abort();
}
#else
# define mdb_assert0(env, expr, expr_txt) ((void) 0)
#endif /* NDEBUG */

#if MDB_DEBUG
/** Return the page number of \b mp which may be sub-page, for debug output */
static pgno_t
mdb_dbg_pgno(MDB_page *mp)
{
        pgno_t ret;
        COPY_PGNO(ret, mp->mp_pgno);
        return ret;
}

/** Display a key in hexadecimal and return the address of the result.
 * @param[in] key the key to display
 * @param[in] buf the buffer to write into. Should always be #DKBUF.
 * @return The key in hexadecimal form.
 */
char *
mdb_dkey(MDB_val *key, char *buf)
{
        char *ptr = buf;
        unsigned char *c = key->mv_data;
        unsigned int i;

        if (!key)
                return "";

        if (key->mv_size > DKBUF_MAXKEYSIZE)
                return "MDB_MAXKEYSIZE";
        /* may want to make this a dynamic check: if the key is mostly
         * printable characters, print it as-is instead of converting to hex.
         */
#if 1
        buf[0] = '\0';
        for (i=0; i<key->mv_size; i++)
                ptr += sprintf(ptr, "%02x", *c++);
#else
        sprintf(buf, "%.*s", key->mv_size, key->mv_data);
#endif
        return buf;
}

static const char *
mdb_leafnode_type(MDB_node *n)
{
        static char *const tp[2][2] = {{"", ": DB"}, {": sub-page", ": sub-DB"}};
        return F_ISSET(n->mn_flags, F_BIGDATA) ? ": overflow page" :
                tp[F_ISSET(n->mn_flags, F_DUPDATA)][F_ISSET(n->mn_flags, F_SUBDATA)];
}

/** Display all the keys in the page. */
void
mdb_page_list(MDB_page *mp)
{
        pgno_t pgno = mdb_dbg_pgno(mp);
        const char *type, *state = (mp->mp_flags & P_DIRTY) ? ", dirty" : "";
        MDB_node *node;
        unsigned int i, nkeys, nsize, total = 0;
        MDB_val key;
        DKBUF;

        switch (mp->mp_flags & (P_BRANCH|P_LEAF|P_LEAF2|P_META|P_OVERFLOW|P_SUBP)) {
        case P_BRANCH:              type = "Branch page";               break;
        case P_LEAF:                type = "Leaf page";                 break;
        case P_LEAF|P_SUBP:         type = "Sub-page";                  break;
        case P_LEAF|P_LEAF2:        type = "LEAF2 page";                break;
        case P_LEAF|P_LEAF2|P_SUBP: type = "LEAF2 sub-page";    break;
        case P_OVERFLOW:
                fprintf(stderr, "Overflow page %"Z"u pages %u%s\n",
                        pgno, mp->mp_pages, state);
                return;
        case P_META:
                fprintf(stderr, "Meta-page %"Z"u txnid %"Z"u\n",
                        pgno, ((MDB_meta *)METADATA(mp))->mm_txnid);
                return;
        default:
                fprintf(stderr, "Bad page %"Z"u flags 0x%u\n", pgno, mp->mp_flags);
                return;
        }

        nkeys = NUMKEYS(mp);
        fprintf(stderr, "%s %"Z"u numkeys %d%s\n", type, pgno, nkeys, state);

        for (i=0; i<nkeys; i++) {
                if (IS_LEAF2(mp)) {     /* LEAF2 pages have no mp_ptrs[] or node headers */
                        key.mv_size = nsize = mp->mp_pad;
                        key.mv_data = LEAF2KEY(mp, i, nsize);
                        total += nsize;
                        fprintf(stderr, "key %d: nsize %d, %s\n", i, nsize, DKEY(&key));
                        continue;
                }
                node = NODEPTR(mp, i);
                key.mv_size = node->mn_ksize;
                key.mv_data = node->mn_data;
                nsize = NODESIZE + key.mv_size;
                if (IS_BRANCH(mp)) {
                        fprintf(stderr, "key %d: page %"Z"u, %s\n", i, NODEPGNO(node),
                                DKEY(&key));
                        total += nsize;
                } else {
                        if (F_ISSET(node->mn_flags, F_BIGDATA))
                                nsize += sizeof(pgno_t);
                        else
                                nsize += NODEDSZ(node);
                        total += nsize;
                        nsize += sizeof(indx_t);
                        fprintf(stderr, "key %d: nsize %d, %s%s\n",
                                i, nsize, DKEY(&key), mdb_leafnode_type(node));
                }
                total = EVEN(total);
        }
        fprintf(stderr, "Total: header %d + contents %d + unused %d\n",
                IS_LEAF2(mp) ? PAGEHDRSZ : PAGEBASE + mp->mp_lower, total, SIZELEFT(mp));
}

void
mdb_cursor_chk(MDB_cursor *mc)
{
        unsigned int i;
        MDB_node *node;
        MDB_page *mp;

        if (!mc->mc_snum && !(mc->mc_flags & C_INITIALIZED)) return;
        for (i=0; i<mc->mc_top; i++) {
                mp = mc->mc_pg[i];
                node = NODEPTR(mp, mc->mc_ki[i]);
                if (NODEPGNO(node) != mc->mc_pg[i+1]->mp_pgno)
                        printf("oops!\n");
        }
        if (mc->mc_ki[i] >= NUMKEYS(mc->mc_pg[i]))
                printf("ack!\n");
}
#endif

#if (MDB_DEBUG) > 2
/** Count all the pages in each DB and in the freelist
 *  and make sure it matches the actual number of pages
 *  being used.
 *  All named DBs must be open for a correct count.
 */
static void mdb_audit(MDB_txn *txn)
{
        MDB_cursor mc;
        MDB_val key, data;
        MDB_ID freecount, count;
        MDB_dbi i;
        int rc;

        freecount = 0;
        mdb_cursor_init(&mc, txn, FREE_DBI, NULL);
        while ((rc = mdb_cursor_get(&mc, &key, &data, MDB_NEXT)) == 0)
                freecount += *(MDB_ID *)data.mv_data;
        mdb_tassert(txn, rc == MDB_NOTFOUND);

        count = 0;
        for (i = 0; i<txn->mt_numdbs; i++) {
                MDB_xcursor mx;
                if (!(txn->mt_dbflags[i] & DB_VALID))
                        continue;
                mdb_cursor_init(&mc, txn, i, &mx);
                if (txn->mt_dbs[i].md_root == P_INVALID)
                        continue;
                count += txn->mt_dbs[i].md_branch_pages +
                        txn->mt_dbs[i].md_leaf_pages +
                        txn->mt_dbs[i].md_overflow_pages;
                if (txn->mt_dbs[i].md_flags & MDB_DUPSORT) {
                        rc = mdb_page_search(&mc, NULL, MDB_PS_FIRST);
                        for (; rc == MDB_SUCCESS; rc = mdb_cursor_sibling(&mc, 1)) {
                                unsigned j;
                                MDB_page *mp;
                                mp = mc.mc_pg[mc.mc_top];
                                for (j=0; j<NUMKEYS(mp); j++) {
                                        MDB_node *leaf = NODEPTR(mp, j);
                                        if (leaf->mn_flags & F_SUBDATA) {
                                                MDB_db db;
                                                memcpy(&db, NODEDATA(leaf), sizeof(db));
                                                count += db.md_branch_pages + db.md_leaf_pages +
                                                        db.md_overflow_pages;
                                        }
                                }
                        }
                        mdb_tassert(txn, rc == MDB_NOTFOUND);
                }
        }
        if (freecount + count + 2 /* metapages */ != txn->mt_next_pgno) {
                fprintf(stderr, "audit: %lu freecount: %lu count: %lu total: %lu next_pgno: %lu\n",
                        txn->mt_txnid, freecount, count+2, freecount+count+2, txn->mt_next_pgno);
        }
}
#endif

int
mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b)
{
        return txn->mt_dbxs[dbi].md_cmp(a, b);
}

int
mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b)
{
        return txn->mt_dbxs[dbi].md_dcmp(a, b);
}

/** Allocate memory for a page.
 * Re-use old malloc'd pages first for singletons, otherwise just malloc.
 */
static MDB_page *
mdb_page_malloc(MDB_txn *txn, unsigned num)
{
        MDB_env *env = txn->mt_env;
        MDB_page *ret = env->me_dpages;
        size_t psize = env->me_psize, sz = psize, off;
        /* For ! #MDB_NOMEMINIT, psize counts how much to init.
         * For a single page alloc, we init everything after the page header.
         * For multi-page, we init the final page; if the caller needed that
         * many pages they will be filling in at least up to the last page.
         */
        if (num == 1) {
                if (ret) {
                        VGMEMP_ALLOC(env, ret, sz);
                        VGMEMP_DEFINED(ret, sizeof(ret->mp_next));
                        env->me_dpages = ret->mp_next;
                        return ret;
                }
                psize -= off = PAGEHDRSZ;
        } else {
                sz *= num;
                off = sz - psize;
        }
        if ((ret = malloc(sz)) != NULL) {
                VGMEMP_ALLOC(env, ret, sz);
                if (!(env->me_flags & MDB_NOMEMINIT)) {
                        memset((char *)ret + off, 0, psize);
                        ret->mp_pad = 0;
                }
        } else {
                txn->mt_flags |= MDB_TXN_ERROR;
        }
        return ret;
}
/** Free a single page.
 * Saves single pages to a list, for future reuse.
 * (This is not used for multi-page overflow pages.)
 */
static void
mdb_page_free(MDB_env *env, MDB_page *mp)
{
        mp->mp_next = env->me_dpages;
        VGMEMP_FREE(env, mp);
        env->me_dpages = mp;
}

/** Free a dirty page */
static void
mdb_dpage_free(MDB_env *env, MDB_page *dp)
{
        if (!IS_OVERFLOW(dp) || dp->mp_pages == 1) {
                mdb_page_free(env, dp);
        } else {
                /* large pages just get freed directly */
                VGMEMP_FREE(env, dp);
                free(dp);
        }
}

/**     Return all dirty pages to dpage list */
static void
mdb_dlist_free(MDB_txn *txn)
{
        MDB_env *env = txn->mt_env;
        MDB_ID2L dl = txn->mt_u.dirty_list;
        unsigned i, n = dl[0].mid;

        for (i = 1; i <= n; i++) {
                mdb_dpage_free(env, dl[i].mptr);
        }
        dl[0].mid = 0;
}

/** Loosen or free a single page.
 * Saves single pages to a list for future reuse
 * in this same txn. It has been pulled from the freeDB
 * and already resides on the dirty list, but has been
 * deleted. Use these pages first before pulling again
 * from the freeDB.
 *
 * If the page wasn't dirtied in this txn, just add it
 * to this txn's free list.
 */
static int
mdb_page_loose(MDB_cursor *mc, MDB_page *mp)
{
        int loose = 0;
        pgno_t pgno = mp->mp_pgno;
        MDB_txn *txn = mc->mc_txn;

        if ((mp->mp_flags & P_DIRTY) && mc->mc_dbi != FREE_DBI) {
                if (txn->mt_parent) {
                        MDB_ID2 *dl = txn->mt_u.dirty_list;
                        /* If txn has a parent, make sure the page is in our
                         * dirty list.
                         */
                        if (dl[0].mid) {
                                unsigned x = mdb_mid2l_search(dl, pgno);
                                if (x <= dl[0].mid && dl[x].mid == pgno) {
                                        if (mp != dl[x].mptr) { /* bad cursor? */
                                                mc->mc_flags &= ~(C_INITIALIZED|C_EOF);
                                                txn->mt_flags |= MDB_TXN_ERROR;
                                                return MDB_CORRUPTED;
                                        }
                                        /* ok, it's ours */
                                        loose = 1;
                                }
                        }
                } else {
                        /* no parent txn, so it's just ours */
                        loose = 1;
                }
        }
        if (loose) {
                DPRINTF(("loosen db %d page %"Z"u", DDBI(mc),
                        mp->mp_pgno));
                NEXT_LOOSE_PAGE(mp) = txn->mt_loose_pgs;
                txn->mt_loose_pgs = mp;
                txn->mt_loose_count++;
                mp->mp_flags |= P_LOOSE;
        } else {
                int rc = mdb_midl_append(&txn->mt_free_pgs, pgno);
                if (rc)
                        return rc;
        }

        return MDB_SUCCESS;
}

/** Set or clear P_KEEP in dirty, non-overflow, non-sub pages watched by txn.
 * @param[in] mc A cursor handle for the current operation.
 * @param[in] pflags Flags of the pages to update:
 * P_DIRTY to set P_KEEP, P_DIRTY|P_KEEP to clear it.
 * @param[in] all No shortcuts. Needed except after a full #mdb_page_flush().
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_pages_xkeep(MDB_cursor *mc, unsigned pflags, int all)
{
        enum { Mask = P_SUBP|P_DIRTY|P_LOOSE|P_KEEP };
        MDB_txn *txn = mc->mc_txn;
        MDB_cursor *m3;
        MDB_xcursor *mx;
        MDB_page *dp, *mp;
        MDB_node *leaf;
        unsigned i, j;
        int rc = MDB_SUCCESS, level;

        /* Mark pages seen by cursors */
        if (mc->mc_flags & C_UNTRACK)
                mc = NULL;                              /* will find mc in mt_cursors */
        for (i = txn->mt_numdbs;; mc = txn->mt_cursors[--i]) {
                for (; mc; mc=mc->mc_next) {
                        if (!(mc->mc_flags & C_INITIALIZED))
                                continue;
                        for (m3 = mc;; m3 = &mx->mx_cursor) {
                                mp = NULL;
                                for (j=0; j<m3->mc_snum; j++) {
                                        mp = m3->mc_pg[j];
                                        if ((mp->mp_flags & Mask) == pflags)
                                                mp->mp_flags ^= P_KEEP;
                                }
                                mx = m3->mc_xcursor;
                                /* Proceed to mx if it is at a sub-database */
                                if (! (mx && (mx->mx_cursor.mc_flags & C_INITIALIZED)))
                                        break;
                                if (! (mp && (mp->mp_flags & P_LEAF)))
                                        break;
                                leaf = NODEPTR(mp, m3->mc_ki[j-1]);
                                if (!(leaf->mn_flags & F_SUBDATA))
                                        break;
                        }
                }
                if (i == 0)
                        break;
        }

        if (all) {
                /* Mark dirty root pages */
                for (i=0; i<txn->mt_numdbs; i++) {
                        if (txn->mt_dbflags[i] & DB_DIRTY) {
                                pgno_t pgno = txn->mt_dbs[i].md_root;
                                if (pgno == P_INVALID)
                                        continue;
                                if ((rc = mdb_page_get(txn, pgno, &dp, &level)) != MDB_SUCCESS)
                                        break;
                                if ((dp->mp_flags & Mask) == pflags && level <= 1)
                                        dp->mp_flags ^= P_KEEP;
                        }
                }
        }

        return rc;
}

static int mdb_page_flush(MDB_txn *txn, int keep);

/**     Spill pages from the dirty list back to disk.
 * This is intended to prevent running into #MDB_TXN_FULL situations,
 * but note that they may still occur in a few cases:
 *      1) our estimate of the txn size could be too small. Currently this
 *       seems unlikely, except with a large number of #MDB_MULTIPLE items.
 *      2) child txns may run out of space if their parents dirtied a
 *       lot of pages and never spilled them. TODO: we probably should do
 *       a preemptive spill during #mdb_txn_begin() of a child txn, if
 *       the parent's dirty_room is below a given threshold.
 *
 * Otherwise, if not using nested txns, it is expected that apps will
 * not run into #MDB_TXN_FULL any more. The pages are flushed to disk
 * the same way as for a txn commit, e.g. their P_DIRTY flag is cleared.
 * If the txn never references them again, they can be left alone.
 * If the txn only reads them, they can be used without any fuss.
 * If the txn writes them again, they can be dirtied immediately without
 * going thru all of the work of #mdb_page_touch(). Such references are
 * handled by #mdb_page_unspill().
 *
 * Also note, we never spill DB root pages, nor pages of active cursors,
 * because we'll need these back again soon anyway. And in nested txns,
 * we can't spill a page in a child txn if it was already spilled in a
 * parent txn. That would alter the parent txns' data even though
 * the child hasn't committed yet, and we'd have no way to undo it if
 * the child aborted.
 *
 * @param[in] m0 cursor A cursor handle identifying the transaction and
 *      database for which we are checking space.
 * @param[in] key For a put operation, the key being stored.
 * @param[in] data For a put operation, the data being stored.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_spill(MDB_cursor *m0, MDB_val *key, MDB_val *data)
{
        MDB_txn *txn = m0->mc_txn;
        MDB_page *dp;
        MDB_ID2L dl = txn->mt_u.dirty_list;
        unsigned int i, j, need;
        int rc;

        if (m0->mc_flags & C_SUB)
                return MDB_SUCCESS;

        /* Estimate how much space this op will take */
        i = m0->mc_db->md_depth;
        /* Named DBs also dirty the main DB */
        if (m0->mc_dbi > MAIN_DBI)
                i += txn->mt_dbs[MAIN_DBI].md_depth;
        /* For puts, roughly factor in the key+data size */
        if (key)
                i += (LEAFSIZE(key, data) + txn->mt_env->me_psize) / txn->mt_env->me_psize;
        i += i; /* double it for good measure */
        need = i;

        if (txn->mt_dirty_room > i)
                return MDB_SUCCESS;

        if (!txn->mt_spill_pgs) {
                txn->mt_spill_pgs = mdb_midl_alloc(MDB_IDL_UM_MAX);
                if (!txn->mt_spill_pgs)
                        return ENOMEM;
        } else {
                /* purge deleted slots */
                MDB_IDL sl = txn->mt_spill_pgs;
                unsigned int num = sl[0];
                j=0;
                for (i=1; i<=num; i++) {
                        if (!(sl[i] & 1))
                                sl[++j] = sl[i];
                }
                sl[0] = j;
        }

        /* Preserve pages which may soon be dirtied again */
        if ((rc = mdb_pages_xkeep(m0, P_DIRTY, 1)) != MDB_SUCCESS)
                goto done;

        /* Less aggressive spill - we originally spilled the entire dirty list,
         * with a few exceptions for cursor pages and DB root pages. But this
         * turns out to be a lot of wasted effort because in a large txn many
         * of those pages will need to be used again. So now we spill only 1/8th
         * of the dirty pages. Testing revealed this to be a good tradeoff,
         * better than 1/2, 1/4, or 1/10.
         */
        if (need < MDB_IDL_UM_MAX / 8)
                need = MDB_IDL_UM_MAX / 8;

        /* Save the page IDs of all the pages we're flushing */
        /* flush from the tail forward, this saves a lot of shifting later on. */
        for (i=dl[0].mid; i && need; i--) {
                MDB_ID pn = dl[i].mid << 1;
                dp = dl[i].mptr;
                if (dp->mp_flags & (P_LOOSE|P_KEEP))
                        continue;
                /* Can't spill twice, make sure it's not already in a parent's
                 * spill list.
                 */
                if (txn->mt_parent) {
                        MDB_txn *tx2;
                        for (tx2 = txn->mt_parent; tx2; tx2 = tx2->mt_parent) {
                                if (tx2->mt_spill_pgs) {
                                        j = mdb_midl_search(tx2->mt_spill_pgs, pn);
                                        if (j <= tx2->mt_spill_pgs[0] && tx2->mt_spill_pgs[j] == pn) {
                                                dp->mp_flags |= P_KEEP;
                                                break;
                                        }
                                }
                        }
                        if (tx2)
                                continue;
                }
                if ((rc = mdb_midl_append(&txn->mt_spill_pgs, pn)))
                        goto done;
                need--;
        }
        mdb_midl_sort(txn->mt_spill_pgs);

        /* Flush the spilled part of dirty list */
        if ((rc = mdb_page_flush(txn, i)) != MDB_SUCCESS)
                goto done;

        /* Reset any dirty pages we kept that page_flush didn't see */
        rc = mdb_pages_xkeep(m0, P_DIRTY|P_KEEP, i);

done:
        txn->mt_flags |= rc ? MDB_TXN_ERROR : MDB_TXN_SPILLS;
        return rc;
}

/** Find oldest txnid still referenced. Expects txn->mt_txnid > 0. */
static txnid_t
mdb_find_oldest(MDB_txn *txn)
{
        int i;
        txnid_t mr, oldest = txn->mt_txnid - 1;
        if (txn->mt_env->me_txns) {
                MDB_reader *r = txn->mt_env->me_txns->mti_readers;
                for (i = txn->mt_env->me_txns->mti_numreaders; --i >= 0; ) {
                        if (r[i].mr_pid) {
                                mr = r[i].mr_txnid;
                                if (oldest > mr)
                                        oldest = mr;
                        }
                }
        }
        return oldest;
}

/** Add a page to the txn's dirty list */
static void
mdb_page_dirty(MDB_txn *txn, MDB_page *mp)
{
        MDB_ID2 mid;
        int rc, (*insert)(MDB_ID2L, MDB_ID2 *);

        if (txn->mt_env->me_flags & MDB_WRITEMAP) {
                insert = mdb_mid2l_append;
        } else {
                insert = mdb_mid2l_insert;
        }
        mid.mid = mp->mp_pgno;
        mid.mptr = mp;
        rc = insert(txn->mt_u.dirty_list, &mid);
        mdb_tassert(txn, rc == 0);
        txn->mt_dirty_room--;
}

/** Allocate page numbers and memory for writing.  Maintain me_pglast,
 * me_pghead and mt_next_pgno.
 *
 * If there are free pages available from older transactions, they
 * are re-used first. Otherwise allocate a new page at mt_next_pgno.
 * Do not modify the freedB, just merge freeDB records into me_pghead[]
 * and move me_pglast to say which records were consumed.  Only this
 * function can create me_pghead and move me_pglast/mt_next_pgno.
 * @param[in] mc cursor A cursor handle identifying the transaction and
 *      database for which we are allocating.
 * @param[in] num the number of pages to allocate.
 * @param[out] mp Address of the allocated page(s). Requests for multiple pages
 *  will always be satisfied by a single contiguous chunk of memory.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp)
{
#ifdef MDB_PARANOID     /* Seems like we can ignore this now */
        /* Get at most <Max_retries> more freeDB records once me_pghead
         * has enough pages.  If not enough, use new pages from the map.
         * If <Paranoid> and mc is updating the freeDB, only get new
         * records if me_pghead is empty. Then the freelist cannot play
         * catch-up with itself by growing while trying to save it.
         */
        enum { Paranoid = 1, Max_retries = 500 };
#else
        enum { Paranoid = 0, Max_retries = INT_MAX /*infinite*/ };
#endif
        int rc, retry = num * 20;
        MDB_txn *txn = mc->mc_txn;
        MDB_env *env = txn->mt_env;
        pgno_t pgno, *mop = env->me_pghead;
        unsigned i, j, mop_len = mop ? mop[0] : 0, n2 = num-1;
        MDB_page *np;
        txnid_t oldest = 0, last;
        MDB_cursor_op op;
        MDB_cursor m2;

        /* If there are any loose pages, just use them */
        if (num == 1 && txn->mt_loose_pgs) {
                np = txn->mt_loose_pgs;
                txn->mt_loose_pgs = NEXT_LOOSE_PAGE(np);
                txn->mt_loose_count--;
                DPRINTF(("db %d use loose page %"Z"u", DDBI(mc),
                                np->mp_pgno));
                *mp = np;
                return MDB_SUCCESS;
        }

        *mp = NULL;

        /* If our dirty list is already full, we can't do anything */
        if (txn->mt_dirty_room == 0) {
                rc = MDB_TXN_FULL;
                goto fail;
        }

        for (op = MDB_FIRST;; op = MDB_NEXT) {
                MDB_val key, data;
                MDB_node *leaf;
                pgno_t *idl;

                /* Seek a big enough contiguous page range. Prefer
                 * pages at the tail, just truncating the list.
                 */
                if (mop_len > n2) {
                        i = mop_len;
                        do {
                                pgno = mop[i];
                                if (mop[i-n2] == pgno+n2)
                                        goto search_done;
                        } while (--i > n2);
                        if (--retry < 0)
                                break;
                }

                if (op == MDB_FIRST) {  /* 1st iteration */
                        /* Prepare to fetch more and coalesce */
                        oldest = mdb_find_oldest(txn);
                        last = env->me_pglast;
                        mdb_cursor_init(&m2, txn, FREE_DBI, NULL);
                        if (last) {
                                op = MDB_SET_RANGE;
                                key.mv_data = &last; /* will look up last+1 */
                                key.mv_size = sizeof(last);
                        }
                        if (Paranoid && mc->mc_dbi == FREE_DBI)
                                retry = -1;
                }
                if (Paranoid && retry < 0 && mop_len)
                        break;

                last++;
                /* Do not fetch more if the record will be too recent */
                if (oldest <= last)
                        break;
                rc = mdb_cursor_get(&m2, &key, NULL, op);
                if (rc) {
                        if (rc == MDB_NOTFOUND)
                                break;
                        goto fail;
                }
                last = *(txnid_t*)key.mv_data;
                if (oldest <= last)
                        break;
                np = m2.mc_pg[m2.mc_top];
                leaf = NODEPTR(np, m2.mc_ki[m2.mc_top]);
                if ((rc = mdb_node_read(txn, leaf, &data)) != MDB_SUCCESS)
                        return rc;

                idl = (MDB_ID *) data.mv_data;
                i = idl[0];
                if (!mop) {
                        if (!(env->me_pghead = mop = mdb_midl_alloc(i))) {
                                rc = ENOMEM;
                                goto fail;
                        }
                } else {
                        if ((rc = mdb_midl_need(&env->me_pghead, i)) != 0)
                                goto fail;
                        mop = env->me_pghead;
                }
                env->me_pglast = last;
#if (MDB_DEBUG) > 1
                DPRINTF(("IDL read txn %"Z"u root %"Z"u num %u",
                        last, txn->mt_dbs[FREE_DBI].md_root, i));
                for (j = i; j; j--)
                        DPRINTF(("IDL %"Z"u", idl[j]));
#endif
                /* Merge in descending sorted order */
                mdb_midl_xmerge(mop, idl);
                mop_len = mop[0];
        }

        /* Use new pages from the map when nothing suitable in the freeDB */
        i = 0;
        pgno = txn->mt_next_pgno;
        if (pgno + num >= env->me_maxpg) {
                        DPUTS("DB size maxed out");
                        rc = MDB_MAP_FULL;
                        goto fail;
        }

search_done:
        if (env->me_flags & MDB_WRITEMAP) {
                np = (MDB_page *)(env->me_map + env->me_psize * pgno);
        } else {
                if (!(np = mdb_page_malloc(txn, num))) {
                        rc = ENOMEM;
                        goto fail;
                }
        }
        if (i) {
                mop[0] = mop_len -= num;
                /* Move any stragglers down */
                for (j = i-num; j < mop_len; )
                        mop[++j] = mop[++i];
        } else {
                txn->mt_next_pgno = pgno + num;
        }
        np->mp_pgno = pgno;
        mdb_page_dirty(txn, np);
        *mp = np;

        return MDB_SUCCESS;

fail:
        txn->mt_flags |= MDB_TXN_ERROR;
        return rc;
}

/** Copy the used portions of a non-overflow page.
 * @param[in] dst page to copy into
 * @param[in] src page to copy from
 * @param[in] psize size of a page
 */
static void
mdb_page_copy(MDB_page *dst, MDB_page *src, unsigned int psize)
{
        enum { Align = sizeof(pgno_t) };
        indx_t upper = src->mp_upper, lower = src->mp_lower, unused = upper-lower;

        /* If page isn't full, just copy the used portion. Adjust
         * alignment so memcpy may copy words instead of bytes.
         */
        if ((unused &= -Align) && !IS_LEAF2(src)) {
                upper = (upper + PAGEBASE) & -Align;
                memcpy(dst, src, (lower + PAGEBASE + (Align-1)) & -Align);
                memcpy((pgno_t *)((char *)dst+upper), (pgno_t *)((char *)src+upper),
                        psize - upper);
        } else {
                memcpy(dst, src, psize - unused);
        }
}

/** Pull a page off the txn's spill list, if present.
 * If a page being referenced was spilled to disk in this txn, bring
 * it back and make it dirty/writable again.
 * @param[in] txn the transaction handle.
 * @param[in] mp the page being referenced. It must not be dirty.
 * @param[out] ret the writable page, if any. ret is unchanged if
 * mp wasn't spilled.
 */
static int
mdb_page_unspill(MDB_txn *txn, MDB_page *mp, MDB_page **ret)
{
        MDB_env *env = txn->mt_env;
        const MDB_txn *tx2;
        unsigned x;
        pgno_t pgno = mp->mp_pgno, pn = pgno << 1;

        for (tx2 = txn; tx2; tx2=tx2->mt_parent) {
                if (!tx2->mt_spill_pgs)
                        continue;
                x = mdb_midl_search(tx2->mt_spill_pgs, pn);
                if (x <= tx2->mt_spill_pgs[0] && tx2->mt_spill_pgs[x] == pn) {
                        MDB_page *np;
                        int num;
                        if (txn->mt_dirty_room == 0)
                                return MDB_TXN_FULL;
                        if (IS_OVERFLOW(mp))
                                num = mp->mp_pages;
                        else
                                num = 1;
                        if (env->me_flags & MDB_WRITEMAP) {
                                np = mp;
                        } else {
                                np = mdb_page_malloc(txn, num);
                                if (!np)
                                        return ENOMEM;
                                if (num > 1)
                                        memcpy(np, mp, num * env->me_psize);
                                else
                                        mdb_page_copy(np, mp, env->me_psize);
                        }
                        if (tx2 == txn) {
                                /* If in current txn, this page is no longer spilled.
                                 * If it happens to be the last page, truncate the spill list.
                                 * Otherwise mark it as deleted by setting the LSB.
                                 */
                                if (x == txn->mt_spill_pgs[0])
                                        txn->mt_spill_pgs[0]--;
                                else
                                        txn->mt_spill_pgs[x] |= 1;
                        }       /* otherwise, if belonging to a parent txn, the
                                 * page remains spilled until child commits
                                 */

                        mdb_page_dirty(txn, np);
                        np->mp_flags |= P_DIRTY;
                        *ret = np;
                        break;
                }
        }
        return MDB_SUCCESS;
}

/** Touch a page: make it dirty and re-insert into tree with updated pgno.
 * @param[in] mc cursor pointing to the page to be touched
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_touch(MDB_cursor *mc)
{
        MDB_page *mp = mc->mc_pg[mc->mc_top], *np;
        MDB_txn *txn = mc->mc_txn;
        MDB_cursor *m2, *m3;
        pgno_t  pgno;
        int rc;

        if (!F_ISSET(mp->mp_flags, P_DIRTY)) {
                if (txn->mt_flags & MDB_TXN_SPILLS) {
                        np = NULL;
                        rc = mdb_page_unspill(txn, mp, &np);
                        if (rc)
                                goto fail;
                        if (np)
                                goto done;
                }
                if ((rc = mdb_midl_need(&txn->mt_free_pgs, 1)) ||
                        (rc = mdb_page_alloc(mc, 1, &np)))
                        goto fail;
                pgno = np->mp_pgno;
                DPRINTF(("touched db %d page %"Z"u -> %"Z"u", DDBI(mc),
                        mp->mp_pgno, pgno));
                mdb_cassert(mc, mp->mp_pgno != pgno);
                mdb_midl_xappend(txn->mt_free_pgs, mp->mp_pgno);
                /* Update the parent page, if any, to point to the new page */
                if (mc->mc_top) {
                        MDB_page *parent = mc->mc_pg[mc->mc_top-1];
                        MDB_node *node = NODEPTR(parent, mc->mc_ki[mc->mc_top-1]);
                        SETPGNO(node, pgno);
                } else {
                        mc->mc_db->md_root = pgno;
                }
        } else if (txn->mt_parent && !IS_SUBP(mp)) {
                MDB_ID2 mid, *dl = txn->mt_u.dirty_list;
                pgno = mp->mp_pgno;
                /* If txn has a parent, make sure the page is in our
                 * dirty list.
                 */
                if (dl[0].mid) {
                        unsigned x = mdb_mid2l_search(dl, pgno);
                        if (x <= dl[0].mid && dl[x].mid == pgno) {
                                if (mp != dl[x].mptr) { /* bad cursor? */
                                        mc->mc_flags &= ~(C_INITIALIZED|C_EOF);
                                        txn->mt_flags |= MDB_TXN_ERROR;
                                        return MDB_CORRUPTED;
                                }
                                return 0;
                        }
                }
                mdb_cassert(mc, dl[0].mid < MDB_IDL_UM_MAX);
                /* No - copy it */
                np = mdb_page_malloc(txn, 1);
                if (!np)
                        return ENOMEM;
                mid.mid = pgno;
                mid.mptr = np;
                rc = mdb_mid2l_insert(dl, &mid);
                mdb_cassert(mc, rc == 0);
        } else {
                return 0;
        }

        mdb_page_copy(np, mp, txn->mt_env->me_psize);
        np->mp_pgno = pgno;
        np->mp_flags |= P_DIRTY;

done:
        /* Adjust cursors pointing to mp */
        mc->mc_pg[mc->mc_top] = np;
        m2 = txn->mt_cursors[mc->mc_dbi];
        if (mc->mc_flags & C_SUB) {
                for (; m2; m2=m2->mc_next) {
                        m3 = &m2->mc_xcursor->mx_cursor;
                        if (m3->mc_snum < mc->mc_snum) continue;
                        if (m3->mc_pg[mc->mc_top] == mp)
                                m3->mc_pg[mc->mc_top] = np;
                }
        } else {
                for (; m2; m2=m2->mc_next) {
                        if (m2->mc_snum < mc->mc_snum) continue;
                        if (m2->mc_pg[mc->mc_top] == mp) {
                                m2->mc_pg[mc->mc_top] = np;
                                if ((mc->mc_db->md_flags & MDB_DUPSORT) &&
                                        IS_LEAF(np) &&
                                        m2->mc_ki[mc->mc_top] == mc->mc_ki[mc->mc_top])
                                {
                                        MDB_node *leaf = NODEPTR(np, mc->mc_ki[mc->mc_top]);
                                        if (!(leaf->mn_flags & F_SUBDATA))
                                                m2->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
                                }
                        }
                }
        }
        return 0;

fail:
        txn->mt_flags |= MDB_TXN_ERROR;
        return rc;
}

int
mdb_env_sync(MDB_env *env, int force)
{
        int rc = 0;
        if (force || !F_ISSET(env->me_flags, MDB_NOSYNC)) {
                if (env->me_flags & MDB_WRITEMAP) {
                        int flags = ((env->me_flags & MDB_MAPASYNC) && !force)
                                ? MS_ASYNC : MS_SYNC;
                        if (MDB_MSYNC(env->me_map, env->me_mapsize, flags))
                                rc = ErrCode();
#ifdef _WIN32
                        else if (flags == MS_SYNC && MDB_FDATASYNC(env->me_fd))
                                rc = ErrCode();
#endif
                } else {
                        if (MDB_FDATASYNC(env->me_fd))
                                rc = ErrCode();
                }
        }
        return rc;
}

/** Back up parent txn's cursors, then grab the originals for tracking */
static int
mdb_cursor_shadow(MDB_txn *src, MDB_txn *dst)
{
        MDB_cursor *mc, *bk;
        MDB_xcursor *mx;
        size_t size;
        int i;

        for (i = src->mt_numdbs; --i >= 0; ) {
                if ((mc = src->mt_cursors[i]) != NULL) {
                        size = sizeof(MDB_cursor);
                        if (mc->mc_xcursor)
                                size += sizeof(MDB_xcursor);
                        for (; mc; mc = bk->mc_next) {
                                bk = malloc(size);
                                if (!bk)
                                        return ENOMEM;
                                *bk = *mc;
                                mc->mc_backup = bk;
                                mc->mc_db = &dst->mt_dbs[i];
                                /* Kill pointers into src - and dst to reduce abuse: The
                                 * user may not use mc until dst ends. Otherwise we'd...
                                 */
                                mc->mc_txn    = NULL;   /* ...set this to dst */
                                mc->mc_dbflag = NULL;   /* ...and &dst->mt_dbflags[i] */
                                if ((mx = mc->mc_xcursor) != NULL) {
                                        *(MDB_xcursor *)(bk+1) = *mx;
                                        mx->mx_cursor.mc_txn = NULL; /* ...and dst. */
                                }
                                mc->mc_next = dst->mt_cursors[i];
                                dst->mt_cursors[i] = mc;
                        }
                }
        }
        return MDB_SUCCESS;
}

/** Close this write txn's cursors, give parent txn's cursors back to parent.
 * @param[in] txn the transaction handle.
 * @param[in] merge true to keep changes to parent cursors, false to revert.
 * @return 0 on success, non-zero on failure.
 */
static void
mdb_cursors_close(MDB_txn *txn, unsigned merge)
{
        MDB_cursor **cursors = txn->mt_cursors, *mc, *next, *bk;
        MDB_xcursor *mx;
        int i;

        for (i = txn->mt_numdbs; --i >= 0; ) {
                for (mc = cursors[i]; mc; mc = next) {
                        next = mc->mc_next;
                        if ((bk = mc->mc_backup) != NULL) {
                                if (merge) {
                                        /* Commit changes to parent txn */
                                        mc->mc_next = bk->mc_next;
                                        mc->mc_backup = bk->mc_backup;
                                        mc->mc_txn = bk->mc_txn;
                                        mc->mc_db = bk->mc_db;
                                        mc->mc_dbflag = bk->mc_dbflag;
                                        if ((mx = mc->mc_xcursor) != NULL)
                                                mx->mx_cursor.mc_txn = bk->mc_txn;
                                } else {
                                        /* Abort nested txn */
                                        *mc = *bk;
                                        if ((mx = mc->mc_xcursor) != NULL)
                                                *mx = *(MDB_xcursor *)(bk+1);
                                }
                                mc = bk;
                        }
                        /* Only malloced cursors are permanently tracked. */
                        free(mc);
                }
                cursors[i] = NULL;
        }
}

#if !(MDB_DEBUG)
#define mdb_txn_reset0(txn, act) mdb_txn_reset0(txn)
#endif
static void
mdb_txn_reset0(MDB_txn *txn, const char *act);

#if !(MDB_PIDLOCK)              /* Currently the same as defined(_WIN32) */
enum Pidlock_op {
        Pidset, Pidcheck
};
#else
enum Pidlock_op {
        Pidset = F_SETLK, Pidcheck = F_GETLK
};
#endif

/** Set or check a pid lock. Set returns 0 on success.
 * Check returns 0 if the process is certainly dead, nonzero if it may
 * be alive (the lock exists or an error happened so we do not know).
 *
 * On Windows Pidset is a no-op, we merely check for the existence
 * of the process with the given pid. On POSIX we use a single byte
 * lock on the lockfile, set at an offset equal to the pid.
 */
static int
mdb_reader_pid(MDB_env *env, enum Pidlock_op op, MDB_PID_T pid)
{
#if !(MDB_PIDLOCK)              /* Currently the same as defined(_WIN32) */
        int ret = 0;
        HANDLE h;
        if (op == Pidcheck) {
                h = OpenProcess(env->me_pidquery, FALSE, pid);
                /* No documented "no such process" code, but other program use this: */
                if (!h)
                        return ErrCode() != ERROR_INVALID_PARAMETER;
                /* A process exists until all handles to it close. Has it exited? */
                ret = WaitForSingleObject(h, 0) != 0;
                CloseHandle(h);
        }
        return ret;
#else
        for (;;) {
                int rc;
                struct flock lock_info;
                memset(&lock_info, 0, sizeof(lock_info));
                lock_info.l_type = F_WRLCK;
                lock_info.l_whence = SEEK_SET;
                lock_info.l_start = pid;
                lock_info.l_len = 1;
                if ((rc = fcntl(env->me_lfd, op, &lock_info)) == 0) {
                        if (op == F_GETLK && lock_info.l_type != F_UNLCK)
                                rc = -1;
                } else if ((rc = ErrCode()) == EINTR) {
                        continue;
                }
                return rc;
        }
#endif
}

/** Common code for #mdb_txn_begin() and #mdb_txn_renew().
 * @param[in] txn the transaction handle to initialize
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_txn_renew0(MDB_txn *txn)
{
        MDB_env *env = txn->mt_env;
        MDB_txninfo *ti = env->me_txns;
        MDB_meta *meta;
        unsigned int i, nr;
        uint16_t x;
        int rc, new_notls = 0;

        /* Setup db info */
        txn->mt_numdbs = env->me_numdbs;
        txn->mt_dbxs = env->me_dbxs;    /* mostly static anyway */

        if (txn->mt_flags & MDB_TXN_RDONLY) {
                if (!ti) {
                        meta = env->me_metas[ mdb_env_pick_meta(env) ];
                        txn->mt_txnid = meta->mm_txnid;
                        txn->mt_u.reader = NULL;
                } else {
                        MDB_reader *r = (env->me_flags & MDB_NOTLS) ? txn->mt_u.reader :
                                pthread_getspecific(env->me_txkey);
                        if (r) {
                                if (r->mr_pid != env->me_pid || r->mr_txnid != (txnid_t)-1)
                                        return MDB_BAD_RSLOT;
                        } else {
                                MDB_PID_T pid = env->me_pid;
                                MDB_THR_T tid = pthread_self();

                                if (!env->me_live_reader) {
                                        rc = mdb_reader_pid(env, Pidset, pid);
                                        if (rc)
                                                return rc;
                                        env->me_live_reader = 1;
                                }

                                LOCK_MUTEX_R(env);
                                nr = ti->mti_numreaders;
                                for (i=0; i<nr; i++)
                                        if (ti->mti_readers[i].mr_pid == 0)
                                                break;
                                if (i == env->me_maxreaders) {
                                        UNLOCK_MUTEX_R(env);
                                        return MDB_READERS_FULL;
                                }
                                ti->mti_readers[i].mr_pid = pid;
                                ti->mti_readers[i].mr_tid = tid;
                                if (i == nr)
                                        ti->mti_numreaders = ++nr;
                                /* Save numreaders for un-mutexed mdb_env_close() */
                                env->me_numreaders = nr;
                                UNLOCK_MUTEX_R(env);

                                r = &ti->mti_readers[i];
                                new_notls = (env->me_flags & MDB_NOTLS);
                                if (!new_notls && (rc=pthread_setspecific(env->me_txkey, r))) {
                                        r->mr_pid = 0;
                                        return rc;
                                }
                        }
                        txn->mt_txnid = r->mr_txnid = ti->mti_txnid;
                        txn->mt_u.reader = r;
                        meta = env->me_metas[txn->mt_txnid & 1];
                }
        } else {
                if (ti) {
                        LOCK_MUTEX_W(env);

                        txn->mt_txnid = ti->mti_txnid;
                        meta = env->me_metas[txn->mt_txnid & 1];
                } else {
                        meta = env->me_metas[ mdb_env_pick_meta(env) ];
                        txn->mt_txnid = meta->mm_txnid;
                }
                txn->mt_txnid++;
#if MDB_DEBUG
                if (txn->mt_txnid == mdb_debug_start)
                        mdb_debug = 1;
#endif
                txn->mt_dirty_room = MDB_IDL_UM_MAX;
                txn->mt_u.dirty_list = env->me_dirty_list;
                txn->mt_u.dirty_list[0].mid = 0;
                txn->mt_free_pgs = env->me_free_pgs;
                txn->mt_free_pgs[0] = 0;
                txn->mt_spill_pgs = NULL;
                env->me_txn = txn;
                memcpy(txn->mt_dbiseqs, env->me_dbiseqs, env->me_maxdbs * sizeof(unsigned int));
        }

        /* Copy the DB info and flags */
        memcpy(txn->mt_dbs, meta->mm_dbs, 2 * sizeof(MDB_db));

        /* Moved to here to avoid a data race in read TXNs */
        txn->mt_next_pgno = meta->mm_last_pg+1;

        for (i=2; i<txn->mt_numdbs; i++) {
                x = env->me_dbflags[i];
                txn->mt_dbs[i].md_flags = x & PERSISTENT_FLAGS;
                txn->mt_dbflags[i] = (x & MDB_VALID) ? DB_VALID|DB_STALE : 0;
        }
        txn->mt_dbflags[0] = txn->mt_dbflags[1] = DB_VALID;

        if (env->me_maxpg < txn->mt_next_pgno) {
                mdb_txn_reset0(txn, "renew0-mapfail");
                if (new_notls) {
                        txn->mt_u.reader->mr_pid = 0;
                        txn->mt_u.reader = NULL;
                }
                return MDB_MAP_RESIZED;
        }

        return MDB_SUCCESS;
}

int
mdb_txn_renew(MDB_txn *txn)
{
        int rc;

        if (!txn || txn->mt_dbxs)       /* A reset txn has mt_dbxs==NULL */
                return EINVAL;

        if (txn->mt_env->me_flags & MDB_FATAL_ERROR) {
                DPUTS("environment had fatal error, must shutdown!");
                return MDB_PANIC;
        }

        rc = mdb_txn_renew0(txn);
        if (rc == MDB_SUCCESS) {
                DPRINTF(("renew txn %"Z"u%c %p on mdbenv %p, root page %"Z"u",
                        txn->mt_txnid, (txn->mt_flags & MDB_TXN_RDONLY) ? 'r' : 'w',
                        (void *)txn, (void *)txn->mt_env, txn->mt_dbs[MAIN_DBI].md_root));
        }
        return rc;
}

int
mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **ret)
{
        MDB_txn *txn;
        MDB_ntxn *ntxn;
        int rc, size, tsize = sizeof(MDB_txn);

        if (env->me_flags & MDB_FATAL_ERROR) {
                DPUTS("environment had fatal error, must shutdown!");
                return MDB_PANIC;
        }
        if ((env->me_flags & MDB_RDONLY) && !(flags & MDB_RDONLY))
                return EACCES;
        if (parent) {
                /* Nested transactions: Max 1 child, write txns only, no writemap */
                if (parent->mt_child ||
                        (flags & MDB_RDONLY) ||
                        (parent->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_ERROR)) ||
                        (env->me_flags & MDB_WRITEMAP))
                {
                        return (parent->mt_flags & MDB_TXN_RDONLY) ? EINVAL : MDB_BAD_TXN;
                }
                tsize = sizeof(MDB_ntxn);
        }
        size = tsize + env->me_maxdbs * (sizeof(MDB_db)+1);
        if (!(flags & MDB_RDONLY)) {
                size += env->me_maxdbs * sizeof(MDB_cursor *);
                /* child txns use parent's dbiseqs */
                if (!parent)
                        size += env->me_maxdbs * sizeof(unsigned int);
        }

        if ((txn = calloc(1, size)) == NULL) {
                DPRINTF(("calloc: %s", strerror(errno)));
                return ENOMEM;
        }
        txn->mt_dbs = (MDB_db *) ((char *)txn + tsize);
        if (flags & MDB_RDONLY) {
                txn->mt_flags |= MDB_TXN_RDONLY;
                txn->mt_dbflags = (unsigned char *)(txn->mt_dbs + env->me_maxdbs);
                txn->mt_dbiseqs = env->me_dbiseqs;
        } else {
                txn->mt_cursors = (MDB_cursor **)(txn->mt_dbs + env->me_maxdbs);
                if (parent) {
                        txn->mt_dbiseqs = parent->mt_dbiseqs;
                        txn->mt_dbflags = (unsigned char *)(txn->mt_cursors + env->me_maxdbs);
                } else {
                        txn->mt_dbiseqs = (unsigned int *)(txn->mt_cursors + env->me_maxdbs);
                        txn->mt_dbflags = (unsigned char *)(txn->mt_dbiseqs + env->me_maxdbs);
                }
        }
        txn->mt_env = env;

        if (parent) {
                unsigned int i;
                txn->mt_u.dirty_list = malloc(sizeof(MDB_ID2)*MDB_IDL_UM_SIZE);
                if (!txn->mt_u.dirty_list ||
                        !(txn->mt_free_pgs = mdb_midl_alloc(MDB_IDL_UM_MAX)))
                {
                        free(txn->mt_u.dirty_list);
                        free(txn);
                        return ENOMEM;
                }
                txn->mt_txnid = parent->mt_txnid;
                txn->mt_dirty_room = parent->mt_dirty_room;
                txn->mt_u.dirty_list[0].mid = 0;
                txn->mt_spill_pgs = NULL;
                txn->mt_next_pgno = parent->mt_next_pgno;
                parent->mt_child = txn;
                txn->mt_parent = parent;
                txn->mt_numdbs = parent->mt_numdbs;
                txn->mt_flags = parent->mt_flags;
                txn->mt_dbxs = parent->mt_dbxs;
                memcpy(txn->mt_dbs, parent->mt_dbs, txn->mt_numdbs * sizeof(MDB_db));
                /* Copy parent's mt_dbflags, but clear DB_NEW */
                for (i=0; i<txn->mt_numdbs; i++)
                        txn->mt_dbflags[i] = parent->mt_dbflags[i] & ~DB_NEW;
                rc = 0;
                ntxn = (MDB_ntxn *)txn;
                ntxn->mnt_pgstate = env->me_pgstate; /* save parent me_pghead & co */
                if (env->me_pghead) {
                        size = MDB_IDL_SIZEOF(env->me_pghead);
                        env->me_pghead = mdb_midl_alloc(env->me_pghead[0]);
                        if (env->me_pghead)
                                memcpy(env->me_pghead, ntxn->mnt_pgstate.mf_pghead, size);
                        else
                                rc = ENOMEM;
                }
                if (!rc)
                        rc = mdb_cursor_shadow(parent, txn);
                if (rc)
                        mdb_txn_reset0(txn, "beginchild-fail");
        } else {
                rc = mdb_txn_renew0(txn);
        }
        if (rc)
                free(txn);
        else {
                *ret = txn;
                DPRINTF(("begin txn %"Z"u%c %p on mdbenv %p, root page %"Z"u",
                        txn->mt_txnid, (txn->mt_flags & MDB_TXN_RDONLY) ? 'r' : 'w',
                        (void *) txn, (void *) env, txn->mt_dbs[MAIN_DBI].md_root));
        }

        return rc;
}

MDB_env *
mdb_txn_env(MDB_txn *txn)
{
        if(!txn) return NULL;
        return txn->mt_env;
}

/** Export or close DBI handles opened in this txn. */
static void
mdb_dbis_update(MDB_txn *txn, int keep)
{
        int i;
        MDB_dbi n = txn->mt_numdbs;
        MDB_env *env = txn->mt_env;
        unsigned char *tdbflags = txn->mt_dbflags;

        for (i = n; --i >= 2;) {
                if (tdbflags[i] & DB_NEW) {
                        if (keep) {
                                env->me_dbflags[i] = txn->mt_dbs[i].md_flags | MDB_VALID;
                        } else {
                                char *ptr = env->me_dbxs[i].md_name.mv_data;
                                if (ptr) {
                                        env->me_dbxs[i].md_name.mv_data = NULL;
                                        env->me_dbxs[i].md_name.mv_size = 0;
                                        env->me_dbflags[i] = 0;
                                        env->me_dbiseqs[i]++;
                                        free(ptr);
                                }
                        }
                }
        }
        if (keep && env->me_numdbs < n)
                env->me_numdbs = n;
}

/** Common code for #mdb_txn_reset() and #mdb_txn_abort().
 * May be called twice for readonly txns: First reset it, then abort.
 * @param[in] txn the transaction handle to reset
 * @param[in] act why the transaction is being reset
 */
static void
mdb_txn_reset0(MDB_txn *txn, const char *act)
{
        MDB_env *env = txn->mt_env;

        /* Close any DBI handles opened in this txn */
        mdb_dbis_update(txn, 0);

        DPRINTF(("%s txn %"Z"u%c %p on mdbenv %p, root page %"Z"u",
                act, txn->mt_txnid, (txn->mt_flags & MDB_TXN_RDONLY) ? 'r' : 'w',
                (void *) txn, (void *)env, txn->mt_dbs[MAIN_DBI].md_root));

        if (F_ISSET(txn->mt_flags, MDB_TXN_RDONLY)) {
                if (txn->mt_u.reader) {
                        txn->mt_u.reader->mr_txnid = (txnid_t)-1;
                        if (!(env->me_flags & MDB_NOTLS))
                                txn->mt_u.reader = NULL; /* txn does not own reader */
                }
                txn->mt_numdbs = 0;             /* close nothing if called again */
                txn->mt_dbxs = NULL;    /* mark txn as reset */
        } else {
                mdb_cursors_close(txn, 0);

                if (!(env->me_flags & MDB_WRITEMAP)) {
                        mdb_dlist_free(txn);
                }
                mdb_midl_free(env->me_pghead);

                if (txn->mt_parent) {
                        txn->mt_parent->mt_child = NULL;
                        env->me_pgstate = ((MDB_ntxn *)txn)->mnt_pgstate;
                        mdb_midl_free(txn->mt_free_pgs);
                        mdb_midl_free(txn->mt_spill_pgs);
                        free(txn->mt_u.dirty_list);
                        return;
                }

                if (mdb_midl_shrink(&txn->mt_free_pgs))
                        env->me_free_pgs = txn->mt_free_pgs;
                env->me_pghead = NULL;
                env->me_pglast = 0;

                env->me_txn = NULL;
                /* The writer mutex was locked in mdb_txn_begin. */
                if (env->me_txns)
                        UNLOCK_MUTEX_W(env);
        }
}

void
mdb_txn_reset(MDB_txn *txn)
{
        if (txn == NULL)
                return;

        /* This call is only valid for read-only txns */
        if (!(txn->mt_flags & MDB_TXN_RDONLY))
                return;

        mdb_txn_reset0(txn, "reset");
}

void
mdb_txn_abort(MDB_txn *txn)
{
        if (txn == NULL)
                return;

        if (txn->mt_child)
                mdb_txn_abort(txn->mt_child);

        mdb_txn_reset0(txn, "abort");
        /* Free reader slot tied to this txn (if MDB_NOTLS && writable FS) */
        if ((txn->mt_flags & MDB_TXN_RDONLY) && txn->mt_u.reader)
                txn->mt_u.reader->mr_pid = 0;

        free(txn);
}

/** Save the freelist as of this transaction to the freeDB.
 * This changes the freelist. Keep trying until it stabilizes.
 */
static int
mdb_freelist_save(MDB_txn *txn)
{
        /* env->me_pghead[] can grow and shrink during this call.
         * env->me_pglast and txn->mt_free_pgs[] can only grow.
         * Page numbers cannot disappear from txn->mt_free_pgs[].
         */
        MDB_cursor mc;
        MDB_env *env = txn->mt_env;
        int rc, maxfree_1pg = env->me_maxfree_1pg, more = 1;
        txnid_t pglast = 0, head_id = 0;
        pgno_t  freecnt = 0, *free_pgs, *mop;
        ssize_t head_room = 0, total_room = 0, mop_len, clean_limit;

        mdb_cursor_init(&mc, txn, FREE_DBI, NULL);

        if (env->me_pghead) {
                /* Make sure first page of freeDB is touched and on freelist */
                rc = mdb_page_search(&mc, NULL, MDB_PS_FIRST|MDB_PS_MODIFY);
                if (rc && rc != MDB_NOTFOUND)
                        return rc;
        }

        if (!env->me_pghead && txn->mt_loose_pgs) {
                /* Put loose page numbers in mt_free_pgs, since
                 * we may be unable to return them to me_pghead.
                 */
                MDB_page *mp = txn->mt_loose_pgs;
                if ((rc = mdb_midl_need(&txn->mt_free_pgs, txn->mt_loose_count)) != 0)
                        return rc;
                for (; mp; mp = NEXT_LOOSE_PAGE(mp))
                        mdb_midl_xappend(txn->mt_free_pgs, mp->mp_pgno);
                txn->mt_loose_pgs = NULL;
                txn->mt_loose_count = 0;
        }

        /* MDB_RESERVE cancels meminit in ovpage malloc (when no WRITEMAP) */
        clean_limit = (env->me_flags & (MDB_NOMEMINIT|MDB_WRITEMAP))
                ? SSIZE_MAX : maxfree_1pg;

        for (;;) {
                /* Come back here after each Put() in case freelist changed */
                MDB_val key, data;
                pgno_t *pgs;
                ssize_t j;

                /* If using records from freeDB which we have not yet
                 * deleted, delete them and any we reserved for me_pghead.
                 */
                while (pglast < env->me_pglast) {
                        rc = mdb_cursor_first(&mc, &key, NULL);
                        if (rc)
                                return rc;
                        pglast = head_id = *(txnid_t *)key.mv_data;
                        total_room = head_room = 0;
                        mdb_tassert(txn, pglast <= env->me_pglast);
                        rc = mdb_cursor_del(&mc, 0);
                        if (rc)
                                return rc;
                }

                /* Save the IDL of pages freed by this txn, to a single record */
                if (freecnt < txn->mt_free_pgs[0]) {
                        if (!freecnt) {
                                /* Make sure last page of freeDB is touched and on freelist */
                                rc = mdb_page_search(&mc, NULL, MDB_PS_LAST|MDB_PS_MODIFY);
                                if (rc && rc != MDB_NOTFOUND)
                                        return rc;
                        }
                        free_pgs = txn->mt_free_pgs;
                        /* Write to last page of freeDB */
                        key.mv_size = sizeof(txn->mt_txnid);
                        key.mv_data = &txn->mt_txnid;
                        do {
                                freecnt = free_pgs[0];
                                data.mv_size = MDB_IDL_SIZEOF(free_pgs);
                                rc = mdb_cursor_put(&mc, &key, &data, MDB_RESERVE);
                                if (rc)
                                        return rc;
                                /* Retry if mt_free_pgs[] grew during the Put() */
                                free_pgs = txn->mt_free_pgs;
                        } while (freecnt < free_pgs[0]);
                        mdb_midl_sort(free_pgs);
                        memcpy(data.mv_data, free_pgs, data.mv_size);
#if (MDB_DEBUG) > 1
                        {
                                unsigned int i = free_pgs[0];
                                DPRINTF(("IDL write txn %"Z"u root %"Z"u num %u",
                                        txn->mt_txnid, txn->mt_dbs[FREE_DBI].md_root, i));
                                for (; i; i--)
                                        DPRINTF(("IDL %"Z"u", free_pgs[i]));
                        }
#endif
                        continue;
                }

                mop = env->me_pghead;
                mop_len = (mop ? mop[0] : 0) + txn->mt_loose_count;

                /* Reserve records for me_pghead[]. Split it if multi-page,
                 * to avoid searching freeDB for a page range. Use keys in
                 * range [1,me_pglast]: Smaller than txnid of oldest reader.
                 */
                if (total_room >= mop_len) {
                        if (total_room == mop_len || --more < 0)
                                break;
                } else if (head_room >= maxfree_1pg && head_id > 1) {
                        /* Keep current record (overflow page), add a new one */
                        head_id--;
                        head_room = 0;
                }
                /* (Re)write {key = head_id, IDL length = head_room} */
                total_room -= head_room;
                head_room = mop_len - total_room;
                if (head_room > maxfree_1pg && head_id > 1) {
                        /* Overflow multi-page for part of me_pghead */
                        head_room /= head_id; /* amortize page sizes */
                        head_room += maxfree_1pg - head_room % (maxfree_1pg + 1);
                } else if (head_room < 0) {
                        /* Rare case, not bothering to delete this record */
                        head_room = 0;
                }
                key.mv_size = sizeof(head_id);
                key.mv_data = &head_id;
                data.mv_size = (head_room + 1) * sizeof(pgno_t);
                rc = mdb_cursor_put(&mc, &key, &data, MDB_RESERVE);
                if (rc)
                        return rc;
                /* IDL is initially empty, zero out at least the length */
                pgs = (pgno_t *)data.mv_data;
                j = head_room > clean_limit ? head_room : 0;
                do {
                        pgs[j] = 0;
                } while (--j >= 0);
                total_room += head_room;
        }

        /* Return loose page numbers to me_pghead, though usually none are
         * left at this point.  The pages themselves remain in dirty_list.
         */
        if (txn->mt_loose_pgs) {
                MDB_page *mp = txn->mt_loose_pgs;
                unsigned count = txn->mt_loose_count;
                MDB_IDL loose;
                /* Room for loose pages + temp IDL with same */
                if ((rc = mdb_midl_need(&env->me_pghead, 2*count+1)) != 0)
                        return rc;
                mop = env->me_pghead;
                loose = mop + MDB_IDL_ALLOCLEN(mop) - count;
                for (count = 0; mp; mp = NEXT_LOOSE_PAGE(mp))
                        loose[ ++count ] = mp->mp_pgno;
                loose[0] = count;
                mdb_midl_sort(loose);
                mdb_midl_xmerge(mop, loose);
                txn->mt_loose_pgs = NULL;
                txn->mt_loose_count = 0;
                mop_len = mop[0];
        }

        /* Fill in the reserved me_pghead records */
        rc = MDB_SUCCESS;
        if (mop_len) {
                MDB_val key, data;

                mop += mop_len;
                rc = mdb_cursor_first(&mc, &key, &data);
                for (; !rc; rc = mdb_cursor_next(&mc, &key, &data, MDB_NEXT)) {
                        txnid_t id = *(txnid_t *)key.mv_data;
                        ssize_t len = (ssize_t)(data.mv_size / sizeof(MDB_ID)) - 1;
                        MDB_ID save;

                        mdb_tassert(txn, len >= 0 && id <= env->me_pglast);
                        key.mv_data = &id;
                        if (len > mop_len) {
                                len = mop_len;
                                data.mv_size = (len + 1) * sizeof(MDB_ID);
                        }
                        data.mv_data = mop -= len;
                        save = mop[0];
                        mop[0] = len;
                        rc = mdb_cursor_put(&mc, &key, &data, MDB_CURRENT);
                        mop[0] = save;
                        if (rc || !(mop_len -= len))
                                break;
                }
        }
        return rc;
}

/** Flush (some) dirty pages to the map, after clearing their dirty flag.
 * @param[in] txn the transaction that's being committed
 * @param[in] keep number of initial pages in dirty_list to keep dirty.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_flush(MDB_txn *txn, int keep)
{
        MDB_env         *env = txn->mt_env;
        MDB_ID2L        dl = txn->mt_u.dirty_list;
        unsigned        psize = env->me_psize, j;
        int                     i, pagecount = dl[0].mid, rc;
        size_t          size = 0, pos = 0;
        pgno_t          pgno = 0;
        MDB_page        *dp = NULL;
#ifdef _WIN32
        OVERLAPPED      ov;
#else
        struct iovec iov[MDB_COMMIT_PAGES];
        ssize_t         wpos = 0, wsize = 0, wres;
        size_t          next_pos = 1; /* impossible pos, so pos != next_pos */
        int                     n = 0;
#endif

        j = i = keep;

        if (env->me_flags & MDB_WRITEMAP) {
                /* Clear dirty flags */
                while (++i <= pagecount) {
                        dp = dl[i].mptr;
                        /* Don't flush this page yet */
                        if (dp->mp_flags & (P_LOOSE|P_KEEP)) {
                                dp->mp_flags &= ~P_KEEP;
                                dl[++j] = dl[i];
                                continue;
                        }
                        dp->mp_flags &= ~P_DIRTY;
                }
                goto done;
        }

        /* Write the pages */
        for (;;) {
                if (++i <= pagecount) {
                        dp = dl[i].mptr;
                        /* Don't flush this page yet */
                        if (dp->mp_flags & (P_LOOSE|P_KEEP)) {
                                dp->mp_flags &= ~P_KEEP;
                                dl[i].mid = 0;
                                continue;
                        }
                        pgno = dl[i].mid;
                        /* clear dirty flag */
                        dp->mp_flags &= ~P_DIRTY;
                        pos = pgno * psize;
                        size = psize;
                        if (IS_OVERFLOW(dp)) size *= dp->mp_pages;
                }
#ifdef _WIN32
                else break;

                /* Windows actually supports scatter/gather I/O, but only on
                 * unbuffered file handles. Since we're relying on the OS page
                 * cache for all our data, that's self-defeating. So we just
                 * write pages one at a time. We use the ov structure to set
                 * the write offset, to at least save the overhead of a Seek
                 * system call.
                 */
                DPRINTF(("committing page %"Z"u", pgno));
                memset(&ov, 0, sizeof(ov));
                ov.Offset = pos & 0xffffffff;
                ov.OffsetHigh = pos >> 16 >> 16;
                if (!WriteFile(env->me_fd, dp, size, NULL, &ov)) {
                        rc = ErrCode();
                        DPRINTF(("WriteFile: %d", rc));
                        return rc;
                }
#else
                /* Write up to MDB_COMMIT_PAGES dirty pages at a time. */
                if (pos!=next_pos || n==MDB_COMMIT_PAGES || wsize+size>MAX_WRITE) {
                        if (n) {
                                /* Write previous page(s) */
#ifdef MDB_USE_PWRITEV
                                wres = pwritev(env->me_fd, iov, n, wpos);
#else
                                if (n == 1) {
                                        wres = pwrite(env->me_fd, iov[0].iov_base, wsize, wpos);
                                } else {
                                        if (lseek(env->me_fd, wpos, SEEK_SET) == -1) {
                                                rc = ErrCode();
                                                DPRINTF(("lseek: %s", strerror(rc)));
                                                return rc;
                                        }
                                        wres = writev(env->me_fd, iov, n);
                                }
#endif
                                if (wres != wsize) {
                                        if (wres < 0) {
                                                rc = ErrCode();
                                                DPRINTF(("Write error: %s", strerror(rc)));
                                        } else {
                                                rc = EIO; /* TODO: Use which error code? */
                                                DPUTS("short write, filesystem full?");
                                        }
                                        return rc;
                                }
                                n = 0;
                        }
                        if (i > pagecount)
                                break;
                        wpos = pos;
                        wsize = 0;
                }
                DPRINTF(("committing page %"Z"u", pgno));
                next_pos = pos + size;
                iov[n].iov_len = size;
                iov[n].iov_base = (char *)dp;
                wsize += size;
                n++;
#endif  /* _WIN32 */
        }

        /* MIPS has cache coherency issues, this is a no-op everywhere else
         * Note: for any size >= on-chip cache size, entire on-chip cache is
         * flushed.
         */
        CACHEFLUSH(env->me_map, txn->mt_next_pgno * env->me_psize, DCACHE);

        for (i = keep; ++i <= pagecount; ) {
                dp = dl[i].mptr;
                /* This is a page we skipped above */
                if (!dl[i].mid) {
                        dl[++j] = dl[i];
                        dl[j].mid = dp->mp_pgno;
                        continue;
                }
                mdb_dpage_free(env, dp);
        }

done:
        i--;
        txn->mt_dirty_room += i - j;
        dl[0].mid = j;
        return MDB_SUCCESS;
}

int
mdb_txn_commit(MDB_txn *txn)
{
        int             rc;
        unsigned int i;
        MDB_env *env;

        if (txn == NULL || txn->mt_env == NULL)
                return EINVAL;

        if (txn->mt_child) {
                rc = mdb_txn_commit(txn->mt_child);
                txn->mt_child = NULL;
                if (rc)
                        goto fail;
        }

        env = txn->mt_env;

        if (F_ISSET(txn->mt_flags, MDB_TXN_RDONLY)) {
                mdb_dbis_update(txn, 1);
                txn->mt_numdbs = 2; /* so txn_abort() doesn't close any new handles */
                mdb_txn_abort(txn);
                return MDB_SUCCESS;
        }

        if (F_ISSET(txn->mt_flags, MDB_TXN_ERROR)) {
                DPUTS("error flag is set, can't commit");
                if (txn->mt_parent)
                        txn->mt_parent->mt_flags |= MDB_TXN_ERROR;
                rc = MDB_BAD_TXN;
                goto fail;
        }

        if (txn->mt_parent) {
                MDB_txn *parent = txn->mt_parent;
                MDB_page **lp;
                MDB_ID2L dst, src;
                MDB_IDL pspill;
                unsigned x, y, len, ps_len;

                /* Append our free list to parent's */
                rc = mdb_midl_append_list(&parent->mt_free_pgs, txn->mt_free_pgs);
                if (rc)
                        goto fail;
                mdb_midl_free(txn->mt_free_pgs);
                /* Failures after this must either undo the changes
                 * to the parent or set MDB_TXN_ERROR in the parent.
                 */

                parent->mt_next_pgno = txn->mt_next_pgno;
                parent->mt_flags = txn->mt_flags;

                /* Merge our cursors into parent's and close them */
                mdb_cursors_close(txn, 1);

                /* Update parent's DB table. */
                memcpy(parent->mt_dbs, txn->mt_dbs, txn->mt_numdbs * sizeof(MDB_db));
                parent->mt_numdbs = txn->mt_numdbs;
                parent->mt_dbflags[0] = txn->mt_dbflags[0];
                parent->mt_dbflags[1] = txn->mt_dbflags[1];
                for (i=2; i<txn->mt_numdbs; i++) {
                        /* preserve parent's DB_NEW status */
                        x = parent->mt_dbflags[i] & DB_NEW;
                        parent->mt_dbflags[i] = txn->mt_dbflags[i] | x;
                }

                dst = parent->mt_u.dirty_list;
                src = txn->mt_u.dirty_list;
                /* Remove anything in our dirty list from parent's spill list */
                if ((pspill = parent->mt_spill_pgs) && (ps_len = pspill[0])) {
                        x = y = ps_len;
                        pspill[0] = (pgno_t)-1;
                        /* Mark our dirty pages as deleted in parent spill list */
                        for (i=0, len=src[0].mid; ++i <= len; ) {
                                MDB_ID pn = src[i].mid << 1;
                                while (pn > pspill[x])
                                        x--;
                                if (pn == pspill[x]) {
                                        pspill[x] = 1;
                                        y = --x;
                                }
                        }
                        /* Squash deleted pagenums if we deleted any */
                        for (x=y; ++x <= ps_len; )
                                if (!(pspill[x] & 1))
                                        pspill[++y] = pspill[x];
                        pspill[0] = y;
                }

                /* Find len = length of merging our dirty list with parent's */
                x = dst[0].mid;
                dst[0].mid = 0;         /* simplify loops */
                if (parent->mt_parent) {
                        len = x + src[0].mid;
                        y = mdb_mid2l_search(src, dst[x].mid + 1) - 1;
                        for (i = x; y && i; y--) {
                                pgno_t yp = src[y].mid;
                                while (yp < dst[i].mid)
                                        i--;
                                if (yp == dst[i].mid) {
                                        i--;
                                        len--;
                                }
                        }
                } else { /* Simplify the above for single-ancestor case */
                        len = MDB_IDL_UM_MAX - txn->mt_dirty_room;
                }
                /* Merge our dirty list with parent's */
                y = src[0].mid;
                for (i = len; y; dst[i--] = src[y--]) {
                        pgno_t yp = src[y].mid;
                        while (yp < dst[x].mid)
                                dst[i--] = dst[x--];
                        if (yp == dst[x].mid)
                                free(dst[x--].mptr);
                }
                mdb_tassert(txn, i == x);
                dst[0].mid = len;
                free(txn->mt_u.dirty_list);
                parent->mt_dirty_room = txn->mt_dirty_room;
                if (txn->mt_spill_pgs) {
                        if (parent->mt_spill_pgs) {
                                /* TODO: Prevent failure here, so parent does not fail */
                                rc = mdb_midl_append_list(&parent->mt_spill_pgs, txn->mt_spill_pgs);
                                if (rc)
                                        parent->mt_flags |= MDB_TXN_ERROR;
                                mdb_midl_free(txn->mt_spill_pgs);
                                mdb_midl_sort(parent->mt_spill_pgs);
                        } else {
                                parent->mt_spill_pgs = txn->mt_spill_pgs;
                        }
                }

                /* Append our loose page list to parent's */
                for (lp = &parent->mt_loose_pgs; *lp; lp = &NEXT_LOOSE_PAGE(lp))
                        ;
                *lp = txn->mt_loose_pgs;
                parent->mt_loose_count += txn->mt_loose_count;

                parent->mt_child = NULL;
                mdb_midl_free(((MDB_ntxn *)txn)->mnt_pgstate.mf_pghead);
                free(txn);
                return rc;
        }

        if (txn != env->me_txn) {
                DPUTS("attempt to commit unknown transaction");
                rc = EINVAL;
                goto fail;
        }

        mdb_cursors_close(txn, 0);

        if (!txn->mt_u.dirty_list[0].mid &&
                !(txn->mt_flags & (MDB_TXN_DIRTY|MDB_TXN_SPILLS)))
                goto done;

        DPRINTF(("committing txn %"Z"u %p on mdbenv %p, root page %"Z"u",
            txn->mt_txnid, (void*)txn, (void*)env, txn->mt_dbs[MAIN_DBI].md_root));

        /* Update DB root pointers */
        if (txn->mt_numdbs > 2) {
                MDB_cursor mc;
                MDB_dbi i;
                MDB_val data;
                data.mv_size = sizeof(MDB_db);

                mdb_cursor_init(&mc, txn, MAIN_DBI, NULL);
                for (i = 2; i < txn->mt_numdbs; i++) {
                        if (txn->mt_dbflags[i] & DB_DIRTY) {
                                if (TXN_DBI_CHANGED(txn, i)) {
                                        rc = MDB_BAD_DBI;
                                        goto fail;
                                }
                                data.mv_data = &txn->mt_dbs[i];
                                rc = mdb_cursor_put(&mc, &txn->mt_dbxs[i].md_name, &data, 0);
                                if (rc)
                                        goto fail;
                        }
                }
        }

        rc = mdb_freelist_save(txn);
        if (rc)
                goto fail;

        mdb_midl_free(env->me_pghead);
        env->me_pghead = NULL;
        if (mdb_midl_shrink(&txn->mt_free_pgs))
                env->me_free_pgs = txn->mt_free_pgs;

#if (MDB_DEBUG) > 2
        mdb_audit(txn);
#endif

        if ((rc = mdb_page_flush(txn, 0)) ||
                (rc = mdb_env_sync(env, 0)) ||
                (rc = mdb_env_write_meta(txn)))
                goto fail;

        /* Free P_LOOSE pages left behind in dirty_list */
        if (!(env->me_flags & MDB_WRITEMAP))
                mdb_dlist_free(txn);

done:
        env->me_pglast = 0;
        env->me_txn = NULL;
        mdb_dbis_update(txn, 1);

        if (env->me_txns)
                UNLOCK_MUTEX_W(env);
        free(txn);

        return MDB_SUCCESS;

fail:
        mdb_txn_abort(txn);
        return rc;
}

/** Read the environment parameters of a DB environment before
 * mapping it into memory.
 * @param[in] env the environment handle
 * @param[out] meta address of where to store the meta information
 * @return 0 on success, non-zero on failure.
 */
static int ESECT
mdb_env_read_header(MDB_env *env, MDB_meta *meta)
{
        MDB_metabuf     pbuf;
        MDB_page        *p;
        MDB_meta        *m;
        int                     i, rc, off;
        enum { Size = sizeof(pbuf) };

        /* We don't know the page size yet, so use a minimum value.
         * Read both meta pages so we can use the latest one.
         */

        for (i=off=0; i<2; i++, off = meta->mm_psize) {
#ifdef _WIN32
                DWORD len;
                OVERLAPPED ov;
                memset(&ov, 0, sizeof(ov));
                ov.Offset = off;
                rc = ReadFile(env->me_fd, &pbuf, Size, &len, &ov) ? (int)len : -1;
                if (rc == -1 && ErrCode() == ERROR_HANDLE_EOF)
                        rc = 0;
#else
                rc = pread(env->me_fd, &pbuf, Size, off);
#endif
                if (rc != Size) {
                        if (rc == 0 && off == 0)
                                return ENOENT;
                        rc = rc < 0 ? (int) ErrCode() : MDB_INVALID;
                        DPRINTF(("read: %s", mdb_strerror(rc)));
                        return rc;
                }

                p = (MDB_page *)&pbuf;

                if (!F_ISSET(p->mp_flags, P_META)) {
                        DPRINTF(("page %"Z"u not a meta page", p->mp_pgno));
                        return MDB_INVALID;
                }

                m = METADATA(p);
                if (m->mm_magic != MDB_MAGIC) {
                        DPUTS("meta has invalid magic");
                        return MDB_INVALID;
                }

                if (m->mm_version != MDB_DATA_VERSION) {
                        DPRINTF(("database is version %u, expected version %u",
                                m->mm_version, MDB_DATA_VERSION));
                        return MDB_VERSION_MISMATCH;
                }

                if (off == 0 || m->mm_txnid > meta->mm_txnid)
                        *meta = *m;
        }
        return 0;
}

static void ESECT
mdb_env_init_meta0(MDB_env *env, MDB_meta *meta)
{
        meta->mm_magic = MDB_MAGIC;
        meta->mm_version = MDB_DATA_VERSION;
        meta->mm_mapsize = env->me_mapsize;
        meta->mm_psize = env->me_psize;
        meta->mm_last_pg = 1;
        meta->mm_flags = env->me_flags & 0xffff;
        meta->mm_flags |= MDB_INTEGERKEY;
        meta->mm_dbs[0].md_root = P_INVALID;
        meta->mm_dbs[1].md_root = P_INVALID;
}

/** Write the environment parameters of a freshly created DB environment.
 * @param[in] env the environment handle
 * @param[out] meta address of where to store the meta information
 * @return 0 on success, non-zero on failure.
 */
static int ESECT
mdb_env_init_meta(MDB_env *env, MDB_meta *meta)
{
        MDB_page *p, *q;
        int rc;
        unsigned int     psize;
#ifdef _WIN32
        DWORD len;
        OVERLAPPED ov;
        memset(&ov, 0, sizeof(ov));
#define DO_PWRITE(rc, fd, ptr, size, len, pos)  do { \
        ov.Offset = pos;        \
        rc = WriteFile(fd, ptr, size, &len, &ov);       } while(0)
#else
        int len;
#define DO_PWRITE(rc, fd, ptr, size, len, pos)  do { \
        len = pwrite(fd, ptr, size, pos);       \
        rc = (len >= 0); } while(0)
#endif

        DPUTS("writing new meta page");

        psize = env->me_psize;

        mdb_env_init_meta0(env, meta);

        p = calloc(2, psize);
        p->mp_pgno = 0;
        p->mp_flags = P_META;
        *(MDB_meta *)METADATA(p) = *meta;

        q = (MDB_page *)((char *)p + psize);
        q->mp_pgno = 1;
        q->mp_flags = P_META;
        *(MDB_meta *)METADATA(q) = *meta;

        DO_PWRITE(rc, env->me_fd, p, psize * 2, len, 0);
        if (!rc)
                rc = ErrCode();
        else if ((unsigned) len == psize * 2)
                rc = MDB_SUCCESS;
        else
                rc = ENOSPC;
        free(p);
        return rc;
}

/** Update the environment info to commit a transaction.
 * @param[in] txn the transaction that's being committed
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_env_write_meta(MDB_txn *txn)
{
        MDB_env *env;
        MDB_meta        meta, metab, *mp;
        size_t mapsize;
        off_t off;
        int rc, len, toggle;
        char *ptr;
        HANDLE mfd;
#ifdef _WIN32
        OVERLAPPED ov;
#else
        int r2;
#endif

        toggle = txn->mt_txnid & 1;
        DPRINTF(("writing meta page %d for root page %"Z"u",
                toggle, txn->mt_dbs[MAIN_DBI].md_root));

        env = txn->mt_env;
        mp = env->me_metas[toggle];
        mapsize = env->me_metas[toggle ^ 1]->mm_mapsize;
        /* Persist any increases of mapsize config */
        if (mapsize < env->me_mapsize)
                mapsize = env->me_mapsize;

        if (env->me_flags & MDB_WRITEMAP) {
                mp->mm_mapsize = mapsize;
                mp->mm_dbs[0] = txn->mt_dbs[0];
                mp->mm_dbs[1] = txn->mt_dbs[1];
                mp->mm_last_pg = txn->mt_next_pgno - 1;
                mp->mm_txnid = txn->mt_txnid;
                if (!(env->me_flags & (MDB_NOMETASYNC|MDB_NOSYNC))) {
                        unsigned meta_size = env->me_psize;
                        rc = (env->me_flags & MDB_MAPASYNC) ? MS_ASYNC : MS_SYNC;
                        ptr = env->me_map;
                        if (toggle) {
#ifndef _WIN32  /* POSIX msync() requires ptr = start of OS page */
                                if (meta_size < env->me_os_psize)
                                        meta_size += meta_size;
                                else
#endif
                                        ptr += meta_size;
                        }
                        if (MDB_MSYNC(ptr, meta_size, rc)) {
                                rc = ErrCode();
                                goto fail;
                        }
                }
                goto done;
        }
        metab.mm_txnid = env->me_metas[toggle]->mm_txnid;
        metab.mm_last_pg = env->me_metas[toggle]->mm_last_pg;

        meta.mm_mapsize = mapsize;
        meta.mm_dbs[0] = txn->mt_dbs[0];
        meta.mm_dbs[1] = txn->mt_dbs[1];
        meta.mm_last_pg = txn->mt_next_pgno - 1;
        meta.mm_txnid = txn->mt_txnid;

        off = offsetof(MDB_meta, mm_mapsize);
        ptr = (char *)&meta + off;
        len = sizeof(MDB_meta) - off;
        if (toggle)
                off += env->me_psize;
        off += PAGEHDRSZ;

        /* Write to the SYNC fd */
        mfd = env->me_flags & (MDB_NOSYNC|MDB_NOMETASYNC) ?
                env->me_fd : env->me_mfd;
#ifdef _WIN32
        {
                memset(&ov, 0, sizeof(ov));
                ov.Offset = off;
                if (!WriteFile(mfd, ptr, len, (DWORD *)&rc, &ov))
                        rc = -1;
        }
#else
        rc = pwrite(mfd, ptr, len, off);
#endif
        if (rc != len) {
                rc = rc < 0 ? ErrCode() : EIO;
                DPUTS("write failed, disk error?");
                /* On a failure, the pagecache still contains the new data.
                 * Write some old data back, to prevent it from being used.
                 * Use the non-SYNC fd; we know it will fail anyway.
                 */
                meta.mm_last_pg = metab.mm_last_pg;
                meta.mm_txnid = metab.mm_txnid;
#ifdef _WIN32
                memset(&ov, 0, sizeof(ov));
                ov.Offset = off;
                WriteFile(env->me_fd, ptr, len, NULL, &ov);
#else
                r2 = pwrite(env->me_fd, ptr, len, off);
                (void)r2;       /* Silence warnings. We don't care about pwrite's return value */
#endif
fail:
                env->me_flags |= MDB_FATAL_ERROR;
                return rc;
        }
        /* MIPS has cache coherency issues, this is a no-op everywhere else */
        CACHEFLUSH(env->me_map + off, len, DCACHE);
done:
        /* Memory ordering issues are irrelevant; since the entire writer
         * is wrapped by wmutex, all of these changes will become visible
         * after the wmutex is unlocked. Since the DB is multi-version,
         * readers will get consistent data regardless of how fresh or
         * how stale their view of these values is.
         */
        if (env->me_txns)
                env->me_txns->mti_txnid = txn->mt_txnid;

        return MDB_SUCCESS;
}

/** Check both meta pages to see which one is newer.
 * @param[in] env the environment handle
 * @return meta toggle (0 or 1).
 */
static int
mdb_env_pick_meta(const MDB_env *env)
{
        return (env->me_metas[0]->mm_txnid < env->me_metas[1]->mm_txnid);
}

int ESECT
mdb_env_create(MDB_env **env)
{
        MDB_env *e;

        e = calloc(1, sizeof(MDB_env));
        if (!e)
                return ENOMEM;

        e->me_maxreaders = DEFAULT_READERS;
        e->me_maxdbs = e->me_numdbs = 2;
        e->me_fd = INVALID_HANDLE_VALUE;
        e->me_lfd = INVALID_HANDLE_VALUE;
        e->me_mfd = INVALID_HANDLE_VALUE;
#ifdef MDB_USE_POSIX_SEM
        e->me_rmutex = SEM_FAILED;
        e->me_wmutex = SEM_FAILED;
#endif
        e->me_pid = getpid();
        GET_PAGESIZE(e->me_os_psize);
        VGMEMP_CREATE(e,0,0);
        *env = e;
        return MDB_SUCCESS;
}

static int ESECT
mdb_env_map(MDB_env *env, void *addr)
{
        MDB_page *p;
        unsigned int flags = env->me_flags;
#ifdef _WIN32
        int rc;
        HANDLE mh;
        LONG sizelo, sizehi;
        size_t msize;

        if (flags & MDB_RDONLY) {
                /* Don't set explicit map size, use whatever exists */
                msize = 0;
                sizelo = 0;
                sizehi = 0;
        } else {
                msize = env->me_mapsize;
                sizelo = msize & 0xffffffff;
                sizehi = msize >> 16 >> 16; /* only needed on Win64 */

                /* Windows won't create mappings for zero length files.
                 * and won't map more than the file size.
                 * Just set the maxsize right now.
                 */
                if (SetFilePointer(env->me_fd, sizelo, &sizehi, 0) != (DWORD)sizelo
                        || !SetEndOfFile(env->me_fd)
                        || SetFilePointer(env->me_fd, 0, NULL, 0) != 0)
                        return ErrCode();
        }

        mh = CreateFileMapping(env->me_fd, NULL, flags & MDB_WRITEMAP ?
                PAGE_READWRITE : PAGE_READONLY,
                sizehi, sizelo, NULL);
        if (!mh)
                return ErrCode();
        env->me_map = MapViewOfFileEx(mh, flags & MDB_WRITEMAP ?
                FILE_MAP_WRITE : FILE_MAP_READ,
                0, 0, msize, addr);
        rc = env->me_map ? 0 : ErrCode();
        CloseHandle(mh);
        if (rc)
                return rc;
#else
        int prot = PROT_READ;
        if (flags & MDB_WRITEMAP) {
                prot |= PROT_WRITE;
                if (ftruncate(env->me_fd, env->me_mapsize) < 0)
                        return ErrCode();
        }
        env->me_map = mmap(addr, env->me_mapsize, prot, MAP_SHARED,
                env->me_fd, 0);
        if (env->me_map == MAP_FAILED) {
                env->me_map = NULL;
                return ErrCode();
        }

        if (flags & MDB_NORDAHEAD) {
                /* Turn off readahead. It's harmful when the DB is larger than RAM. */
#ifdef MADV_RANDOM
                madvise(env->me_map, env->me_mapsize, MADV_RANDOM);
#else
#ifdef POSIX_MADV_RANDOM
                posix_madvise(env->me_map, env->me_mapsize, POSIX_MADV_RANDOM);
#endif /* POSIX_MADV_RANDOM */
#endif /* MADV_RANDOM */
        }
#endif /* _WIN32 */

        /* Can happen because the address argument to mmap() is just a
         * hint.  mmap() can pick another, e.g. if the range is in use.
         * The MAP_FIXED flag would prevent that, but then mmap could
         * instead unmap existing pages to make room for the new map.
         */
        if (addr && env->me_map != addr)
                return EBUSY;   /* TODO: Make a new MDB_* error code? */

        p = (MDB_page *)env->me_map;
        env->me_metas[0] = METADATA(p);
        env->me_metas[1] = (MDB_meta *)((char *)env->me_metas[0] + env->me_psize);

        return MDB_SUCCESS;
}

int ESECT
mdb_env_set_mapsize(MDB_env *env, size_t size)
{
        /* If env is already open, caller is responsible for making
         * sure there are no active txns.
         */
        if (env->me_map) {
                int rc;
                void *old;
                if (env->me_txn)
                        return EINVAL;
                if (!size)
                        size = env->me_metas[mdb_env_pick_meta(env)]->mm_mapsize;
                else if (size < env->me_mapsize) {
                        /* If the configured size is smaller, make sure it's
                         * still big enough. Silently round up to minimum if not.
                         */
                        size_t minsize = (env->me_metas[mdb_env_pick_meta(env)]->mm_last_pg + 1) * env->me_psize;
                        if (size < minsize)
                                size = minsize;
                }
                munmap(env->me_map, env->me_mapsize);
                env->me_mapsize = size;
                old = (env->me_flags & MDB_FIXEDMAP) ? env->me_map : NULL;
                rc = mdb_env_map(env, old);
                if (rc)
                        return rc;
        }
        env->me_mapsize = size;
        if (env->me_psize)
                env->me_maxpg = env->me_mapsize / env->me_psize;
        return MDB_SUCCESS;
}

int ESECT
mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs)
{
        if (env->me_map)
                return EINVAL;
        env->me_maxdbs = dbs + 2; /* Named databases + main and free DB */
        return MDB_SUCCESS;
}

int ESECT
mdb_env_set_maxreaders(MDB_env *env, unsigned int readers)
{
        if (env->me_map || readers < 1)
                return EINVAL;
        env->me_maxreaders = readers;
        return MDB_SUCCESS;
}

int ESECT
mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers)
{
        if (!env || !readers)
                return EINVAL;
        *readers = env->me_maxreaders;
        return MDB_SUCCESS;
}

/** Further setup required for opening an LMDB environment
 */
static int ESECT
mdb_env_open2(MDB_env *env)
{
        unsigned int flags = env->me_flags;
        int i, newenv = 0, rc;
        MDB_meta meta;

#ifdef _WIN32
        /* See if we should use QueryLimited */
        rc = GetVersion();
        if ((rc & 0xff) > 5)
                env->me_pidquery = MDB_PROCESS_QUERY_LIMITED_INFORMATION;
        else
                env->me_pidquery = PROCESS_QUERY_INFORMATION;
#endif /* _WIN32 */

        memset(&meta, 0, sizeof(meta));

        if ((i = mdb_env_read_header(env, &meta)) != 0) {
                if (i != ENOENT)
                        return i;
                DPUTS("new mdbenv");
                newenv = 1;
                env->me_psize = env->me_os_psize;
                if (env->me_psize > MAX_PAGESIZE)
                        env->me_psize = MAX_PAGESIZE;
        } else {
                env->me_psize = meta.mm_psize;
        }

        /* Was a mapsize configured? */
        if (!env->me_mapsize) {
                /* If this is a new environment, take the default,
                 * else use the size recorded in the existing env.
                 */
                env->me_mapsize = newenv ? DEFAULT_MAPSIZE : meta.mm_mapsize;
        } else if (env->me_mapsize < meta.mm_mapsize) {
                /* If the configured size is smaller, make sure it's
                 * still big enough. Silently round up to minimum if not.
                 */
                size_t minsize = (meta.mm_last_pg + 1) * meta.mm_psize;
                if (env->me_mapsize < minsize)
                        env->me_mapsize = minsize;
        }

        rc = mdb_env_map(env, (flags & MDB_FIXEDMAP) ? meta.mm_address : NULL);
        if (rc)
                return rc;

        if (newenv) {
                if (flags & MDB_FIXEDMAP)
                        meta.mm_address = env->me_map;
                i = mdb_env_init_meta(env, &meta);
                if (i != MDB_SUCCESS) {
                        return i;
                }
        }

        env->me_maxfree_1pg = (env->me_psize - PAGEHDRSZ) / sizeof(pgno_t) - 1;
        env->me_nodemax = (((env->me_psize - PAGEHDRSZ) / MDB_MINKEYS) & -2)
                - sizeof(indx_t);
#if !(MDB_MAXKEYSIZE)
        env->me_maxkey = env->me_nodemax - (NODESIZE + sizeof(MDB_db));
#endif
        env->me_maxpg = env->me_mapsize / env->me_psize;

#if MDB_DEBUG
        {
                int toggle = mdb_env_pick_meta(env);
                MDB_db *db = &env->me_metas[toggle]->mm_dbs[MAIN_DBI];

                DPRINTF(("opened database version %u, pagesize %u",
                        env->me_metas[0]->mm_version, env->me_psize));
                DPRINTF(("using meta page %d",    toggle));
                DPRINTF(("depth: %u",             db->md_depth));
                DPRINTF(("entries: %"Z"u",        db->md_entries));
                DPRINTF(("branch pages: %"Z"u",   db->md_branch_pages));
                DPRINTF(("leaf pages: %"Z"u",     db->md_leaf_pages));
                DPRINTF(("overflow pages: %"Z"u", db->md_overflow_pages));
                DPRINTF(("root: %"Z"u",           db->md_root));
        }
#endif

        return MDB_SUCCESS;
}


/** Release a reader thread's slot in the reader lock table.
 *      This function is called automatically when a thread exits.
 * @param[in] ptr This points to the slot in the reader lock table.
 */
static void
mdb_env_reader_dest(void *ptr)
{
        MDB_reader *reader = ptr;

        reader->mr_pid = 0;
}

#ifdef _WIN32
/** Junk for arranging thread-specific callbacks on Windows. This is
 *      necessarily platform and compiler-specific. Windows supports up
 *      to 1088 keys. Let's assume nobody opens more than 64 environments
 *      in a single process, for now. They can override this if needed.
 */
#ifndef MAX_TLS_KEYS
#define MAX_TLS_KEYS    64
#endif
static pthread_key_t mdb_tls_keys[MAX_TLS_KEYS];
static int mdb_tls_nkeys;

static void NTAPI mdb_tls_callback(PVOID module, DWORD reason, PVOID ptr)
{
        int i;
        switch(reason) {
        case DLL_PROCESS_ATTACH: break;
        case DLL_THREAD_ATTACH: break;
        case DLL_THREAD_DETACH:
                for (i=0; i<mdb_tls_nkeys; i++) {
                        MDB_reader *r = pthread_getspecific(mdb_tls_keys[i]);
                        if (r) {
                                mdb_env_reader_dest(r);
                        }
                }
                break;
        case DLL_PROCESS_DETACH: break;
        }
}
#ifdef __GNUC__
#ifdef _WIN64
const PIMAGE_TLS_CALLBACK mdb_tls_cbp __attribute__((section (".CRT$XLB"))) = mdb_tls_callback;
#else
PIMAGE_TLS_CALLBACK mdb_tls_cbp __attribute__((section (".CRT$XLB"))) = mdb_tls_callback;
#endif
#else
#ifdef _WIN64
/* Force some symbol references.
 *      _tls_used forces the linker to create the TLS directory if not already done
 *      mdb_tls_cbp prevents whole-program-optimizer from dropping the symbol.
 */
#pragma comment(linker, "/INCLUDE:_tls_used")
#pragma comment(linker, "/INCLUDE:mdb_tls_cbp")
#pragma const_seg(".CRT$XLB")
extern const PIMAGE_TLS_CALLBACK mdb_tls_cbp;
const PIMAGE_TLS_CALLBACK mdb_tls_cbp = mdb_tls_callback;
#pragma const_seg()
#else   /* WIN32 */
#pragma comment(linker, "/INCLUDE:__tls_used")
#pragma comment(linker, "/INCLUDE:_mdb_tls_cbp")
#pragma data_seg(".CRT$XLB")
PIMAGE_TLS_CALLBACK mdb_tls_cbp = mdb_tls_callback;
#pragma data_seg()
#endif  /* WIN 32/64 */
#endif  /* !__GNUC__ */
#endif

/** Downgrade the exclusive lock on the region back to shared */
static int ESECT
mdb_env_share_locks(MDB_env *env, int *excl)
{
        int rc = 0, toggle = mdb_env_pick_meta(env);

        env->me_txns->mti_txnid = env->me_metas[toggle]->mm_txnid;

#ifdef _WIN32
        {
                OVERLAPPED ov;
                /* First acquire a shared lock. The Unlock will
                 * then release the existing exclusive lock.
                 */
                memset(&ov, 0, sizeof(ov));
                if (!LockFileEx(env->me_lfd, 0, 0, 1, 0, &ov)) {
                        rc = ErrCode();
                } else {
                        UnlockFile(env->me_lfd, 0, 0, 1, 0);
                        *excl = 0;
                }
        }
#else
        {
                struct flock lock_info;
                /* The shared lock replaces the existing lock */
                memset((void *)&lock_info, 0, sizeof(lock_info));
                lock_info.l_type = F_RDLCK;
                lock_info.l_whence = SEEK_SET;
                lock_info.l_start = 0;
                lock_info.l_len = 1;
                while ((rc = fcntl(env->me_lfd, F_SETLK, &lock_info)) &&
                                (rc = ErrCode()) == EINTR) ;
                *excl = rc ? -1 : 0;    /* error may mean we lost the lock */
        }
#endif

        return rc;
}

/** Try to get exlusive lock, otherwise shared.
 *      Maintain *excl = -1: no/unknown lock, 0: shared, 1: exclusive.
 */
static int ESECT
mdb_env_excl_lock(MDB_env *env, int *excl)
{
        int rc = 0;
#ifdef _WIN32
        if (LockFile(env->me_lfd, 0, 0, 1, 0)) {
                *excl = 1;
        } else {
                OVERLAPPED ov;
                memset(&ov, 0, sizeof(ov));
                if (LockFileEx(env->me_lfd, 0, 0, 1, 0, &ov)) {
                        *excl = 0;
                } else {
                        rc = ErrCode();
                }
        }
#else
        struct flock lock_info;
        memset((void *)&lock_info, 0, sizeof(lock_info));
        lock_info.l_type = F_WRLCK;
        lock_info.l_whence = SEEK_SET;
        lock_info.l_start = 0;
        lock_info.l_len = 1;
        while ((rc = fcntl(env->me_lfd, F_SETLK, &lock_info)) &&
                        (rc = ErrCode()) == EINTR) ;
        if (!rc) {
                *excl = 1;
        } else
# ifdef MDB_USE_POSIX_SEM
        if (*excl < 0) /* always true when !MDB_USE_POSIX_SEM */
# endif
        {
                lock_info.l_type = F_RDLCK;
                while ((rc = fcntl(env->me_lfd, F_SETLKW, &lock_info)) &&
                                (rc = ErrCode()) == EINTR) ;
                if (rc == 0)
                        *excl = 0;
        }
#endif
        return rc;
}

#ifdef MDB_USE_HASH
/*
 * hash_64 - 64 bit Fowler/Noll/Vo-0 FNV-1a hash code
 *
 * @(#) $Revision: 5.1 $
 * @(#) $Id: hash_64a.c,v 5.1 2009/06/30 09:01:38 chongo Exp $
 * @(#) $Source: /usr/local/src/cmd/fnv/RCS/hash_64a.c,v $
 *
 *        http://www.isthe.com/chongo/tech/comp/fnv/index.html
 *
 ***
 *
 * Please do not copyright this code.  This code is in the public domain.
 *
 * LANDON CURT NOLL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO
 * EVENT SHALL LANDON CURT NOLL BE LIABLE FOR ANY SPECIAL, INDIRECT OR
 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
 * USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
 * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 *
 * By:
 *      chongo <Landon Curt Noll> /\oo/\
 *        http://www.isthe.com/chongo/
 *
 * Share and Enjoy!     :-)
 */

typedef unsigned long long      mdb_hash_t;
#define MDB_HASH_INIT ((mdb_hash_t)0xcbf29ce484222325ULL)

/** perform a 64 bit Fowler/Noll/Vo FNV-1a hash on a buffer
 * @param[in] val       value to hash
 * @param[in] hval      initial value for hash
 * @return 64 bit hash
 *
 * NOTE: To use the recommended 64 bit FNV-1a hash, use MDB_HASH_INIT as the
 *       hval arg on the first call.
 */
static mdb_hash_t
mdb_hash_val(MDB_val *val, mdb_hash_t hval)
{
        unsigned char *s = (unsigned char *)val->mv_data;       /* unsigned string */
        unsigned char *end = s + val->mv_size;
        /*
         * FNV-1a hash each octet of the string
         */
        while (s < end) {
                /* xor the bottom with the current octet */
                hval ^= (mdb_hash_t)*s++;

                /* multiply by the 64 bit FNV magic prime mod 2^64 */
                hval += (hval << 1) + (hval << 4) + (hval << 5) +
                        (hval << 7) + (hval << 8) + (hval << 40);
        }
        /* return our new hash value */
        return hval;
}

/** Hash the string and output the encoded hash.
 * This uses modified RFC1924 Ascii85 encoding to accommodate systems with
 * very short name limits. We don't care about the encoding being reversible,
 * we just want to preserve as many bits of the input as possible in a
 * small printable string.
 * @param[in] str string to hash
 * @param[out] encbuf an array of 11 chars to hold the hash
 */
static const char mdb_a85[]= "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~";

static void
mdb_pack85(unsigned long l, char *out)
{
        int i;

        for (i=0; i<5; i++) {
                *out++ = mdb_a85[l % 85];
                l /= 85;
        }
}

static void
mdb_hash_enc(MDB_val *val, char *encbuf)
{
        mdb_hash_t h = mdb_hash_val(val, MDB_HASH_INIT);

        mdb_pack85(h, encbuf);
        mdb_pack85(h>>32, encbuf+5);
        encbuf[10] = '\0';
}
#endif

/** Open and/or initialize the lock region for the environment.
 * @param[in] env The LMDB environment.
 * @param[in] lpath The pathname of the file used for the lock region.
 * @param[in] mode The Unix permissions for the file, if we create it.
 * @param[out] excl Resulting file lock type: -1 none, 0 shared, 1 exclusive
 * @param[in,out] excl In -1, out lock type: -1 none, 0 shared, 1 exclusive
 * @return 0 on success, non-zero on failure.
 */
static int ESECT
mdb_env_setup_locks(MDB_env *env, char *lpath, int mode, int *excl)
{
#ifdef _WIN32
#       define MDB_ERRCODE_ROFS ERROR_WRITE_PROTECT
#else
#       define MDB_ERRCODE_ROFS EROFS
#ifdef O_CLOEXEC        /* Linux: Open file and set FD_CLOEXEC atomically */
#       define MDB_CLOEXEC              O_CLOEXEC
#else
        int fdflags;
#       define MDB_CLOEXEC              0
#endif
#endif
        int rc;
        off_t size, rsize;

#ifdef _WIN32
        env->me_lfd = CreateFile(lpath, GENERIC_READ|GENERIC_WRITE,
                FILE_SHARE_READ|FILE_SHARE_WRITE, NULL, OPEN_ALWAYS,
                FILE_ATTRIBUTE_NORMAL, NULL);
#else
        env->me_lfd = open(lpath, O_RDWR|O_CREAT|MDB_CLOEXEC, mode);
#endif
        if (env->me_lfd == INVALID_HANDLE_VALUE) {
                rc = ErrCode();
                if (rc == MDB_ERRCODE_ROFS && (env->me_flags & MDB_RDONLY)) {
                        return MDB_SUCCESS;
                }
                goto fail_errno;
        }
#if ! ((MDB_CLOEXEC) || defined(_WIN32))
        /* Lose record locks when exec*() */
        if ((fdflags = fcntl(env->me_lfd, F_GETFD) | FD_CLOEXEC) >= 0)
                        fcntl(env->me_lfd, F_SETFD, fdflags);
#endif

        if (!(env->me_flags & MDB_NOTLS)) {
                rc = pthread_key_create(&env->me_txkey, mdb_env_reader_dest);
                if (rc)
                        goto fail;
                env->me_flags |= MDB_ENV_TXKEY;
#ifdef _WIN32
                /* Windows TLS callbacks need help finding their TLS info. */
                if (mdb_tls_nkeys >= MAX_TLS_KEYS) {
                        rc = MDB_TLS_FULL;
                        goto fail;
                }
                mdb_tls_keys[mdb_tls_nkeys++] = env->me_txkey;
#endif
        }

        /* Try to get exclusive lock. If we succeed, then
         * nobody is using the lock region and we should initialize it.
         */
        if ((rc = mdb_env_excl_lock(env, excl))) goto fail;

#ifdef _WIN32
        size = GetFileSize(env->me_lfd, NULL);
#else
        size = lseek(env->me_lfd, 0, SEEK_END);
        if (size == -1) goto fail_errno;
#endif
        rsize = (env->me_maxreaders-1) * sizeof(MDB_reader) + sizeof(MDB_txninfo);
        if (size < rsize && *excl > 0) {
#ifdef _WIN32
                if (SetFilePointer(env->me_lfd, rsize, NULL, FILE_BEGIN) != (DWORD)rsize
                        || !SetEndOfFile(env->me_lfd))
                        goto fail_errno;
#else
                if (ftruncate(env->me_lfd, rsize) != 0) goto fail_errno;
#endif
        } else {
                rsize = size;
                size = rsize - sizeof(MDB_txninfo);
                env->me_maxreaders = size/sizeof(MDB_reader) + 1;
        }
        {
#ifdef _WIN32
                HANDLE mh;
                mh = CreateFileMapping(env->me_lfd, NULL, PAGE_READWRITE,
                        0, 0, NULL);
                if (!mh) goto fail_errno;
                env->me_txns = MapViewOfFileEx(mh, FILE_MAP_WRITE, 0, 0, rsize, NULL);
                CloseHandle(mh);
                if (!env->me_txns) goto fail_errno;
#else
                void *m = mmap(NULL, rsize, PROT_READ|PROT_WRITE, MAP_SHARED,
                        env->me_lfd, 0);
                if (m == MAP_FAILED) goto fail_errno;
                env->me_txns = m;
#endif
        }
        if (*excl > 0) {
#ifdef _WIN32
                BY_HANDLE_FILE_INFORMATION stbuf;
                struct {
                        DWORD volume;
                        DWORD nhigh;
                        DWORD nlow;
                } idbuf;
                MDB_val val;
                char encbuf[11];

                if (!mdb_sec_inited) {
                        InitializeSecurityDescriptor(&mdb_null_sd,
                                SECURITY_DESCRIPTOR_REVISION);
                        SetSecurityDescriptorDacl(&mdb_null_sd, TRUE, 0, FALSE);
                        mdb_all_sa.nLength = sizeof(SECURITY_ATTRIBUTES);
                        mdb_all_sa.bInheritHandle = FALSE;
                        mdb_all_sa.lpSecurityDescriptor = &mdb_null_sd;
                        mdb_sec_inited = 1;
                }
                if (!GetFileInformationByHandle(env->me_lfd, &stbuf)) goto fail_errno;
                idbuf.volume = stbuf.dwVolumeSerialNumber;
                idbuf.nhigh  = stbuf.nFileIndexHigh;
                idbuf.nlow   = stbuf.nFileIndexLow;
                val.mv_data = &idbuf;
                val.mv_size = sizeof(idbuf);
                mdb_hash_enc(&val, encbuf);
                sprintf(env->me_txns->mti_rmname, "Global\\MDBr%s", encbuf);
                sprintf(env->me_txns->mti_wmname, "Global\\MDBw%s", encbuf);
                env->me_rmutex = CreateMutex(&mdb_all_sa, FALSE, env->me_txns->mti_rmname);
                if (!env->me_rmutex) goto fail_errno;
                env->me_wmutex = CreateMutex(&mdb_all_sa, FALSE, env->me_txns->mti_wmname);
                if (!env->me_wmutex) goto fail_errno;
#elif defined(MDB_USE_POSIX_SEM)
                struct stat stbuf;
                struct {
                        dev_t dev;
                        ino_t ino;
                } idbuf;
                MDB_val val;
                char encbuf[11];

#if defined(__NetBSD__)
#define MDB_SHORT_SEMNAMES      1       /* limited to 14 chars */
#endif
                if (fstat(env->me_lfd, &stbuf)) goto fail_errno;
                idbuf.dev = stbuf.st_dev;
                idbuf.ino = stbuf.st_ino;
                val.mv_data = &idbuf;
                val.mv_size = sizeof(idbuf);
                mdb_hash_enc(&val, encbuf);
#ifdef MDB_SHORT_SEMNAMES
                encbuf[9] = '\0';       /* drop name from 15 chars to 14 chars */
#endif
                sprintf(env->me_txns->mti_rmname, "/MDBr%s", encbuf);
                sprintf(env->me_txns->mti_wmname, "/MDBw%s", encbuf);
                /* Clean up after a previous run, if needed:  Try to
                 * remove both semaphores before doing anything else.
                 */
                sem_unlink(env->me_txns->mti_rmname);
                sem_unlink(env->me_txns->mti_wmname);
                env->me_rmutex = sem_open(env->me_txns->mti_rmname,
                        O_CREAT|O_EXCL, mode, 1);
                if (env->me_rmutex == SEM_FAILED) goto fail_errno;
                env->me_wmutex = sem_open(env->me_txns->mti_wmname,
                        O_CREAT|O_EXCL, mode, 1);
                if (env->me_wmutex == SEM_FAILED) goto fail_errno;
#else   /* MDB_USE_POSIX_SEM */
                pthread_mutexattr_t mattr;

                if ((rc = pthread_mutexattr_init(&mattr))
                        || (rc = pthread_mutexattr_setpshared(&mattr, PTHREAD_PROCESS_SHARED))
                        || (rc = pthread_mutex_init(&env->me_txns->mti_mutex, &mattr))
                        || (rc = pthread_mutex_init(&env->me_txns->mti_wmutex, &mattr)))
                        goto fail;
                pthread_mutexattr_destroy(&mattr);
#endif  /* _WIN32 || MDB_USE_POSIX_SEM */

                env->me_txns->mti_magic = MDB_MAGIC;
                env->me_txns->mti_format = MDB_LOCK_FORMAT;
                env->me_txns->mti_txnid = 0;
                env->me_txns->mti_numreaders = 0;

        } else {
                if (env->me_txns->mti_magic != MDB_MAGIC) {
                        DPUTS("lock region has invalid magic");
                        rc = MDB_INVALID;
                        goto fail;
                }
                if (env->me_txns->mti_format != MDB_LOCK_FORMAT) {
                        DPRINTF(("lock region has format+version 0x%x, expected 0x%x",
                                env->me_txns->mti_format, MDB_LOCK_FORMAT));
                        rc = MDB_VERSION_MISMATCH;
                        goto fail;
                }
                rc = ErrCode();
                if (rc && rc != EACCES && rc != EAGAIN) {
                        goto fail;
                }
#ifdef _WIN32
                env->me_rmutex = OpenMutex(SYNCHRONIZE, FALSE, env->me_txns->mti_rmname);
                if (!env->me_rmutex) goto fail_errno;
                env->me_wmutex = OpenMutex(SYNCHRONIZE, FALSE, env->me_txns->mti_wmname);
                if (!env->me_wmutex) goto fail_errno;
#elif defined(MDB_USE_POSIX_SEM)
                env->me_rmutex = sem_open(env->me_txns->mti_rmname, 0);
                if (env->me_rmutex == SEM_FAILED) goto fail_errno;
                env->me_wmutex = sem_open(env->me_txns->mti_wmname, 0);
                if (env->me_wmutex == SEM_FAILED) goto fail_errno;
#endif
        }
        return MDB_SUCCESS;

fail_errno:
        rc = ErrCode();
fail:
        return rc;
}

        /** The name of the lock file in the DB environment */
#define LOCKNAME        "/lock.mdb"
        /** The name of the data file in the DB environment */
#define DATANAME        "/data.mdb"
        /** The suffix of the lock file when no subdir is used */
#define LOCKSUFF        "-lock"
        /** Only a subset of the @ref mdb_env flags can be changed
         *      at runtime. Changing other flags requires closing the
         *      environment and re-opening it with the new flags.
         */
#define CHANGEABLE      (MDB_NOSYNC|MDB_NOMETASYNC|MDB_MAPASYNC|MDB_NOMEMINIT)
#define CHANGELESS      (MDB_FIXEDMAP|MDB_NOSUBDIR|MDB_RDONLY|MDB_WRITEMAP| \
        MDB_NOTLS|MDB_NOLOCK|MDB_NORDAHEAD)

#if VALID_FLAGS & PERSISTENT_FLAGS & (CHANGEABLE|CHANGELESS)
# error "Persistent DB flags & env flags overlap, but both go in mm_flags"
#endif

int ESECT
mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode)
{
        int             oflags, rc, len, excl = -1;
        char *lpath, *dpath;

        if (env->me_fd!=INVALID_HANDLE_VALUE || (flags & ~(CHANGEABLE|CHANGELESS)))
                return EINVAL;

        len = strlen(path);
        if (flags & MDB_NOSUBDIR) {
                rc = len + sizeof(LOCKSUFF) + len + 1;
        } else {
                rc = len + sizeof(LOCKNAME) + len + sizeof(DATANAME);
        }
        lpath = malloc(rc);
        if (!lpath)
                return ENOMEM;
        if (flags & MDB_NOSUBDIR) {
                dpath = lpath + len + sizeof(LOCKSUFF);
                sprintf(lpath, "%s" LOCKSUFF, path);
                strcpy(dpath, path);
        } else {
                dpath = lpath + len + sizeof(LOCKNAME);
                sprintf(lpath, "%s" LOCKNAME, path);
                sprintf(dpath, "%s" DATANAME, path);
        }

        rc = MDB_SUCCESS;
        flags |= env->me_flags;
        if (flags & MDB_RDONLY) {
                /* silently ignore WRITEMAP when we're only getting read access */
                flags &= ~MDB_WRITEMAP;
        } else {
                if (!((env->me_free_pgs = mdb_midl_alloc(MDB_IDL_UM_MAX)) &&
                          (env->me_dirty_list = calloc(MDB_IDL_UM_SIZE, sizeof(MDB_ID2)))))
                        rc = ENOMEM;
        }
        env->me_flags = flags |= MDB_ENV_ACTIVE;
        if (rc)
                goto leave;

        env->me_path = strdup(path);
        env->me_dbxs = calloc(env->me_maxdbs, sizeof(MDB_dbx));
        env->me_dbflags = calloc(env->me_maxdbs, sizeof(uint16_t));
        env->me_dbiseqs = calloc(env->me_maxdbs, sizeof(unsigned int));
        if (!(env->me_dbxs && env->me_path && env->me_dbflags && env->me_dbiseqs)) {
                rc = ENOMEM;
                goto leave;
        }

        /* For RDONLY, get lockfile after we know datafile exists */
        if (!(flags & (MDB_RDONLY|MDB_NOLOCK))) {
                rc = mdb_env_setup_locks(env, lpath, mode, &excl);
                if (rc)
                        goto leave;
        }

#ifdef _WIN32
        if (F_ISSET(flags, MDB_RDONLY)) {
                oflags = GENERIC_READ;
                len = OPEN_EXISTING;
        } else {
                oflags = GENERIC_READ|GENERIC_WRITE;
                len = OPEN_ALWAYS;
        }
        mode = FILE_ATTRIBUTE_NORMAL;
        env->me_fd = CreateFile(dpath, oflags, FILE_SHARE_READ|FILE_SHARE_WRITE,
                NULL, len, mode, NULL);
#else
        if (F_ISSET(flags, MDB_RDONLY))
                oflags = O_RDONLY;
        else
                oflags = O_RDWR | O_CREAT;

        env->me_fd = open(dpath, oflags, mode);
#endif
        if (env->me_fd == INVALID_HANDLE_VALUE) {
                rc = ErrCode();
                goto leave;
        }

        if ((flags & (MDB_RDONLY|MDB_NOLOCK)) == MDB_RDONLY) {
                rc = mdb_env_setup_locks(env, lpath, mode, &excl);
                if (rc)
                        goto leave;
        }

        if ((rc = mdb_env_open2(env)) == MDB_SUCCESS) {
                if (flags & (MDB_RDONLY|MDB_WRITEMAP)) {
                        env->me_mfd = env->me_fd;
                } else {
                        /* Synchronous fd for meta writes. Needed even with
                         * MDB_NOSYNC/MDB_NOMETASYNC, in case these get reset.
                         */
#ifdef _WIN32
                        len = OPEN_EXISTING;
                        env->me_mfd = CreateFile(dpath, oflags,
                                FILE_SHARE_READ|FILE_SHARE_WRITE, NULL, len,
                                mode | FILE_FLAG_WRITE_THROUGH, NULL);
#else
                        oflags &= ~O_CREAT;
                        env->me_mfd = open(dpath, oflags | MDB_DSYNC, mode);
#endif
                        if (env->me_mfd == INVALID_HANDLE_VALUE) {
                                rc = ErrCode();
                                goto leave;
                        }
                }
                DPRINTF(("opened dbenv %p", (void *) env));
                if (excl > 0) {
                        rc = mdb_env_share_locks(env, &excl);
                        if (rc)
                                goto leave;
                }
                if (!((flags & MDB_RDONLY) ||
                          (env->me_pbuf = calloc(1, env->me_psize))))
                        rc = ENOMEM;
        }

leave:
        if (rc) {
                mdb_env_close0(env, excl);
        }
        free(lpath);
        return rc;
}

/** Destroy resources from mdb_env_open(), clear our readers & DBIs */
static void ESECT
mdb_env_close0(MDB_env *env, int excl)
{
        int i;

        if (!(env->me_flags & MDB_ENV_ACTIVE))
                return;

        /* Doing this here since me_dbxs may not exist during mdb_env_close */
        for (i = env->me_maxdbs; --i > MAIN_DBI; )
                free(env->me_dbxs[i].md_name.mv_data);

        free(env->me_pbuf);
        free(env->me_dbiseqs);
        free(env->me_dbflags);
        free(env->me_dbxs);
        free(env->me_path);
        free(env->me_dirty_list);
        mdb_midl_free(env->me_free_pgs);

        if (env->me_flags & MDB_ENV_TXKEY) {
                pthread_key_delete(env->me_txkey);
#ifdef _WIN32
                /* Delete our key from the global list */
                for (i=0; i<mdb_tls_nkeys; i++)
                        if (mdb_tls_keys[i] == env->me_txkey) {
                                mdb_tls_keys[i] = mdb_tls_keys[mdb_tls_nkeys-1];
                                mdb_tls_nkeys--;
                                break;
                        }
#endif
        }

        if (env->me_map) {
                munmap(env->me_map, env->me_mapsize);
        }
        if (env->me_mfd != env->me_fd && env->me_mfd != INVALID_HANDLE_VALUE)
                (void) close(env->me_mfd);
        if (env->me_fd != INVALID_HANDLE_VALUE)
                (void) close(env->me_fd);
        if (env->me_txns) {
                MDB_PID_T pid = env->me_pid;
                /* Clearing readers is done in this function because
                 * me_txkey with its destructor must be disabled first.
                 */
                for (i = env->me_numreaders; --i >= 0; )
                        if (env->me_txns->mti_readers[i].mr_pid == pid)
                                env->me_txns->mti_readers[i].mr_pid = 0;
#ifdef _WIN32
                if (env->me_rmutex) {
                        CloseHandle(env->me_rmutex);
                        if (env->me_wmutex) CloseHandle(env->me_wmutex);
                }
                /* Windows automatically destroys the mutexes when
                 * the last handle closes.
                 */
#elif defined(MDB_USE_POSIX_SEM)
                if (env->me_rmutex != SEM_FAILED) {
                        sem_close(env->me_rmutex);
                        if (env->me_wmutex != SEM_FAILED)
                                sem_close(env->me_wmutex);
                        /* If we have the filelock:  If we are the
                         * only remaining user, clean up semaphores.
                         */
                        if (excl == 0)
                                mdb_env_excl_lock(env, &excl);
                        if (excl > 0) {
                                sem_unlink(env->me_txns->mti_rmname);
                                sem_unlink(env->me_txns->mti_wmname);
                        }
                }
#endif
                munmap((void *)env->me_txns, (env->me_maxreaders-1)*sizeof(MDB_reader)+sizeof(MDB_txninfo));
        }
        if (env->me_lfd != INVALID_HANDLE_VALUE) {
#ifdef _WIN32
                if (excl >= 0) {
                        /* Unlock the lockfile.  Windows would have unlocked it
                         * after closing anyway, but not necessarily at once.
                         */
                        UnlockFile(env->me_lfd, 0, 0, 1, 0);
                }
#endif
                (void) close(env->me_lfd);
        }

        env->me_flags &= ~(MDB_ENV_ACTIVE|MDB_ENV_TXKEY);
}


void ESECT
mdb_env_close(MDB_env *env)
{
        MDB_page *dp;

        if (env == NULL)
                return;

        VGMEMP_DESTROY(env);
        while ((dp = env->me_dpages) != NULL) {
                VGMEMP_DEFINED(&dp->mp_next, sizeof(dp->mp_next));
                env->me_dpages = dp->mp_next;
                free(dp);
        }

        mdb_env_close0(env, 0);
        free(env);
}

/** Compare two items pointing at aligned size_t's */
static int
mdb_cmp_long(const MDB_val *a, const MDB_val *b)
{
        return (*(size_t *)a->mv_data < *(size_t *)b->mv_data) ? -1 :
                *(size_t *)a->mv_data > *(size_t *)b->mv_data;
}

/** Compare two items pointing at aligned unsigned int's */
static int
mdb_cmp_int(const MDB_val *a, const MDB_val *b)
{
        return (*(unsigned int *)a->mv_data < *(unsigned int *)b->mv_data) ? -1 :
                *(unsigned int *)a->mv_data > *(unsigned int *)b->mv_data;
}

/** Compare two items pointing at unsigned ints of unknown alignment.
 *      Nodes and keys are guaranteed to be 2-byte aligned.
 */
static int
mdb_cmp_cint(const MDB_val *a, const MDB_val *b)
{
#if BYTE_ORDER == LITTLE_ENDIAN
        unsigned short *u, *c;
        int x;

        u = (unsigned short *) ((char *) a->mv_data + a->mv_size);
        c = (unsigned short *) ((char *) b->mv_data + a->mv_size);
        do {
                x = *--u - *--c;
        } while(!x && u > (unsigned short *)a->mv_data);
        return x;
#else
        unsigned short *u, *c, *end;
        int x;

        end = (unsigned short *) ((char *) a->mv_data + a->mv_size);
        u = (unsigned short *)a->mv_data;
        c = (unsigned short *)b->mv_data;
        do {
                x = *u++ - *c++;
        } while(!x && u < end);
        return x;
#endif
}

/** Compare two items pointing at size_t's of unknown alignment. */
#ifdef MISALIGNED_OK
# define mdb_cmp_clong mdb_cmp_long
#else
# define mdb_cmp_clong mdb_cmp_cint
#endif

/** Compare two items lexically */
static int
mdb_cmp_memn(const MDB_val *a, const MDB_val *b)
{
        int diff;
        ssize_t len_diff;
        unsigned int len;

        len = a->mv_size;
        len_diff = (ssize_t) a->mv_size - (ssize_t) b->mv_size;
        if (len_diff > 0) {
                len = b->mv_size;
                len_diff = 1;
        }

        diff = memcmp(a->mv_data, b->mv_data, len);
        return diff ? diff : len_diff<0 ? -1 : len_diff;
}

/** Compare two items in reverse byte order */
static int
mdb_cmp_memnr(const MDB_val *a, const MDB_val *b)
{
        const unsigned char     *p1, *p2, *p1_lim;
        ssize_t len_diff;
        int diff;

        p1_lim = (const unsigned char *)a->mv_data;
        p1 = (const unsigned char *)a->mv_data + a->mv_size;
        p2 = (const unsigned char *)b->mv_data + b->mv_size;

        len_diff = (ssize_t) a->mv_size - (ssize_t) b->mv_size;
        if (len_diff > 0) {
                p1_lim += len_diff;
                len_diff = 1;
        }

        while (p1 > p1_lim) {
                diff = *--p1 - *--p2;
                if (diff)
                        return diff;
        }
        return len_diff<0 ? -1 : len_diff;
}

/** Search for key within a page, using binary search.
 * Returns the smallest entry larger or equal to the key.
 * If exactp is non-null, stores whether the found entry was an exact match
 * in *exactp (1 or 0).
 * Updates the cursor index with the index of the found entry.
 * If no entry larger or equal to the key is found, returns NULL.
 */
static MDB_node *
mdb_node_search(MDB_cursor *mc, MDB_val *key, int *exactp)
{
        unsigned int     i = 0, nkeys;
        int              low, high;
        int              rc = 0;
        MDB_page *mp = mc->mc_pg[mc->mc_top];
        MDB_node        *node = NULL;
        MDB_val  nodekey;
        MDB_cmp_func *cmp;
        DKBUF;

        nkeys = NUMKEYS(mp);

        DPRINTF(("searching %u keys in %s %spage %"Z"u",
            nkeys, IS_LEAF(mp) ? "leaf" : "branch", IS_SUBP(mp) ? "sub-" : "",
            mdb_dbg_pgno(mp)));

        low = IS_LEAF(mp) ? 0 : 1;
        high = nkeys - 1;
        cmp = mc->mc_dbx->md_cmp;

        /* Branch pages have no data, so if using integer keys,
         * alignment is guaranteed. Use faster mdb_cmp_int.
         */
        if (cmp == mdb_cmp_cint && IS_BRANCH(mp)) {
                if (NODEPTR(mp, 1)->mn_ksize == sizeof(size_t))
                        cmp = mdb_cmp_long;
                else
                        cmp = mdb_cmp_int;
        }

        if (IS_LEAF2(mp)) {
                nodekey.mv_size = mc->mc_db->md_pad;
                node = NODEPTR(mp, 0);  /* fake */
                while (low <= high) {
                        i = (low + high) >> 1;
                        nodekey.mv_data = LEAF2KEY(mp, i, nodekey.mv_size);
                        rc = cmp(key, &nodekey);
                        DPRINTF(("found leaf index %u [%s], rc = %i",
                            i, DKEY(&nodekey), rc));
                        if (rc == 0)
                                break;
                        if (rc > 0)
                                low = i + 1;
                        else
                                high = i - 1;
                }
        } else {
                while (low <= high) {
                        i = (low + high) >> 1;

                        node = NODEPTR(mp, i);
                        nodekey.mv_size = NODEKSZ(node);
                        nodekey.mv_data = NODEKEY(node);

                        rc = cmp(key, &nodekey);
#if MDB_DEBUG
                        if (IS_LEAF(mp))
                                DPRINTF(("found leaf index %u [%s], rc = %i",
                                    i, DKEY(&nodekey), rc));
                        else
                                DPRINTF(("found branch index %u [%s -> %"Z"u], rc = %i",
                                    i, DKEY(&nodekey), NODEPGNO(node), rc));
#endif
                        if (rc == 0)
                                break;
                        if (rc > 0)
                                low = i + 1;
                        else
                                high = i - 1;
                }
        }

        if (rc > 0) {   /* Found entry is less than the key. */
                i++;    /* Skip to get the smallest entry larger than key. */
                if (!IS_LEAF2(mp))
                        node = NODEPTR(mp, i);
        }
        if (exactp)
                *exactp = (rc == 0 && nkeys > 0);
        /* store the key index */
        mc->mc_ki[mc->mc_top] = i;
        if (i >= nkeys)
                /* There is no entry larger or equal to the key. */
                return NULL;

        /* nodeptr is fake for LEAF2 */
        return node;
}

#if 0
static void
mdb_cursor_adjust(MDB_cursor *mc, func)
{
        MDB_cursor *m2;

        for (m2 = mc->mc_txn->mt_cursors[mc->mc_dbi]; m2; m2=m2->mc_next) {
                if (m2->mc_pg[m2->mc_top] == mc->mc_pg[mc->mc_top]) {
                        func(mc, m2);
                }
        }
}
#endif

/** Pop a page off the top of the cursor's stack. */
static void
mdb_cursor_pop(MDB_cursor *mc)
{
        if (mc->mc_snum) {
#if MDB_DEBUG
                MDB_page        *top = mc->mc_pg[mc->mc_top];
#endif
                mc->mc_snum--;
                if (mc->mc_snum)
                        mc->mc_top--;

                DPRINTF(("popped page %"Z"u off db %d cursor %p", top->mp_pgno,
                        DDBI(mc), (void *) mc));
        }
}

/** Push a page onto the top of the cursor's stack. */
static int
mdb_cursor_push(MDB_cursor *mc, MDB_page *mp)
{
        DPRINTF(("pushing page %"Z"u on db %d cursor %p", mp->mp_pgno,
                DDBI(mc), (void *) mc));

        if (mc->mc_snum >= CURSOR_STACK) {
                mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
                return MDB_CURSOR_FULL;
        }

        mc->mc_top = mc->mc_snum++;
        mc->mc_pg[mc->mc_top] = mp;
        mc->mc_ki[mc->mc_top] = 0;

        return MDB_SUCCESS;
}

/** Find the address of the page corresponding to a given page number.
 * @param[in] txn the transaction for this access.
 * @param[in] pgno the page number for the page to retrieve.
 * @param[out] ret address of a pointer where the page's address will be stored.
 * @param[out] lvl dirty_list inheritance level of found page. 1=current txn, 0=mapped page.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_get(MDB_txn *txn, pgno_t pgno, MDB_page **ret, int *lvl)
{
        MDB_env *env = txn->mt_env;
        MDB_page *p = NULL;
        int level;

        if (!((txn->mt_flags & MDB_TXN_RDONLY) | (env->me_flags & MDB_WRITEMAP))) {
                MDB_txn *tx2 = txn;
                level = 1;
                do {
                        MDB_ID2L dl = tx2->mt_u.dirty_list;
                        unsigned x;
                        /* Spilled pages were dirtied in this txn and flushed
                         * because the dirty list got full. Bring this page
                         * back in from the map (but don't unspill it here,
                         * leave that unless page_touch happens again).
                         */
                        if (tx2->mt_spill_pgs) {
                                MDB_ID pn = pgno << 1;
                                x = mdb_midl_search(tx2->mt_spill_pgs, pn);
                                if (x <= tx2->mt_spill_pgs[0] && tx2->mt_spill_pgs[x] == pn) {
                                        p = (MDB_page *)(env->me_map + env->me_psize * pgno);
                                        goto done;
                                }
                        }
                        if (dl[0].mid) {
                                unsigned x = mdb_mid2l_search(dl, pgno);
                                if (x <= dl[0].mid && dl[x].mid == pgno) {
                                        p = dl[x].mptr;
                                        goto done;
                                }
                        }
                        level++;
                } while ((tx2 = tx2->mt_parent) != NULL);
        }

        if (pgno < txn->mt_next_pgno) {
                level = 0;
                p = (MDB_page *)(env->me_map + env->me_psize * pgno);
        } else {
                DPRINTF(("page %"Z"u not found", pgno));
                txn->mt_flags |= MDB_TXN_ERROR;
                return MDB_PAGE_NOTFOUND;
        }

done:
        *ret = p;
        if (lvl)
                *lvl = level;
        return MDB_SUCCESS;
}

/** Finish #mdb_page_search() / #mdb_page_search_lowest().
 *      The cursor is at the root page, set up the rest of it.
 */
static int
mdb_page_search_root(MDB_cursor *mc, MDB_val *key, int flags)
{
        MDB_page        *mp = mc->mc_pg[mc->mc_top];
        int rc;
        DKBUF;

        while (IS_BRANCH(mp)) {
                MDB_node        *node;
                indx_t          i;

                DPRINTF(("branch page %"Z"u has %u keys", mp->mp_pgno, NUMKEYS(mp)));
                mdb_cassert(mc, NUMKEYS(mp) > 1);
                DPRINTF(("found index 0 to page %"Z"u", NODEPGNO(NODEPTR(mp, 0))));

                if (flags & (MDB_PS_FIRST|MDB_PS_LAST)) {
                        i = 0;
                        if (flags & MDB_PS_LAST)
                                i = NUMKEYS(mp) - 1;
                } else {
                        int      exact;
                        node = mdb_node_search(mc, key, &exact);
                        if (node == NULL)
                                i = NUMKEYS(mp) - 1;
                        else {
                                i = mc->mc_ki[mc->mc_top];
                                if (!exact) {
                                        mdb_cassert(mc, i > 0);
                                        i--;
                                }
                        }
                        DPRINTF(("following index %u for key [%s]", i, DKEY(key)));
                }

                mdb_cassert(mc, i < NUMKEYS(mp));
                node = NODEPTR(mp, i);

                if ((rc = mdb_page_get(mc->mc_txn, NODEPGNO(node), &mp, NULL)) != 0)
                        return rc;

                mc->mc_ki[mc->mc_top] = i;
                if ((rc = mdb_cursor_push(mc, mp)))
                        return rc;

                if (flags & MDB_PS_MODIFY) {
                        if ((rc = mdb_page_touch(mc)) != 0)
                                return rc;
                        mp = mc->mc_pg[mc->mc_top];
                }
        }

        if (!IS_LEAF(mp)) {
                DPRINTF(("internal error, index points to a %02X page!?",
                    mp->mp_flags));
                mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
                return MDB_CORRUPTED;
        }

        DPRINTF(("found leaf page %"Z"u for key [%s]", mp->mp_pgno,
            key ? DKEY(key) : "null"));
        mc->mc_flags |= C_INITIALIZED;
        mc->mc_flags &= ~C_EOF;

        return MDB_SUCCESS;
}

/** Search for the lowest key under the current branch page.
 * This just bypasses a NUMKEYS check in the current page
 * before calling mdb_page_search_root(), because the callers
 * are all in situations where the current page is known to
 * be underfilled.
 */
static int
mdb_page_search_lowest(MDB_cursor *mc)
{
        MDB_page        *mp = mc->mc_pg[mc->mc_top];
        MDB_node        *node = NODEPTR(mp, 0);
        int rc;

        if ((rc = mdb_page_get(mc->mc_txn, NODEPGNO(node), &mp, NULL)) != 0)
                return rc;

        mc->mc_ki[mc->mc_top] = 0;
        if ((rc = mdb_cursor_push(mc, mp)))
                return rc;
        return mdb_page_search_root(mc, NULL, MDB_PS_FIRST);
}

/** Search for the page a given key should be in.
 * Push it and its parent pages on the cursor stack.
 * @param[in,out] mc the cursor for this operation.
 * @param[in] key the key to search for, or NULL for first/last page.
 * @param[in] flags If MDB_PS_MODIFY is set, visited pages in the DB
 *   are touched (updated with new page numbers).
 *   If MDB_PS_FIRST or MDB_PS_LAST is set, find first or last leaf.
 *   This is used by #mdb_cursor_first() and #mdb_cursor_last().
 *   If MDB_PS_ROOTONLY set, just fetch root node, no further lookups.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_search(MDB_cursor *mc, MDB_val *key, int flags)
{
        int              rc;
        pgno_t           root;

        /* Make sure the txn is still viable, then find the root from
         * the txn's db table and set it as the root of the cursor's stack.
         */
        if (F_ISSET(mc->mc_txn->mt_flags, MDB_TXN_ERROR)) {
                DPUTS("transaction has failed, must abort");
                return MDB_BAD_TXN;
        } else {
                /* Make sure we're using an up-to-date root */
                if (*mc->mc_dbflag & DB_STALE) {
                                MDB_cursor mc2;
                                if (TXN_DBI_CHANGED(mc->mc_txn, mc->mc_dbi))
                                        return MDB_BAD_DBI;
                                mdb_cursor_init(&mc2, mc->mc_txn, MAIN_DBI, NULL);
                                rc = mdb_page_search(&mc2, &mc->mc_dbx->md_name, 0);
                                if (rc)
                                        return rc;
                                {
                                        MDB_val data;
                                        int exact = 0;
                                        uint16_t flags;
                                        MDB_node *leaf = mdb_node_search(&mc2,
                                                &mc->mc_dbx->md_name, &exact);
                                        if (!exact)
                                                return MDB_NOTFOUND;
                                        rc = mdb_node_read(mc->mc_txn, leaf, &data);
                                        if (rc)
                                                return rc;
                                        memcpy(&flags, ((char *) data.mv_data + offsetof(MDB_db, md_flags)),
                                                sizeof(uint16_t));
                                        /* The txn may not know this DBI, or another process may
                                         * have dropped and recreated the DB with other flags.
                                         */
                                        if ((mc->mc_db->md_flags & PERSISTENT_FLAGS) != flags)
                                                return MDB_INCOMPATIBLE;
                                        memcpy(mc->mc_db, data.mv_data, sizeof(MDB_db));
                                }
                                *mc->mc_dbflag &= ~DB_STALE;
                }
                root = mc->mc_db->md_root;

                if (root == P_INVALID) {                /* Tree is empty. */
                        DPUTS("tree is empty");
                        return MDB_NOTFOUND;
                }
        }

        mdb_cassert(mc, root > 1);
        if (!mc->mc_pg[0] || mc->mc_pg[0]->mp_pgno != root)
                if ((rc = mdb_page_get(mc->mc_txn, root, &mc->mc_pg[0], NULL)) != 0)
                        return rc;

        mc->mc_snum = 1;
        mc->mc_top = 0;

        DPRINTF(("db %d root page %"Z"u has flags 0x%X",
                DDBI(mc), root, mc->mc_pg[0]->mp_flags));

        if (flags & MDB_PS_MODIFY) {
                if ((rc = mdb_page_touch(mc)))
                        return rc;
        }

        if (flags & MDB_PS_ROOTONLY)
                return MDB_SUCCESS;

        return mdb_page_search_root(mc, key, flags);
}

static int
mdb_ovpage_free(MDB_cursor *mc, MDB_page *mp)
{
        MDB_txn *txn = mc->mc_txn;
        pgno_t pg = mp->mp_pgno;
        unsigned x = 0, ovpages = mp->mp_pages;
        MDB_env *env = txn->mt_env;
        MDB_IDL sl = txn->mt_spill_pgs;
        MDB_ID pn = pg << 1;
        int rc;

        DPRINTF(("free ov page %"Z"u (%d)", pg, ovpages));
        /* If the page is dirty or on the spill list we just acquired it,
         * so we should give it back to our current free list, if any.
         * Otherwise put it onto the list of pages we freed in this txn.
         *
         * Won't create me_pghead: me_pglast must be inited along with it.
         * Unsupported in nested txns: They would need to hide the page
         * range in ancestor txns' dirty and spilled lists.
         */
        if (env->me_pghead &&
                !txn->mt_parent &&
                ((mp->mp_flags & P_DIRTY) ||
                 (sl && (x = mdb_midl_search(sl, pn)) <= sl[0] && sl[x] == pn)))
        {
                unsigned i, j;
                pgno_t *mop;
                MDB_ID2 *dl, ix, iy;
                rc = mdb_midl_need(&env->me_pghead, ovpages);
                if (rc)
                        return rc;
                if (!(mp->mp_flags & P_DIRTY)) {
                        /* This page is no longer spilled */
                        if (x == sl[0])
                                sl[0]--;
                        else
                                sl[x] |= 1;
                        goto release;
                }
                /* Remove from dirty list */
                dl = txn->mt_u.dirty_list;
                x = dl[0].mid--;
                for (ix = dl[x]; ix.mptr != mp; ix = iy) {
                        if (x > 1) {
                                x--;
                                iy = dl[x];
                                dl[x] = ix;
                        } else {
                                mdb_cassert(mc, x > 1);
                                j = ++(dl[0].mid);
                                dl[j] = ix;             /* Unsorted. OK when MDB_TXN_ERROR. */
                                txn->mt_flags |= MDB_TXN_ERROR;
                                return MDB_CORRUPTED;
                        }
                }
                if (!(env->me_flags & MDB_WRITEMAP))
                        mdb_dpage_free(env, mp);
release:
                /* Insert in me_pghead */
                mop = env->me_pghead;
                j = mop[0] + ovpages;
                for (i = mop[0]; i && mop[i] < pg; i--)
                        mop[j--] = mop[i];
                while (j>i)
                        mop[j--] = pg++;
                mop[0] += ovpages;
        } else {
                rc = mdb_midl_append_range(&txn->mt_free_pgs, pg, ovpages);
                if (rc)
                        return rc;
        }
        mc->mc_db->md_overflow_pages -= ovpages;
        return 0;
}

/** Return the data associated with a given node.
 * @param[in] txn The transaction for this operation.
 * @param[in] leaf The node being read.
 * @param[out] data Updated to point to the node's data.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_node_read(MDB_txn *txn, MDB_node *leaf, MDB_val *data)
{
        MDB_page        *omp;           /* overflow page */
        pgno_t           pgno;
        int rc;

        if (!F_ISSET(leaf->mn_flags, F_BIGDATA)) {
                data->mv_size = NODEDSZ(leaf);
                data->mv_data = NODEDATA(leaf);
                return MDB_SUCCESS;
        }

        /* Read overflow data.
         */
        data->mv_size = NODEDSZ(leaf);
        memcpy(&pgno, NODEDATA(leaf), sizeof(pgno));
        if ((rc = mdb_page_get(txn, pgno, &omp, NULL)) != 0) {
                DPRINTF(("read overflow page %"Z"u failed", pgno));
                return rc;
        }
        data->mv_data = METADATA(omp);

        return MDB_SUCCESS;
}

int
mdb_get(MDB_txn *txn, MDB_dbi dbi,
    MDB_val *key, MDB_val *data)
{
        MDB_cursor      mc;
        MDB_xcursor     mx;
        int exact = 0;
        DKBUF;

        DPRINTF(("===> get db %u key [%s]", dbi, DKEY(key)));

        if (!key || !data || dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
                return EINVAL;

        if (txn->mt_flags & MDB_TXN_ERROR)
                return MDB_BAD_TXN;

        mdb_cursor_init(&mc, txn, dbi, &mx);
        return mdb_cursor_set(&mc, key, data, MDB_SET, &exact);
}

/** Find a sibling for a page.
 * Replaces the page at the top of the cursor's stack with the
 * specified sibling, if one exists.
 * @param[in] mc The cursor for this operation.
 * @param[in] move_right Non-zero if the right sibling is requested,
 * otherwise the left sibling.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_cursor_sibling(MDB_cursor *mc, int move_right)
{
        int              rc;
        MDB_node        *indx;
        MDB_page        *mp;

        if (mc->mc_snum < 2) {
                return MDB_NOTFOUND;            /* root has no siblings */
        }

        mdb_cursor_pop(mc);
        DPRINTF(("parent page is page %"Z"u, index %u",
                mc->mc_pg[mc->mc_top]->mp_pgno, mc->mc_ki[mc->mc_top]));

        if (move_right ? (mc->mc_ki[mc->mc_top] + 1u >= NUMKEYS(mc->mc_pg[mc->mc_top]))
                       : (mc->mc_ki[mc->mc_top] == 0)) {
                DPRINTF(("no more keys left, moving to %s sibling",
                    move_right ? "right" : "left"));
                if ((rc = mdb_cursor_sibling(mc, move_right)) != MDB_SUCCESS) {
                        /* undo cursor_pop before returning */
                        mc->mc_top++;
                        mc->mc_snum++;
                        return rc;
                }
        } else {
                if (move_right)
                        mc->mc_ki[mc->mc_top]++;
                else
                        mc->mc_ki[mc->mc_top]--;
                DPRINTF(("just moving to %s index key %u",
                    move_right ? "right" : "left", mc->mc_ki[mc->mc_top]));
        }
        mdb_cassert(mc, IS_BRANCH(mc->mc_pg[mc->mc_top]));

        indx = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
        if ((rc = mdb_page_get(mc->mc_txn, NODEPGNO(indx), &mp, NULL)) != 0) {
                /* mc will be inconsistent if caller does mc_snum++ as above */
                mc->mc_flags &= ~(C_INITIALIZED|C_EOF);
                return rc;
        }

        mdb_cursor_push(mc, mp);
        if (!move_right)
                mc->mc_ki[mc->mc_top] = NUMKEYS(mp)-1;

        return MDB_SUCCESS;
}

/** Move the cursor to the next data item. */
static int
mdb_cursor_next(MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op)
{
        MDB_page        *mp;
        MDB_node        *leaf;
        int rc;

        if (mc->mc_flags & C_EOF) {
                return MDB_NOTFOUND;
        }

        mdb_cassert(mc, mc->mc_flags & C_INITIALIZED);

        mp = mc->mc_pg[mc->mc_top];

        if (mc->mc_db->md_flags & MDB_DUPSORT) {
                leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
                if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                        if (op == MDB_NEXT || op == MDB_NEXT_DUP) {
                                rc = mdb_cursor_next(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_NEXT);
                                if (op != MDB_NEXT || rc != MDB_NOTFOUND) {
                                        if (rc == MDB_SUCCESS)
                                                MDB_GET_KEY(leaf, key);
                                        return rc;
                                }
                        }
                } else {
                        mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);
                        if (op == MDB_NEXT_DUP)
                                return MDB_NOTFOUND;
                }
        }

        DPRINTF(("cursor_next: top page is %"Z"u in cursor %p",
                mdb_dbg_pgno(mp), (void *) mc));
        if (mc->mc_flags & C_DEL)
                goto skip;

        if (mc->mc_ki[mc->mc_top] + 1u >= NUMKEYS(mp)) {
                DPUTS("=====> move to next sibling page");
                if ((rc = mdb_cursor_sibling(mc, 1)) != MDB_SUCCESS) {
                        mc->mc_flags |= C_EOF;
                        return rc;
                }
                mp = mc->mc_pg[mc->mc_top];
                DPRINTF(("next page is %"Z"u, key index %u", mp->mp_pgno, mc->mc_ki[mc->mc_top]));
        } else
                mc->mc_ki[mc->mc_top]++;

skip:
        DPRINTF(("==> cursor points to page %"Z"u with %u keys, key index %u",
            mdb_dbg_pgno(mp), NUMKEYS(mp), mc->mc_ki[mc->mc_top]));

        if (IS_LEAF2(mp)) {
                key->mv_size = mc->mc_db->md_pad;
                key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
                return MDB_SUCCESS;
        }

        mdb_cassert(mc, IS_LEAF(mp));
        leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);

        if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                mdb_xcursor_init1(mc, leaf);
        }
        if (data) {
                if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
                        return rc;

                if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                        rc = mdb_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
                        if (rc != MDB_SUCCESS)
                                return rc;
                }
        }

        MDB_GET_KEY(leaf, key);
        return MDB_SUCCESS;
}

/** Move the cursor to the previous data item. */
static int
mdb_cursor_prev(MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op)
{
        MDB_page        *mp;
        MDB_node        *leaf;
        int rc;

        mdb_cassert(mc, mc->mc_flags & C_INITIALIZED);

        mp = mc->mc_pg[mc->mc_top];

        if (mc->mc_db->md_flags & MDB_DUPSORT) {
                leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
                if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                        if (op == MDB_PREV || op == MDB_PREV_DUP) {
                                rc = mdb_cursor_prev(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_PREV);
                                if (op != MDB_PREV || rc != MDB_NOTFOUND) {
                                        if (rc == MDB_SUCCESS) {
                                                MDB_GET_KEY(leaf, key);
                                                mc->mc_flags &= ~C_EOF;
                                        }
                                        return rc;
                                }
                        } else {
                                mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);
                                if (op == MDB_PREV_DUP)
                                        return MDB_NOTFOUND;
                        }
                }
        }

        DPRINTF(("cursor_prev: top page is %"Z"u in cursor %p",
                mdb_dbg_pgno(mp), (void *) mc));

        if (mc->mc_ki[mc->mc_top] == 0)  {
                DPUTS("=====> move to prev sibling page");
                if ((rc = mdb_cursor_sibling(mc, 0)) != MDB_SUCCESS) {
                        return rc;
                }
                mp = mc->mc_pg[mc->mc_top];
                mc->mc_ki[mc->mc_top] = NUMKEYS(mp) - 1;
                DPRINTF(("prev page is %"Z"u, key index %u", mp->mp_pgno, mc->mc_ki[mc->mc_top]));
        } else
                mc->mc_ki[mc->mc_top]--;

        mc->mc_flags &= ~C_EOF;

        DPRINTF(("==> cursor points to page %"Z"u with %u keys, key index %u",
            mdb_dbg_pgno(mp), NUMKEYS(mp), mc->mc_ki[mc->mc_top]));

        if (IS_LEAF2(mp)) {
                key->mv_size = mc->mc_db->md_pad;
                key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
                return MDB_SUCCESS;
        }

        mdb_cassert(mc, IS_LEAF(mp));
        leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);

        if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                mdb_xcursor_init1(mc, leaf);
        }
        if (data) {
                if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
                        return rc;

                if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                        rc = mdb_cursor_last(&mc->mc_xcursor->mx_cursor, data, NULL);
                        if (rc != MDB_SUCCESS)
                                return rc;
                }
        }

        MDB_GET_KEY(leaf, key);
        return MDB_SUCCESS;
}

/** Set the cursor on a specific data item. */
static int
mdb_cursor_set(MDB_cursor *mc, MDB_val *key, MDB_val *data,
    MDB_cursor_op op, int *exactp)
{
        int              rc;
        MDB_page        *mp;
        MDB_node        *leaf = NULL;
        DKBUF;

        if (key->mv_size == 0)
                return MDB_BAD_VALSIZE;

        if (mc->mc_xcursor)
                mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);

        /* See if we're already on the right page */
        if (mc->mc_flags & C_INITIALIZED) {
                MDB_val nodekey;

                mp = mc->mc_pg[mc->mc_top];
                if (!NUMKEYS(mp)) {
                        mc->mc_ki[mc->mc_top] = 0;
                        return MDB_NOTFOUND;
                }
                if (mp->mp_flags & P_LEAF2) {
                        nodekey.mv_size = mc->mc_db->md_pad;
                        nodekey.mv_data = LEAF2KEY(mp, 0, nodekey.mv_size);
                } else {
                        leaf = NODEPTR(mp, 0);
                        MDB_GET_KEY2(leaf, nodekey);
                }
                rc = mc->mc_dbx->md_cmp(key, &nodekey);
                if (rc == 0) {
                        /* Probably happens rarely, but first node on the page
                         * was the one we wanted.
                         */
                        mc->mc_ki[mc->mc_top] = 0;
                        if (exactp)
                                *exactp = 1;
                        goto set1;
                }
                if (rc > 0) {
                        unsigned int i;
                        unsigned int nkeys = NUMKEYS(mp);
                        if (nkeys > 1) {
                                if (mp->mp_flags & P_LEAF2) {
                                        nodekey.mv_data = LEAF2KEY(mp,
                                                 nkeys-1, nodekey.mv_size);
                                } else {
                                        leaf = NODEPTR(mp, nkeys-1);
                                        MDB_GET_KEY2(leaf, nodekey);
                                }
                                rc = mc->mc_dbx->md_cmp(key, &nodekey);
                                if (rc == 0) {
                                        /* last node was the one we wanted */
                                        mc->mc_ki[mc->mc_top] = nkeys-1;
                                        if (exactp)
                                                *exactp = 1;
                                        goto set1;
                                }
                                if (rc < 0) {
                                        if (mc->mc_ki[mc->mc_top] < NUMKEYS(mp)) {
                                                /* This is definitely the right page, skip search_page */
                                                if (mp->mp_flags & P_LEAF2) {
                                                        nodekey.mv_data = LEAF2KEY(mp,
                                                                 mc->mc_ki[mc->mc_top], nodekey.mv_size);
                                                } else {
                                                        leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
                                                        MDB_GET_KEY2(leaf, nodekey);
                                                }
                                                rc = mc->mc_dbx->md_cmp(key, &nodekey);
                                                if (rc == 0) {
                                                        /* current node was the one we wanted */
                                                        if (exactp)
                                                                *exactp = 1;
                                                        goto set1;
                                                }
                                        }
                                        rc = 0;
                                        goto set2;
                                }
                        }
                        /* If any parents have right-sibs, search.
                         * Otherwise, there's nothing further.
                         */
                        for (i=0; i<mc->mc_top; i++)
                                if (mc->mc_ki[i] <
                                        NUMKEYS(mc->mc_pg[i])-1)
                                        break;
                        if (i == mc->mc_top) {
                                /* There are no other pages */
                                mc->mc_ki[mc->mc_top] = nkeys;
                                return MDB_NOTFOUND;
                        }
                }
                if (!mc->mc_top) {
                        /* There are no other pages */
                        mc->mc_ki[mc->mc_top] = 0;
                        if (op == MDB_SET_RANGE && !exactp) {
                                rc = 0;
                                goto set1;
                        } else
                                return MDB_NOTFOUND;
                }
        }

        rc = mdb_page_search(mc, key, 0);
        if (rc != MDB_SUCCESS)
                return rc;

        mp = mc->mc_pg[mc->mc_top];
        mdb_cassert(mc, IS_LEAF(mp));

set2:
        leaf = mdb_node_search(mc, key, exactp);
        if (exactp != NULL && !*exactp) {
                /* MDB_SET specified and not an exact match. */
                return MDB_NOTFOUND;
        }

        if (leaf == NULL) {
                DPUTS("===> inexact leaf not found, goto sibling");
                if ((rc = mdb_cursor_sibling(mc, 1)) != MDB_SUCCESS)
                        return rc;              /* no entries matched */
                mp = mc->mc_pg[mc->mc_top];
                mdb_cassert(mc, IS_LEAF(mp));
                leaf = NODEPTR(mp, 0);
        }

set1:
        mc->mc_flags |= C_INITIALIZED;
        mc->mc_flags &= ~C_EOF;

        if (IS_LEAF2(mp)) {
                if (op == MDB_SET_RANGE || op == MDB_SET_KEY) {
                        key->mv_size = mc->mc_db->md_pad;
                        key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
                }
                return MDB_SUCCESS;
        }

        if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                mdb_xcursor_init1(mc, leaf);
        }
        if (data) {
                if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                        if (op == MDB_SET || op == MDB_SET_KEY || op == MDB_SET_RANGE) {
                                rc = mdb_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
                        } else {
                                int ex2, *ex2p;
                                if (op == MDB_GET_BOTH) {
                                        ex2p = &ex2;
                                        ex2 = 0;
                                } else {
                                        ex2p = NULL;
                                }
                                rc = mdb_cursor_set(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_SET_RANGE, ex2p);
                                if (rc != MDB_SUCCESS)
                                        return rc;
                        }
                } else if (op == MDB_GET_BOTH || op == MDB_GET_BOTH_RANGE) {
                        MDB_val d2;
                        if ((rc = mdb_node_read(mc->mc_txn, leaf, &d2)) != MDB_SUCCESS)
                                return rc;
                        rc = mc->mc_dbx->md_dcmp(data, &d2);
                        if (rc) {
                                if (op == MDB_GET_BOTH || rc > 0)
                                        return MDB_NOTFOUND;
                                rc = 0;
                                *data = d2;
                        }

                } else {
                        if (mc->mc_xcursor)
                                mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);
                        if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
                                return rc;
                }
        }

        /* The key already matches in all other cases */
        if (op == MDB_SET_RANGE || op == MDB_SET_KEY)
                MDB_GET_KEY(leaf, key);
        DPRINTF(("==> cursor placed on key [%s]", DKEY(key)));

        return rc;
}

/** Move the cursor to the first item in the database. */
static int
mdb_cursor_first(MDB_cursor *mc, MDB_val *key, MDB_val *data)
{
        int              rc;
        MDB_node        *leaf;

        if (mc->mc_xcursor)
                mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);

        if (!(mc->mc_flags & C_INITIALIZED) || mc->mc_top) {
                rc = mdb_page_search(mc, NULL, MDB_PS_FIRST);
                if (rc != MDB_SUCCESS)
                        return rc;
        }
        mdb_cassert(mc, IS_LEAF(mc->mc_pg[mc->mc_top]));

        leaf = NODEPTR(mc->mc_pg[mc->mc_top], 0);
        mc->mc_flags |= C_INITIALIZED;
        mc->mc_flags &= ~C_EOF;

        mc->mc_ki[mc->mc_top] = 0;

        if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
                key->mv_size = mc->mc_db->md_pad;
                key->mv_data = LEAF2KEY(mc->mc_pg[mc->mc_top], 0, key->mv_size);
                return MDB_SUCCESS;
        }

        if (data) {
                if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                        mdb_xcursor_init1(mc, leaf);
                        rc = mdb_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
                        if (rc)
                                return rc;
                } else {
                        if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
                                return rc;
                }
        }
        MDB_GET_KEY(leaf, key);
        return MDB_SUCCESS;
}

/** Move the cursor to the last item in the database. */
static int
mdb_cursor_last(MDB_cursor *mc, MDB_val *key, MDB_val *data)
{
        int              rc;
        MDB_node        *leaf;

        if (mc->mc_xcursor)
                mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);

        if (!(mc->mc_flags & C_EOF)) {

                if (!(mc->mc_flags & C_INITIALIZED) || mc->mc_top) {
                        rc = mdb_page_search(mc, NULL, MDB_PS_LAST);
                        if (rc != MDB_SUCCESS)
                                return rc;
                }
                mdb_cassert(mc, IS_LEAF(mc->mc_pg[mc->mc_top]));

        }
        mc->mc_ki[mc->mc_top] = NUMKEYS(mc->mc_pg[mc->mc_top]) - 1;
        mc->mc_flags |= C_INITIALIZED|C_EOF;
        leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);

        if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
                key->mv_size = mc->mc_db->md_pad;
                key->mv_data = LEAF2KEY(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], key->mv_size);
                return MDB_SUCCESS;
        }

        if (data) {
                if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                        mdb_xcursor_init1(mc, leaf);
                        rc = mdb_cursor_last(&mc->mc_xcursor->mx_cursor, data, NULL);
                        if (rc)
                                return rc;
                } else {
                        if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
                                return rc;
                }
        }

        MDB_GET_KEY(leaf, key);
        return MDB_SUCCESS;
}

int
mdb_cursor_get(MDB_cursor *mc, MDB_val *key, MDB_val *data,
    MDB_cursor_op op)
{
        int              rc;
        int              exact = 0;
        int              (*mfunc)(MDB_cursor *mc, MDB_val *key, MDB_val *data);

        if (mc == NULL)
                return EINVAL;

        if (mc->mc_txn->mt_flags & MDB_TXN_ERROR)
                return MDB_BAD_TXN;

        switch (op) {
        case MDB_GET_CURRENT:
                if (!(mc->mc_flags & C_INITIALIZED)) {
                        rc = EINVAL;
                } else {
                        MDB_page *mp = mc->mc_pg[mc->mc_top];
                        int nkeys = NUMKEYS(mp);
                        if (!nkeys || mc->mc_ki[mc->mc_top] >= nkeys) {
                                mc->mc_ki[mc->mc_top] = nkeys;
                                rc = MDB_NOTFOUND;
                                break;
                        }
                        rc = MDB_SUCCESS;
                        if (IS_LEAF2(mp)) {
                                key->mv_size = mc->mc_db->md_pad;
                                key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
                        } else {
                                MDB_node *leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
                                MDB_GET_KEY(leaf, key);
                                if (data) {
                                        if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                                                if (mc->mc_flags & C_DEL)
                                                        mdb_xcursor_init1(mc, leaf);
                                                rc = mdb_cursor_get(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_GET_CURRENT);
                                        } else {
                                                rc = mdb_node_read(mc->mc_txn, leaf, data);
                                        }
                                }
                        }
                }
                break;
        case MDB_GET_BOTH:
        case MDB_GET_BOTH_RANGE:
                if (data == NULL) {
                        rc = EINVAL;
                        break;
                }
                if (mc->mc_xcursor == NULL) {
                        rc = MDB_INCOMPATIBLE;
                        break;
                }
                /* FALLTHRU */
        case MDB_SET:
        case MDB_SET_KEY:
        case MDB_SET_RANGE:
                if (key == NULL) {
                        rc = EINVAL;
                } else {
                        rc = mdb_cursor_set(mc, key, data, op,
                                op == MDB_SET_RANGE ? NULL : &exact);
                }
                break;
        case MDB_GET_MULTIPLE:
                if (data == NULL || !(mc->mc_flags & C_INITIALIZED)) {
                        rc = EINVAL;
                        break;
                }
                if (!(mc->mc_db->md_flags & MDB_DUPFIXED)) {
                        rc = MDB_INCOMPATIBLE;
                        break;
                }
                rc = MDB_SUCCESS;
                if (!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) ||
                        (mc->mc_xcursor->mx_cursor.mc_flags & C_EOF))
                        break;
                goto fetchm;
        case MDB_NEXT_MULTIPLE:
                if (data == NULL) {
                        rc = EINVAL;
                        break;
                }
                if (!(mc->mc_db->md_flags & MDB_DUPFIXED)) {
                        rc = MDB_INCOMPATIBLE;
                        break;
                }
                if (!(mc->mc_flags & C_INITIALIZED))
                        rc = mdb_cursor_first(mc, key, data);
                else
                        rc = mdb_cursor_next(mc, key, data, MDB_NEXT_DUP);
                if (rc == MDB_SUCCESS) {
                        if (mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) {
                                MDB_cursor *mx;
fetchm:
                                mx = &mc->mc_xcursor->mx_cursor;
                                data->mv_size = NUMKEYS(mx->mc_pg[mx->mc_top]) *
                                        mx->mc_db->md_pad;
                                data->mv_data = METADATA(mx->mc_pg[mx->mc_top]);
                                mx->mc_ki[mx->mc_top] = NUMKEYS(mx->mc_pg[mx->mc_top])-1;
                        } else {
                                rc = MDB_NOTFOUND;
                        }
                }
                break;
        case MDB_NEXT:
        case MDB_NEXT_DUP:
        case MDB_NEXT_NODUP:
                if (!(mc->mc_flags & C_INITIALIZED))
                        rc = mdb_cursor_first(mc, key, data);
                else
                        rc = mdb_cursor_next(mc, key, data, op);
                break;
        case MDB_PREV:
        case MDB_PREV_DUP:
        case MDB_PREV_NODUP:
                if (!(mc->mc_flags & C_INITIALIZED)) {
                        rc = mdb_cursor_last(mc, key, data);
                        if (rc)
                                break;
                        mc->mc_flags |= C_INITIALIZED;
                        mc->mc_ki[mc->mc_top]++;
                }
                rc = mdb_cursor_prev(mc, key, data, op);
                break;
        case MDB_FIRST:
                rc = mdb_cursor_first(mc, key, data);
                break;
        case MDB_FIRST_DUP:
                mfunc = mdb_cursor_first;
        mmove:
                if (data == NULL || !(mc->mc_flags & C_INITIALIZED)) {
                        rc = EINVAL;
                        break;
                }
                if (mc->mc_xcursor == NULL) {
                        rc = MDB_INCOMPATIBLE;
                        break;
                }
                {
                        MDB_node *leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
                        if (!F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                                MDB_GET_KEY(leaf, key);
                                if (data)
                                        rc = mdb_node_read(mc->mc_txn, leaf, data);
                                break;
                        }
                }
                if (!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED)) {
                        rc = EINVAL;
                        break;
                }
                rc = mfunc(&mc->mc_xcursor->mx_cursor, data, NULL);
                break;
        case MDB_LAST:
                rc = mdb_cursor_last(mc, key, data);
                break;
        case MDB_LAST_DUP:
                mfunc = mdb_cursor_last;
                goto mmove;
        default:
                DPRINTF(("unhandled/unimplemented cursor operation %u", op));
                rc = EINVAL;
                break;
        }

        if (mc->mc_flags & C_DEL)
                mc->mc_flags ^= C_DEL;

        return rc;
}

/** Touch all the pages in the cursor stack. Set mc_top.
 *      Makes sure all the pages are writable, before attempting a write operation.
 * @param[in] mc The cursor to operate on.
 */
static int
mdb_cursor_touch(MDB_cursor *mc)
{
        int rc = MDB_SUCCESS;

        if (mc->mc_dbi > MAIN_DBI && !(*mc->mc_dbflag & DB_DIRTY)) {
                MDB_cursor mc2;
                MDB_xcursor mcx;
                if (TXN_DBI_CHANGED(mc->mc_txn, mc->mc_dbi))
                        return MDB_BAD_DBI;
                mdb_cursor_init(&mc2, mc->mc_txn, MAIN_DBI, &mcx);
                rc = mdb_page_search(&mc2, &mc->mc_dbx->md_name, MDB_PS_MODIFY);
                if (rc)
                         return rc;
                *mc->mc_dbflag |= DB_DIRTY;
        }
        mc->mc_top = 0;
        if (mc->mc_snum) {
                do {
                        rc = mdb_page_touch(mc);
                } while (!rc && ++(mc->mc_top) < mc->mc_snum);
                mc->mc_top = mc->mc_snum-1;
        }
        return rc;
}

/** Do not spill pages to disk if txn is getting full, may fail instead */
#define MDB_NOSPILL     0x8000

int
mdb_cursor_put(MDB_cursor *mc, MDB_val *key, MDB_val *data,
    unsigned int flags)
{
        enum { MDB_NO_ROOT = MDB_LAST_ERRCODE+10 }; /* internal code */
        MDB_env         *env;
        MDB_node        *leaf = NULL;
        MDB_page        *fp, *mp;
        uint16_t        fp_flags;
        MDB_val         xdata, *rdata, dkey, olddata;
        MDB_db dummy;
        int do_sub = 0, insert_key, insert_data;
        unsigned int mcount = 0, dcount = 0, nospill;
        size_t nsize;
        int rc, rc2;
        unsigned int nflags;
        DKBUF;

        if (mc == NULL || key == NULL)
                return EINVAL;

        env = mc->mc_txn->mt_env;

        /* Check this first so counter will always be zero on any
         * early failures.
         */
        if (flags & MDB_MULTIPLE) {
                dcount = data[1].mv_size;
                data[1].mv_size = 0;
                if (!F_ISSET(mc->mc_db->md_flags, MDB_DUPFIXED))
                        return MDB_INCOMPATIBLE;
        }

        nospill = flags & MDB_NOSPILL;
        flags &= ~MDB_NOSPILL;

        if (mc->mc_txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_ERROR))
                return (mc->mc_txn->mt_flags & MDB_TXN_RDONLY) ? EACCES : MDB_BAD_TXN;

        if (key->mv_size-1 >= ENV_MAXKEY(env))
                return MDB_BAD_VALSIZE;

#if SIZE_MAX > MAXDATASIZE
        if (data->mv_size > ((mc->mc_db->md_flags & MDB_DUPSORT) ? ENV_MAXKEY(env) : MAXDATASIZE))
                return MDB_BAD_VALSIZE;
#else
        if ((mc->mc_db->md_flags & MDB_DUPSORT) && data->mv_size > ENV_MAXKEY(env))
                return MDB_BAD_VALSIZE;
#endif

        DPRINTF(("==> put db %d key [%s], size %"Z"u, data size %"Z"u",
                DDBI(mc), DKEY(key), key ? key->mv_size : 0, data->mv_size));

        dkey.mv_size = 0;

        if (flags == MDB_CURRENT) {
                if (!(mc->mc_flags & C_INITIALIZED))
                        return EINVAL;
                rc = MDB_SUCCESS;
        } else if (mc->mc_db->md_root == P_INVALID) {
                /* new database, cursor has nothing to point to */
                mc->mc_snum = 0;
                mc->mc_top = 0;
                mc->mc_flags &= ~C_INITIALIZED;
                rc = MDB_NO_ROOT;
        } else {
                int exact = 0;
                MDB_val d2;
                if (flags & MDB_APPEND) {
                        MDB_val k2;
                        rc = mdb_cursor_last(mc, &k2, &d2);
                        if (rc == 0) {
                                rc = mc->mc_dbx->md_cmp(key, &k2);
                                if (rc > 0) {
                                        rc = MDB_NOTFOUND;
                                        mc->mc_ki[mc->mc_top]++;
                                } else {
                                        /* new key is <= last key */
                                        rc = MDB_KEYEXIST;
                                }
                        }
                } else {
                        rc = mdb_cursor_set(mc, key, &d2, MDB_SET, &exact);
                }
                if ((flags & MDB_NOOVERWRITE) && rc == 0) {
                        DPRINTF(("duplicate key [%s]", DKEY(key)));
                        *data = d2;
                        return MDB_KEYEXIST;
                }
                if (rc && rc != MDB_NOTFOUND)
                        return rc;
        }

        if (mc->mc_flags & C_DEL)
                mc->mc_flags ^= C_DEL;

        /* Cursor is positioned, check for room in the dirty list */
        if (!nospill) {
                if (flags & MDB_MULTIPLE) {
                        rdata = &xdata;
                        xdata.mv_size = data->mv_size * dcount;
                } else {
                        rdata = data;
                }
                if ((rc2 = mdb_page_spill(mc, key, rdata)))
                        return rc2;
        }

        if (rc == MDB_NO_ROOT) {
                MDB_page *np;
                /* new database, write a root leaf page */
                DPUTS("allocating new root leaf page");
                if ((rc2 = mdb_page_new(mc, P_LEAF, 1, &np))) {
                        return rc2;
                }
                mdb_cursor_push(mc, np);
                mc->mc_db->md_root = np->mp_pgno;
                mc->mc_db->md_depth++;
                *mc->mc_dbflag |= DB_DIRTY;
                if ((mc->mc_db->md_flags & (MDB_DUPSORT|MDB_DUPFIXED))
                        == MDB_DUPFIXED)
                        np->mp_flags |= P_LEAF2;
                mc->mc_flags |= C_INITIALIZED;
        } else {
                /* make sure all cursor pages are writable */
                rc2 = mdb_cursor_touch(mc);
                if (rc2)
                        return rc2;
        }

        insert_key = insert_data = rc;
        if (insert_key) {
                /* The key does not exist */
                DPRINTF(("inserting key at index %i", mc->mc_ki[mc->mc_top]));
                if ((mc->mc_db->md_flags & MDB_DUPSORT) &&
                        LEAFSIZE(key, data) > env->me_nodemax)
                {
                        /* Too big for a node, insert in sub-DB.  Set up an empty
                         * "old sub-page" for prep_subDB to expand to a full page.
                         */
                        fp_flags = P_LEAF|P_DIRTY;
                        fp = env->me_pbuf;
                        fp->mp_pad = data->mv_size; /* used if MDB_DUPFIXED */
                        fp->mp_lower = fp->mp_upper = (PAGEHDRSZ-PAGEBASE);
                        olddata.mv_size = PAGEHDRSZ;
                        goto prep_subDB;
                }
        } else {
                /* there's only a key anyway, so this is a no-op */
                if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
                        char *ptr;
                        unsigned int ksize = mc->mc_db->md_pad;
                        if (key->mv_size != ksize)
                                return MDB_BAD_VALSIZE;
                        ptr = LEAF2KEY(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], ksize);
                        memcpy(ptr, key->mv_data, ksize);
fix_parent:
                        /* if overwriting slot 0 of leaf, need to
                         * update branch key if there is a parent page
                         */
                        if (mc->mc_top && !mc->mc_ki[mc->mc_top]) {
                                unsigned short top = mc->mc_top;
                                mc->mc_top--;
                                /* slot 0 is always an empty key, find real slot */
                                while (mc->mc_top && !mc->mc_ki[mc->mc_top])
                                        mc->mc_top--;
                                if (mc->mc_ki[mc->mc_top])
                                        rc2 = mdb_update_key(mc, key);
                                else
                                        rc2 = MDB_SUCCESS;
                                mc->mc_top = top;
                                if (rc2)
                                        return rc2;
                        }
                        return MDB_SUCCESS;
                }

more:
                leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
                olddata.mv_size = NODEDSZ(leaf);
                olddata.mv_data = NODEDATA(leaf);

                /* DB has dups? */
                if (F_ISSET(mc->mc_db->md_flags, MDB_DUPSORT)) {
                        /* Prepare (sub-)page/sub-DB to accept the new item,
                         * if needed.  fp: old sub-page or a header faking
                         * it.  mp: new (sub-)page.  offset: growth in page
                         * size.  xdata: node data with new page or DB.
                         */
                        unsigned        i, offset = 0;
                        mp = fp = xdata.mv_data = env->me_pbuf;
                        mp->mp_pgno = mc->mc_pg[mc->mc_top]->mp_pgno;

                        /* Was a single item before, must convert now */
                        if (!F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                                /* Just overwrite the current item */
                                if (flags == MDB_CURRENT)
                                        goto current;

#if UINT_MAX < SIZE_MAX
                                if (mc->mc_dbx->md_dcmp == mdb_cmp_int && olddata.mv_size == sizeof(size_t))
                                        mc->mc_dbx->md_dcmp = mdb_cmp_clong;
#endif
                                /* does data match? */
                                if (!mc->mc_dbx->md_dcmp(data, &olddata)) {
                                        if (flags & MDB_NODUPDATA)
                                                return MDB_KEYEXIST;
                                        /* overwrite it */
                                        goto current;
                                }

                                /* Back up original data item */
                                dkey.mv_size = olddata.mv_size;
                                dkey.mv_data = memcpy(fp+1, olddata.mv_data, olddata.mv_size);

                                /* Make sub-page header for the dup items, with dummy body */
                                fp->mp_flags = P_LEAF|P_DIRTY|P_SUBP;
                                fp->mp_lower = (PAGEHDRSZ-PAGEBASE);
                                xdata.mv_size = PAGEHDRSZ + dkey.mv_size + data->mv_size;
                                if (mc->mc_db->md_flags & MDB_DUPFIXED) {
                                        fp->mp_flags |= P_LEAF2;
                                        fp->mp_pad = data->mv_size;
                                        xdata.mv_size += 2 * data->mv_size;     /* leave space for 2 more */
                                } else {
                                        xdata.mv_size += 2 * (sizeof(indx_t) + NODESIZE) +
                                                (dkey.mv_size & 1) + (data->mv_size & 1);
                                }
                                fp->mp_upper = xdata.mv_size - PAGEBASE;
                                olddata.mv_size = xdata.mv_size; /* pretend olddata is fp */
                        } else if (leaf->mn_flags & F_SUBDATA) {
                                /* Data is on sub-DB, just store it */
                                flags |= F_DUPDATA|F_SUBDATA;
                                goto put_sub;
                        } else {
                                /* Data is on sub-page */
                                fp = olddata.mv_data;
                                switch (flags) {
                                default:
                                        if (!(mc->mc_db->md_flags & MDB_DUPFIXED)) {
                                                offset = EVEN(NODESIZE + sizeof(indx_t) +
                                                        data->mv_size);
                                                break;
                                        }
                                        offset = fp->mp_pad;
                                        if (SIZELEFT(fp) < offset) {
                                                offset *= 4; /* space for 4 more */
                                                break;
                                        }
                                        /* FALLTHRU: Big enough MDB_DUPFIXED sub-page */
                                case MDB_CURRENT:
                                        fp->mp_flags |= P_DIRTY;
                                        COPY_PGNO(fp->mp_pgno, mp->mp_pgno);
                                        mc->mc_xcursor->mx_cursor.mc_pg[0] = fp;
                                        flags |= F_DUPDATA;
                                        goto put_sub;
                                }
                                xdata.mv_size = olddata.mv_size + offset;
                        }

                        fp_flags = fp->mp_flags;
                        if (NODESIZE + NODEKSZ(leaf) + xdata.mv_size > env->me_nodemax) {
                                        /* Too big for a sub-page, convert to sub-DB */
                                        fp_flags &= ~P_SUBP;
prep_subDB:
                                        if (mc->mc_db->md_flags & MDB_DUPFIXED) {
                                                fp_flags |= P_LEAF2;
                                                dummy.md_pad = fp->mp_pad;
                                                dummy.md_flags = MDB_DUPFIXED;
                                                if (mc->mc_db->md_flags & MDB_INTEGERDUP)
                                                        dummy.md_flags |= MDB_INTEGERKEY;
                                        } else {
                                                dummy.md_pad = 0;
                                                dummy.md_flags = 0;
                                        }
                                        dummy.md_depth = 1;
                                        dummy.md_branch_pages = 0;
                                        dummy.md_leaf_pages = 1;
                                        dummy.md_overflow_pages = 0;
                                        dummy.md_entries = NUMKEYS(fp);
                                        xdata.mv_size = sizeof(MDB_db);
                                        xdata.mv_data = &dummy;
                                        if ((rc = mdb_page_alloc(mc, 1, &mp)))
                                                return rc;
                                        offset = env->me_psize - olddata.mv_size;
                                        flags |= F_DUPDATA|F_SUBDATA;
                                        dummy.md_root = mp->mp_pgno;
                        }
                        if (mp != fp) {
                                mp->mp_flags = fp_flags | P_DIRTY;
                                mp->mp_pad   = fp->mp_pad;
                                mp->mp_lower = fp->mp_lower;
                                mp->mp_upper = fp->mp_upper + offset;
                                if (fp_flags & P_LEAF2) {
                                        memcpy(METADATA(mp), METADATA(fp), NUMKEYS(fp) * fp->mp_pad);
                                } else {
                                        memcpy((char *)mp + mp->mp_upper + PAGEBASE, (char *)fp + fp->mp_upper + PAGEBASE,
                                                olddata.mv_size - fp->mp_upper - PAGEBASE);
                                        for (i=0; i<NUMKEYS(fp); i++)
                                                mp->mp_ptrs[i] = fp->mp_ptrs[i] + offset;
                                }
                        }

                        rdata = &xdata;
                        flags |= F_DUPDATA;
                        do_sub = 1;
                        if (!insert_key)
                                mdb_node_del(mc, 0);
                        goto new_sub;
                }
current:
                /* overflow page overwrites need special handling */
                if (F_ISSET(leaf->mn_flags, F_BIGDATA)) {
                        MDB_page *omp;
                        pgno_t pg;
                        int level, ovpages, dpages = OVPAGES(data->mv_size, env->me_psize);

                        memcpy(&pg, olddata.mv_data, sizeof(pg));
                        if ((rc2 = mdb_page_get(mc->mc_txn, pg, &omp, &level)) != 0)
                                return rc2;
                        ovpages = omp->mp_pages;

                        /* Is the ov page large enough? */
                        if (ovpages >= dpages) {
                          if (!(omp->mp_flags & P_DIRTY) &&
                                  (level || (env->me_flags & MDB_WRITEMAP)))
                          {
                                rc = mdb_page_unspill(mc->mc_txn, omp, &omp);
                                if (rc)
                                        return rc;
                                level = 0;              /* dirty in this txn or clean */
                          }
                          /* Is it dirty? */
                          if (omp->mp_flags & P_DIRTY) {
                                /* yes, overwrite it. Note in this case we don't
                                 * bother to try shrinking the page if the new data
                                 * is smaller than the overflow threshold.
                                 */
                                if (level > 1) {
                                        /* It is writable only in a parent txn */
                                        size_t sz = (size_t) env->me_psize * ovpages, off;
                                        MDB_page *np = mdb_page_malloc(mc->mc_txn, ovpages);
                                        MDB_ID2 id2;
                                        if (!np)
                                                return ENOMEM;
                                        id2.mid = pg;
                                        id2.mptr = np;
                                        rc2 = mdb_mid2l_insert(mc->mc_txn->mt_u.dirty_list, &id2);
                                        mdb_cassert(mc, rc2 == 0);
                                        if (!(flags & MDB_RESERVE)) {
                                                /* Copy end of page, adjusting alignment so
                                                 * compiler may copy words instead of bytes.
                                                 */
                                                off = (PAGEHDRSZ + data->mv_size) & -sizeof(size_t);
                                                memcpy((size_t *)((char *)np + off),
                                                        (size_t *)((char *)omp + off), sz - off);
                                                sz = PAGEHDRSZ;
                                        }
                                        memcpy(np, omp, sz); /* Copy beginning of page */
                                        omp = np;
                                }
                                SETDSZ(leaf, data->mv_size);
                                if (F_ISSET(flags, MDB_RESERVE))
                                        data->mv_data = METADATA(omp);
                                else
                                        memcpy(METADATA(omp), data->mv_data, data->mv_size);
                                return MDB_SUCCESS;
                          }
                        }
                        if ((rc2 = mdb_ovpage_free(mc, omp)) != MDB_SUCCESS)
                                return rc2;
                } else if (data->mv_size == olddata.mv_size) {
                        /* same size, just replace it. Note that we could
                         * also reuse this node if the new data is smaller,
                         * but instead we opt to shrink the node in that case.
                         */
                        if (F_ISSET(flags, MDB_RESERVE))
                                data->mv_data = olddata.mv_data;
                        else if (!(mc->mc_flags & C_SUB))
                                memcpy(olddata.mv_data, data->mv_data, data->mv_size);
                        else {
                                memcpy(NODEKEY(leaf), key->mv_data, key->mv_size);
                                goto fix_parent;
                        }
                        return MDB_SUCCESS;
                }
                mdb_node_del(mc, 0);
        }

        rdata = data;

new_sub:
        nflags = flags & NODE_ADD_FLAGS;
        nsize = IS_LEAF2(mc->mc_pg[mc->mc_top]) ? key->mv_size : mdb_leaf_size(env, key, rdata);
        if (SIZELEFT(mc->mc_pg[mc->mc_top]) < nsize) {
                if (( flags & (F_DUPDATA|F_SUBDATA)) == F_DUPDATA )
                        nflags &= ~MDB_APPEND; /* sub-page may need room to grow */
                if (!insert_key)
                        nflags |= MDB_SPLIT_REPLACE;
                rc = mdb_page_split(mc, key, rdata, P_INVALID, nflags);
        } else {
                /* There is room already in this leaf page. */
                rc = mdb_node_add(mc, mc->mc_ki[mc->mc_top], key, rdata, 0, nflags);
                if (rc == 0 && insert_key) {
                        /* Adjust other cursors pointing to mp */
                        MDB_cursor *m2, *m3;
                        MDB_dbi dbi = mc->mc_dbi;
                        unsigned i = mc->mc_top;
                        MDB_page *mp = mc->mc_pg[i];

                        for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
                                if (mc->mc_flags & C_SUB)
                                        m3 = &m2->mc_xcursor->mx_cursor;
                                else
                                        m3 = m2;
                                if (m3 == mc || m3->mc_snum < mc->mc_snum) continue;
                                if (m3->mc_pg[i] == mp && m3->mc_ki[i] >= mc->mc_ki[i]) {
                                        m3->mc_ki[i]++;
                                }
                        }
                }
        }

        if (rc == MDB_SUCCESS) {
                /* Now store the actual data in the child DB. Note that we're
                 * storing the user data in the keys field, so there are strict
                 * size limits on dupdata. The actual data fields of the child
                 * DB are all zero size.
                 */
                if (do_sub) {
                        int xflags;
                        size_t ecount;
put_sub:
                        xdata.mv_size = 0;
                        xdata.mv_data = "";
                        leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
                        if (flags & MDB_CURRENT) {
                                xflags = MDB_CURRENT|MDB_NOSPILL;
                        } else {
                                mdb_xcursor_init1(mc, leaf);
                                xflags = (flags & MDB_NODUPDATA) ?
                                        MDB_NOOVERWRITE|MDB_NOSPILL : MDB_NOSPILL;
                        }
                        /* converted, write the original data first */
                        if (dkey.mv_size) {
                                rc = mdb_cursor_put(&mc->mc_xcursor->mx_cursor, &dkey, &xdata, xflags);
                                if (rc)
                                        goto bad_sub;
                                {
                                        /* Adjust other cursors pointing to mp */
                                        MDB_cursor *m2;
                                        unsigned i = mc->mc_top;
                                        MDB_page *mp = mc->mc_pg[i];

                                        for (m2 = mc->mc_txn->mt_cursors[mc->mc_dbi]; m2; m2=m2->mc_next) {
                                                if (m2 == mc || m2->mc_snum < mc->mc_snum) continue;
                                                if (!(m2->mc_flags & C_INITIALIZED)) continue;
                                                if (m2->mc_pg[i] == mp && m2->mc_ki[i] == mc->mc_ki[i]) {
                                                        mdb_xcursor_init1(m2, leaf);
                                                }
                                        }
                                }
                                /* we've done our job */
                                dkey.mv_size = 0;
                        }
                        ecount = mc->mc_xcursor->mx_db.md_entries;
                        if (flags & MDB_APPENDDUP)
                                xflags |= MDB_APPEND;
                        rc = mdb_cursor_put(&mc->mc_xcursor->mx_cursor, data, &xdata, xflags);
                        if (flags & F_SUBDATA) {
                                void *db = NODEDATA(leaf);
                                memcpy(db, &mc->mc_xcursor->mx_db, sizeof(MDB_db));
                        }
                        insert_data = mc->mc_xcursor->mx_db.md_entries - ecount;
                }
                /* Increment count unless we just replaced an existing item. */
                if (insert_data)
                        mc->mc_db->md_entries++;
                if (insert_key) {
                        /* Invalidate txn if we created an empty sub-DB */
                        if (rc)
                                goto bad_sub;
                        /* If we succeeded and the key didn't exist before,
                         * make sure the cursor is marked valid.
                         */
                        mc->mc_flags |= C_INITIALIZED;
                }
                if (flags & MDB_MULTIPLE) {
                        if (!rc) {
                                mcount++;
                                /* let caller know how many succeeded, if any */
                                data[1].mv_size = mcount;
                                if (mcount < dcount) {
                                        data[0].mv_data = (char *)data[0].mv_data + data[0].mv_size;
                                        insert_key = insert_data = 0;
                                        goto more;
                                }
                        }
                }
                return rc;
bad_sub:
                if (rc == MDB_KEYEXIST) /* should not happen, we deleted that item */
                        rc = MDB_CORRUPTED;
        }
        mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
        return rc;
}

int
mdb_cursor_del(MDB_cursor *mc, unsigned int flags)
{
        MDB_node        *leaf;
        MDB_page        *mp;
        int rc;

        if (mc->mc_txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_ERROR))
                return (mc->mc_txn->mt_flags & MDB_TXN_RDONLY) ? EACCES : MDB_BAD_TXN;

        if (!(mc->mc_flags & C_INITIALIZED))
                return EINVAL;

        if (mc->mc_ki[mc->mc_top] >= NUMKEYS(mc->mc_pg[mc->mc_top]))
                return MDB_NOTFOUND;

        if (!(flags & MDB_NOSPILL) && (rc = mdb_page_spill(mc, NULL, NULL)))
                return rc;

        rc = mdb_cursor_touch(mc);
        if (rc)
                return rc;

        mp = mc->mc_pg[mc->mc_top];
        if (IS_LEAF2(mp))
                goto del_key;
        leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);

        if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                if (flags & MDB_NODUPDATA) {
                        /* mdb_cursor_del0() will subtract the final entry */
                        mc->mc_db->md_entries -= mc->mc_xcursor->mx_db.md_entries - 1;
                } else {
                        if (!F_ISSET(leaf->mn_flags, F_SUBDATA)) {
                                mc->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
                        }
                        rc = mdb_cursor_del(&mc->mc_xcursor->mx_cursor, MDB_NOSPILL);
                        if (rc)
                                return rc;
                        /* If sub-DB still has entries, we're done */
                        if (mc->mc_xcursor->mx_db.md_entries) {
                                if (leaf->mn_flags & F_SUBDATA) {
                                        /* update subDB info */
                                        void *db = NODEDATA(leaf);
                                        memcpy(db, &mc->mc_xcursor->mx_db, sizeof(MDB_db));
                                } else {
                                        MDB_cursor *m2;
                                        /* shrink fake page */
                                        mdb_node_shrink(mp, mc->mc_ki[mc->mc_top]);
                                        leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
                                        mc->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
                                        /* fix other sub-DB cursors pointed at this fake page */
                                        for (m2 = mc->mc_txn->mt_cursors[mc->mc_dbi]; m2; m2=m2->mc_next) {
                                                if (m2 == mc || m2->mc_snum < mc->mc_snum) continue;
                                                if (m2->mc_pg[mc->mc_top] == mp &&
                                                        m2->mc_ki[mc->mc_top] == mc->mc_ki[mc->mc_top])
                                                        m2->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
                                        }
                                }
                                mc->mc_db->md_entries--;
                                mc->mc_flags |= C_DEL;
                                return rc;
                        }
                        /* otherwise fall thru and delete the sub-DB */
                }

                if (leaf->mn_flags & F_SUBDATA) {
                        /* add all the child DB's pages to the free list */
                        rc = mdb_drop0(&mc->mc_xcursor->mx_cursor, 0);
                        if (rc)
                                goto fail;
                }
        }

        /* add overflow pages to free list */
        if (F_ISSET(leaf->mn_flags, F_BIGDATA)) {
                MDB_page *omp;
                pgno_t pg;

                memcpy(&pg, NODEDATA(leaf), sizeof(pg));
                if ((rc = mdb_page_get(mc->mc_txn, pg, &omp, NULL)) ||
                        (rc = mdb_ovpage_free(mc, omp)))
                        goto fail;
        }

del_key:
        return mdb_cursor_del0(mc);

fail:
        mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
        return rc;
}

/** Allocate and initialize new pages for a database.
 * @param[in] mc a cursor on the database being added to.
 * @param[in] flags flags defining what type of page is being allocated.
 * @param[in] num the number of pages to allocate. This is usually 1,
 * unless allocating overflow pages for a large record.
 * @param[out] mp Address of a page, or NULL on failure.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_new(MDB_cursor *mc, uint32_t flags, int num, MDB_page **mp)
{
        MDB_page        *np;
        int rc;

        if ((rc = mdb_page_alloc(mc, num, &np)))
                return rc;
        DPRINTF(("allocated new mpage %"Z"u, page size %u",
            np->mp_pgno, mc->mc_txn->mt_env->me_psize));
        np->mp_flags = flags | P_DIRTY;
        np->mp_lower = (PAGEHDRSZ-PAGEBASE);
        np->mp_upper = mc->mc_txn->mt_env->me_psize - PAGEBASE;

        if (IS_BRANCH(np))
                mc->mc_db->md_branch_pages++;
        else if (IS_LEAF(np))
                mc->mc_db->md_leaf_pages++;
        else if (IS_OVERFLOW(np)) {
                mc->mc_db->md_overflow_pages += num;
                np->mp_pages = num;
        }
        *mp = np;

        return 0;
}

/** Calculate the size of a leaf node.
 * The size depends on the environment's page size; if a data item
 * is too large it will be put onto an overflow page and the node
 * size will only include the key and not the data. Sizes are always
 * rounded up to an even number of bytes, to guarantee 2-byte alignment
 * of the #MDB_node headers.
 * @param[in] env The environment handle.
 * @param[in] key The key for the node.
 * @param[in] data The data for the node.
 * @return The number of bytes needed to store the node.
 */
static size_t
mdb_leaf_size(MDB_env *env, MDB_val *key, MDB_val *data)
{
        size_t           sz;

        sz = LEAFSIZE(key, data);
        if (sz > env->me_nodemax) {
                /* put on overflow page */
                sz -= data->mv_size - sizeof(pgno_t);
        }

        return EVEN(sz + sizeof(indx_t));
}

/** Calculate the size of a branch node.
 * The size should depend on the environment's page size but since
 * we currently don't support spilling large keys onto overflow
 * pages, it's simply the size of the #MDB_node header plus the
 * size of the key. Sizes are always rounded up to an even number
 * of bytes, to guarantee 2-byte alignment of the #MDB_node headers.
 * @param[in] env The environment handle.
 * @param[in] key The key for the node.
 * @return The number of bytes needed to store the node.
 */
static size_t
mdb_branch_size(MDB_env *env, MDB_val *key)
{
        size_t           sz;

        sz = INDXSIZE(key);
        if (sz > env->me_nodemax) {
                /* put on overflow page */
                /* not implemented */
                /* sz -= key->size - sizeof(pgno_t); */
        }

        return sz + sizeof(indx_t);
}

/** Add a node to the page pointed to by the cursor.
 * @param[in] mc The cursor for this operation.
 * @param[in] indx The index on the page where the new node should be added.
 * @param[in] key The key for the new node.
 * @param[in] data The data for the new node, if any.
 * @param[in] pgno The page number, if adding a branch node.
 * @param[in] flags Flags for the node.
 * @return 0 on success, non-zero on failure. Possible errors are:
 * <ul>
 *      <li>ENOMEM - failed to allocate overflow pages for the node.
 *      <li>MDB_PAGE_FULL - there is insufficient room in the page. This error
 *      should never happen since all callers already calculate the
 *      page's free space before calling this function.
 * </ul>
 */
static int
mdb_node_add(MDB_cursor *mc, indx_t indx,
    MDB_val *key, MDB_val *data, pgno_t pgno, unsigned int flags)
{
        unsigned int     i;
        size_t           node_size = NODESIZE;
        ssize_t          room;
        indx_t           ofs;
        MDB_node        *node;
        MDB_page        *mp = mc->mc_pg[mc->mc_top];
        MDB_page        *ofp = NULL;            /* overflow page */
        DKBUF;

        mdb_cassert(mc, mp->mp_upper >= mp->mp_lower);

        DPRINTF(("add to %s %spage %"Z"u index %i, data size %"Z"u key size %"Z"u [%s]",
            IS_LEAF(mp) ? "leaf" : "branch",
                IS_SUBP(mp) ? "sub-" : "",
                mdb_dbg_pgno(mp), indx, data ? data->mv_size : 0,
                key ? key->mv_size : 0, key ? DKEY(key) : "null"));

        if (IS_LEAF2(mp)) {
                /* Move higher keys up one slot. */
                int ksize = mc->mc_db->md_pad, dif;
                char *ptr = LEAF2KEY(mp, indx, ksize);
                dif = NUMKEYS(mp) - indx;
                if (dif > 0)
                        memmove(ptr+ksize, ptr, dif*ksize);
                /* insert new key */
                memcpy(ptr, key->mv_data, ksize);

                /* Just using these for counting */
                mp->mp_lower += sizeof(indx_t);
                mp->mp_upper -= ksize - sizeof(indx_t);
                return MDB_SUCCESS;
        }

        room = (ssize_t)SIZELEFT(mp) - (ssize_t)sizeof(indx_t);
        if (key != NULL)
                node_size += key->mv_size;
        if (IS_LEAF(mp)) {
                mdb_cassert(mc, data);
                if (F_ISSET(flags, F_BIGDATA)) {
                        /* Data already on overflow page. */
                        node_size += sizeof(pgno_t);
                } else if (node_size + data->mv_size > mc->mc_txn->mt_env->me_nodemax) {
                        int ovpages = OVPAGES(data->mv_size, mc->mc_txn->mt_env->me_psize);
                        int rc;
                        /* Put data on overflow page. */
                        DPRINTF(("data size is %"Z"u, node would be %"Z"u, put data on overflow page",
                            data->mv_size, node_size+data->mv_size));
                        node_size = EVEN(node_size + sizeof(pgno_t));
                        if ((ssize_t)node_size > room)
                                goto full;
                        if ((rc = mdb_page_new(mc, P_OVERFLOW, ovpages, &ofp)))
                                return rc;
                        DPRINTF(("allocated overflow page %"Z"u", ofp->mp_pgno));
                        flags |= F_BIGDATA;
                        goto update;
                } else {
                        node_size += data->mv_size;
                }
        }
        node_size = EVEN(node_size);
        if ((ssize_t)node_size > room)
                goto full;

update:
        /* Move higher pointers up one slot. */
        for (i = NUMKEYS(mp); i > indx; i--)
                mp->mp_ptrs[i] = mp->mp_ptrs[i - 1];

        /* Adjust free space offsets. */
        ofs = mp->mp_upper - node_size;
        mdb_cassert(mc, ofs >= mp->mp_lower + sizeof(indx_t));
        mp->mp_ptrs[indx] = ofs;
        mp->mp_upper = ofs;
        mp->mp_lower += sizeof(indx_t);

        /* Write the node data. */
        node = NODEPTR(mp, indx);
        node->mn_ksize = (key == NULL) ? 0 : key->mv_size;
        node->mn_flags = flags;
        if (IS_LEAF(mp))
                SETDSZ(node,data->mv_size);
        else
                SETPGNO(node,pgno);

        if (key)
                memcpy(NODEKEY(node), key->mv_data, key->mv_size);

        if (IS_LEAF(mp)) {
                mdb_cassert(mc, key);
                if (ofp == NULL) {
                        if (F_ISSET(flags, F_BIGDATA))
                                memcpy(node->mn_data + key->mv_size, data->mv_data,
                                    sizeof(pgno_t));
                        else if (F_ISSET(flags, MDB_RESERVE))
                                data->mv_data = node->mn_data + key->mv_size;
                        else
                                memcpy(node->mn_data + key->mv_size, data->mv_data,
                                    data->mv_size);
                } else {
                        memcpy(node->mn_data + key->mv_size, &ofp->mp_pgno,
                            sizeof(pgno_t));
                        if (F_ISSET(flags, MDB_RESERVE))
                                data->mv_data = METADATA(ofp);
                        else
                                memcpy(METADATA(ofp), data->mv_data, data->mv_size);
                }
        }

        return MDB_SUCCESS;

full:
        DPRINTF(("not enough room in page %"Z"u, got %u ptrs",
                mdb_dbg_pgno(mp), NUMKEYS(mp)));
        DPRINTF(("upper-lower = %u - %u = %"Z"d", mp->mp_upper,mp->mp_lower,room));
        DPRINTF(("node size = %"Z"u", node_size));
        mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
        return MDB_PAGE_FULL;
}

/** Delete the specified node from a page.
 * @param[in] mc Cursor pointing to the node to delete.
 * @param[in] ksize The size of a node. Only used if the page is
 * part of a #MDB_DUPFIXED database.
 */
static void
mdb_node_del(MDB_cursor *mc, int ksize)
{
        MDB_page *mp = mc->mc_pg[mc->mc_top];
        indx_t  indx = mc->mc_ki[mc->mc_top];
        unsigned int     sz;
        indx_t           i, j, numkeys, ptr;
        MDB_node        *node;
        char            *base;

        DPRINTF(("delete node %u on %s page %"Z"u", indx,
            IS_LEAF(mp) ? "leaf" : "branch", mdb_dbg_pgno(mp)));
        numkeys = NUMKEYS(mp);
        mdb_cassert(mc, indx < numkeys);

        if (IS_LEAF2(mp)) {
                int x = numkeys - 1 - indx;
                base = LEAF2KEY(mp, indx, ksize);
                if (x)
                        memmove(base, base + ksize, x * ksize);
                mp->mp_lower -= sizeof(indx_t);
                mp->mp_upper += ksize - sizeof(indx_t);
                return;
        }

        node = NODEPTR(mp, indx);
        sz = NODESIZE + node->mn_ksize;
        if (IS_LEAF(mp)) {
                if (F_ISSET(node->mn_flags, F_BIGDATA))
                        sz += sizeof(pgno_t);
                else
                        sz += NODEDSZ(node);
        }
        sz = EVEN(sz);

        ptr = mp->mp_ptrs[indx];
        for (i = j = 0; i < numkeys; i++) {
                if (i != indx) {
                        mp->mp_ptrs[j] = mp->mp_ptrs[i];
                        if (mp->mp_ptrs[i] < ptr)
                                mp->mp_ptrs[j] += sz;
                        j++;
                }
        }

        base = (char *)mp + mp->mp_upper + PAGEBASE;
        memmove(base + sz, base, ptr - mp->mp_upper);

        mp->mp_lower -= sizeof(indx_t);
        mp->mp_upper += sz;
}

/** Compact the main page after deleting a node on a subpage.
 * @param[in] mp The main page to operate on.
 * @param[in] indx The index of the subpage on the main page.
 */
static void
mdb_node_shrink(MDB_page *mp, indx_t indx)
{
        MDB_node *node;
        MDB_page *sp, *xp;
        char *base;
        int nsize, delta;
        indx_t           i, numkeys, ptr;

        node = NODEPTR(mp, indx);
        sp = (MDB_page *)NODEDATA(node);
        delta = SIZELEFT(sp);
        xp = (MDB_page *)((char *)sp + delta);

        /* shift subpage upward */
        if (IS_LEAF2(sp)) {
                nsize = NUMKEYS(sp) * sp->mp_pad;
                if (nsize & 1)
                        return;         /* do not make the node uneven-sized */
                memmove(METADATA(xp), METADATA(sp), nsize);
        } else {
                int i;
                numkeys = NUMKEYS(sp);
                for (i=numkeys-1; i>=0; i--)
                        xp->mp_ptrs[i] = sp->mp_ptrs[i] - delta;
        }
        xp->mp_upper = sp->mp_lower;
        xp->mp_lower = sp->mp_lower;
        xp->mp_flags = sp->mp_flags;
        xp->mp_pad = sp->mp_pad;
        COPY_PGNO(xp->mp_pgno, mp->mp_pgno);

        nsize = NODEDSZ(node) - delta;
        SETDSZ(node, nsize);

        /* shift lower nodes upward */
        ptr = mp->mp_ptrs[indx];
        numkeys = NUMKEYS(mp);
        for (i = 0; i < numkeys; i++) {
                if (mp->mp_ptrs[i] <= ptr)
                        mp->mp_ptrs[i] += delta;
        }

        base = (char *)mp + mp->mp_upper + PAGEBASE;
        memmove(base + delta, base, ptr - mp->mp_upper + NODESIZE + NODEKSZ(node));
        mp->mp_upper += delta;
}

/** Initial setup of a sorted-dups cursor.
 * Sorted duplicates are implemented as a sub-database for the given key.
 * The duplicate data items are actually keys of the sub-database.
 * Operations on the duplicate data items are performed using a sub-cursor
 * initialized when the sub-database is first accessed. This function does
 * the preliminary setup of the sub-cursor, filling in the fields that
 * depend only on the parent DB.
 * @param[in] mc The main cursor whose sorted-dups cursor is to be initialized.
 */
static void
mdb_xcursor_init0(MDB_cursor *mc)
{
        MDB_xcursor *mx = mc->mc_xcursor;

        mx->mx_cursor.mc_xcursor = NULL;
        mx->mx_cursor.mc_txn = mc->mc_txn;
        mx->mx_cursor.mc_db = &mx->mx_db;
        mx->mx_cursor.mc_dbx = &mx->mx_dbx;
        mx->mx_cursor.mc_dbi = mc->mc_dbi;
        mx->mx_cursor.mc_dbflag = &mx->mx_dbflag;
        mx->mx_cursor.mc_snum = 0;
        mx->mx_cursor.mc_top = 0;
        mx->mx_cursor.mc_flags = C_SUB;
        mx->mx_dbx.md_name.mv_size = 0;
        mx->mx_dbx.md_name.mv_data = NULL;
        mx->mx_dbx.md_cmp = mc->mc_dbx->md_dcmp;
        mx->mx_dbx.md_dcmp = NULL;
        mx->mx_dbx.md_rel = mc->mc_dbx->md_rel;
}

/** Final setup of a sorted-dups cursor.
 *      Sets up the fields that depend on the data from the main cursor.
 * @param[in] mc The main cursor whose sorted-dups cursor is to be initialized.
 * @param[in] node The data containing the #MDB_db record for the
 * sorted-dup database.
 */
static void
mdb_xcursor_init1(MDB_cursor *mc, MDB_node *node)
{
        MDB_xcursor *mx = mc->mc_xcursor;

        if (node->mn_flags & F_SUBDATA) {
                memcpy(&mx->mx_db, NODEDATA(node), sizeof(MDB_db));
                mx->mx_cursor.mc_pg[0] = 0;
                mx->mx_cursor.mc_snum = 0;
                mx->mx_cursor.mc_top = 0;
                mx->mx_cursor.mc_flags = C_SUB;
        } else {
                MDB_page *fp = NODEDATA(node);
                mx->mx_db.md_pad = mc->mc_pg[mc->mc_top]->mp_pad;
                mx->mx_db.md_flags = 0;
                mx->mx_db.md_depth = 1;
                mx->mx_db.md_branch_pages = 0;
                mx->mx_db.md_leaf_pages = 1;
                mx->mx_db.md_overflow_pages = 0;
                mx->mx_db.md_entries = NUMKEYS(fp);
                COPY_PGNO(mx->mx_db.md_root, fp->mp_pgno);
                mx->mx_cursor.mc_snum = 1;
                mx->mx_cursor.mc_top = 0;
                mx->mx_cursor.mc_flags = C_INITIALIZED|C_SUB;
                mx->mx_cursor.mc_pg[0] = fp;
                mx->mx_cursor.mc_ki[0] = 0;
                if (mc->mc_db->md_flags & MDB_DUPFIXED) {
                        mx->mx_db.md_flags = MDB_DUPFIXED;
                        mx->mx_db.md_pad = fp->mp_pad;
                        if (mc->mc_db->md_flags & MDB_INTEGERDUP)
                                mx->mx_db.md_flags |= MDB_INTEGERKEY;
                }
        }
        DPRINTF(("Sub-db -%u root page %"Z"u", mx->mx_cursor.mc_dbi,
                mx->mx_db.md_root));
        mx->mx_dbflag = DB_VALID|DB_DIRTY; /* DB_DIRTY guides mdb_cursor_touch */
#if UINT_MAX < SIZE_MAX
        if (mx->mx_dbx.md_cmp == mdb_cmp_int && mx->mx_db.md_pad == sizeof(size_t))
                mx->mx_dbx.md_cmp = mdb_cmp_clong;
#endif
}

/** Initialize a cursor for a given transaction and database. */
static void
mdb_cursor_init(MDB_cursor *mc, MDB_txn *txn, MDB_dbi dbi, MDB_xcursor *mx)
{
        mc->mc_next = NULL;
        mc->mc_backup = NULL;
        mc->mc_dbi = dbi;
        mc->mc_txn = txn;
        mc->mc_db = &txn->mt_dbs[dbi];
        mc->mc_dbx = &txn->mt_dbxs[dbi];
        mc->mc_dbflag = &txn->mt_dbflags[dbi];
        mc->mc_snum = 0;
        mc->mc_top = 0;
        mc->mc_pg[0] = 0;
        mc->mc_flags = 0;
        if (txn->mt_dbs[dbi].md_flags & MDB_DUPSORT) {
                mdb_tassert(txn, mx != NULL);
                mc->mc_xcursor = mx;
                mdb_xcursor_init0(mc);
        } else {
                mc->mc_xcursor = NULL;
        }
        if (*mc->mc_dbflag & DB_STALE) {
                mdb_page_search(mc, NULL, MDB_PS_ROOTONLY);
        }
}

int
mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **ret)
{
        MDB_cursor      *mc;
        size_t size = sizeof(MDB_cursor);

        if (!ret || !TXN_DBI_EXIST(txn, dbi))
                return EINVAL;

        if (txn->mt_flags & MDB_TXN_ERROR)
                return MDB_BAD_TXN;

        /* Allow read access to the freelist */
        if (!dbi && !F_ISSET(txn->mt_flags, MDB_TXN_RDONLY))
                return EINVAL;

        if (txn->mt_dbs[dbi].md_flags & MDB_DUPSORT)
                size += sizeof(MDB_xcursor);

        if ((mc = malloc(size)) != NULL) {
                mdb_cursor_init(mc, txn, dbi, (MDB_xcursor *)(mc + 1));
                if (txn->mt_cursors) {
                        mc->mc_next = txn->mt_cursors[dbi];
                        txn->mt_cursors[dbi] = mc;
                        mc->mc_flags |= C_UNTRACK;
                }
        } else {
                return ENOMEM;
        }

        *ret = mc;

        return MDB_SUCCESS;
}

int
mdb_cursor_renew(MDB_txn *txn, MDB_cursor *mc)
{
        if (!mc || !TXN_DBI_EXIST(txn, mc->mc_dbi))
                return EINVAL;

        if ((mc->mc_flags & C_UNTRACK) || txn->mt_cursors)
                return EINVAL;

        if (txn->mt_flags & MDB_TXN_ERROR)
                return MDB_BAD_TXN;

        mdb_cursor_init(mc, txn, mc->mc_dbi, mc->mc_xcursor);
        return MDB_SUCCESS;
}

/* Return the count of duplicate data items for the current key */
int
mdb_cursor_count(MDB_cursor *mc, size_t *countp)
{
        MDB_node        *leaf;

        if (mc == NULL || countp == NULL)
                return EINVAL;

        if (mc->mc_xcursor == NULL)
                return MDB_INCOMPATIBLE;

        if (mc->mc_txn->mt_flags & MDB_TXN_ERROR)
                return MDB_BAD_TXN;

        if (!(mc->mc_flags & C_INITIALIZED))
                return EINVAL;

        if (!mc->mc_snum || (mc->mc_flags & C_EOF))
                return MDB_NOTFOUND;

        leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
        if (!F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                *countp = 1;
        } else {
                if (!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED))
                        return EINVAL;

                *countp = mc->mc_xcursor->mx_db.md_entries;
        }
        return MDB_SUCCESS;
}

void
mdb_cursor_close(MDB_cursor *mc)
{
        if (mc && !mc->mc_backup) {
                /* remove from txn, if tracked */
                if ((mc->mc_flags & C_UNTRACK) && mc->mc_txn->mt_cursors) {
                        MDB_cursor **prev = &mc->mc_txn->mt_cursors[mc->mc_dbi];
                        while (*prev && *prev != mc) prev = &(*prev)->mc_next;
                        if (*prev == mc)
                                *prev = mc->mc_next;
                }
                free(mc);
        }
}

MDB_txn *
mdb_cursor_txn(MDB_cursor *mc)
{
        if (!mc) return NULL;
        return mc->mc_txn;
}

MDB_dbi
mdb_cursor_dbi(MDB_cursor *mc)
{
        return mc->mc_dbi;
}

/** Replace the key for a branch node with a new key.
 * @param[in] mc Cursor pointing to the node to operate on.
 * @param[in] key The new key to use.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_update_key(MDB_cursor *mc, MDB_val *key)
{
        MDB_page                *mp;
        MDB_node                *node;
        char                    *base;
        size_t                   len;
        int                              delta, ksize, oksize;
        indx_t                   ptr, i, numkeys, indx;
        DKBUF;

        indx = mc->mc_ki[mc->mc_top];
        mp = mc->mc_pg[mc->mc_top];
        node = NODEPTR(mp, indx);
        ptr = mp->mp_ptrs[indx];
#if MDB_DEBUG
        {
                MDB_val k2;
                char kbuf2[DKBUF_MAXKEYSIZE*2+1];
                k2.mv_data = NODEKEY(node);
                k2.mv_size = node->mn_ksize;
                DPRINTF(("update key %u (ofs %u) [%s] to [%s] on page %"Z"u",
                        indx, ptr,
                        mdb_dkey(&k2, kbuf2),
                        DKEY(key),
                        mp->mp_pgno));
        }
#endif

        /* Sizes must be 2-byte aligned. */
        ksize = EVEN(key->mv_size);
        oksize = EVEN(node->mn_ksize);
        delta = ksize - oksize;

        /* Shift node contents if EVEN(key length) changed. */
        if (delta) {
                if (delta > 0 && SIZELEFT(mp) < delta) {
                        pgno_t pgno;
                        /* not enough space left, do a delete and split */
                        DPRINTF(("Not enough room, delta = %d, splitting...", delta));
                        pgno = NODEPGNO(node);
                        mdb_node_del(mc, 0);
                        return mdb_page_split(mc, key, NULL, pgno, MDB_SPLIT_REPLACE);
                }

                numkeys = NUMKEYS(mp);
                for (i = 0; i < numkeys; i++) {
                        if (mp->mp_ptrs[i] <= ptr)
                                mp->mp_ptrs[i] -= delta;
                }

                base = (char *)mp + mp->mp_upper + PAGEBASE;
                len = ptr - mp->mp_upper + NODESIZE;
                memmove(base - delta, base, len);
                mp->mp_upper -= delta;

                node = NODEPTR(mp, indx);
        }

        /* But even if no shift was needed, update ksize */
        if (node->mn_ksize != key->mv_size)
                node->mn_ksize = key->mv_size;

        if (key->mv_size)
                memcpy(NODEKEY(node), key->mv_data, key->mv_size);

        return MDB_SUCCESS;
}

static void
mdb_cursor_copy(const MDB_cursor *csrc, MDB_cursor *cdst);

/** Move a node from csrc to cdst.
 */
static int
mdb_node_move(MDB_cursor *csrc, MDB_cursor *cdst)
{
        MDB_node                *srcnode;
        MDB_val          key, data;
        pgno_t  srcpg;
        MDB_cursor mn;
        int                      rc;
        unsigned short flags;

        DKBUF;

        /* Mark src and dst as dirty. */
        if ((rc = mdb_page_touch(csrc)) ||
            (rc = mdb_page_touch(cdst)))
                return rc;

        if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
                key.mv_size = csrc->mc_db->md_pad;
                key.mv_data = LEAF2KEY(csrc->mc_pg[csrc->mc_top], csrc->mc_ki[csrc->mc_top], key.mv_size);
                data.mv_size = 0;
                data.mv_data = NULL;
                srcpg = 0;
                flags = 0;
        } else {
                srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], csrc->mc_ki[csrc->mc_top]);
                mdb_cassert(csrc, !((size_t)srcnode & 1));
                srcpg = NODEPGNO(srcnode);
                flags = srcnode->mn_flags;
                if (csrc->mc_ki[csrc->mc_top] == 0 && IS_BRANCH(csrc->mc_pg[csrc->mc_top])) {
                        unsigned int snum = csrc->mc_snum;
                        MDB_node *s2;
                        /* must find the lowest key below src */
                        rc = mdb_page_search_lowest(csrc);
                        if (rc)
                                return rc;
                        if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
                                key.mv_size = csrc->mc_db->md_pad;
                                key.mv_data = LEAF2KEY(csrc->mc_pg[csrc->mc_top], 0, key.mv_size);
                        } else {
                                s2 = NODEPTR(csrc->mc_pg[csrc->mc_top], 0);
                                key.mv_size = NODEKSZ(s2);
                                key.mv_data = NODEKEY(s2);
                        }
                        csrc->mc_snum = snum--;
                        csrc->mc_top = snum;
                } else {
                        key.mv_size = NODEKSZ(srcnode);
                        key.mv_data = NODEKEY(srcnode);
                }
                data.mv_size = NODEDSZ(srcnode);
                data.mv_data = NODEDATA(srcnode);
        }
        if (IS_BRANCH(cdst->mc_pg[cdst->mc_top]) && cdst->mc_ki[cdst->mc_top] == 0) {
                unsigned int snum = cdst->mc_snum;
                MDB_node *s2;
                MDB_val bkey;
                /* must find the lowest key below dst */
                mdb_cursor_copy(cdst, &mn);
                rc = mdb_page_search_lowest(&mn);
                if (rc)
                        return rc;
                if (IS_LEAF2(mn.mc_pg[mn.mc_top])) {
                        bkey.mv_size = mn.mc_db->md_pad;
                        bkey.mv_data = LEAF2KEY(mn.mc_pg[mn.mc_top], 0, bkey.mv_size);
                } else {
                        s2 = NODEPTR(mn.mc_pg[mn.mc_top], 0);
                        bkey.mv_size = NODEKSZ(s2);
                        bkey.mv_data = NODEKEY(s2);
                }
                mn.mc_snum = snum--;
                mn.mc_top = snum;
                mn.mc_ki[snum] = 0;
                rc = mdb_update_key(&mn, &bkey);
                if (rc)
                        return rc;
        }

        DPRINTF(("moving %s node %u [%s] on page %"Z"u to node %u on page %"Z"u",
            IS_LEAF(csrc->mc_pg[csrc->mc_top]) ? "leaf" : "branch",
            csrc->mc_ki[csrc->mc_top],
                DKEY(&key),
            csrc->mc_pg[csrc->mc_top]->mp_pgno,
            cdst->mc_ki[cdst->mc_top], cdst->mc_pg[cdst->mc_top]->mp_pgno));

        /* Add the node to the destination page.
         */
        rc = mdb_node_add(cdst, cdst->mc_ki[cdst->mc_top], &key, &data, srcpg, flags);
        if (rc != MDB_SUCCESS)
                return rc;

        /* Delete the node from the source page.
         */
        mdb_node_del(csrc, key.mv_size);

        {
                /* Adjust other cursors pointing to mp */
                MDB_cursor *m2, *m3;
                MDB_dbi dbi = csrc->mc_dbi;
                MDB_page *mp = csrc->mc_pg[csrc->mc_top];

                for (m2 = csrc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
                        if (csrc->mc_flags & C_SUB)
                                m3 = &m2->mc_xcursor->mx_cursor;
                        else
                                m3 = m2;
                        if (m3 == csrc) continue;
                        if (m3->mc_pg[csrc->mc_top] == mp && m3->mc_ki[csrc->mc_top] ==
                                csrc->mc_ki[csrc->mc_top]) {
                                m3->mc_pg[csrc->mc_top] = cdst->mc_pg[cdst->mc_top];
                                m3->mc_ki[csrc->mc_top] = cdst->mc_ki[cdst->mc_top];
                        }
                }
        }

        /* Update the parent separators.
         */
        if (csrc->mc_ki[csrc->mc_top] == 0) {
                if (csrc->mc_ki[csrc->mc_top-1] != 0) {
                        if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
                                key.mv_data = LEAF2KEY(csrc->mc_pg[csrc->mc_top], 0, key.mv_size);
                        } else {
                                srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], 0);
                                key.mv_size = NODEKSZ(srcnode);
                                key.mv_data = NODEKEY(srcnode);
                        }
                        DPRINTF(("update separator for source page %"Z"u to [%s]",
                                csrc->mc_pg[csrc->mc_top]->mp_pgno, DKEY(&key)));
                        mdb_cursor_copy(csrc, &mn);
                        mn.mc_snum--;
                        mn.mc_top--;
                        if ((rc = mdb_update_key(&mn, &key)) != MDB_SUCCESS)
                                return rc;
                }
                if (IS_BRANCH(csrc->mc_pg[csrc->mc_top])) {
                        MDB_val  nullkey;
                        indx_t  ix = csrc->mc_ki[csrc->mc_top];
                        nullkey.mv_size = 0;
                        csrc->mc_ki[csrc->mc_top] = 0;
                        rc = mdb_update_key(csrc, &nullkey);
                        csrc->mc_ki[csrc->mc_top] = ix;
                        mdb_cassert(csrc, rc == MDB_SUCCESS);
                }
        }

        if (cdst->mc_ki[cdst->mc_top] == 0) {
                if (cdst->mc_ki[cdst->mc_top-1] != 0) {
                        if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
                                key.mv_data = LEAF2KEY(cdst->mc_pg[cdst->mc_top], 0, key.mv_size);
                        } else {
                                srcnode = NODEPTR(cdst->mc_pg[cdst->mc_top], 0);
                                key.mv_size = NODEKSZ(srcnode);
                                key.mv_data = NODEKEY(srcnode);
                        }
                        DPRINTF(("update separator for destination page %"Z"u to [%s]",
                                cdst->mc_pg[cdst->mc_top]->mp_pgno, DKEY(&key)));
                        mdb_cursor_copy(cdst, &mn);
                        mn.mc_snum--;
                        mn.mc_top--;
                        if ((rc = mdb_update_key(&mn, &key)) != MDB_SUCCESS)
                                return rc;
                }
                if (IS_BRANCH(cdst->mc_pg[cdst->mc_top])) {
                        MDB_val  nullkey;
                        indx_t  ix = cdst->mc_ki[cdst->mc_top];
                        nullkey.mv_size = 0;
                        cdst->mc_ki[cdst->mc_top] = 0;
                        rc = mdb_update_key(cdst, &nullkey);
                        cdst->mc_ki[cdst->mc_top] = ix;
                        mdb_cassert(csrc, rc == MDB_SUCCESS);
                }
        }

        return MDB_SUCCESS;
}

/** Merge one page into another.
 *  The nodes from the page pointed to by \b csrc will
 *      be copied to the page pointed to by \b cdst and then
 *      the \b csrc page will be freed.
 * @param[in] csrc Cursor pointing to the source page.
 * @param[in] cdst Cursor pointing to the destination page.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_merge(MDB_cursor *csrc, MDB_cursor *cdst)
{
        MDB_page        *psrc, *pdst;
        MDB_node        *srcnode;
        MDB_val          key, data;
        unsigned         nkeys;
        int                      rc;
        indx_t           i, j;

        psrc = csrc->mc_pg[csrc->mc_top];
        pdst = cdst->mc_pg[cdst->mc_top];

        DPRINTF(("merging page %"Z"u into %"Z"u", psrc->mp_pgno, pdst->mp_pgno));

        mdb_cassert(csrc, csrc->mc_snum > 1);   /* can't merge root page */
        mdb_cassert(csrc, cdst->mc_snum > 1);

        /* Mark dst as dirty. */
        if ((rc = mdb_page_touch(cdst)))
                return rc;

        /* Move all nodes from src to dst.
         */
        j = nkeys = NUMKEYS(pdst);
        if (IS_LEAF2(psrc)) {
                key.mv_size = csrc->mc_db->md_pad;
                key.mv_data = METADATA(psrc);
                for (i = 0; i < NUMKEYS(psrc); i++, j++) {
                        rc = mdb_node_add(cdst, j, &key, NULL, 0, 0);
                        if (rc != MDB_SUCCESS)
                                return rc;
                        key.mv_data = (char *)key.mv_data + key.mv_size;
                }
        } else {
                for (i = 0; i < NUMKEYS(psrc); i++, j++) {
                        srcnode = NODEPTR(psrc, i);
                        if (i == 0 && IS_BRANCH(psrc)) {
                                MDB_cursor mn;
                                MDB_node *s2;
                                mdb_cursor_copy(csrc, &mn);
                                /* must find the lowest key below src */
                                rc = mdb_page_search_lowest(&mn);
                                if (rc)
                                        return rc;
                                if (IS_LEAF2(mn.mc_pg[mn.mc_top])) {
                                        key.mv_size = mn.mc_db->md_pad;
                                        key.mv_data = LEAF2KEY(mn.mc_pg[mn.mc_top], 0, key.mv_size);
                                } else {
                                        s2 = NODEPTR(mn.mc_pg[mn.mc_top], 0);
                                        key.mv_size = NODEKSZ(s2);
                                        key.mv_data = NODEKEY(s2);
                                }
                        } else {
                                key.mv_size = srcnode->mn_ksize;
                                key.mv_data = NODEKEY(srcnode);
                        }

                        data.mv_size = NODEDSZ(srcnode);
                        data.mv_data = NODEDATA(srcnode);
                        rc = mdb_node_add(cdst, j, &key, &data, NODEPGNO(srcnode), srcnode->mn_flags);
                        if (rc != MDB_SUCCESS)
                                return rc;
                }
        }

        DPRINTF(("dst page %"Z"u now has %u keys (%.1f%% filled)",
            pdst->mp_pgno, NUMKEYS(pdst),
                (float)PAGEFILL(cdst->mc_txn->mt_env, pdst) / 10));

        /* Unlink the src page from parent and add to free list.
         */
        csrc->mc_top--;
        mdb_node_del(csrc, 0);
        if (csrc->mc_ki[csrc->mc_top] == 0) {
                key.mv_size = 0;
                rc = mdb_update_key(csrc, &key);
                if (rc) {
                        csrc->mc_top++;
                        return rc;
                }
        }
        csrc->mc_top++;

        psrc = csrc->mc_pg[csrc->mc_top];
        /* If not operating on FreeDB, allow this page to be reused
         * in this txn. Otherwise just add to free list.
         */
        rc = mdb_page_loose(csrc, psrc);
        if (rc)
                return rc;
        if (IS_LEAF(psrc))
                csrc->mc_db->md_leaf_pages--;
        else
                csrc->mc_db->md_branch_pages--;
        {
                /* Adjust other cursors pointing to mp */
                MDB_cursor *m2, *m3;
                MDB_dbi dbi = csrc->mc_dbi;

                for (m2 = csrc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
                        if (csrc->mc_flags & C_SUB)
                                m3 = &m2->mc_xcursor->mx_cursor;
                        else
                                m3 = m2;
                        if (m3 == csrc) continue;
                        if (m3->mc_snum < csrc->mc_snum) continue;
                        if (m3->mc_pg[csrc->mc_top] == psrc) {
                                m3->mc_pg[csrc->mc_top] = pdst;
                                m3->mc_ki[csrc->mc_top] += nkeys;
                        }
                }
        }
        {
                unsigned int snum = cdst->mc_snum;
                uint16_t depth = cdst->mc_db->md_depth;
                mdb_cursor_pop(cdst);
                rc = mdb_rebalance(cdst);
                /* Did the tree shrink? */
                if (depth > cdst->mc_db->md_depth)
                        snum--;
                cdst->mc_snum = snum;
                cdst->mc_top = snum-1;
        }
        return rc;
}

/** Copy the contents of a cursor.
 * @param[in] csrc The cursor to copy from.
 * @param[out] cdst The cursor to copy to.
 */
static void
mdb_cursor_copy(const MDB_cursor *csrc, MDB_cursor *cdst)
{
        unsigned int i;

        cdst->mc_txn = csrc->mc_txn;
        cdst->mc_dbi = csrc->mc_dbi;
        cdst->mc_db  = csrc->mc_db;
        cdst->mc_dbx = csrc->mc_dbx;
        cdst->mc_snum = csrc->mc_snum;
        cdst->mc_top = csrc->mc_top;
        cdst->mc_flags = csrc->mc_flags;

        for (i=0; i<csrc->mc_snum; i++) {
                cdst->mc_pg[i] = csrc->mc_pg[i];
                cdst->mc_ki[i] = csrc->mc_ki[i];
        }
}

/** Rebalance the tree after a delete operation.
 * @param[in] mc Cursor pointing to the page where rebalancing
 * should begin.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_rebalance(MDB_cursor *mc)
{
        MDB_node        *node;
        int rc;
        unsigned int ptop, minkeys;
        MDB_cursor      mn;
        indx_t oldki;

        minkeys = 1 + (IS_BRANCH(mc->mc_pg[mc->mc_top]));
        DPRINTF(("rebalancing %s page %"Z"u (has %u keys, %.1f%% full)",
            IS_LEAF(mc->mc_pg[mc->mc_top]) ? "leaf" : "branch",
            mdb_dbg_pgno(mc->mc_pg[mc->mc_top]), NUMKEYS(mc->mc_pg[mc->mc_top]),
                (float)PAGEFILL(mc->mc_txn->mt_env, mc->mc_pg[mc->mc_top]) / 10));

        if (PAGEFILL(mc->mc_txn->mt_env, mc->mc_pg[mc->mc_top]) >= FILL_THRESHOLD &&
                NUMKEYS(mc->mc_pg[mc->mc_top]) >= minkeys) {
                DPRINTF(("no need to rebalance page %"Z"u, above fill threshold",
                    mdb_dbg_pgno(mc->mc_pg[mc->mc_top])));
                return MDB_SUCCESS;
        }

        if (mc->mc_snum < 2) {
                MDB_page *mp = mc->mc_pg[0];
                if (IS_SUBP(mp)) {
                        DPUTS("Can't rebalance a subpage, ignoring");
                        return MDB_SUCCESS;
                }
                if (NUMKEYS(mp) == 0) {
                        DPUTS("tree is completely empty");
                        mc->mc_db->md_root = P_INVALID;
                        mc->mc_db->md_depth = 0;
                        mc->mc_db->md_leaf_pages = 0;
                        rc = mdb_midl_append(&mc->mc_txn->mt_free_pgs, mp->mp_pgno);
                        if (rc)
                                return rc;
                        /* Adjust cursors pointing to mp */
                        mc->mc_snum = 0;
                        mc->mc_top = 0;
                        mc->mc_flags &= ~C_INITIALIZED;
                        {
                                MDB_cursor *m2, *m3;
                                MDB_dbi dbi = mc->mc_dbi;

                                for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
                                        if (mc->mc_flags & C_SUB)
                                                m3 = &m2->mc_xcursor->mx_cursor;
                                        else
                                                m3 = m2;
                                        if (m3->mc_snum < mc->mc_snum) continue;
                                        if (m3->mc_pg[0] == mp) {
                                                m3->mc_snum = 0;
                                                m3->mc_top = 0;
                                                m3->mc_flags &= ~C_INITIALIZED;
                                        }
                                }
                        }
                } else if (IS_BRANCH(mp) && NUMKEYS(mp) == 1) {
                        int i;
                        DPUTS("collapsing root page!");
                        rc = mdb_midl_append(&mc->mc_txn->mt_free_pgs, mp->mp_pgno);
                        if (rc)
                                return rc;
                        mc->mc_db->md_root = NODEPGNO(NODEPTR(mp, 0));
                        rc = mdb_page_get(mc->mc_txn,mc->mc_db->md_root,&mc->mc_pg[0],NULL);
                        if (rc)
                                return rc;
                        mc->mc_db->md_depth--;
                        mc->mc_db->md_branch_pages--;
                        mc->mc_ki[0] = mc->mc_ki[1];
                        for (i = 1; i<mc->mc_db->md_depth; i++) {
                                mc->mc_pg[i] = mc->mc_pg[i+1];
                                mc->mc_ki[i] = mc->mc_ki[i+1];
                        }
                        {
                                /* Adjust other cursors pointing to mp */
                                MDB_cursor *m2, *m3;
                                MDB_dbi dbi = mc->mc_dbi;

                                for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
                                        if (mc->mc_flags & C_SUB)
                                                m3 = &m2->mc_xcursor->mx_cursor;
                                        else
                                                m3 = m2;
                                        if (m3 == mc || m3->mc_snum < mc->mc_snum) continue;
                                        if (m3->mc_pg[0] == mp) {
                                                m3->mc_snum--;
                                                m3->mc_top--;
                                                for (i=0; i<m3->mc_snum; i++) {
                                                        m3->mc_pg[i] = m3->mc_pg[i+1];
                                                        m3->mc_ki[i] = m3->mc_ki[i+1];
                                                }
                                        }
                                }
                        }
                } else
                        DPUTS("root page doesn't need rebalancing");
                return MDB_SUCCESS;
        }

        /* The parent (branch page) must have at least 2 pointers,
         * otherwise the tree is invalid.
         */
        ptop = mc->mc_top-1;
        mdb_cassert(mc, NUMKEYS(mc->mc_pg[ptop]) > 1);

        /* Leaf page fill factor is below the threshold.
         * Try to move keys from left or right neighbor, or
         * merge with a neighbor page.
         */

        /* Find neighbors.
         */
        mdb_cursor_copy(mc, &mn);
        mn.mc_xcursor = NULL;

        oldki = mc->mc_ki[mc->mc_top];
        if (mc->mc_ki[ptop] == 0) {
                /* We're the leftmost leaf in our parent.
                 */
                DPUTS("reading right neighbor");
                mn.mc_ki[ptop]++;
                node = NODEPTR(mc->mc_pg[ptop], mn.mc_ki[ptop]);
                rc = mdb_page_get(mc->mc_txn,NODEPGNO(node),&mn.mc_pg[mn.mc_top],NULL);
                if (rc)
                        return rc;
                mn.mc_ki[mn.mc_top] = 0;
                mc->mc_ki[mc->mc_top] = NUMKEYS(mc->mc_pg[mc->mc_top]);
        } else {
                /* There is at least one neighbor to the left.
                 */
                DPUTS("reading left neighbor");
                mn.mc_ki[ptop]--;
                node = NODEPTR(mc->mc_pg[ptop], mn.mc_ki[ptop]);
                rc = mdb_page_get(mc->mc_txn,NODEPGNO(node),&mn.mc_pg[mn.mc_top],NULL);
                if (rc)
                        return rc;
                mn.mc_ki[mn.mc_top] = NUMKEYS(mn.mc_pg[mn.mc_top]) - 1;
                mc->mc_ki[mc->mc_top] = 0;
        }

        DPRINTF(("found neighbor page %"Z"u (%u keys, %.1f%% full)",
            mn.mc_pg[mn.mc_top]->mp_pgno, NUMKEYS(mn.mc_pg[mn.mc_top]),
                (float)PAGEFILL(mc->mc_txn->mt_env, mn.mc_pg[mn.mc_top]) / 10));

        /* If the neighbor page is above threshold and has enough keys,
         * move one key from it. Otherwise we should try to merge them.
         * (A branch page must never have less than 2 keys.)
         */
        minkeys = 1 + (IS_BRANCH(mn.mc_pg[mn.mc_top]));
        if (PAGEFILL(mc->mc_txn->mt_env, mn.mc_pg[mn.mc_top]) >= FILL_THRESHOLD && NUMKEYS(mn.mc_pg[mn.mc_top]) > minkeys) {
                rc = mdb_node_move(&mn, mc);
                if (mc->mc_ki[ptop]) {
                        oldki++;
                }
        } else {
                if (mc->mc_ki[ptop] == 0) {
                        rc = mdb_page_merge(&mn, mc);
                } else {
                        oldki += NUMKEYS(mn.mc_pg[mn.mc_top]);
                        mn.mc_ki[mn.mc_top] += mc->mc_ki[mn.mc_top] + 1;
                        rc = mdb_page_merge(mc, &mn);
                        mdb_cursor_copy(&mn, mc);
                }
                mc->mc_flags &= ~C_EOF;
        }
        mc->mc_ki[mc->mc_top] = oldki;
        return rc;
}

/** Complete a delete operation started by #mdb_cursor_del(). */
static int
mdb_cursor_del0(MDB_cursor *mc)
{
        int rc;
        MDB_page *mp;
        indx_t ki;
        unsigned int nkeys;

        ki = mc->mc_ki[mc->mc_top];
        mdb_node_del(mc, mc->mc_db->md_pad);
        mc->mc_db->md_entries--;
        rc = mdb_rebalance(mc);

        if (rc == MDB_SUCCESS) {
                MDB_cursor *m2, *m3;
                MDB_dbi dbi = mc->mc_dbi;

                mp = mc->mc_pg[mc->mc_top];
                nkeys = NUMKEYS(mp);

                /* if mc points past last node in page, find next sibling */
                if (mc->mc_ki[mc->mc_top] >= nkeys) {
                        rc = mdb_cursor_sibling(mc, 1);
                        if (rc == MDB_NOTFOUND) {
                                mc->mc_flags |= C_EOF;
                                rc = MDB_SUCCESS;
                        }
                }

                /* Adjust other cursors pointing to mp */
                for (m2 = mc->mc_txn->mt_cursors[dbi]; !rc && m2; m2=m2->mc_next) {
                        m3 = (mc->mc_flags & C_SUB) ? &m2->mc_xcursor->mx_cursor : m2;
                        if (! (m2->mc_flags & m3->mc_flags & C_INITIALIZED))
                                continue;
                        if (m3 == mc || m3->mc_snum < mc->mc_snum)
                                continue;
                        if (m3->mc_pg[mc->mc_top] == mp) {
                                if (m3->mc_ki[mc->mc_top] >= ki) {
                                        m3->mc_flags |= C_DEL;
                                        if (m3->mc_ki[mc->mc_top] > ki)
                                                m3->mc_ki[mc->mc_top]--;
                                        else if (mc->mc_db->md_flags & MDB_DUPSORT)
                                                m3->mc_xcursor->mx_cursor.mc_flags |= C_EOF;
                                }
                                if (m3->mc_ki[mc->mc_top] >= nkeys) {
                                        rc = mdb_cursor_sibling(m3, 1);
                                        if (rc == MDB_NOTFOUND) {
                                                m3->mc_flags |= C_EOF;
                                                rc = MDB_SUCCESS;
                                        }
                                }
                        }
                }
                mc->mc_flags |= C_DEL;
        }

        if (rc)
                mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
        return rc;
}

int
mdb_del(MDB_txn *txn, MDB_dbi dbi,
    MDB_val *key, MDB_val *data)
{
        if (!key || dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
                return EINVAL;

        if (txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_ERROR))
                return (txn->mt_flags & MDB_TXN_RDONLY) ? EACCES : MDB_BAD_TXN;

        if (!F_ISSET(txn->mt_dbs[dbi].md_flags, MDB_DUPSORT)) {
                /* must ignore any data */
                data = NULL;
        }

        return mdb_del0(txn, dbi, key, data, 0);
}

static int
mdb_del0(MDB_txn *txn, MDB_dbi dbi,
        MDB_val *key, MDB_val *data, unsigned flags)
{
        MDB_cursor mc;
        MDB_xcursor mx;
        MDB_cursor_op op;
        MDB_val rdata, *xdata;
        int              rc, exact = 0;
        DKBUF;

        DPRINTF(("====> delete db %u key [%s]", dbi, DKEY(key)));

        mdb_cursor_init(&mc, txn, dbi, &mx);

        if (data) {
                op = MDB_GET_BOTH;
                rdata = *data;
                xdata = &rdata;
        } else {
                op = MDB_SET;
                xdata = NULL;
                flags |= MDB_NODUPDATA;
        }
        rc = mdb_cursor_set(&mc, key, xdata, op, &exact);
        if (rc == 0) {
                /* let mdb_page_split know about this cursor if needed:
                 * delete will trigger a rebalance; if it needs to move
                 * a node from one page to another, it will have to
                 * update the parent's separator key(s). If the new sepkey
                 * is larger than the current one, the parent page may
                 * run out of space, triggering a split. We need this
                 * cursor to be consistent until the end of the rebalance.
                 */
                mc.mc_flags |= C_UNTRACK;
                mc.mc_next = txn->mt_cursors[dbi];
                txn->mt_cursors[dbi] = &mc;
                rc = mdb_cursor_del(&mc, flags);
                txn->mt_cursors[dbi] = mc.mc_next;
        }
        return rc;
}

/** Split a page and insert a new node.
 * @param[in,out] mc Cursor pointing to the page and desired insertion index.
 * The cursor will be updated to point to the actual page and index where
 * the node got inserted after the split.
 * @param[in] newkey The key for the newly inserted node.
 * @param[in] newdata The data for the newly inserted node.
 * @param[in] newpgno The page number, if the new node is a branch node.
 * @param[in] nflags The #NODE_ADD_FLAGS for the new node.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata, pgno_t newpgno,
        unsigned int nflags)
{
        unsigned int flags;
        int              rc = MDB_SUCCESS, new_root = 0, did_split = 0;
        indx_t           newindx;
        pgno_t           pgno = 0;
        int      i, j, split_indx, nkeys, pmax;
        MDB_env         *env = mc->mc_txn->mt_env;
        MDB_node        *node;
        MDB_val  sepkey, rkey, xdata, *rdata = &xdata;
        MDB_page        *copy = NULL;
        MDB_page        *mp, *rp, *pp;
        int ptop;
        MDB_cursor      mn;
        DKBUF;

        mp = mc->mc_pg[mc->mc_top];
        newindx = mc->mc_ki[mc->mc_top];
        nkeys = NUMKEYS(mp);

        DPRINTF(("-----> splitting %s page %"Z"u and adding [%s] at index %i/%i",
            IS_LEAF(mp) ? "leaf" : "branch", mp->mp_pgno,
            DKEY(newkey), mc->mc_ki[mc->mc_top], nkeys));

        /* Create a right sibling. */
        if ((rc = mdb_page_new(mc, mp->mp_flags, 1, &rp)))
                return rc;
        DPRINTF(("new right sibling: page %"Z"u", rp->mp_pgno));

        if (mc->mc_snum < 2) {
                if ((rc = mdb_page_new(mc, P_BRANCH, 1, &pp)))
                        goto done;
                /* shift current top to make room for new parent */
                mc->mc_pg[1] = mc->mc_pg[0];
                mc->mc_ki[1] = mc->mc_ki[0];
                mc->mc_pg[0] = pp;
                mc->mc_ki[0] = 0;
                mc->mc_db->md_root = pp->mp_pgno;
                DPRINTF(("root split! new root = %"Z"u", pp->mp_pgno));
                mc->mc_db->md_depth++;
                new_root = 1;

                /* Add left (implicit) pointer. */
                if ((rc = mdb_node_add(mc, 0, NULL, NULL, mp->mp_pgno, 0)) != MDB_SUCCESS) {
                        /* undo the pre-push */
                        mc->mc_pg[0] = mc->mc_pg[1];
                        mc->mc_ki[0] = mc->mc_ki[1];
                        mc->mc_db->md_root = mp->mp_pgno;
                        mc->mc_db->md_depth--;
                        goto done;
                }
                mc->mc_snum = 2;
                mc->mc_top = 1;
                ptop = 0;
        } else {
                ptop = mc->mc_top-1;
                DPRINTF(("parent branch page is %"Z"u", mc->mc_pg[ptop]->mp_pgno));
        }

        mc->mc_flags |= C_SPLITTING;
        mdb_cursor_copy(mc, &mn);
        mn.mc_pg[mn.mc_top] = rp;
        mn.mc_ki[ptop] = mc->mc_ki[ptop]+1;

        if (nflags & MDB_APPEND) {
                mn.mc_ki[mn.mc_top] = 0;
                sepkey = *newkey;
                split_indx = newindx;
                nkeys = 0;
        } else {

                split_indx = (nkeys+1) / 2;

                if (IS_LEAF2(rp)) {
                        char *split, *ins;
                        int x;
                        unsigned int lsize, rsize, ksize;
                        /* Move half of the keys to the right sibling */
                        x = mc->mc_ki[mc->mc_top] - split_indx;
                        ksize = mc->mc_db->md_pad;
                        split = LEAF2KEY(mp, split_indx, ksize);
                        rsize = (nkeys - split_indx) * ksize;
                        lsize = (nkeys - split_indx) * sizeof(indx_t);
                        mp->mp_lower -= lsize;
                        rp->mp_lower += lsize;
                        mp->mp_upper += rsize - lsize;
                        rp->mp_upper -= rsize - lsize;
                        sepkey.mv_size = ksize;
                        if (newindx == split_indx) {
                                sepkey.mv_data = newkey->mv_data;
                        } else {
                                sepkey.mv_data = split;
                        }
                        if (x<0) {
                                ins = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], ksize);
                                memcpy(rp->mp_ptrs, split, rsize);
                                sepkey.mv_data = rp->mp_ptrs;
                                memmove(ins+ksize, ins, (split_indx - mc->mc_ki[mc->mc_top]) * ksize);
                                memcpy(ins, newkey->mv_data, ksize);
                                mp->mp_lower += sizeof(indx_t);
                                mp->mp_upper -= ksize - sizeof(indx_t);
                        } else {
                                if (x)
                                        memcpy(rp->mp_ptrs, split, x * ksize);
                                ins = LEAF2KEY(rp, x, ksize);
                                memcpy(ins, newkey->mv_data, ksize);
                                memcpy(ins+ksize, split + x * ksize, rsize - x * ksize);
                                rp->mp_lower += sizeof(indx_t);
                                rp->mp_upper -= ksize - sizeof(indx_t);
                                mc->mc_ki[mc->mc_top] = x;
                                mc->mc_pg[mc->mc_top] = rp;
                        }
                } else {
                        int psize, nsize, k;
                        /* Maximum free space in an empty page */
                        pmax = env->me_psize - PAGEHDRSZ;
                        if (IS_LEAF(mp))
                                nsize = mdb_leaf_size(env, newkey, newdata);
                        else
                                nsize = mdb_branch_size(env, newkey);
                        nsize = EVEN(nsize);

                        /* grab a page to hold a temporary copy */
                        copy = mdb_page_malloc(mc->mc_txn, 1);
                        if (copy == NULL) {
                                rc = ENOMEM;
                                goto done;
                        }
                        copy->mp_pgno  = mp->mp_pgno;
                        copy->mp_flags = mp->mp_flags;
                        copy->mp_lower = (PAGEHDRSZ-PAGEBASE);
                        copy->mp_upper = env->me_psize - PAGEBASE;

                        /* prepare to insert */
                        for (i=0, j=0; i<nkeys; i++) {
                                if (i == newindx) {
                                        copy->mp_ptrs[j++] = 0;
                                }
                                copy->mp_ptrs[j++] = mp->mp_ptrs[i];
                        }

                        /* When items are relatively large the split point needs
                         * to be checked, because being off-by-one will make the
                         * difference between success or failure in mdb_node_add.
                         *
                         * It's also relevant if a page happens to be laid out
                         * such that one half of its nodes are all "small" and
                         * the other half of its nodes are "large." If the new
                         * item is also "large" and falls on the half with
                         * "large" nodes, it also may not fit.
                         *
                         * As a final tweak, if the new item goes on the last
                         * spot on the page (and thus, onto the new page), bias
                         * the split so the new page is emptier than the old page.
                         * This yields better packing during sequential inserts.
                         */
                        if (nkeys < 20 || nsize > pmax/16 || newindx >= nkeys) {
                                /* Find split point */
                                psize = 0;
                                if (newindx <= split_indx || newindx >= nkeys) {
                                        i = 0; j = 1;
                                        k = newindx >= nkeys ? nkeys : split_indx+2;
                                } else {
                                        i = nkeys; j = -1;
                                        k = split_indx-1;
                                }
                                for (; i!=k; i+=j) {
                                        if (i == newindx) {
                                                psize += nsize;
                                                node = NULL;
                                        } else {
                                                node = (MDB_node *)((char *)mp + copy->mp_ptrs[i] + PAGEBASE);
                                                psize += NODESIZE + NODEKSZ(node) + sizeof(indx_t);
                                                if (IS_LEAF(mp)) {
                                                        if (F_ISSET(node->mn_flags, F_BIGDATA))
                                                                psize += sizeof(pgno_t);
                                                        else
                                                                psize += NODEDSZ(node);
                                                }
                                                psize = EVEN(psize);
                                        }
                                        if (psize > pmax || i == k-j) {
                                                split_indx = i + (j<0);
                                                break;
                                        }
                                }
                        }
                        if (split_indx == newindx) {
                                sepkey.mv_size = newkey->mv_size;
                                sepkey.mv_data = newkey->mv_data;
                        } else {
                                node = (MDB_node *)((char *)mp + copy->mp_ptrs[split_indx] + PAGEBASE);
                                sepkey.mv_size = node->mn_ksize;
                                sepkey.mv_data = NODEKEY(node);
                        }
                }
        }

        DPRINTF(("separator is %d [%s]", split_indx, DKEY(&sepkey)));

        /* Copy separator key to the parent.
         */
        if (SIZELEFT(mn.mc_pg[ptop]) < mdb_branch_size(env, &sepkey)) {
                mn.mc_snum--;
                mn.mc_top--;
                did_split = 1;
                rc = mdb_page_split(&mn, &sepkey, NULL, rp->mp_pgno, 0);
                if (rc)
                        goto done;

                /* root split? */
                if (mn.mc_snum == mc->mc_snum) {
                        mc->mc_pg[mc->mc_snum] = mc->mc_pg[mc->mc_top];
                        mc->mc_ki[mc->mc_snum] = mc->mc_ki[mc->mc_top];
                        mc->mc_pg[mc->mc_top] = mc->mc_pg[ptop];
                        mc->mc_ki[mc->mc_top] = mc->mc_ki[ptop];
                        mc->mc_snum++;
                        mc->mc_top++;
                        ptop++;
                }
                /* Right page might now have changed parent.
                 * Check if left page also changed parent.
                 */
                if (mn.mc_pg[ptop] != mc->mc_pg[ptop] &&
                    mc->mc_ki[ptop] >= NUMKEYS(mc->mc_pg[ptop])) {
                        for (i=0; i<ptop; i++) {
                                mc->mc_pg[i] = mn.mc_pg[i];
                                mc->mc_ki[i] = mn.mc_ki[i];
                        }
                        mc->mc_pg[ptop] = mn.mc_pg[ptop];
                        if (mn.mc_ki[ptop]) {
                                mc->mc_ki[ptop] = mn.mc_ki[ptop] - 1;
                        } else {
                                /* find right page's left sibling */
                                mc->mc_ki[ptop] = mn.mc_ki[ptop];
                                mdb_cursor_sibling(mc, 0);
                        }
                }
        } else {
                mn.mc_top--;
                rc = mdb_node_add(&mn, mn.mc_ki[ptop], &sepkey, NULL, rp->mp_pgno, 0);
                mn.mc_top++;
        }
        mc->mc_flags ^= C_SPLITTING;
        if (rc != MDB_SUCCESS) {
                goto done;
        }
        if (nflags & MDB_APPEND) {
                mc->mc_pg[mc->mc_top] = rp;
                mc->mc_ki[mc->mc_top] = 0;
                rc = mdb_node_add(mc, 0, newkey, newdata, newpgno, nflags);
                if (rc)
                        goto done;
                for (i=0; i<mc->mc_top; i++)
                        mc->mc_ki[i] = mn.mc_ki[i];
        } else if (!IS_LEAF2(mp)) {
                /* Move nodes */
                mc->mc_pg[mc->mc_top] = rp;
                i = split_indx;
                j = 0;
                do {
                        if (i == newindx) {
                                rkey.mv_data = newkey->mv_data;
                                rkey.mv_size = newkey->mv_size;
                                if (IS_LEAF(mp)) {
                                        rdata = newdata;
                                } else
                                        pgno = newpgno;
                                flags = nflags;
                                /* Update index for the new key. */
                                mc->mc_ki[mc->mc_top] = j;
                        } else {
                                node = (MDB_node *)((char *)mp + copy->mp_ptrs[i] + PAGEBASE);
                                rkey.mv_data = NODEKEY(node);
                                rkey.mv_size = node->mn_ksize;
                                if (IS_LEAF(mp)) {
                                        xdata.mv_data = NODEDATA(node);
                                        xdata.mv_size = NODEDSZ(node);
                                        rdata = &xdata;
                                } else
                                        pgno = NODEPGNO(node);
                                flags = node->mn_flags;
                        }

                        if (!IS_LEAF(mp) && j == 0) {
                                /* First branch index doesn't need key data. */
                                rkey.mv_size = 0;
                        }

                        rc = mdb_node_add(mc, j, &rkey, rdata, pgno, flags);
                        if (rc)
                                goto done;
                        if (i == nkeys) {
                                i = 0;
                                j = 0;
                                mc->mc_pg[mc->mc_top] = copy;
                        } else {
                                i++;
                                j++;
                        }
                } while (i != split_indx);

                nkeys = NUMKEYS(copy);
                for (i=0; i<nkeys; i++)
                        mp->mp_ptrs[i] = copy->mp_ptrs[i];
                mp->mp_lower = copy->mp_lower;
                mp->mp_upper = copy->mp_upper;
                memcpy(NODEPTR(mp, nkeys-1), NODEPTR(copy, nkeys-1),
                        env->me_psize - copy->mp_upper - PAGEBASE);

                /* reset back to original page */
                if (newindx < split_indx) {
                        mc->mc_pg[mc->mc_top] = mp;
                        if (nflags & MDB_RESERVE) {
                                node = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
                                if (!(node->mn_flags & F_BIGDATA))
                                        newdata->mv_data = NODEDATA(node);
                        }
                } else {
                        mc->mc_pg[mc->mc_top] = rp;
                        mc->mc_ki[ptop]++;
                        /* Make sure mc_ki is still valid.
                         */
                        if (mn.mc_pg[ptop] != mc->mc_pg[ptop] &&
                                mc->mc_ki[ptop] >= NUMKEYS(mc->mc_pg[ptop])) {
                                for (i=0; i<=ptop; i++) {
                                        mc->mc_pg[i] = mn.mc_pg[i];
                                        mc->mc_ki[i] = mn.mc_ki[i];
                                }
                        }
                }
        }

        {
                /* Adjust other cursors pointing to mp */
                MDB_cursor *m2, *m3;
                MDB_dbi dbi = mc->mc_dbi;
                int fixup = NUMKEYS(mp);

                for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
                        if (mc->mc_flags & C_SUB)
                                m3 = &m2->mc_xcursor->mx_cursor;
                        else
                                m3 = m2;
                        if (m3 == mc)
                                continue;
                        if (!(m2->mc_flags & m3->mc_flags & C_INITIALIZED))
                                continue;
                        if (m3->mc_flags & C_SPLITTING)
                                continue;
                        if (new_root) {
                                int k;
                                /* root split */
                                for (k=m3->mc_top; k>=0; k--) {
                                        m3->mc_ki[k+1] = m3->mc_ki[k];
                                        m3->mc_pg[k+1] = m3->mc_pg[k];
                                }
                                if (m3->mc_ki[0] >= split_indx) {
                                        m3->mc_ki[0] = 1;
                                } else {
                                        m3->mc_ki[0] = 0;
                                }
                                m3->mc_pg[0] = mc->mc_pg[0];
                                m3->mc_snum++;
                                m3->mc_top++;
                        }
                        if (m3->mc_top >= mc->mc_top && m3->mc_pg[mc->mc_top] == mp) {
                                if (m3->mc_ki[mc->mc_top] >= newindx && !(nflags & MDB_SPLIT_REPLACE))
                                        m3->mc_ki[mc->mc_top]++;
                                if (m3->mc_ki[mc->mc_top] >= fixup) {
                                        m3->mc_pg[mc->mc_top] = rp;
                                        m3->mc_ki[mc->mc_top] -= fixup;
                                        m3->mc_ki[ptop] = mn.mc_ki[ptop];
                                }
                        } else if (!did_split && m3->mc_top >= ptop && m3->mc_pg[ptop] == mc->mc_pg[ptop] &&
                                m3->mc_ki[ptop] >= mc->mc_ki[ptop]) {
                                m3->mc_ki[ptop]++;
                        }
                }
        }
        DPRINTF(("mp left: %d, rp left: %d", SIZELEFT(mp), SIZELEFT(rp)));

done:
        if (copy)                                       /* tmp page */
                mdb_page_free(env, copy);
        if (rc)
                mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
        return rc;
}

int
mdb_put(MDB_txn *txn, MDB_dbi dbi,
    MDB_val *key, MDB_val *data, unsigned int flags)
{
        MDB_cursor mc;
        MDB_xcursor mx;

        if (!key || !data || dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
                return EINVAL;

        if ((flags & (MDB_NOOVERWRITE|MDB_NODUPDATA|MDB_RESERVE|MDB_APPEND|MDB_APPENDDUP)) != flags)
                return EINVAL;

        mdb_cursor_init(&mc, txn, dbi, &mx);
        return mdb_cursor_put(&mc, key, data, flags);
}

#ifndef MDB_WBUF
#define MDB_WBUF        (1024*1024)
#endif

        /** State needed for a compacting copy. */
typedef struct mdb_copy {
        pthread_mutex_t mc_mutex;
        pthread_cond_t mc_cond;
        char *mc_wbuf[2];
        char *mc_over[2];
        MDB_env *mc_env;
        MDB_txn *mc_txn;
        int mc_wlen[2];
        int mc_olen[2];
        pgno_t mc_next_pgno;
        HANDLE mc_fd;
        int mc_status;
        volatile int mc_new;
        int mc_toggle;

} mdb_copy;

        /** Dedicated writer thread for compacting copy. */
static THREAD_RET ESECT
mdb_env_copythr(void *arg)
{
        mdb_copy *my = arg;
        char *ptr;
        int toggle = 0, wsize, rc;
#ifdef _WIN32
        DWORD len;
#define DO_WRITE(rc, fd, ptr, w2, len)  rc = WriteFile(fd, ptr, w2, &len, NULL)
#else
        int len;
#define DO_WRITE(rc, fd, ptr, w2, len)  len = write(fd, ptr, w2); rc = (len >= 0)
#endif

        pthread_mutex_lock(&my->mc_mutex);
        my->mc_new = 0;
        pthread_cond_signal(&my->mc_cond);
        for(;;) {
                while (!my->mc_new)
                        pthread_cond_wait(&my->mc_cond, &my->mc_mutex);
                if (my->mc_new < 0) {
                        my->mc_new = 0;
                        break;
                }
                my->mc_new = 0;
                wsize = my->mc_wlen[toggle];
                ptr = my->mc_wbuf[toggle];
again:
                while (wsize > 0) {
                        DO_WRITE(rc, my->mc_fd, ptr, wsize, len);
                        if (!rc) {
                                rc = ErrCode();
                                break;
                        } else if (len > 0) {
                                rc = MDB_SUCCESS;
                                ptr += len;
                                wsize -= len;
                                continue;
                        } else {
                                rc = EIO;
                                break;
                        }
                }
                if (rc) {
                        my->mc_status = rc;
                        break;
                }
                /* If there's an overflow page tail, write it too */
                if (my->mc_olen[toggle]) {
                        wsize = my->mc_olen[toggle];
                        ptr = my->mc_over[toggle];
                        my->mc_olen[toggle] = 0;
                        goto again;
                }
                my->mc_wlen[toggle] = 0;
                toggle ^= 1;
                pthread_cond_signal(&my->mc_cond);
        }
        pthread_cond_signal(&my->mc_cond);
        pthread_mutex_unlock(&my->mc_mutex);
        return (THREAD_RET)0;
#undef DO_WRITE
}

        /** Tell the writer thread there's a buffer ready to write */
static int ESECT
mdb_env_cthr_toggle(mdb_copy *my, int st)
{
        int toggle = my->mc_toggle ^ 1;
        pthread_mutex_lock(&my->mc_mutex);
        if (my->mc_status) {
                pthread_mutex_unlock(&my->mc_mutex);
                return my->mc_status;
        }
        while (my->mc_new == 1)
                pthread_cond_wait(&my->mc_cond, &my->mc_mutex);
        my->mc_new = st;
        my->mc_toggle = toggle;
        pthread_cond_signal(&my->mc_cond);
        pthread_mutex_unlock(&my->mc_mutex);
        return 0;
}

        /** Depth-first tree traversal for compacting copy. */
static int ESECT
mdb_env_cwalk(mdb_copy *my, pgno_t *pg, int flags)
{
        MDB_cursor mc;
        MDB_txn *txn = my->mc_txn;
        MDB_node *ni;
        MDB_page *mo, *mp, *leaf;
        char *buf, *ptr;
        int rc, toggle;
        unsigned int i;

        /* Empty DB, nothing to do */
        if (*pg == P_INVALID)
                return MDB_SUCCESS;

        mc.mc_snum = 1;
        mc.mc_top = 0;
        mc.mc_txn = txn;

        rc = mdb_page_get(my->mc_txn, *pg, &mc.mc_pg[0], NULL);
        if (rc)
                return rc;
        rc = mdb_page_search_root(&mc, NULL, MDB_PS_FIRST);
        if (rc)
                return rc;

        /* Make cursor pages writable */
        buf = ptr = malloc(my->mc_env->me_psize * mc.mc_snum);
        if (buf == NULL)
                return ENOMEM;

        for (i=0; i<mc.mc_top; i++) {
                mdb_page_copy((MDB_page *)ptr, mc.mc_pg[i], my->mc_env->me_psize);
                mc.mc_pg[i] = (MDB_page *)ptr;
                ptr += my->mc_env->me_psize;
        }

        /* This is writable space for a leaf page. Usually not needed. */
        leaf = (MDB_page *)ptr;

        toggle = my->mc_toggle;
        while (mc.mc_snum > 0) {
                unsigned n;
                mp = mc.mc_pg[mc.mc_top];
                n = NUMKEYS(mp);

                if (IS_LEAF(mp)) {
                        if (!IS_LEAF2(mp) && !(flags & F_DUPDATA)) {
                                for (i=0; i<n; i++) {
                                        ni = NODEPTR(mp, i);
                                        if (ni->mn_flags & F_BIGDATA) {
                                                MDB_page *omp;
                                                pgno_t pg;

                                                /* Need writable leaf */
                                                if (mp != leaf) {
                                                        mc.mc_pg[mc.mc_top] = leaf;
                                                        mdb_page_copy(leaf, mp, my->mc_env->me_psize);
                                                        mp = leaf;
                                                        ni = NODEPTR(mp, i);
                                                }

                                                memcpy(&pg, NODEDATA(ni), sizeof(pg));
                                                rc = mdb_page_get(txn, pg, &omp, NULL);
                                                if (rc)
                                                        goto done;
                                                if (my->mc_wlen[toggle] >= MDB_WBUF) {
                                                        rc = mdb_env_cthr_toggle(my, 1);
                                                        if (rc)
                                                                goto done;
                                                        toggle = my->mc_toggle;
                                                }
                                                mo = (MDB_page *)(my->mc_wbuf[toggle] + my->mc_wlen[toggle]);
                                                memcpy(mo, omp, my->mc_env->me_psize);
                                                mo->mp_pgno = my->mc_next_pgno;
                                                my->mc_next_pgno += omp->mp_pages;
                                                my->mc_wlen[toggle] += my->mc_env->me_psize;
                                                if (omp->mp_pages > 1) {
                                                        my->mc_olen[toggle] = my->mc_env->me_psize * (omp->mp_pages - 1);
                                                        my->mc_over[toggle] = (char *)omp + my->mc_env->me_psize;
                                                        rc = mdb_env_cthr_toggle(my, 1);
                                                        if (rc)
                                                                goto done;
                                                        toggle = my->mc_toggle;
                                                }
                                                memcpy(NODEDATA(ni), &mo->mp_pgno, sizeof(pgno_t));
                                        } else if (ni->mn_flags & F_SUBDATA) {
                                                MDB_db db;

                                                /* Need writable leaf */
                                                if (mp != leaf) {
                                                        mc.mc_pg[mc.mc_top] = leaf;
                                                        mdb_page_copy(leaf, mp, my->mc_env->me_psize);
                                                        mp = leaf;
                                                        ni = NODEPTR(mp, i);
                                                }

                                                memcpy(&db, NODEDATA(ni), sizeof(db));
                                                my->mc_toggle = toggle;
                                                rc = mdb_env_cwalk(my, &db.md_root, ni->mn_flags & F_DUPDATA);
                                                if (rc)
                                                        goto done;
                                                toggle = my->mc_toggle;
                                                memcpy(NODEDATA(ni), &db, sizeof(db));
                                        }
                                }
                        }
                } else {
                        mc.mc_ki[mc.mc_top]++;
                        if (mc.mc_ki[mc.mc_top] < n) {
                                pgno_t pg;
again:
                                ni = NODEPTR(mp, mc.mc_ki[mc.mc_top]);
                                pg = NODEPGNO(ni);
                                rc = mdb_page_get(txn, pg, &mp, NULL);
                                if (rc)
                                        goto done;
                                mc.mc_top++;
                                mc.mc_snum++;
                                mc.mc_ki[mc.mc_top] = 0;
                                if (IS_BRANCH(mp)) {
                                        /* Whenever we advance to a sibling branch page,
                                         * we must proceed all the way down to its first leaf.
                                         */
                                        mdb_page_copy(mc.mc_pg[mc.mc_top], mp, my->mc_env->me_psize);
                                        goto again;
                                } else
                                        mc.mc_pg[mc.mc_top] = mp;
                                continue;
                        }
                }
                if (my->mc_wlen[toggle] >= MDB_WBUF) {
                        rc = mdb_env_cthr_toggle(my, 1);
                        if (rc)
                                goto done;
                        toggle = my->mc_toggle;
                }
                mo = (MDB_page *)(my->mc_wbuf[toggle] + my->mc_wlen[toggle]);
                mdb_page_copy(mo, mp, my->mc_env->me_psize);
                mo->mp_pgno = my->mc_next_pgno++;
                my->mc_wlen[toggle] += my->mc_env->me_psize;
                if (mc.mc_top) {
                        /* Update parent if there is one */
                        ni = NODEPTR(mc.mc_pg[mc.mc_top-1], mc.mc_ki[mc.mc_top-1]);
                        SETPGNO(ni, mo->mp_pgno);
                        mdb_cursor_pop(&mc);
                } else {
                        /* Otherwise we're done */
                        *pg = mo->mp_pgno;
                        break;
                }
        }
done:
        free(buf);
        return rc;
}

        /** Copy environment with compaction. */
static int ESECT
mdb_env_copyfd1(MDB_env *env, HANDLE fd)
{
        MDB_meta *mm;
        MDB_page *mp;
        mdb_copy my;
        MDB_txn *txn = NULL;
        pthread_t thr;
        int rc;

#ifdef _WIN32
        my.mc_mutex = CreateMutex(NULL, FALSE, NULL);
        my.mc_cond = CreateEvent(NULL, FALSE, FALSE, NULL);
        my.mc_wbuf[0] = _aligned_malloc(MDB_WBUF*2, env->me_os_psize);
        if (my.mc_wbuf[0] == NULL)
                return errno;
#else
        pthread_mutex_init(&my.mc_mutex, NULL);
        pthread_cond_init(&my.mc_cond, NULL);
#ifdef HAVE_MEMALIGN
        my.mc_wbuf[0] = memalign(env->me_os_psize, MDB_WBUF*2);
        if (my.mc_wbuf[0] == NULL)
                return errno;
#else
        rc = posix_memalign((void **)&my.mc_wbuf[0], env->me_os_psize, MDB_WBUF*2);
        if (rc)
                return rc;
#endif
#endif
        memset(my.mc_wbuf[0], 0, MDB_WBUF*2);
        my.mc_wbuf[1] = my.mc_wbuf[0] + MDB_WBUF;
        my.mc_wlen[0] = 0;
        my.mc_wlen[1] = 0;
        my.mc_olen[0] = 0;
        my.mc_olen[1] = 0;
        my.mc_next_pgno = 2;
        my.mc_status = 0;
        my.mc_new = 1;
        my.mc_toggle = 0;
        my.mc_env = env;
        my.mc_fd = fd;
        THREAD_CREATE(thr, mdb_env_copythr, &my);

        rc = mdb_txn_begin(env, NULL, MDB_RDONLY, &txn);
        if (rc)
                return rc;

        mp = (MDB_page *)my.mc_wbuf[0];
        memset(mp, 0, 2*env->me_psize);
        mp->mp_pgno = 0;
        mp->mp_flags = P_META;
        mm = (MDB_meta *)METADATA(mp);
        mdb_env_init_meta0(env, mm);
        mm->mm_address = env->me_metas[0]->mm_address;

        mp = (MDB_page *)(my.mc_wbuf[0] + env->me_psize);
        mp->mp_pgno = 1;
        mp->mp_flags = P_META;
        *(MDB_meta *)METADATA(mp) = *mm;
        mm = (MDB_meta *)METADATA(mp);

        /* Count the number of free pages, subtract from lastpg to find
         * number of active pages
         */
        {
                MDB_ID freecount = 0;
                MDB_cursor mc;
                MDB_val key, data;
                mdb_cursor_init(&mc, txn, FREE_DBI, NULL);
                while ((rc = mdb_cursor_get(&mc, &key, &data, MDB_NEXT)) == 0)
                        freecount += *(MDB_ID *)data.mv_data;
                freecount += txn->mt_dbs[0].md_branch_pages +
                        txn->mt_dbs[0].md_leaf_pages +
                        txn->mt_dbs[0].md_overflow_pages;

                /* Set metapage 1 */
                mm->mm_last_pg = txn->mt_next_pgno - freecount - 1;
                mm->mm_dbs[1] = txn->mt_dbs[1];
                mm->mm_dbs[1].md_root = mm->mm_last_pg;
                mm->mm_txnid = 1;
        }
        my.mc_wlen[0] = env->me_psize * 2;
        my.mc_txn = txn;
        pthread_mutex_lock(&my.mc_mutex);
        while(my.mc_new)
                pthread_cond_wait(&my.mc_cond, &my.mc_mutex);
        pthread_mutex_unlock(&my.mc_mutex);
        rc = mdb_env_cwalk(&my, &txn->mt_dbs[1].md_root, 0);
        if (rc == MDB_SUCCESS && my.mc_wlen[my.mc_toggle])
                rc = mdb_env_cthr_toggle(&my, 1);
        mdb_env_cthr_toggle(&my, -1);
        pthread_mutex_lock(&my.mc_mutex);
        while(my.mc_new)
                pthread_cond_wait(&my.mc_cond, &my.mc_mutex);
        pthread_mutex_unlock(&my.mc_mutex);
        THREAD_FINISH(thr);

        mdb_txn_abort(txn);
#ifdef _WIN32
        CloseHandle(my.mc_cond);
        CloseHandle(my.mc_mutex);
        _aligned_free(my.mc_wbuf[0]);
#else
        pthread_cond_destroy(&my.mc_cond);
        pthread_mutex_destroy(&my.mc_mutex);
        free(my.mc_wbuf[0]);
#endif
        return rc;
}

        /** Copy environment as-is. */
static int ESECT
mdb_env_copyfd0(MDB_env *env, HANDLE fd)
{
        MDB_txn *txn = NULL;
        int rc;
        size_t wsize;
        char *ptr;
#ifdef _WIN32
        DWORD len, w2;
#define DO_WRITE(rc, fd, ptr, w2, len)  rc = WriteFile(fd, ptr, w2, &len, NULL)
#else
        ssize_t len;
        size_t w2;
#define DO_WRITE(rc, fd, ptr, w2, len)  len = write(fd, ptr, w2); rc = (len >= 0)
#endif

        /* Do the lock/unlock of the reader mutex before starting the
         * write txn.  Otherwise other read txns could block writers.
         */
        rc = mdb_txn_begin(env, NULL, MDB_RDONLY, &txn);
        if (rc)
                return rc;

        if (env->me_txns) {
                /* We must start the actual read txn after blocking writers */
                mdb_txn_reset0(txn, "reset-stage1");

                /* Temporarily block writers until we snapshot the meta pages */
                LOCK_MUTEX_W(env);

                rc = mdb_txn_renew0(txn);
                if (rc) {
                        UNLOCK_MUTEX_W(env);
                        goto leave;
                }
        }

        wsize = env->me_psize * 2;
        ptr = env->me_map;
        w2 = wsize;
        while (w2 > 0) {
                DO_WRITE(rc, fd, ptr, w2, len);
                if (!rc) {
                        rc = ErrCode();
                        break;
                } else if (len > 0) {
                        rc = MDB_SUCCESS;
                        ptr += len;
                        w2 -= len;
                        continue;
                } else {
                        /* Non-blocking or async handles are not supported */
                        rc = EIO;
                        break;
                }
        }
        if (env->me_txns)
                UNLOCK_MUTEX_W(env);

        if (rc)
                goto leave;

        w2 = txn->mt_next_pgno * env->me_psize;
#ifdef WIN32
        {
                LARGE_INTEGER fsize;
                GetFileSizeEx(env->me_fd, &fsize);
                if (w2 > fsize.QuadPart)
                        w2 = fsize.QuadPart;
        }
#else
        {
                struct stat st;
                fstat(env->me_fd, &st);
                if (w2 > (size_t)st.st_size)
                        w2 = st.st_size;
        }
#endif
        wsize = w2 - wsize;
        while (wsize > 0) {
                if (wsize > MAX_WRITE)
                        w2 = MAX_WRITE;
                else
                        w2 = wsize;
                DO_WRITE(rc, fd, ptr, w2, len);
                if (!rc) {
                        rc = ErrCode();
                        break;
                } else if (len > 0) {
                        rc = MDB_SUCCESS;
                        ptr += len;
                        wsize -= len;
                        continue;
                } else {
                        rc = EIO;
                        break;
                }
        }

leave:
        mdb_txn_abort(txn);
        return rc;
}

int ESECT
mdb_env_copyfd2(MDB_env *env, HANDLE fd, unsigned int flags)
{
        if (flags & MDB_CP_COMPACT)
                return mdb_env_copyfd1(env, fd);
        else
                return mdb_env_copyfd0(env, fd);
}

int ESECT
mdb_env_copyfd(MDB_env *env, HANDLE fd)
{
        return mdb_env_copyfd2(env, fd, 0);
}

int ESECT
mdb_env_copy2(MDB_env *env, const char *path, unsigned int flags)
{
        int rc, len;
        char *lpath;
        HANDLE newfd = INVALID_HANDLE_VALUE;

        if (env->me_flags & MDB_NOSUBDIR) {
                lpath = (char *)path;
        } else {
                len = strlen(path);
                len += sizeof(DATANAME);
                lpath = malloc(len);
                if (!lpath)
                        return ENOMEM;
                sprintf(lpath, "%s" DATANAME, path);
        }

        /* The destination path must exist, but the destination file must not.
         * We don't want the OS to cache the writes, since the source data is
         * already in the OS cache.
         */
#ifdef _WIN32
        newfd = CreateFile(lpath, GENERIC_WRITE, 0, NULL, CREATE_NEW,
                                FILE_FLAG_NO_BUFFERING|FILE_FLAG_WRITE_THROUGH, NULL);
#else
        newfd = open(lpath, O_WRONLY|O_CREAT|O_EXCL, 0666);
#endif
        if (newfd == INVALID_HANDLE_VALUE) {
                rc = ErrCode();
                goto leave;
        }

        if (env->me_psize >= env->me_os_psize) {
#ifdef O_DIRECT
        /* Set O_DIRECT if the file system supports it */
        if ((rc = fcntl(newfd, F_GETFL)) != -1)
                (void) fcntl(newfd, F_SETFL, rc | O_DIRECT);
#endif
#ifdef F_NOCACHE        /* __APPLE__ */
        rc = fcntl(newfd, F_NOCACHE, 1);
        if (rc) {
                rc = ErrCode();
                goto leave;
        }
#endif
        }

        rc = mdb_env_copyfd2(env, newfd, flags);

leave:
        if (!(env->me_flags & MDB_NOSUBDIR))
                free(lpath);
        if (newfd != INVALID_HANDLE_VALUE)
                if (close(newfd) < 0 && rc == MDB_SUCCESS)
                        rc = ErrCode();

        return rc;
}

int ESECT
mdb_env_copy(MDB_env *env, const char *path)
{
        return mdb_env_copy2(env, path, 0);
}

int ESECT
mdb_env_set_flags(MDB_env *env, unsigned int flag, int onoff)
{
        if ((flag & CHANGEABLE) != flag)
                return EINVAL;
        if (onoff)
                env->me_flags |= flag;
        else
                env->me_flags &= ~flag;
        return MDB_SUCCESS;
}

int ESECT
mdb_env_get_flags(MDB_env *env, unsigned int *arg)
{
        if (!env || !arg)
                return EINVAL;

        *arg = env->me_flags;
        return MDB_SUCCESS;
}

int ESECT
mdb_env_set_userctx(MDB_env *env, void *ctx)
{
        if (!env)
                return EINVAL;
        env->me_userctx = ctx;
        return MDB_SUCCESS;
}

void * ESECT
mdb_env_get_userctx(MDB_env *env)
{
        return env ? env->me_userctx : NULL;
}

int ESECT
mdb_env_set_assert(MDB_env *env, MDB_assert_func *func)
{
        if (!env)
                return EINVAL;
#ifndef NDEBUG
        env->me_assert_func = func;
#endif
        return MDB_SUCCESS;
}

int ESECT
mdb_env_get_path(MDB_env *env, const char **arg)
{
        if (!env || !arg)
                return EINVAL;

        *arg = env->me_path;
        return MDB_SUCCESS;
}

int ESECT
mdb_env_get_fd(MDB_env *env, mdb_filehandle_t *arg)
{
        if (!env || !arg)
                return EINVAL;

        *arg = env->me_fd;
        return MDB_SUCCESS;
}

/** Common code for #mdb_stat() and #mdb_env_stat().
 * @param[in] env the environment to operate in.
 * @param[in] db the #MDB_db record containing the stats to return.
 * @param[out] arg the address of an #MDB_stat structure to receive the stats.
 * @return 0, this function always succeeds.
 */
static int ESECT
mdb_stat0(MDB_env *env, MDB_db *db, MDB_stat *arg)
{
        arg->ms_psize = env->me_psize;
        arg->ms_depth = db->md_depth;
        arg->ms_branch_pages = db->md_branch_pages;
        arg->ms_leaf_pages = db->md_leaf_pages;
        arg->ms_overflow_pages = db->md_overflow_pages;
        arg->ms_entries = db->md_entries;

        return MDB_SUCCESS;
}

int ESECT
mdb_env_stat(MDB_env *env, MDB_stat *arg)
{
        int toggle;

        if (env == NULL || arg == NULL)
                return EINVAL;

        toggle = mdb_env_pick_meta(env);

        return mdb_stat0(env, &env->me_metas[toggle]->mm_dbs[MAIN_DBI], arg);
}

int ESECT
mdb_env_info(MDB_env *env, MDB_envinfo *arg)
{
        int toggle;

        if (env == NULL || arg == NULL)
                return EINVAL;

        toggle = mdb_env_pick_meta(env);
        arg->me_mapaddr = env->me_metas[toggle]->mm_address;
        arg->me_mapsize = env->me_mapsize;
        arg->me_maxreaders = env->me_maxreaders;

        /* me_numreaders may be zero if this process never used any readers. Use
         * the shared numreader count if it exists.
         */
        arg->me_numreaders = env->me_txns ? env->me_txns->mti_numreaders : env->me_numreaders;

        arg->me_last_pgno = env->me_metas[toggle]->mm_last_pg;
        arg->me_last_txnid = env->me_metas[toggle]->mm_txnid;
        return MDB_SUCCESS;
}

/** Set the default comparison functions for a database.
 * Called immediately after a database is opened to set the defaults.
 * The user can then override them with #mdb_set_compare() or
 * #mdb_set_dupsort().
 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
 * @param[in] dbi A database handle returned by #mdb_dbi_open()
 */
static void
mdb_default_cmp(MDB_txn *txn, MDB_dbi dbi)
{
        uint16_t f = txn->mt_dbs[dbi].md_flags;

        txn->mt_dbxs[dbi].md_cmp =
                (f & MDB_REVERSEKEY) ? mdb_cmp_memnr :
                (f & MDB_INTEGERKEY) ? mdb_cmp_cint  : mdb_cmp_memn;

        txn->mt_dbxs[dbi].md_dcmp =
                !(f & MDB_DUPSORT) ? 0 :
                ((f & MDB_INTEGERDUP)
                 ? ((f & MDB_DUPFIXED)   ? mdb_cmp_int   : mdb_cmp_cint)
                 : ((f & MDB_REVERSEDUP) ? mdb_cmp_memnr : mdb_cmp_memn));
}

int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi)
{
        MDB_val key, data;
        MDB_dbi i;
        MDB_cursor mc;
        MDB_db dummy;
        int rc, dbflag, exact;
        unsigned int unused = 0, seq;
        size_t len;

        if (txn->mt_dbxs[FREE_DBI].md_cmp == NULL) {
                mdb_default_cmp(txn, FREE_DBI);
        }

        if ((flags & VALID_FLAGS) != flags)
                return EINVAL;
        if (txn->mt_flags & MDB_TXN_ERROR)
                return MDB_BAD_TXN;

        /* main DB? */
        if (!name) {
                *dbi = MAIN_DBI;
                if (flags & PERSISTENT_FLAGS) {
                        uint16_t f2 = flags & PERSISTENT_FLAGS;
                        /* make sure flag changes get committed */
                        if ((txn->mt_dbs[MAIN_DBI].md_flags | f2) != txn->mt_dbs[MAIN_DBI].md_flags) {
                                txn->mt_dbs[MAIN_DBI].md_flags |= f2;
                                txn->mt_flags |= MDB_TXN_DIRTY;
                        }
                }
                mdb_default_cmp(txn, MAIN_DBI);
                return MDB_SUCCESS;
        }

        if (txn->mt_dbxs[MAIN_DBI].md_cmp == NULL) {
                mdb_default_cmp(txn, MAIN_DBI);
        }

        /* Is the DB already open? */
        len = strlen(name);
        for (i=2; i<txn->mt_numdbs; i++) {
                if (!txn->mt_dbxs[i].md_name.mv_size) {
                        /* Remember this free slot */
                        if (!unused) unused = i;
                        continue;
                }
                if (len == txn->mt_dbxs[i].md_name.mv_size &&
                        !strncmp(name, txn->mt_dbxs[i].md_name.mv_data, len)) {
                        *dbi = i;
                        return MDB_SUCCESS;
                }
        }

        /* If no free slot and max hit, fail */
        if (!unused && txn->mt_numdbs >= txn->mt_env->me_maxdbs)
                return MDB_DBS_FULL;

        /* Cannot mix named databases with some mainDB flags */
        if (txn->mt_dbs[MAIN_DBI].md_flags & (MDB_DUPSORT|MDB_INTEGERKEY))
                return (flags & MDB_CREATE) ? MDB_INCOMPATIBLE : MDB_NOTFOUND;

        /* Find the DB info */
        dbflag = DB_NEW|DB_VALID;
        exact = 0;
        key.mv_size = len;
        key.mv_data = (void *)name;
        mdb_cursor_init(&mc, txn, MAIN_DBI, NULL);
        rc = mdb_cursor_set(&mc, &key, &data, MDB_SET, &exact);
        if (rc == MDB_SUCCESS) {
                /* make sure this is actually a DB */
                MDB_node *node = NODEPTR(mc.mc_pg[mc.mc_top], mc.mc_ki[mc.mc_top]);
                if (!(node->mn_flags & F_SUBDATA))
                        return MDB_INCOMPATIBLE;
        } else if (rc == MDB_NOTFOUND && (flags & MDB_CREATE)) {
                /* Create if requested */
                data.mv_size = sizeof(MDB_db);
                data.mv_data = &dummy;
                memset(&dummy, 0, sizeof(dummy));
                dummy.md_root = P_INVALID;
                dummy.md_flags = flags & PERSISTENT_FLAGS;
                rc = mdb_cursor_put(&mc, &key, &data, F_SUBDATA);
                dbflag |= DB_DIRTY;
        }

        /* OK, got info, add to table */
        if (rc == MDB_SUCCESS) {
                unsigned int slot = unused ? unused : txn->mt_numdbs;
                txn->mt_dbxs[slot].md_name.mv_data = strdup(name);
                txn->mt_dbxs[slot].md_name.mv_size = len;
                txn->mt_dbxs[slot].md_rel = NULL;
                txn->mt_dbflags[slot] = dbflag;
                /* txn-> and env-> are the same in read txns, use
                 * tmp variable to avoid undefined assignment
                 */
                seq = ++txn->mt_env->me_dbiseqs[slot];
                txn->mt_dbiseqs[slot] = seq;

                memcpy(&txn->mt_dbs[slot], data.mv_data, sizeof(MDB_db));
                *dbi = slot;
                mdb_default_cmp(txn, slot);
                if (!unused) {
                        txn->mt_numdbs++;
                }
        }

        return rc;
}

int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *arg)
{
        if (!arg || !TXN_DBI_EXIST(txn, dbi))
                return EINVAL;

        if (txn->mt_flags & MDB_TXN_ERROR)
                return MDB_BAD_TXN;

        if (txn->mt_dbflags[dbi] & DB_STALE) {
                MDB_cursor mc;
                MDB_xcursor mx;
                /* Stale, must read the DB's root. cursor_init does it for us. */
                mdb_cursor_init(&mc, txn, dbi, &mx);
        }
        return mdb_stat0(txn->mt_env, &txn->mt_dbs[dbi], arg);
}

void mdb_dbi_close(MDB_env *env, MDB_dbi dbi)
{
        char *ptr;
        if (dbi <= MAIN_DBI || dbi >= env->me_maxdbs)
                return;
        ptr = env->me_dbxs[dbi].md_name.mv_data;
        /* If there was no name, this was already closed */
        if (ptr) {
                env->me_dbxs[dbi].md_name.mv_data = NULL;
                env->me_dbxs[dbi].md_name.mv_size = 0;
                env->me_dbflags[dbi] = 0;
                env->me_dbiseqs[dbi]++;
                free(ptr);
        }
}

int mdb_dbi_flags(MDB_txn *txn, MDB_dbi dbi, unsigned int *flags)
{
        /* We could return the flags for the FREE_DBI too but what's the point? */
        if (dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
                return EINVAL;
        *flags = txn->mt_dbs[dbi].md_flags & PERSISTENT_FLAGS;
        return MDB_SUCCESS;
}

/** Add all the DB's pages to the free list.
 * @param[in] mc Cursor on the DB to free.
 * @param[in] subs non-Zero to check for sub-DBs in this DB.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_drop0(MDB_cursor *mc, int subs)
{
        int rc;

        rc = mdb_page_search(mc, NULL, MDB_PS_FIRST);
        if (rc == MDB_SUCCESS) {
                MDB_txn *txn = mc->mc_txn;
                MDB_node *ni;
                MDB_cursor mx;
                unsigned int i;

                /* LEAF2 pages have no nodes, cannot have sub-DBs */
                if (IS_LEAF2(mc->mc_pg[mc->mc_top]))
                        mdb_cursor_pop(mc);

                mdb_cursor_copy(mc, &mx);
                while (mc->mc_snum > 0) {
                        MDB_page *mp = mc->mc_pg[mc->mc_top];
                        unsigned n = NUMKEYS(mp);
                        if (IS_LEAF(mp)) {
                                for (i=0; i<n; i++) {
                                        ni = NODEPTR(mp, i);
                                        if (ni->mn_flags & F_BIGDATA) {
                                                MDB_page *omp;
                                                pgno_t pg;
                                                memcpy(&pg, NODEDATA(ni), sizeof(pg));
                                                rc = mdb_page_get(txn, pg, &omp, NULL);
                                                if (rc != 0)
                                                        goto done;
                                                mdb_cassert(mc, IS_OVERFLOW(omp));
                                                rc = mdb_midl_append_range(&txn->mt_free_pgs,
                                                        pg, omp->mp_pages);
                                                if (rc)
                                                        goto done;
                                        } else if (subs && (ni->mn_flags & F_SUBDATA)) {
                                                mdb_xcursor_init1(mc, ni);
                                                rc = mdb_drop0(&mc->mc_xcursor->mx_cursor, 0);
                                                if (rc)
                                                        goto done;
                                        }
                                }
                        } else {
                                if ((rc = mdb_midl_need(&txn->mt_free_pgs, n)) != 0)
                                        goto done;
                                for (i=0; i<n; i++) {
                                        pgno_t pg;
                                        ni = NODEPTR(mp, i);
                                        pg = NODEPGNO(ni);
                                        /* free it */
                                        mdb_midl_xappend(txn->mt_free_pgs, pg);
                                }
                        }
                        if (!mc->mc_top)
                                break;
                        mc->mc_ki[mc->mc_top] = i;
                        rc = mdb_cursor_sibling(mc, 1);
                        if (rc) {
                                if (rc != MDB_NOTFOUND)
                                        goto done;
                                /* no more siblings, go back to beginning
                                 * of previous level.
                                 */
                                mdb_cursor_pop(mc);
                                mc->mc_ki[0] = 0;
                                for (i=1; i<mc->mc_snum; i++) {
                                        mc->mc_ki[i] = 0;
                                        mc->mc_pg[i] = mx.mc_pg[i];
                                }
                        }
                }
                /* free it */
                rc = mdb_midl_append(&txn->mt_free_pgs, mc->mc_db->md_root);
done:
                if (rc)
                        txn->mt_flags |= MDB_TXN_ERROR;
        } else if (rc == MDB_NOTFOUND) {
                rc = MDB_SUCCESS;
        }
        return rc;
}

int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del)
{
        MDB_cursor *mc, *m2;
        int rc;

        if ((unsigned)del > 1 || dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
                return EINVAL;

        if (F_ISSET(txn->mt_flags, MDB_TXN_RDONLY))
                return EACCES;

        if (dbi > MAIN_DBI && TXN_DBI_CHANGED(txn, dbi))
                return MDB_BAD_DBI;

        rc = mdb_cursor_open(txn, dbi, &mc);
        if (rc)
                return rc;

        rc = mdb_drop0(mc, mc->mc_db->md_flags & MDB_DUPSORT);
        /* Invalidate the dropped DB's cursors */
        for (m2 = txn->mt_cursors[dbi]; m2; m2 = m2->mc_next)
                m2->mc_flags &= ~(C_INITIALIZED|C_EOF);
        if (rc)
                goto leave;

        /* Can't delete the main DB */
        if (del && dbi > MAIN_DBI) {
                rc = mdb_del0(txn, MAIN_DBI, &mc->mc_dbx->md_name, NULL, 0);
                if (!rc) {
                        txn->mt_dbflags[dbi] = DB_STALE;
                        mdb_dbi_close(txn->mt_env, dbi);
                } else {
                        txn->mt_flags |= MDB_TXN_ERROR;
                }
        } else {
                /* reset the DB record, mark it dirty */
                txn->mt_dbflags[dbi] |= DB_DIRTY;
                txn->mt_dbs[dbi].md_depth = 0;
                txn->mt_dbs[dbi].md_branch_pages = 0;
                txn->mt_dbs[dbi].md_leaf_pages = 0;
                txn->mt_dbs[dbi].md_overflow_pages = 0;
                txn->mt_dbs[dbi].md_entries = 0;
                txn->mt_dbs[dbi].md_root = P_INVALID;

                txn->mt_flags |= MDB_TXN_DIRTY;
        }
leave:
        mdb_cursor_close(mc);
        return rc;
}

int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp)
{
        if (dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
                return EINVAL;

        txn->mt_dbxs[dbi].md_cmp = cmp;
        return MDB_SUCCESS;
}

int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp)
{
        if (dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
                return EINVAL;

        txn->mt_dbxs[dbi].md_dcmp = cmp;
        return MDB_SUCCESS;
}

int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel)
{
        if (dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
                return EINVAL;

        txn->mt_dbxs[dbi].md_rel = rel;
        return MDB_SUCCESS;
}

int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx)
{
        if (dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
                return EINVAL;

        txn->mt_dbxs[dbi].md_relctx = ctx;
        return MDB_SUCCESS;
}

int ESECT
mdb_env_get_maxkeysize(MDB_env *env)
{
        return ENV_MAXKEY(env);
}

int ESECT
mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx)
{
        unsigned int i, rdrs;
        MDB_reader *mr;
        char buf[64];
        int rc = 0, first = 1;

        if (!env || !func)
                return -1;
        if (!env->me_txns) {
                return func("(no reader locks)\n", ctx);
        }
        rdrs = env->me_txns->mti_numreaders;
        mr = env->me_txns->mti_readers;
        for (i=0; i<rdrs; i++) {
                if (mr[i].mr_pid) {
                        txnid_t txnid = mr[i].mr_txnid;
                        sprintf(buf, txnid == (txnid_t)-1 ?
                                "%10d %"Z"x -\n" : "%10d %"Z"x %"Z"u\n",
                                (int)mr[i].mr_pid, (size_t)mr[i].mr_tid, txnid);
                        if (first) {
                                first = 0;
                                rc = func("    pid     thread     txnid\n", ctx);
                                if (rc < 0)
                                        break;
                        }
                        rc = func(buf, ctx);
                        if (rc < 0)
                                break;
                }
        }
        if (first) {
                rc = func("(no active readers)\n", ctx);
        }
        return rc;
}

/** Insert pid into list if not already present.
 * return -1 if already present.
 */
static int ESECT
mdb_pid_insert(MDB_PID_T *ids, MDB_PID_T pid)
{
        /* binary search of pid in list */
        unsigned base = 0;
        unsigned cursor = 1;
        int val = 0;
        unsigned n = ids[0];

        while( 0 < n ) {
                unsigned pivot = n >> 1;
                cursor = base + pivot + 1;
                val = pid - ids[cursor];

                if( val < 0 ) {
                        n = pivot;

                } else if ( val > 0 ) {
                        base = cursor;
                        n -= pivot + 1;

                } else {
                        /* found, so it's a duplicate */
                        return -1;
                }
        }

        if( val > 0 ) {
                ++cursor;
        }
        ids[0]++;
        for (n = ids[0]; n > cursor; n--)
                ids[n] = ids[n-1];
        ids[n] = pid;
        return 0;
}

int ESECT
mdb_reader_check(MDB_env *env, int *dead)
{
        unsigned int i, j, rdrs;
        MDB_reader *mr;
        MDB_PID_T *pids, pid;
        int count = 0;

        if (!env)
                return EINVAL;
        if (dead)
                *dead = 0;
        if (!env->me_txns)
                return MDB_SUCCESS;
        rdrs = env->me_txns->mti_numreaders;
        pids = malloc((rdrs+1) * sizeof(MDB_PID_T));
        if (!pids)
                return ENOMEM;
        pids[0] = 0;
        mr = env->me_txns->mti_readers;
        for (i=0; i<rdrs; i++) {
                if (mr[i].mr_pid && mr[i].mr_pid != env->me_pid) {
                        pid = mr[i].mr_pid;
                        if (mdb_pid_insert(pids, pid) == 0) {
                                if (!mdb_reader_pid(env, Pidcheck, pid)) {
                                        LOCK_MUTEX_R(env);
                                        /* Recheck, a new process may have reused pid */
                                        if (!mdb_reader_pid(env, Pidcheck, pid)) {
                                                for (j=i; j<rdrs; j++)
                                                        if (mr[j].mr_pid == pid) {
                                                                DPRINTF(("clear stale reader pid %u txn %"Z"d",
                                                                        (unsigned) pid, mr[j].mr_txnid));
                                                                mr[j].mr_pid = 0;
                                                                count++;
                                                        }
                                        }
                                        UNLOCK_MUTEX_R(env);
                                }
                        }
                }
        }
        free(pids);
        if (dead)
                *dead = count;
        return MDB_SUCCESS;
}
/** @} */