Minor doc cleanup

[openldap] / libraries / libmdb / mdb.c

/** @file mdb.c
 *      @brief memory-mapped database library
 *
 *      A Btree-based database management library modeled loosely on the
 *      BerkeleyDB API, but much simplified.
 */
/*
 * Copyright 2011 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.
 */
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/param.h>
#ifdef _WIN32
#include <windows.h>
#else
#include <sys/uio.h>
#include <sys/mman.h>
#ifdef HAVE_SYS_FILE_H
#include <sys/file.h>
#endif
#include <fcntl.h>
#endif

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

#ifndef _WIN32
#include <pthread.h>
#endif

#include "mdb.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

/** @defgroup internal  MDB Internals
 *      @{
 */
/** @defgroup compat    Windows 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.
 *      @{
 */
#ifdef _WIN32
#define pthread_t       DWORD
#define pthread_mutex_t HANDLE
#define pthread_key_t   DWORD
#define pthread_self()  GetCurrentThreadId()
#define pthread_key_create(x,y) (*(x) = TlsAlloc())
#define pthread_key_delete(x)   TlsFree(x)
#define pthread_getspecific(x)  TlsGetValue(x)
#define pthread_setspecific(x,y)        TlsSetValue(x,y)
#define pthread_mutex_unlock(x) ReleaseMutex(x)
#define pthread_mutex_lock(x)   WaitForSingleObject(x, 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 fdatasync(fd)   (!FlushFileBuffers(fd))
#define ErrCode()       GetLastError()
#define GET_PAGESIZE(x) {SYSTEM_INFO si; GetSystemInfo(&si); (x) = si.dwPageSize;}
#define close(fd)       CloseHandle(fd)
#define munmap(ptr,len) UnmapViewOfFile(ptr)
#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)

        /** 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

/** @} */

#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

        /** 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 ID      pgno_t;

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

/** @defgroup debug     Debug Macros
 *      @{
 */
#ifndef DEBUG
        /**     Enable debug output.
         *      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 DEBUG 0
#endif

#if !(__STDC_VERSION__ >= 199901L || defined(__GNUC__))
# define DPRINTF        (void)  /* Vararg macros may be unsupported */
#elif DEBUG
        /**     Print a debug message with printf formatting. */
# define DPRINTF(fmt, ...)      /**< Requires 2 or more args */ \
        fprintf(stderr, "%s:%d " fmt "\n", __func__, __LINE__, __VA_ARGS__)
#else
# define DPRINTF(fmt, ...)      ((void) 0)
#endif
        /**     Print a debug string.
         *      The string is printed literally, with no format processing.
         */
#define DPUTS(arg)      DPRINTF("%s", arg)
/** @} */

        /** A default memory page size.
         *      The actual size is platform-dependent, but we use this for
         *      boot-strapping. We probably should not be using this any more.
         *      The #GET_PAGESIZE() macro is used to get the actual size.
         *
         *      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 PAGESIZE         4096

        /** 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 MDB 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 file format. */
#define MDB_VERSION      1

        /**     The maximum size of a key in the database.
         *      While data items have essentially unbounded size, we require that
         *      keys all fit onto a regular page. This limit could be raised a bit
         *      further if needed; to something just under #PAGESIZE / #MDB_MINKEYS.
         */
#define MAXKEYSIZE       511

#if DEBUG
        /**     A key buffer.
         *      @ingroup debug
         *      This is used for printing a hex dump of a key's contents.
         */
#define DKBUF   char kbuf[(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   typedef int dummy_kbuf  /* so we can put ';' after */
#define DKEY(x)
#endif

/**     @defgroup lazylock      Lazy Locking
 *      Macros for locks that are't actually needed.
 *      The DB view is always consistent because all writes are wrapped in
 *      the wmutex. Finer-grained locks aren't necessary.
 *      @{
 */
#ifndef LAZY_LOCKS
        /**     Use lazy locking. I.e., don't lock these accesses at all. */
#define LAZY_LOCKS      1
#endif
#if     LAZY_LOCKS
        /** Grab the reader lock */
#define LAZY_MUTEX_LOCK(x)
        /** Release the reader lock */
#define LAZY_MUTEX_UNLOCK(x)
        /** Release the DB table reader/writer lock */
#define LAZY_RWLOCK_UNLOCK(x)
        /** Grab the DB table write lock */
#define LAZY_RWLOCK_WRLOCK(x)
        /** Grab the DB table read lock */
#define LAZY_RWLOCK_RDLOCK(x)
        /** Declare the DB table rwlock.  Should not be followed by ';'. */
#define LAZY_RWLOCK_DEF(x)
        /** Initialize the DB table rwlock */
#define LAZY_RWLOCK_INIT(x,y)
        /**     Destroy the DB table rwlock */
#define LAZY_RWLOCK_DESTROY(x)
#else
#define LAZY_MUTEX_LOCK(x)              pthread_mutex_lock(x)
#define LAZY_MUTEX_UNLOCK(x)    pthread_mutex_unlock(x)
#define LAZY_RWLOCK_UNLOCK(x)   pthread_rwlock_unlock(x)
#define LAZY_RWLOCK_WRLOCK(x)   pthread_rwlock_wrlock(x)
#define LAZY_RWLOCK_RDLOCK(x)   pthread_rwlock_rdlock(x)
#define LAZY_RWLOCK_DEF(x)              pthread_rwlock_t        x;
#define LAZY_RWLOCK_INIT(x,y)   pthread_rwlock_init(x,y)
#define LAZY_RWLOCK_DESTROY(x)  pthread_rwlock_destroy(x)
#endif
/** @} */

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

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

        /**     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.
 *
 *      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.
 *
 *      @todo We don't actually do such coalescing yet, we grab pages from one
 *      old transaction at a time.
 *      @{
 */
        /**     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 {
        /**     The current Transaction ID when this transaction began.
         *      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. */
        pid_t           mrb_pid;
        /** The thread ID of the thread owning this txn. */
        pthread_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 will also be used on
         *      MacOSX/Darwin (using named semaphores) since MacOSX doesn't support
         *      process-shared POSIX mutexes.
         */
typedef struct MDB_txbody {
                /** Stamp identifying this as an MDB lock file. It must be set
                 *      to #MDB_MAGIC. */
        uint32_t        mtb_magic;
                /** Version number of this lock file. Must be set to #MDB_VERSION. */
        uint32_t        mtb_version;
#ifdef _WIN32
        char    mtb_rmname[32];
#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;
                /**     The ID of the most recent meta page in the database.
                 *      This is recorded here only for convenience; the value can always
                 *      be determined by reading the main database meta pages.
                 */
        uint32_t        mtb_me_toggle;
} MDB_txbody;

        /** The actual reader table definition. */
typedef struct MDB_txninfo {
        union {
                MDB_txbody mtb;
#define mti_magic       mt1.mtb.mtb_magic
#define mti_version     mt1.mtb.mtb_version
#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
#define mti_me_toggle   mt1.mtb.mtb_me_toggle
                char pad[(sizeof(MDB_txbody)+CACHELINE-1) & ~(CACHELINE-1)];
        } mt1;
        union {
#ifdef _WIN32
                char mt2_wmname[32];
#define mti_wmname      mt2.mt2_wmname
#else
                pthread_mutex_t mt2_wmutex;
#define mti_wmutex      mt2.mt2_wmutex
#endif
                char pad[(sizeof(pthread_mutex_t)+CACHELINE-1) & ~(CACHELINE-1)];
        } mt2;
        MDB_reader      mti_readers[1];
} MDB_txninfo;
/** @} */

/** 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 */
                void *          p_next; /**< for in-memory list of freed structs */
        } mp_p;
/**     @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 */
#define P_LEAF2          0x20           /**< for #MDB_DUPFIXED records */
/** @} */
        uint32_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))

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

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

        /** Header for a single key/data pair within a page.
         * We guarantee 2-byte alignment for nodes.
         */
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.
         */
#define mn_lo mn_offset[__BYTE_ORDER!=__LITTLE_ENDIAN]
#define mn_hi mn_offset[__BYTE_ORDER==__LITTLE_ENDIAN] /**< part of dsize or pgno */
        unsigned short  mn_offset[2];   /**< storage for #mn_lo and #mn_hi */
/** @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 */
/** @} */
        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]))

        /** 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)

        /** 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 key, if requested. */
#define MDB_SET_KEY(node, key)  { if ((key) != NULL) { \
        (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_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;

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

        /** Identify a data item as a valid sub-DB record */
#define MDB_SUBDATA     0x8200

        /** Meta page content. */
typedef struct MDB_meta {
                /** Stamp identifying this as an MDB data file. It must be set
                 *      to #MDB_MAGIC. */
        uint32_t        mm_magic;
                /** Version number of this lock file. Must be set to #MDB_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;

        /** Auxiliary DB info.
         *      The information here is mostly static/read-only. There is
         *      only a single copy of this record in the environment.
         *      The \b md_dirty flag is not read-only, but only a write
         *      transaction can ever update it, and only write transactions
         *      need to worry about it.
         */
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_dbi md_parent;                      /**< parent DB of a sub-DB */
        unsigned int    md_dirty;       /**< TRUE if DB was written in this txn */
} MDB_dbx;

        /** A database transaction.
         *      Every operation requires a transaction handle.
         */
struct MDB_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.
         *      This is an #IDL.
         */
        pgno_t          *mt_free_pgs;
        union {
                ID2L    dirty_list;     /**< modified pages */
                MDB_reader      *reader;        /**< this thread's slot in the reader table */
        } 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;
        /**     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;

#define MDB_TXN_RDONLY          0x01            /**< read-only transaction */
#define MDB_TXN_ERROR           0x02            /**< an error has occurred */
        unsigned int    mt_flags;
        /** Tracks which of the two meta pages was used at the start
         *      of this transaction.
         */
        unsigned int    mt_toggle;
};

/** 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 */
struct MDB_cursor {
        /** 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;
        unsigned short  mc_snum;        /**< number of pushed pages */
        unsigned short  mc_top;         /**< index of top page, 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 */
/** @} */
        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;
} MDB_xcursor;

        /** A set of pages freed by an earlier transaction. */
typedef struct MDB_oldpages {
        /** Usually we only read one record from the FREEDB at a time, but
         *      in case we read more, this will chain them together.
         */
        struct MDB_oldpages *mo_next;
        /**     The ID of the transaction in which these pages were freed. */
        txnid_t         mo_txnid;
        /** An #IDL of the pages */
        pgno_t          mo_pages[1];    /* dynamic */
} MDB_oldpages;

        /** 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
        uint32_t        me_flags;               /**< @ref mdb_env */
        uint32_t        me_extrapad;    /**< unused for now */
        unsigned int    me_maxreaders;  /**< size of the reader table */
        MDB_dbi         me_numdbs;              /**< number of DBs opened */
        MDB_dbi         me_maxdbs;              /**< size of the DB table */
        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 */
        MDB_meta        *me_metas[2];   /**< pointers to the two meta pages */
        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 */
        unsigned int    me_psize;       /**< size of a page, from #GET_PAGESIZE */
        unsigned int    me_db_toggle;   /**< which DB table is current */
        MDB_dbx         *me_dbxs;               /**< array of static DB info */
        MDB_db          *me_dbs[2];             /**< two arrays of MDB_db info */
        MDB_oldpages *me_pghead;        /**< list of old page records */
        pthread_key_t   me_txkey;       /**< thread-key for readers */
        MDB_page        *me_dpages;             /**< list of malloc'd blocks for re-use */
        /** IDL of pages that became unused in a write txn */
        pgno_t          me_free_pgs[MDB_IDL_UM_SIZE];
        /** ID2L of pages that were written during a write txn */
        ID2                     me_dirty_list[MDB_IDL_UM_SIZE];
        /** rwlock for the DB tables, if #LAZY_LOCKS is false */
        LAZY_RWLOCK_DEF(me_dblock)
#ifdef _WIN32
        HANDLE          me_rmutex;              /* Windows mutexes don't reside in shared mem */
        HANDLE          me_wmutex;
#endif
};
        /** max number of pages to commit in one writev() call */
#define MDB_COMMIT_PAGES         64

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

static int  mdb_page_get(MDB_txn *txn, pgno_t pgno, MDB_page **mp);
static int  mdb_page_search_root(MDB_cursor *mc,
                            MDB_val *key, int modify);
static int  mdb_page_search(MDB_cursor *mc,
                            MDB_val *key, int modify);
static int      mdb_page_merge(MDB_cursor *csrc, MDB_cursor *cdst);
static int      mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata,
                                pgno_t newpgno);

static int  mdb_env_read_header(MDB_env *env, MDB_meta *meta);
static int  mdb_env_read_meta(MDB_env *env, int *which);
static int  mdb_env_write_meta(MDB_txn *txn);

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, uint8_t flags);
static void mdb_node_del(MDB_page *mp, indx_t indx, int ksize);
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_page *mp, indx_t indx, 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, MDB_node *leaf);
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 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 MDB @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"
};

char *
mdb_strerror(int err)
{
        if (!err)
                return ("Successful return: 0");

        if (err >= MDB_KEYEXIST && err <= MDB_VERSION_MISMATCH)
                return mdb_errstr[err - MDB_KEYEXIST];

        return strerror(err);
}

#if DEBUG
/** 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->mv_size > MAXKEYSIZE)
                return "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
        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;
}
#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)
{
        if (txn->mt_dbxs[dbi].md_dcmp)
                return txn->mt_dbxs[dbi].md_dcmp(a, b);
        else
                return EINVAL;  /* too bad you can't distinguish this from a valid result */
}

/** Allocate pages for writing.
 * If there are free pages available from older transactions, they
 * will be re-used first. Otherwise a new page will be allocated.
 * @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.
 * @return Address of the allocated page(s). Requests for multiple pages
 *  will always be satisfied by a single contiguous chunk of memory.
 */
static MDB_page *
mdb_page_alloc(MDB_cursor *mc, int num)
{
        MDB_txn *txn = mc->mc_txn;
        MDB_page *np;
        pgno_t pgno = P_INVALID;
        ID2 mid;

        if (txn->mt_txnid > 2) {

                if (!txn->mt_env->me_pghead && mc->mc_dbi != FREE_DBI &&
                        txn->mt_dbs[FREE_DBI].md_root != P_INVALID) {
                        /* See if there's anything in the free DB */
                        MDB_cursor m2;
                        MDB_node *leaf;
                        txnid_t *kptr, oldest;

                        mdb_cursor_init(&m2, txn, FREE_DBI, NULL);
                        mdb_page_search(&m2, NULL, 0);
                        leaf = NODEPTR(m2.mc_pg[m2.mc_top], 0);
                        kptr = (txnid_t *)NODEKEY(leaf);

                        {
                                unsigned int i;
                                oldest = txn->mt_txnid - 1;
                                for (i=0; i<txn->mt_env->me_txns->mti_numreaders; i++) {
                                        txnid_t mr = txn->mt_env->me_txns->mti_readers[i].mr_txnid;
                                        if (mr && mr < oldest)
                                                oldest = mr;
                                }
                        }

                        if (oldest > *kptr) {
                                /* It's usable, grab it.
                                 */
                                MDB_oldpages *mop;
                                MDB_val data;
                                pgno_t *idl;

                                mdb_node_read(txn, leaf, &data);
                                idl = (ID *) data.mv_data;
                                mop = malloc(sizeof(MDB_oldpages) + MDB_IDL_SIZEOF(idl) - sizeof(pgno_t));
                                mop->mo_next = txn->mt_env->me_pghead;
                                mop->mo_txnid = *kptr;
                                txn->mt_env->me_pghead = mop;
                                memcpy(mop->mo_pages, idl, MDB_IDL_SIZEOF(idl));

#if DEBUG > 1
                                {
                                        unsigned int i;
                                        DPRINTF("IDL read txn %zu root %zu num %zu",
                                                mop->mo_txnid, txn->mt_dbs[FREE_DBI].md_root, idl[0]);
                                        for (i=0; i<idl[0]; i++) {
                                                DPRINTF("IDL %zu", idl[i+1]);
                                        }
                                }
#endif
                                /* drop this IDL from the DB */
                                m2.mc_ki[m2.mc_top] = 0;
                                m2.mc_flags = C_INITIALIZED;
                                mdb_cursor_del(&m2, 0);
                        }
                }
                if (txn->mt_env->me_pghead) {
                        MDB_oldpages *mop = txn->mt_env->me_pghead;
                        if (num > 1) {
                                /* FIXME: For now, always use fresh pages. We
                                 * really ought to search the free list for a
                                 * contiguous range.
                                 */
                                ;
                        } else {
                                /* peel pages off tail, so we only have to truncate the list */
                                pgno = MDB_IDL_LAST(mop->mo_pages);
                                if (MDB_IDL_IS_RANGE(mop->mo_pages)) {
                                        mop->mo_pages[2]++;
                                        if (mop->mo_pages[2] > mop->mo_pages[1])
                                                mop->mo_pages[0] = 0;
                                } else {
                                        mop->mo_pages[0]--;
                                }
                                if (MDB_IDL_IS_ZERO(mop->mo_pages)) {
                                        txn->mt_env->me_pghead = mop->mo_next;
                                        free(mop);
                                }
                        }
                }
        }

        if (pgno == P_INVALID) {
                /* DB size is maxed out */
                if (txn->mt_next_pgno + num >= txn->mt_env->me_maxpg) {
                        assert(txn->mt_next_pgno + num < txn->mt_env->me_maxpg);
                        return NULL;
                }
        }
        if (txn->mt_env->me_dpages && num == 1) {
                np = txn->mt_env->me_dpages;
                txn->mt_env->me_dpages = np->mp_next;
        } else {
                if ((np = malloc(txn->mt_env->me_psize * num )) == NULL)
                        return NULL;
        }
        if (pgno == P_INVALID) {
                np->mp_pgno = txn->mt_next_pgno;
                txn->mt_next_pgno += num;
        } else {
                np->mp_pgno = pgno;
        }
        mid.mid = np->mp_pgno;
        mid.mptr = np;
        mdb_mid2l_insert(txn->mt_u.dirty_list, &mid);

        return np;
}

/** 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];
        pgno_t  pgno;

        if (!F_ISSET(mp->mp_flags, P_DIRTY)) {
                MDB_page *np;
                if ((np = mdb_page_alloc(mc, 1)) == NULL)
                        return ENOMEM;
                DPRINTF("touched db %u page %zu -> %zu", mc->mc_dbi, mp->mp_pgno, np->mp_pgno);
                assert(mp->mp_pgno != np->mp_pgno);
                mdb_midl_append(mc->mc_txn->mt_free_pgs, mp->mp_pgno);
                pgno = np->mp_pgno;
                memcpy(np, mp, mc->mc_txn->mt_env->me_psize);
                mp = np;
                mp->mp_pgno = pgno;
                mp->mp_flags |= P_DIRTY;

                mc->mc_pg[mc->mc_top] = mp;
                /** If this page has a parent, update the parent to point to
                 * this new page.
                 */
                if (mc->mc_top)
                        SETPGNO(NODEPTR(mc->mc_pg[mc->mc_top-1], mc->mc_ki[mc->mc_top-1]), mp->mp_pgno);
        }
        return 0;
}

int
mdb_env_sync(MDB_env *env, int force)
{
        int rc = 0;
        if (force || !F_ISSET(env->me_flags, MDB_NOSYNC)) {
                if (fdatasync(env->me_fd))
                        rc = ErrCode();
        }
        return rc;
}

static inline void
mdb_txn_reset0(MDB_txn *txn);

/** 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. This can only
 * fail for read-only transactions, and then only if the
 * reader table is full.
 */
static inline int
mdb_txn_renew0(MDB_txn *txn)
{
        MDB_env *env = txn->mt_env;

        if (txn->mt_flags & MDB_TXN_RDONLY) {
                MDB_reader *r = pthread_getspecific(env->me_txkey);
                if (!r) {
                        unsigned int i;
                        pid_t pid = getpid();
                        pthread_t tid = pthread_self();

                        LOCK_MUTEX_R(env);
                        for (i=0; i<env->me_txns->mti_numreaders; i++)
                                if (env->me_txns->mti_readers[i].mr_pid == 0)
                                        break;
                        if (i == env->me_maxreaders) {
                                UNLOCK_MUTEX_R(env);
                                return ENOMEM;
                        }
                        env->me_txns->mti_readers[i].mr_pid = pid;
                        env->me_txns->mti_readers[i].mr_tid = tid;
                        if (i >= env->me_txns->mti_numreaders)
                                env->me_txns->mti_numreaders = i+1;
                        UNLOCK_MUTEX_R(env);
                        r = &env->me_txns->mti_readers[i];
                        pthread_setspecific(env->me_txkey, r);
                }
                txn->mt_txnid = env->me_txns->mti_txnid;
                txn->mt_toggle = env->me_txns->mti_me_toggle;
                r->mr_txnid = txn->mt_txnid;
                txn->mt_u.reader = r;
        } else {
                LOCK_MUTEX_W(env);

                txn->mt_txnid = env->me_txns->mti_txnid+1;
                txn->mt_toggle = env->me_txns->mti_me_toggle;
                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_next_pgno = env->me_metas[txn->mt_toggle]->mm_last_pg+1;
                env->me_txn = txn;
        }

        /* Copy the DB arrays */
        LAZY_RWLOCK_RDLOCK(&env->me_dblock);
        txn->mt_numdbs = env->me_numdbs;
        txn->mt_dbxs = env->me_dbxs;    /* mostly static anyway */
        memcpy(txn->mt_dbs, env->me_metas[txn->mt_toggle]->mm_dbs, 2 * sizeof(MDB_db));
        if (txn->mt_numdbs > 2)
                memcpy(txn->mt_dbs+2, env->me_dbs[env->me_db_toggle]+2,
                        (txn->mt_numdbs - 2) * sizeof(MDB_db));
        LAZY_RWLOCK_UNLOCK(&env->me_dblock);

        return MDB_SUCCESS;
}

int
mdb_txn_renew(MDB_txn *txn)
{
        int rc;

        if (!txn)
                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 %zu%c %p on mdbenv %p, root page %zu",
                        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, unsigned int flags, MDB_txn **ret)
{
        MDB_txn *txn;
        int rc;

        if (env->me_flags & MDB_FATAL_ERROR) {
                DPUTS("environment had fatal error, must shutdown!");
                return MDB_PANIC;
        }
        if ((txn = calloc(1, sizeof(MDB_txn) + env->me_maxdbs * sizeof(MDB_db))) == NULL) {
                DPRINTF("calloc: %s", strerror(ErrCode()));
                return ENOMEM;
        }
        txn->mt_dbs = (MDB_db *)(txn+1);
        if (flags & MDB_RDONLY) {
                txn->mt_flags |= MDB_TXN_RDONLY;
        }
        txn->mt_env = env;

        rc = mdb_txn_renew0(txn);
        if (rc)
                free(txn);
        else {
                *ret = txn;
                DPRINTF("begin txn %zu%c %p on mdbenv %p, root page %zu",
                        txn->mt_txnid, (txn->mt_flags & MDB_TXN_RDONLY) ? 'r' : 'w',
                        (void *) txn, (void *) env, txn->mt_dbs[MAIN_DBI].md_root);
        }

        return rc;
}

/** Common code for #mdb_txn_reset() and #mdb_txn_abort().
 * @param[in] txn the transaction handle to reset
 */
static inline void
mdb_txn_reset0(MDB_txn *txn)
{
        MDB_env *env = txn->mt_env;

        if (F_ISSET(txn->mt_flags, MDB_TXN_RDONLY)) {
                txn->mt_u.reader->mr_txnid = 0;
        } else {
                MDB_oldpages *mop;
                MDB_page *dp;
                MDB_dbi dbi;
                unsigned int i;

                /* return all dirty pages to dpage list */
                for (i=1; i<=txn->mt_u.dirty_list[0].mid; i++) {
                        dp = txn->mt_u.dirty_list[i].mptr;
                        if (!IS_OVERFLOW(dp) || dp->mp_pages == 1) {
                                dp->mp_next = txn->mt_env->me_dpages;
                                txn->mt_env->me_dpages = dp;
                        } else {
                                /* large pages just get freed directly */
                                free(dp);
                        }
                }

                while ((mop = txn->mt_env->me_pghead)) {
                        txn->mt_env->me_pghead = mop->mo_next;
                        free(mop);
                }

                env->me_txn = NULL;
                for (dbi=2; dbi<env->me_numdbs; dbi++)
                        env->me_dbxs[dbi].md_dirty = 0;
                /* The writer mutex was locked in mdb_txn_begin. */
                UNLOCK_MUTEX_W(env);
        }
}

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

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

        mdb_txn_reset0(txn);
}

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

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

        mdb_txn_reset0(txn);
        free(txn);
}

int
mdb_txn_commit(MDB_txn *txn)
{
        int              n, done;
        unsigned int i;
        ssize_t          rc;
        off_t            size;
        MDB_page        *dp;
        MDB_env *env;
        pgno_t  next;
        MDB_cursor mc;

        assert(txn != NULL);
        assert(txn->mt_env != NULL);

        env = txn->mt_env;

        if (F_ISSET(txn->mt_flags, MDB_TXN_RDONLY)) {
                mdb_txn_abort(txn);
                return MDB_SUCCESS;
        }

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

        if (F_ISSET(txn->mt_flags, MDB_TXN_ERROR)) {
                DPUTS("error flag is set, can't commit");
                mdb_txn_abort(txn);
                return EINVAL;
        }

        if (!txn->mt_u.dirty_list[0].mid)
                goto done;

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

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

        /* should only be one record now */
        if (env->me_pghead) {
                /* make sure first page of freeDB is touched and on freelist */
                mdb_page_search(&mc, NULL, 1);
        }
        /* save to free list */
        if (!MDB_IDL_IS_ZERO(txn->mt_free_pgs)) {
                MDB_val key, data;
                pgno_t i;

                /* make sure last page of freeDB is touched and on freelist */
                key.mv_size = MAXKEYSIZE+1;
                key.mv_data = NULL;
                mdb_page_search(&mc, &key, 1);

                mdb_midl_sort(txn->mt_free_pgs);
#if DEBUG > 1
                {
                        unsigned int i;
                        ID *idl = txn->mt_free_pgs;
                        DPRINTF("IDL write txn %zu root %zu num %zu",
                                txn->mt_txnid, txn->mt_dbs[FREE_DBI].md_root, idl[0]);
                        for (i=0; i<idl[0]; i++) {
                                DPRINTF("IDL %zu", idl[i+1]);
                        }
                }
#endif
                /* write to last page of freeDB */
                key.mv_size = sizeof(pgno_t);
                key.mv_data = &txn->mt_txnid;
                data.mv_data = txn->mt_free_pgs;
                /* The free list can still grow during this call,
                 * despite the pre-emptive touches above. So check
                 * and make sure the entire thing got written.
                 */
                do {
                        i = txn->mt_free_pgs[0];
                        data.mv_size = MDB_IDL_SIZEOF(txn->mt_free_pgs);
                        rc = mdb_cursor_put(&mc, &key, &data, 0);
                        if (rc) {
                                mdb_txn_abort(txn);
                                return rc;
                        }
                } while (i != txn->mt_free_pgs[0]);
        }
        /* should only be one record now */
        if (env->me_pghead) {
                MDB_val key, data;
                MDB_oldpages *mop;

                mop = env->me_pghead;
                key.mv_size = sizeof(pgno_t);
                key.mv_data = &mop->mo_txnid;
                data.mv_size = MDB_IDL_SIZEOF(mop->mo_pages);
                data.mv_data = mop->mo_pages;
                mdb_cursor_put(&mc, &key, &data, 0);
                free(env->me_pghead);
                env->me_pghead = NULL;
        }

        /* Update DB root pointers. Their pages have already been
         * touched so this is all in-place and cannot fail.
         */
        {
                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_dbxs[i].md_dirty) {
                                data.mv_data = &txn->mt_dbs[i];
                                mdb_cursor_put(&mc, &txn->mt_dbxs[i].md_name, &data, 0);
                        }
                }
        }

        /* Commit up to MDB_COMMIT_PAGES dirty pages to disk until done.
         */
        next = 0;
        i = 1;
        do {
#ifdef _WIN32
                /* 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.
                 */
                OVERLAPPED ov;
                memset(&ov, 0, sizeof(ov));
                for (; i<=txn->mt_u.dirty_list[0].mid; i++) {
                        size_t wsize;
                        dp = txn->mt_u.dirty_list[i].mptr;
                        DPRINTF("committing page %zu", dp->mp_pgno);
                        size = dp->mp_pgno * env->me_psize;
                        ov.Offset = size & 0xffffffff;
                        ov.OffsetHigh = size >> 16;
                        ov.OffsetHigh >>= 16;
                        /* clear dirty flag */
                        dp->mp_flags &= ~P_DIRTY;
                        wsize = env->me_psize;
                        if (IS_OVERFLOW(dp)) wsize *= dp->mp_pages;
                        rc = WriteFile(env->me_fd, dp, wsize, NULL, &ov);
                        if (!rc) {
                                n = ErrCode();
                                DPRINTF("WriteFile: %d", n);
                                mdb_txn_abort(txn);
                                return n;
                        }
                }
                done = 1;
#else
                struct iovec     iov[MDB_COMMIT_PAGES];
                n = 0;
                done = 1;
                size = 0;
                for (; i<=txn->mt_u.dirty_list[0].mid; i++) {
                        dp = txn->mt_u.dirty_list[i].mptr;
                        if (dp->mp_pgno != next) {
                                if (n) {
                                        DPRINTF("committing %u dirty pages", n);
                                        rc = writev(env->me_fd, iov, n);
                                        if (rc != size) {
                                                n = ErrCode();
                                                if (rc > 0)
                                                        DPUTS("short write, filesystem full?");
                                                else
                                                        DPRINTF("writev: %s", strerror(n));
                                                mdb_txn_abort(txn);
                                                return n;
                                        }
                                        n = 0;
                                        size = 0;
                                }
                                lseek(env->me_fd, dp->mp_pgno * env->me_psize, SEEK_SET);
                                next = dp->mp_pgno;
                        }
                        DPRINTF("committing page %zu", dp->mp_pgno);
                        iov[n].iov_len = env->me_psize;
                        if (IS_OVERFLOW(dp)) iov[n].iov_len *= dp->mp_pages;
                        iov[n].iov_base = dp;
                        size += iov[n].iov_len;
                        next = dp->mp_pgno + (IS_OVERFLOW(dp) ? dp->mp_pages : 1);
                        /* clear dirty flag */
                        dp->mp_flags &= ~P_DIRTY;
                        if (++n >= MDB_COMMIT_PAGES) {
                                done = 0;
                                i++;
                                break;
                        }
                }

                if (n == 0)
                        break;

                DPRINTF("committing %u dirty pages", n);
                rc = writev(env->me_fd, iov, n);
                if (rc != size) {
                        n = ErrCode();
                        if (rc > 0)
                                DPUTS("short write, filesystem full?");
                        else
                                DPRINTF("writev: %s", strerror(n));
                        mdb_txn_abort(txn);
                        return n;
                }
#endif
        } while (!done);

        /* Drop the dirty pages.
         */
        for (i=1; i<=txn->mt_u.dirty_list[0].mid; i++) {
                dp = txn->mt_u.dirty_list[i].mptr;
                if (!IS_OVERFLOW(dp) || dp->mp_pages == 1) {
                        dp->mp_next = txn->mt_env->me_dpages;
                        txn->mt_env->me_dpages = dp;
                } else {
                        free(dp);
                }
                txn->mt_u.dirty_list[i].mid = 0;
        }
        txn->mt_u.dirty_list[0].mid = 0;

        if ((n = mdb_env_sync(env, 0)) != 0 ||
            (n = mdb_env_write_meta(txn)) != MDB_SUCCESS) {
                mdb_txn_abort(txn);
                return n;
        }

done:
        env->me_txn = NULL;
        /* update the DB tables */
        {
                int toggle = !env->me_db_toggle;
                MDB_db *ip, *jp;
                MDB_dbi i;

                ip = &env->me_dbs[toggle][2];
                jp = &txn->mt_dbs[2];
                LAZY_RWLOCK_WRLOCK(&env->me_dblock);
                for (i = 2; i < txn->mt_numdbs; i++) {
                        if (ip->md_root != jp->md_root)
                                *ip = *jp;
                        ip++; jp++;
                }

                for (i = 2; i < txn->mt_numdbs; i++) {
                        if (txn->mt_dbxs[i].md_dirty)
                                txn->mt_dbxs[i].md_dirty = 0;
                }
                env->me_db_toggle = toggle;
                env->me_numdbs = txn->mt_numdbs;
                LAZY_RWLOCK_UNLOCK(&env->me_dblock);
        }

        UNLOCK_MUTEX_W(env);
        free(txn);

        return MDB_SUCCESS;
}

/** 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
mdb_env_read_header(MDB_env *env, MDB_meta *meta)
{
        char             page[PAGESIZE];
        MDB_page        *p;
        MDB_meta        *m;
        int              rc, err;

        /* We don't know the page size yet, so use a minimum value.
         */

#ifdef _WIN32
        if (!ReadFile(env->me_fd, page, PAGESIZE, (DWORD *)&rc, NULL) || rc == 0)
#else
        if ((rc = read(env->me_fd, page, PAGESIZE)) == 0)
#endif
        {
                return ENOENT;
        }
        else if (rc != PAGESIZE) {
                err = ErrCode();
                if (rc > 0)
                        err = EINVAL;
                DPRINTF("read: %s", strerror(err));
                return err;
        }

        p = (MDB_page *)page;

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

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

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

        memcpy(meta, m, sizeof(*m));
        return 0;
}

/** 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
mdb_env_init_meta(MDB_env *env, MDB_meta *meta)
{
        MDB_page *p, *q;
        MDB_meta *m;
        int rc;
        unsigned int     psize;

        DPUTS("writing new meta page");

        GET_PAGESIZE(psize);

        meta->mm_magic = MDB_MAGIC;
        meta->mm_version = MDB_VERSION;
        meta->mm_psize = 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;

        p = calloc(2, psize);
        p->mp_pgno = 0;
        p->mp_flags = P_META;

        m = METADATA(p);
        memcpy(m, meta, sizeof(*meta));

        q = (MDB_page *)((char *)p + psize);

        q->mp_pgno = 1;
        q->mp_flags = P_META;

        m = METADATA(q);
        memcpy(m, meta, sizeof(*meta));

#ifdef _WIN32
        {
                DWORD len;
                rc = WriteFile(env->me_fd, p, psize * 2, &len, NULL);
                rc = (len == psize * 2) ? MDB_SUCCESS : ErrCode();
        }
#else
        rc = write(env->me_fd, p, psize * 2);
        rc = (rc == (int)psize * 2) ? MDB_SUCCESS : ErrCode();
#endif
        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;
        off_t off;
        int rc, len, toggle;
        char *ptr;
#ifdef _WIN32
        OVERLAPPED ov;
#endif

        assert(txn != NULL);
        assert(txn->mt_env != NULL);

        toggle = !txn->mt_toggle;
        DPRINTF("writing meta page %d for root page %zu",
                toggle, txn->mt_dbs[MAIN_DBI].md_root);

        env = txn->mt_env;

        metab.mm_txnid = env->me_metas[toggle]->mm_txnid;
        metab.mm_last_pg = env->me_metas[toggle]->mm_last_pg;

        ptr = (char *)&meta;
        off = offsetof(MDB_meta, mm_dbs[0].md_depth);
        len = sizeof(MDB_meta) - off;

        ptr += off;
        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;

        if (toggle)
                off += env->me_psize;
        off += PAGEHDRSZ;

        /* Write to the SYNC fd */
#ifdef _WIN32
        {
                memset(&ov, 0, sizeof(ov));
                ov.Offset = off;
                WriteFile(env->me_mfd, ptr, len, (DWORD *)&rc, &ov);
        }
#else
        rc = pwrite(env->me_mfd, ptr, len, off);
#endif
        if (rc != len) {
                int r2;
                rc = ErrCode();
                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
                WriteFile(env->me_fd, ptr, len, NULL, &ov);
#else
                r2 = pwrite(env->me_fd, ptr, len, off);
#endif
                env->me_flags |= MDB_FATAL_ERROR;
                return rc;
        }
        /* 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.
         */
        LAZY_MUTEX_LOCK(&env->me_txns->mti_mutex);
        txn->mt_env->me_txns->mti_me_toggle = toggle;
        txn->mt_env->me_txns->mti_txnid = txn->mt_txnid;
        LAZY_MUTEX_UNLOCK(&env->me_txns->mti_mutex);

        return MDB_SUCCESS;
}

/** Check both meta pages to see which one is newer.
 * @param[in] env the environment handle
 * @param[out] which address of where to store the meta toggle ID
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_env_read_meta(MDB_env *env, int *which)
{
        int toggle = 0;

        assert(env != NULL);

        if (env->me_metas[0]->mm_txnid < env->me_metas[1]->mm_txnid)
                toggle = 1;

        DPRINTF("Using meta page %d", toggle);
        *which = toggle;

        return MDB_SUCCESS;
}

int
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 = 2;
        e->me_fd = INVALID_HANDLE_VALUE;
        e->me_lfd = INVALID_HANDLE_VALUE;
        e->me_mfd = INVALID_HANDLE_VALUE;
        *env = e;
        return MDB_SUCCESS;
}

int
mdb_env_set_mapsize(MDB_env *env, size_t size)
{
        if (env->me_map)
                return EINVAL;
        env->me_mapsize = size;
        return MDB_SUCCESS;
}

int
mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs)
{
        if (env->me_map)
                return EINVAL;
        env->me_maxdbs = dbs;
        return MDB_SUCCESS;
}

int
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
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 MDB environment
 */
static int
mdb_env_open2(MDB_env *env, unsigned int flags)
{
        int i, newenv = 0, toggle;
        MDB_meta meta;
        MDB_page *p;

        env->me_flags = flags;

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

        if ((i = mdb_env_read_header(env, &meta)) != 0) {
                if (i != ENOENT)
                        return i;
                DPUTS("new mdbenv");
                newenv = 1;
        }

        if (!env->me_mapsize) {
                env->me_mapsize = newenv ? DEFAULT_MAPSIZE : meta.mm_mapsize;
        }

#ifdef _WIN32
        {
                HANDLE mh;
                LONG sizelo, sizehi;
                sizelo = env->me_mapsize & 0xffffffff;
                sizehi = env->me_mapsize >> 16;         /* pointless on WIN32, only needed on W64 */
                sizehi >>= 16;
                /* Windows won't create mappings for zero length files.
                 * Just allocate the maxsize right now.
                 */
                if (newenv) {
                        SetFilePointer(env->me_fd, sizelo, sizehi ? &sizehi : NULL, 0);
                        if (!SetEndOfFile(env->me_fd))
                                return ErrCode();
                        SetFilePointer(env->me_fd, 0, NULL, 0);
                }
                mh = CreateFileMapping(env->me_fd, NULL, PAGE_READONLY,
                        sizehi, sizelo, NULL);
                if (!mh)
                        return ErrCode();
                env->me_map = MapViewOfFileEx(mh, FILE_MAP_READ, 0, 0, env->me_mapsize,
                        meta.mm_address);
                CloseHandle(mh);
                if (!env->me_map)
                        return ErrCode();
        }
#else
        i = MAP_SHARED;
        if (meta.mm_address && (flags & MDB_FIXEDMAP))
                i |= MAP_FIXED;
        env->me_map = mmap(meta.mm_address, env->me_mapsize, PROT_READ, i,
                env->me_fd, 0);
        if (env->me_map == MAP_FAILED)
                return ErrCode();
#endif

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

        env->me_maxpg = env->me_mapsize / env->me_psize;

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

        if ((i = mdb_env_read_meta(env, &toggle)) != 0)
                return i;

        DPRINTF("opened database version %u, pagesize %u",
            env->me_metas[toggle]->mm_version, env->me_psize);
        DPRINTF("depth: %u", env->me_metas[toggle]->mm_dbs[MAIN_DBI].md_depth);
        DPRINTF("entries: %zu", env->me_metas[toggle]->mm_dbs[MAIN_DBI].md_entries);
        DPRINTF("branch pages: %zu", env->me_metas[toggle]->mm_dbs[MAIN_DBI].md_branch_pages);
        DPRINTF("leaf pages: %zu", env->me_metas[toggle]->mm_dbs[MAIN_DBI].md_leaf_pages);
        DPRINTF("overflow pages: %zu", env->me_metas[toggle]->mm_dbs[MAIN_DBI].md_overflow_pages);
        DPRINTF("root: %zu", env->me_metas[toggle]->mm_dbs[MAIN_DBI].md_root);

        return MDB_SUCCESS;
}

#ifndef _WIN32
/** Release a reader thread's slot in the reader lock table.
 *      This function is called automatically when a thread exits.
 *      Windows doesn't support destructor callbacks for thread-specific storage,
 *      so this function is not compiled there.
 * @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_txnid = 0;
        reader->mr_pid = 0;
        reader->mr_tid = 0;
}
#endif

/** Downgrade the exclusive lock on the region back to shared */
static void
mdb_env_share_locks(MDB_env *env)
{
        int toggle = 0;

        if (env->me_metas[0]->mm_txnid < env->me_metas[1]->mm_txnid)
                toggle = 1;
        env->me_txns->mti_me_toggle = toggle;
        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));
                LockFileEx(env->me_lfd, 0, 0, 1, 0, &ov);
                UnlockFile(env->me_lfd, 0, 0, 1, 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;
                fcntl(env->me_lfd, F_SETLK, &lock_info);
        }
#endif
}

/** Open and/or initialize the lock region for the environment.
 * @param[in] env The MDB 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 Set to true if we got an exclusive lock on the region.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_env_setup_locks(MDB_env *env, char *lpath, int mode, int *excl)
{
        int rc;
        off_t size, rsize;

        *excl = 0;

#ifdef _WIN32
        if ((env->me_lfd = CreateFile(lpath, GENERIC_READ|GENERIC_WRITE,
                FILE_SHARE_READ|FILE_SHARE_WRITE, NULL, OPEN_ALWAYS,
                FILE_ATTRIBUTE_NORMAL, NULL)) == INVALID_HANDLE_VALUE) {
                rc = ErrCode();
                return rc;
        }
        /* Try to get exclusive lock. If we succeed, then
         * nobody is using the lock region and we should initialize it.
         */
        {
                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)) {
                                rc = ErrCode();
                                goto fail;
                        }
                }
        }
        size = GetFileSize(env->me_lfd, NULL);
#else
        if ((env->me_lfd = open(lpath, O_RDWR|O_CREAT, mode)) == -1) {
                rc = ErrCode();
                return rc;
        }
        /* Try to get exclusive lock. If we succeed, then
         * nobody is using the lock region and we should initialize it.
         */
        {
                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;
                rc = fcntl(env->me_lfd, F_SETLK, &lock_info);
                if (rc == 0) {
                        *excl = 1;
                } else {
                        lock_info.l_type = F_RDLCK;
                        rc = fcntl(env->me_lfd, F_SETLKW, &lock_info);
                        if (rc) {
                                rc = ErrCode();
                                goto fail;
                        }
                }
        }
        size = lseek(env->me_lfd, 0, SEEK_END);
#endif
        rsize = (env->me_maxreaders-1) * sizeof(MDB_reader) + sizeof(MDB_txninfo);
        if (size < rsize && *excl) {
#ifdef _WIN32
                SetFilePointer(env->me_lfd, rsize, NULL, 0);
                if (!SetEndOfFile(env->me_lfd)) {
                        rc = ErrCode();
                        goto fail;
                }
#else
                if (ftruncate(env->me_lfd, rsize) != 0) {
                        rc = ErrCode();
                        goto fail;
                }
#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) {
                        rc = ErrCode();
                        goto fail;
                }
                env->me_txns = MapViewOfFileEx(mh, FILE_MAP_WRITE, 0, 0, rsize, NULL);
                CloseHandle(mh);
                if (!env->me_txns) {
                        rc = ErrCode();
                        goto fail;
                }
        }
#else
        env->me_txns = mmap(0, rsize, PROT_READ|PROT_WRITE, MAP_SHARED,
                env->me_lfd, 0);
        if (env->me_txns == MAP_FAILED) {
                rc = ErrCode();
                goto fail;
        }
#endif
        if (*excl) {
#ifdef _WIN32
                char *ptr;
                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;
                }
                /* FIXME: only using up to 20 characters of the env path here,
                 * probably not enough to assure uniqueness...
                 */
                sprintf(env->me_txns->mti_rmname, "Global\\MDBr%.20s", lpath);
                ptr = env->me_txns->mti_rmname + sizeof("Global\\MDBr");
                while ((ptr = strchr(ptr, '\\')))
                        *ptr++ = '/';
                env->me_rmutex = CreateMutex(&mdb_all_sa, FALSE, env->me_txns->mti_rmname);
                if (!env->me_rmutex) {
                        rc = ErrCode();
                        goto fail;
                }
                sprintf(env->me_txns->mti_rmname, "Global\\MDBw%.20s", lpath);
                ptr = env->me_txns->mti_rmname + sizeof("Global\\MDBw");
                while ((ptr = strchr(ptr, '\\')))
                        *ptr++ = '/';
                env->me_wmutex = CreateMutex(&mdb_all_sa, FALSE, env->me_txns->mti_rmname);
                if (!env->me_wmutex) {
                        rc = ErrCode();
                        goto fail;
                }
#else
                pthread_mutexattr_t mattr;

                pthread_mutexattr_init(&mattr);
                rc = pthread_mutexattr_setpshared(&mattr, PTHREAD_PROCESS_SHARED);
                if (rc) {
                        goto fail;
                }
                pthread_mutex_init(&env->me_txns->mti_mutex, &mattr);
                pthread_mutex_init(&env->me_txns->mti_wmutex, &mattr);
#endif
                env->me_txns->mti_version = MDB_VERSION;
                env->me_txns->mti_magic = MDB_MAGIC;
                env->me_txns->mti_txnid = 0;
                env->me_txns->mti_numreaders = 0;
                env->me_txns->mti_me_toggle = 0;

        } else {
                if (env->me_txns->mti_magic != MDB_MAGIC) {
                        DPUTS("lock region has invalid magic");
                        rc = EINVAL;
                        goto fail;
                }
                if (env->me_txns->mti_version != MDB_VERSION) {
                        DPRINTF("lock region is version %u, expected version %u",
                                env->me_txns->mti_version, MDB_VERSION);
                        rc = MDB_VERSION_MISMATCH;
                        goto fail;
                }
                rc = ErrCode();
                if (rc != EACCES && rc != EAGAIN) {
                        goto fail;
                }
#ifdef _WIN32
                env->me_rmutex = OpenMutex(SYNCHRONIZE, FALSE, env->me_txns->mti_rmname);
                if (!env->me_rmutex) {
                        rc = ErrCode();
                        goto fail;
                }
                env->me_wmutex = OpenMutex(SYNCHRONIZE, FALSE, env->me_txns->mti_wmname);
                if (!env->me_wmutex) {
                        rc = ErrCode();
                        goto fail;
                }
#endif
        }
        return MDB_SUCCESS;

fail:
        close(env->me_lfd);
        env->me_lfd = INVALID_HANDLE_VALUE;
        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"
int
mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mode_t mode)
{
        int             oflags, rc, len, excl;
        char *lpath, *dpath;

        len = strlen(path);
        lpath = malloc(len + sizeof(LOCKNAME) + len + sizeof(DATANAME));
        if (!lpath)
                return ENOMEM;
        dpath = lpath + len + sizeof(LOCKNAME);
        sprintf(lpath, "%s" LOCKNAME, path);
        sprintf(dpath, "%s" DATANAME, path);

        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;
        if ((env->me_fd = CreateFile(dpath, oflags, FILE_SHARE_READ|FILE_SHARE_WRITE,
                        NULL, len, mode, NULL)) == INVALID_HANDLE_VALUE) {
                rc = ErrCode();
                goto leave;
        }
#else
        if (F_ISSET(flags, MDB_RDONLY))
                oflags = O_RDONLY;
        else
                oflags = O_RDWR | O_CREAT;

        if ((env->me_fd = open(dpath, oflags, mode)) == -1) {
                rc = ErrCode();
                goto leave;
        }
#endif

        if ((rc = mdb_env_open2(env, flags)) == MDB_SUCCESS) {
                /* synchronous fd for meta writes */
#ifdef _WIN32
                if (!(flags & (MDB_RDONLY|MDB_NOSYNC)))
                        mode |= FILE_FLAG_WRITE_THROUGH;
                if ((env->me_mfd = CreateFile(dpath, oflags, FILE_SHARE_READ|FILE_SHARE_WRITE,
                        NULL, len, mode, NULL)) == INVALID_HANDLE_VALUE) {
                        rc = ErrCode();
                        goto leave;
                }
#else
                if (!(flags & (MDB_RDONLY|MDB_NOSYNC)))
                        oflags |= MDB_DSYNC;
                if ((env->me_mfd = open(dpath, oflags, mode)) == -1) {
                        rc = ErrCode();
                        goto leave;
                }
#endif
                env->me_path = strdup(path);
                DPRINTF("opened dbenv %p", (void *) env);
                pthread_key_create(&env->me_txkey, mdb_env_reader_dest);
                LAZY_RWLOCK_INIT(&env->me_dblock, NULL);
                if (excl)
                        mdb_env_share_locks(env);
                env->me_dbxs = calloc(env->me_maxdbs, sizeof(MDB_dbx));
                env->me_dbs[0] = calloc(env->me_maxdbs, sizeof(MDB_db));
                env->me_dbs[1] = calloc(env->me_maxdbs, sizeof(MDB_db));
                env->me_numdbs = 2;
        }

leave:
        if (rc) {
                if (env->me_fd != INVALID_HANDLE_VALUE) {
                        close(env->me_fd);
                        env->me_fd = INVALID_HANDLE_VALUE;
                }
                if (env->me_lfd != INVALID_HANDLE_VALUE) {
                        close(env->me_lfd);
                        env->me_lfd = INVALID_HANDLE_VALUE;
                }
        }
        free(lpath);
        return rc;
}

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

        if (env == NULL)
                return;

        while (env->me_dpages) {
                dp = env->me_dpages;
                env->me_dpages = dp->mp_next;
                free(dp);
        }

        free(env->me_dbs[1]);
        free(env->me_dbs[0]);
        free(env->me_dbxs);
        free(env->me_path);

        LAZY_RWLOCK_DESTROY(&env->me_dblock);
        pthread_key_delete(env->me_txkey);

        if (env->me_map) {
                munmap(env->me_map, env->me_mapsize);
        }
        close(env->me_mfd);
        close(env->me_fd);
        if (env->me_txns) {
                pid_t pid = getpid();
                unsigned int i;
                for (i=0; i<env->me_txns->mti_numreaders; i++)
                        if (env->me_txns->mti_readers[i].mr_pid == pid)
                                env->me_txns->mti_readers[i].mr_pid = 0;
                munmap(env->me_txns, (env->me_maxreaders-1)*sizeof(MDB_reader)+sizeof(MDB_txninfo));
        }
        close(env->me_lfd);
        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 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 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
        return memcmp(a->mv_data, b->mv_data, a->mv_size);
#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 page %zu",
            nkeys, IS_LEAF(mp) ? "leaf" : "branch",
            mp->mp_pgno);

        assert(nkeys > 0);

        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 DEBUG
                        if (IS_LEAF(mp))
                                DPRINTF("found leaf index %u [%s], rc = %i",
                                    i, DKEY(&nodekey), rc);
                        else
                                DPRINTF("found branch index %u [%s -> %zu], 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);
        /* 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;
}

/** Pop a page off the top of the cursor's stack. */
static void
mdb_cursor_pop(MDB_cursor *mc)
{
        MDB_page        *top;

        if (mc->mc_snum) {
                top = mc->mc_pg[mc->mc_top];
                mc->mc_snum--;
                if (mc->mc_snum)
                        mc->mc_top--;

                DPRINTF("popped page %zu off db %u cursor %p", top->mp_pgno,
                        mc->mc_dbi, (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 %zu on db %u cursor %p", mp->mp_pgno,
                mc->mc_dbi, (void *) mc);

        if (mc->mc_snum >= CURSOR_STACK) {
                assert(mc->mc_snum < CURSOR_STACK);
                return ENOMEM;
        }

        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.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_get(MDB_txn *txn, pgno_t pgno, MDB_page **ret)
{
        MDB_page *p = NULL;

        if (!F_ISSET(txn->mt_flags, MDB_TXN_RDONLY) && txn->mt_u.dirty_list[0].mid) {
                unsigned x;
                x = mdb_mid2l_search(txn->mt_u.dirty_list, pgno);
                if (x <= txn->mt_u.dirty_list[0].mid && txn->mt_u.dirty_list[x].mid == pgno) {
                        p = txn->mt_u.dirty_list[x].mptr;
                }
        }
        if (!p) {
                if (pgno <= txn->mt_env->me_metas[txn->mt_toggle]->mm_last_pg)
                        p = (MDB_page *)(txn->mt_env->me_map + txn->mt_env->me_psize * pgno);
        }
        *ret = p;
        if (!p) {
                DPRINTF("page %zu not found", pgno);
                assert(p != NULL);
        }
        return (p != NULL) ? MDB_SUCCESS : MDB_PAGE_NOTFOUND;
}

/** Search for the page a given key should be in.
 * Pushes parent pages on the cursor stack. This function continues a
 * search on a cursor that has already been initialized. (Usually by
 * #mdb_page_search() but also by #mdb_node_move().)
 * @param[in,out] mc the cursor for this operation.
 * @param[in] key the key to search for. If NULL, search for the lowest
 * page. (This is used by #mdb_cursor_first().)
 * @param[in] modify If true, visited pages are updated with new page numbers.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_search_root(MDB_cursor *mc, MDB_val *key, int modify)
{
        MDB_page        *mp = mc->mc_pg[mc->mc_top];
        DKBUF;
        int rc;


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

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

                if (key == NULL)        /* Initialize cursor to first page. */
                        i = 0;
                else if (key->mv_size > MAXKEYSIZE && key->mv_data == NULL) {
                                                        /* cursor to last page */
                        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) {
                                        assert(i > 0);
                                        i--;
                                }
                        }
                }

                if (key)
                        DPRINTF("following index %u for key [%s]",
                            i, DKEY(key));
                assert(i < NUMKEYS(mp));
                node = NODEPTR(mp, i);

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

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

                if (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);
                return MDB_CORRUPTED;
        }

        DPRINTF("found leaf page %zu for key [%s]", mp->mp_pgno,
            key ? DKEY(key) : NULL);

        return MDB_SUCCESS;
}

/** Search for the page a given key should be in.
 * Pushes parent pages on the cursor stack. This function just sets up
 * the search; it finds the root page for \b mc's database and sets this
 * as the root of the cursor's stack. Then #mdb_page_search_root() is
 * called to complete the search.
 * @param[in,out] mc the cursor for this operation.
 * @param[in] key the key to search for. If NULL, search for the lowest
 * page. (This is used by #mdb_cursor_first().)
 * @param[in] modify If true, visited pages are updated with new page numbers.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_search(MDB_cursor *mc, MDB_val *key, int modify)
{
        int              rc;
        pgno_t           root;

        /* Make sure the txn is still viable, then find the root from
         * the txn's db table.
         */
        if (F_ISSET(mc->mc_txn->mt_flags, MDB_TXN_ERROR)) {
                DPUTS("transaction has failed, must abort");
                return EINVAL;
        } else
                root = mc->mc_db->md_root;

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

        if ((rc = mdb_page_get(mc->mc_txn, root, &mc->mc_pg[0])))
                return rc;

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

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

        if (modify) {
                /* For sub-databases, update main root first */
                if (mc->mc_dbi > MAIN_DBI && !mc->mc_dbx->md_dirty) {
                        MDB_cursor mc2;
                        mdb_cursor_init(&mc2, mc->mc_txn, MAIN_DBI, NULL);
                        rc = mdb_page_search(&mc2, &mc->mc_dbx->md_name, 1);
                        if (rc)
                                return rc;
                        mc->mc_dbx->md_dirty = 1;
                }
                if (!F_ISSET(mc->mc_pg[0]->mp_flags, P_DIRTY)) {
                        if ((rc = mdb_page_touch(mc)))
                                return rc;
                        mc->mc_db->md_root = mc->mc_pg[0]->mp_pgno;
                }
        }

        return mdb_page_search_root(mc, key, modify);
}

/** 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))) {
                DPRINTF("read overflow page %zu 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;

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

        if (txn == NULL || !dbi || dbi >= txn->mt_numdbs)
                return EINVAL;

        if (key->mv_size == 0 || key->mv_size > MAXKEYSIZE) {
                return EINVAL;
        }

        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 %zu, 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)
                        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]);
        }
        assert(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)))
                return rc;;

        mdb_cursor_push(mc, mp);

        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;
        }

        assert(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_SUCCESS)
                                        return rc;
                        }
                } else {
                        mc->mc_xcursor->mx_cursor.mc_flags = 0;
                        if (op == MDB_NEXT_DUP)
                                return MDB_NOTFOUND;
                }
        }

        DPRINTF("cursor_next: top page is %zu in cursor %p", mp->mp_pgno, (void *) mc);

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

        DPRINTF("==> cursor points to page %zu with %u keys, key index %u",
            mp->mp_pgno, 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;
        }

        assert(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_SET_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;

        assert(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 (op == MDB_PREV || op == MDB_PREV_DUP) {
                        if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                                rc = mdb_cursor_prev(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_PREV);
                                if (op != MDB_PREV || rc == MDB_SUCCESS)
                                        return rc;
                        } else {
                                mc->mc_xcursor->mx_cursor.mc_flags = 0;
                                if (op == MDB_PREV_DUP)
                                        return MDB_NOTFOUND;
                        }
                }
        }

        DPRINTF("cursor_prev: top page is %zu in cursor %p", mp->mp_pgno, (void *) mc);

        if (mc->mc_ki[mc->mc_top] == 0)  {
                DPUTS("=====> move to prev sibling page");
                if (mdb_cursor_sibling(mc, 0) != MDB_SUCCESS) {
                        mc->mc_flags &= ~C_INITIALIZED;
                        return MDB_NOTFOUND;
                }
                mp = mc->mc_pg[mc->mc_top];
                mc->mc_ki[mc->mc_top] = NUMKEYS(mp) - 1;
                DPRINTF("prev page is %zu, 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 %zu with %u keys, key index %u",
            mp->mp_pgno, 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;
        }

        assert(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_SET_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;
        DKBUF;

        assert(mc);
        assert(key);
        assert(key->mv_size > 0);

        /* 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 (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_SET_KEY(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;
                        leaf = NODEPTR(mp, 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_SET_KEY(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;
                                        leaf = NODEPTR(mp, nkeys-1);
                                        if (exactp)
                                                *exactp = 1;
                                        goto set1;
                                }
                                if (rc < 0) {
                                        /* This is definitely the right page, skip search_page */
                                        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;
                        }
                }
        }

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

        mp = mc->mc_pg[mc->mc_top];
        assert(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];
                assert(IS_LEAF(mp));
                leaf = NODEPTR(mp, 0);
        }

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

        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;
        }

        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_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;
                        }

                } else {
                        if (mc->mc_xcursor)
                                mc->mc_xcursor->mx_cursor.mc_flags = 0;
                        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)
                MDB_SET_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;

        rc = mdb_page_search(mc, NULL, 0);
        if (rc != MDB_SUCCESS)
                return rc;
        assert(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 (mc->mc_xcursor)
                                mc->mc_xcursor->mx_cursor.mc_flags = 0;
                        if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
                                return rc;
                }
        }
        MDB_SET_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;
        MDB_val lkey;

        lkey.mv_size = MAXKEYSIZE+1;
        lkey.mv_data = NULL;

        rc = mdb_page_search(mc, &lkey, 0);
        if (rc != MDB_SUCCESS)
                return rc;
        assert(IS_LEAF(mc->mc_pg[mc->mc_top]));

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

        mc->mc_ki[mc->mc_top] = NUMKEYS(mc->mc_pg[mc->mc_top]) - 1;

        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 (mc->mc_xcursor)
                                mc->mc_xcursor->mx_cursor.mc_flags = 0;
                        if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
                                return rc;
                }
        }

        MDB_SET_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;

        assert(mc);

        switch (op) {
        case MDB_GET_BOTH:
        case MDB_GET_BOTH_RANGE:
                if (data == NULL || mc->mc_xcursor == NULL) {
                        rc = EINVAL;
                        break;
                }
                /* FALLTHRU */
        case MDB_SET:
        case MDB_SET_RANGE:
                if (key == NULL || key->mv_size == 0 || key->mv_size > MAXKEYSIZE) {
                        rc = EINVAL;
                } else if (op == MDB_SET_RANGE)
                        rc = mdb_cursor_set(mc, key, data, op, NULL);
                else
                        rc = mdb_cursor_set(mc, key, data, op, &exact);
                break;
        case MDB_GET_MULTIPLE:
                if (data == NULL ||
                        !(mc->mc_db->md_flags & MDB_DUPFIXED) ||
                        !(mc->mc_flags & C_INITIALIZED)) {
                        rc = EINVAL;
                        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 ||
                        !(mc->mc_db->md_flags & MDB_DUPFIXED)) {
                        rc = EINVAL;
                        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) || (mc->mc_flags & C_EOF))
                        rc = mdb_cursor_last(mc, key, data);
                else
                        rc = mdb_cursor_prev(mc, key, data, op);
                break;
        case MDB_FIRST:
                rc = mdb_cursor_first(mc, key, data);
                break;
        case MDB_FIRST_DUP:
                if (data == NULL ||
                        !(mc->mc_db->md_flags & MDB_DUPSORT) ||
                        !(mc->mc_flags & C_INITIALIZED) ||
                        !(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED)) {
                        rc = EINVAL;
                        break;
                }
                rc = mdb_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
                break;
        case MDB_LAST:
                rc = mdb_cursor_last(mc, key, data);
                break;
        case MDB_LAST_DUP:
                if (data == NULL ||
                        !(mc->mc_db->md_flags & MDB_DUPSORT) ||
                        !(mc->mc_flags & C_INITIALIZED) ||
                        !(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED)) {
                        rc = EINVAL;
                        break;
                }
                rc = mdb_cursor_last(&mc->mc_xcursor->mx_cursor, data, NULL);
                break;
        default:
                DPRINTF("unhandled/unimplemented cursor operation %u", op);
                rc = EINVAL;
                break;
        }

        return rc;
}

/** Touch all the pages in the cursor stack.
 *      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;

        if (mc->mc_dbi > MAIN_DBI && !mc->mc_dbx->md_dirty) {
                MDB_cursor mc2;
                mdb_cursor_init(&mc2, mc->mc_txn, MAIN_DBI, NULL);
                rc = mdb_page_search(&mc2, &mc->mc_dbx->md_name, 1);
                if (rc)
                         return rc;
                mc->mc_dbx->md_dirty = 1;
        }
        for (mc->mc_top = 0; mc->mc_top < mc->mc_snum; mc->mc_top++) {
                if (!F_ISSET(mc->mc_pg[mc->mc_top]->mp_flags, P_DIRTY)) {
                        rc = mdb_page_touch(mc);
                        if (rc)
                                return rc;
                        if (!mc->mc_top) {
                                mc->mc_db->md_root =
                                        mc->mc_pg[mc->mc_top]->mp_pgno;
                        }
                }
        }
        mc->mc_top = mc->mc_snum-1;
        return MDB_SUCCESS;
}

int
mdb_cursor_put(MDB_cursor *mc, MDB_val *key, MDB_val *data,
    unsigned int flags)
{
        MDB_node        *leaf;
        MDB_val xdata, *rdata, dkey;
        MDB_db dummy;
        char dbuf[PAGESIZE];
        int do_sub = 0;
        size_t nsize;
        DKBUF;
        int rc, rc2;

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

        DPRINTF("==> put db %u key [%s], size %zu, data size %zu",
                mc->mc_dbi, DKEY(key), key->mv_size, 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) {
                MDB_page *np;
                /* new database, write a root leaf page */
                DPUTS("allocating new root leaf page");
                if ((np = mdb_page_new(mc, P_LEAF, 1)) == NULL) {
                        return ENOMEM;
                }
                mc->mc_snum = 0;
                mdb_cursor_push(mc, np);
                mc->mc_db->md_root = np->mp_pgno;
                mc->mc_db->md_depth++;
                mc->mc_dbx->md_dirty = 1;
                if ((mc->mc_db->md_flags & (MDB_DUPSORT|MDB_DUPFIXED))
                        == MDB_DUPFIXED)
                        np->mp_flags |= P_LEAF2;
                mc->mc_flags |= C_INITIALIZED;
                rc = MDB_NOTFOUND;
                goto top;
        } else {
                int exact = 0;
                MDB_val d2;
                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;
        }

        /* Cursor is positioned, now make sure all pages are writable */
        rc2 = mdb_cursor_touch(mc);
        if (rc2)
                return rc2;

top:
        /* The key already exists */
        if (rc == MDB_SUCCESS) {
                /* there's only a key anyway, so this is a no-op */
                if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
                        unsigned int ksize = mc->mc_db->md_pad;
                        if (key->mv_size != ksize)
                                return EINVAL;
                        if (flags == MDB_CURRENT) {
                                char *ptr = LEAF2KEY(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], ksize);
                                memcpy(ptr, key->mv_data, ksize);
                        }
                        return MDB_SUCCESS;
                }

                leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);

                /* DB has dups? */
                if (F_ISSET(mc->mc_db->md_flags, MDB_DUPSORT)) {
                        /* Was a single item before, must convert now */
                        if (!F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                                dkey.mv_size = NODEDSZ(leaf);
                                dkey.mv_data = dbuf;
                                memcpy(dbuf, NODEDATA(leaf), dkey.mv_size);
                                /* data matches, ignore it */
                                if (!mc->mc_dbx->md_dcmp(data, &dkey))
                                        return (flags == MDB_NODUPDATA) ? MDB_KEYEXIST : MDB_SUCCESS;
                                memset(&dummy, 0, sizeof(dummy));
                                if (mc->mc_db->md_flags & MDB_DUPFIXED) {
                                        dummy.md_pad = data->mv_size;
                                        dummy.md_flags = MDB_DUPFIXED;
                                        if (mc->mc_db->md_flags & MDB_INTEGERDUP)
                                                dummy.md_flags |= MDB_INTEGERKEY;
                                }
                                dummy.md_flags |= MDB_SUBDATA;
                                dummy.md_root = P_INVALID;
                                if (dkey.mv_size == sizeof(MDB_db)) {
                                        memcpy(NODEDATA(leaf), &dummy, sizeof(dummy));
                                        goto put_sub;
                                }
                                mdb_node_del(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], 0);
                                do_sub = 1;
                                rdata = &xdata;
                                xdata.mv_size = sizeof(MDB_db);
                                xdata.mv_data = &dummy;
                                /* new sub-DB, must fully init xcursor */
                                if (flags == MDB_CURRENT)
                                        flags = 0;
                                goto new_sub;
                        }
                        goto put_sub;
                }
                /* same size, just replace it */
                if (!F_ISSET(leaf->mn_flags, F_BIGDATA) &&
                        NODEDSZ(leaf) == data->mv_size) {
                        memcpy(NODEDATA(leaf), data->mv_data, data->mv_size);
                        goto done;
                }
                mdb_node_del(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], 0);
        } else {
                DPRINTF("inserting key at index %i", mc->mc_ki[mc->mc_top]);
        }

        rdata = data;

new_sub:
        nsize = IS_LEAF2(mc->mc_pg[mc->mc_top]) ? key->mv_size : mdb_leaf_size(mc->mc_txn->mt_env, key, rdata);
        if (SIZELEFT(mc->mc_pg[mc->mc_top]) < nsize) {
                rc = mdb_page_split(mc, key, rdata, P_INVALID);
        } else {
                /* There is room already in this leaf page. */
                rc = mdb_node_add(mc, mc->mc_ki[mc->mc_top], key, rdata, 0, 0);
        }

        if (rc != MDB_SUCCESS)
                mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
        else {
                /* Remember if we just added a subdatabase */
                if (flags & F_SUBDATA) {
                        leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
                        leaf->mn_flags |= F_SUBDATA;
                }

                /* 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) {
                        MDB_db *db;
                        leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
put_sub:
                        if (flags != MDB_CURRENT)
                                mdb_xcursor_init1(mc, leaf);
                        xdata.mv_size = 0;
                        xdata.mv_data = "";
                        if (flags == MDB_NODUPDATA)
                                flags = MDB_NOOVERWRITE;
                        /* converted, write the original data first */
                        if (dkey.mv_size) {
                                rc = mdb_cursor_put(&mc->mc_xcursor->mx_cursor, &dkey, &xdata, flags);
                                if (rc)
                                        return rc;
                                leaf->mn_flags |= F_DUPDATA;
                        }
                        rc = mdb_cursor_put(&mc->mc_xcursor->mx_cursor, data, &xdata, flags);
                        db = NODEDATA(leaf);
                        assert((db->md_flags & MDB_SUBDATA) == MDB_SUBDATA);
                        memcpy(db, &mc->mc_xcursor->mx_db, sizeof(MDB_db));
                }
                mc->mc_db->md_entries++;
        }
done:
        return rc;
}

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

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

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

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

        leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);

        if (!IS_LEAF2(mc->mc_pg[mc->mc_top]) && F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                if (flags != MDB_NODUPDATA) {
                        rc = mdb_cursor_del(&mc->mc_xcursor->mx_cursor, 0);
                        /* If sub-DB still has entries, we're done */
                        if (mc->mc_xcursor->mx_db.md_root != P_INVALID) {
                                MDB_db *db = NODEDATA(leaf);
                                assert((db->md_flags & MDB_SUBDATA) == MDB_SUBDATA);
                                memcpy(db, &mc->mc_xcursor->mx_db, sizeof(MDB_db));
                                mc->mc_db->md_entries--;
                                return rc;
                        }
                        /* otherwise fall thru and delete the sub-DB */
                }

                /* add all the child DB's pages to the free list */
                rc = mdb_page_search(&mc->mc_xcursor->mx_cursor, NULL, 0);
                if (rc == MDB_SUCCESS) {
                        MDB_node *ni;
                        MDB_cursor *mx;
                        unsigned int i;

                        mx = &mc->mc_xcursor->mx_cursor;
                        mc->mc_db->md_entries -=
                                mx->mc_db->md_entries;

                        mdb_cursor_pop(mx);
                        while (mx->mc_snum > 1) {
                                for (i=0; i<NUMKEYS(mx->mc_pg[mx->mc_top]); i++) {
                                        MDB_page *mp;
                                        pgno_t pg;
                                        ni = NODEPTR(mx->mc_pg[mx->mc_top], i);
                                        pg = NODEPGNO(ni);
                                        if ((rc = mdb_page_get(mc->mc_txn, pg, &mp)))
                                                return rc;
                                        /* free it */
                                        mdb_midl_append(mc->mc_txn->mt_free_pgs, pg);
                                }
                                rc = mdb_cursor_sibling(mx, 1);
                                if (rc)
                                        break;
                        }
                        /* free it */
                        mdb_midl_append(mc->mc_txn->mt_free_pgs,
                                mx->mc_db->md_root);
                }
        }

        return mdb_cursor_del0(mc, leaf);
}

/** 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.
 * @return Address of a page, or NULL on failure.
 */
static MDB_page *
mdb_page_new(MDB_cursor *mc, uint32_t flags, int num)
{
        MDB_page        *np;

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

        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;
        }

        return np;
}

/** 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 (data->mv_size >= env->me_psize / MDB_MINKEYS) {
                /* put on overflow page */
                sz -= data->mv_size - sizeof(pgno_t);
        }
        sz += sz & 1;

        return 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_psize / MDB_MINKEYS) {
                /* 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>ENOSPC - 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, uint8_t flags)
{
        unsigned int     i;
        size_t           node_size = NODESIZE;
        indx_t           ofs;
        MDB_node        *node;
        MDB_page        *mp = mc->mc_pg[mc->mc_top];
        MDB_page        *ofp = NULL;            /* overflow page */
        DKBUF;

        assert(mp->mp_upper >= mp->mp_lower);

        DPRINTF("add to %s page %zu index %i, data size %zu key size %zu [%s]",
            IS_LEAF(mp) ? "leaf" : "branch",
            mp->mp_pgno, 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;
        }

        if (key != NULL)
                node_size += key->mv_size;

        if (IS_LEAF(mp)) {
                assert(data);
                if (F_ISSET(flags, F_BIGDATA)) {
                        /* Data already on overflow page. */
                        node_size += sizeof(pgno_t);
                } else if (data->mv_size >= mc->mc_txn->mt_env->me_psize / MDB_MINKEYS) {
                        int ovpages = OVPAGES(data->mv_size, mc->mc_txn->mt_env->me_psize);
                        /* Put data on overflow page. */
                        DPRINTF("data size is %zu, put on overflow page",
                            data->mv_size);
                        node_size += sizeof(pgno_t);
                        if ((ofp = mdb_page_new(mc, P_OVERFLOW, ovpages)) == NULL)
                                return ENOMEM;
                        DPRINTF("allocated overflow page %zu", ofp->mp_pgno);
                        flags |= F_BIGDATA;
                } else {
                        node_size += data->mv_size;
                }
        }
        node_size += node_size & 1;

        if (node_size + sizeof(indx_t) > SIZELEFT(mp)) {
                DPRINTF("not enough room in page %zu, got %u ptrs",
                    mp->mp_pgno, NUMKEYS(mp));
                DPRINTF("upper - lower = %u - %u = %u", mp->mp_upper, mp->mp_lower,
                    mp->mp_upper - mp->mp_lower);
                DPRINTF("node size = %zu", node_size);
                return ENOSPC;
        }

        /* 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;
        assert(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)) {
                assert(key);
                if (ofp == NULL) {
                        if (F_ISSET(flags, F_BIGDATA))
                                memcpy(node->mn_data + key->mv_size, data->mv_data,
                                    sizeof(pgno_t));
                        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));
                        memcpy(METADATA(ofp), data->mv_data, data->mv_size);
                }
        }

        return MDB_SUCCESS;
}

/** Delete the specified node from a page.
 * @param[in] mp The page to operate on.
 * @param[in] indx The index of 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_page *mp, indx_t indx, int ksize)
{
        unsigned int     sz;
        indx_t           i, j, numkeys, ptr;
        MDB_node        *node;
        char            *base;

        DPRINTF("delete node %u on %s page %zu", indx,
            IS_LEAF(mp) ? "leaf" : "branch", mp->mp_pgno);
        assert(indx < NUMKEYS(mp));

        if (IS_LEAF2(mp)) {
                int x = NUMKEYS(mp) - 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 += sz & 1;

        ptr = mp->mp_ptrs[indx];
        numkeys = NUMKEYS(mp);
        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;
        memmove(base + sz, base, ptr - mp->mp_upper);

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

/** 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+1;
        mx->mx_dbx.md_parent = mc->mc_dbi;
        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;
        mx->mx_dbx.md_dirty = 0;
}

/** 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_db *db = NODEDATA(node);
        MDB_xcursor *mx = mc->mc_xcursor;
        assert((db->md_flags & MDB_SUBDATA) == MDB_SUBDATA);
        mx->mx_db = *db;
        DPRINTF("Sub-db %u for db %u root page %zu", mx->mx_cursor.mc_dbi, mc->mc_dbi,
                db->md_root);
        if (F_ISSET(mc->mc_pg[mc->mc_top]->mp_flags, P_DIRTY))
                mx->mx_dbx.md_dirty = 1;
        mx->mx_dbx.md_name.mv_data = NODEKEY(node);
        mx->mx_dbx.md_name.mv_size = node->mn_ksize;
        mx->mx_cursor.mc_snum = 0;
        mx->mx_cursor.mc_flags = 0;
        if (mx->mx_dbx.md_cmp == mdb_cmp_int && mx->mx_db.md_pad == sizeof(size_t))
                mx->mx_dbx.md_cmp = mdb_cmp_long;
}

/** 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_dbi = dbi;
        mc->mc_txn = txn;
        mc->mc_db = &txn->mt_dbs[dbi];
        mc->mc_dbx = &txn->mt_dbxs[dbi];
        mc->mc_snum = 0;
        mc->mc_flags = 0;
        if (txn->mt_dbs[dbi].md_flags & MDB_DUPSORT) {
                assert(mx != NULL);
                mc->mc_xcursor = mx;
                mdb_xcursor_init0(mc);
        } else {
                mc->mc_xcursor = NULL;
        }
}

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

        if (txn == NULL || ret == NULL || !dbi || dbi >= txn->mt_numdbs)
                return EINVAL;

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

        if ((mc = malloc(size)) != NULL) {
                if (txn->mt_dbs[dbi].md_flags & MDB_DUPSORT) {
                        mx = (MDB_xcursor *)(mc + 1);
                }
                mdb_cursor_init(mc, txn, dbi, mx);
        } else {
                return ENOMEM;
        }

        *ret = mc;

        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_db->md_flags & MDB_DUPSORT))
                return EINVAL;

        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 != NULL) {
                free(mc);
        }
}

/** Replace the key for a node with a new key.
 * @param[in] mp The page containing the node to operate on.
 * @param[in] indx The index of 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_page *mp, indx_t indx, MDB_val *key)
{
        indx_t                   ptr, i, numkeys;
        int                      delta;
        size_t                   len;
        MDB_node                *node;
        char                    *base;
        DKBUF;

        node = NODEPTR(mp, indx);
        ptr = mp->mp_ptrs[indx];
        DPRINTF("update key %u (ofs %u) [%.*s] to [%s] on page %zu",
            indx, ptr,
            (int)node->mn_ksize, (char *)NODEKEY(node),
                DKEY(key),
            mp->mp_pgno);

        delta = key->mv_size - node->mn_ksize;
        if (delta) {
                if (delta > 0 && SIZELEFT(mp) < delta) {
                        DPRINTF("OUCH! Not enough room, delta = %d", delta);
                        return ENOSPC;
                }

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

                node = NODEPTR(mp, indx);
                node->mn_ksize = key->mv_size;
        }

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

        return MDB_SUCCESS;
}

/** Move a node from csrc to cdst.
 */
static int
mdb_node_move(MDB_cursor *csrc, MDB_cursor *cdst)
{
        int                      rc;
        MDB_node                *srcnode;
        MDB_val          key, data;
        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])) {
                srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], 0);        /* fake */
                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;
        } else {
                srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], csrc->mc_ki[csrc->mc_top]);
                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 */
                        mdb_page_search_root(csrc, NULL, 0);
                        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);
        }
        DPRINTF("moving %s node %u [%s] on page %zu to node %u on page %zu",
            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, NODEPGNO(srcnode),
            srcnode->mn_flags);
        if (rc != MDB_SUCCESS)
                return rc;

        /* Delete the node from the source page.
         */
        mdb_node_del(csrc->mc_pg[csrc->mc_top], csrc->mc_ki[csrc->mc_top], key.mv_size);

        /* 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 %zu to [%s]",
                                csrc->mc_pg[csrc->mc_top]->mp_pgno, DKEY(&key));
                        if ((rc = mdb_update_key(csrc->mc_pg[csrc->mc_top-1], csrc->mc_ki[csrc->mc_top-1],
                                &key)) != MDB_SUCCESS)
                                return rc;
                }
                if (IS_BRANCH(csrc->mc_pg[csrc->mc_top])) {
                        MDB_val  nullkey;
                        nullkey.mv_size = 0;
                        assert(mdb_update_key(csrc->mc_pg[csrc->mc_top], 0, &nullkey) == 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 %zu to [%s]",
                                cdst->mc_pg[cdst->mc_top]->mp_pgno, DKEY(&key));
                        if ((rc = mdb_update_key(cdst->mc_pg[cdst->mc_top-1], cdst->mc_ki[cdst->mc_top-1],
                                &key)) != MDB_SUCCESS)
                                return rc;
                }
                if (IS_BRANCH(cdst->mc_pg[cdst->mc_top])) {
                        MDB_val  nullkey;
                        nullkey.mv_size = 0;
                        assert(mdb_update_key(cdst->mc_pg[cdst->mc_top], 0, &nullkey) == 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.
 */
static int
mdb_page_merge(MDB_cursor *csrc, MDB_cursor *cdst)
{
        int                      rc;
        indx_t                   i, j;
        MDB_node                *srcnode;
        MDB_val          key, data;

        DPRINTF("merging page %zu into %zu", csrc->mc_pg[csrc->mc_top]->mp_pgno,
                cdst->mc_pg[cdst->mc_top]->mp_pgno);

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

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

        /* Move all nodes from src to dst.
         */
        j = NUMKEYS(cdst->mc_pg[cdst->mc_top]);
        if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
                key.mv_size = csrc->mc_db->md_pad;
                key.mv_data = METADATA(csrc->mc_pg[csrc->mc_top]);
                for (i = 0; i < NUMKEYS(csrc->mc_pg[csrc->mc_top]); 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(csrc->mc_pg[csrc->mc_top]); i++, j++) {
                        srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], i);

                        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 %zu now has %u keys (%.1f%% filled)",
            cdst->mc_pg[cdst->mc_top]->mp_pgno, NUMKEYS(cdst->mc_pg[cdst->mc_top]), (float)PAGEFILL(cdst->mc_txn->mt_env, cdst->mc_pg[cdst->mc_top]) / 10);

        /* Unlink the src page from parent and add to free list.
         */
        mdb_node_del(csrc->mc_pg[csrc->mc_top-1], csrc->mc_ki[csrc->mc_top-1], 0);
        if (csrc->mc_ki[csrc->mc_top-1] == 0) {
                key.mv_size = 0;
                if ((rc = mdb_update_key(csrc->mc_pg[csrc->mc_top-1], 0, &key)) != MDB_SUCCESS)
                        return rc;
        }

        mdb_midl_append(csrc->mc_txn->mt_free_pgs, csrc->mc_pg[csrc->mc_top]->mp_pgno);
        if (IS_LEAF(csrc->mc_pg[csrc->mc_top]))
                csrc->mc_db->md_leaf_pages--;
        else
                csrc->mc_db->md_branch_pages--;
        mdb_cursor_pop(csrc);

        return mdb_rebalance(csrc);
}

/** 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;
        MDB_cursor      mn;

        DPRINTF("rebalancing %s page %zu (has %u keys, %.1f%% full)",
            IS_LEAF(mc->mc_pg[mc->mc_top]) ? "leaf" : "branch",
            mc->mc_pg[mc->mc_top]->mp_pgno, 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) {
                DPRINTF("no need to rebalance page %zu, above fill threshold",
                    mc->mc_pg[mc->mc_top]->mp_pgno);
                return MDB_SUCCESS;
        }

        if (mc->mc_snum < 2) {
                if (NUMKEYS(mc->mc_pg[mc->mc_top]) == 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;
                        mdb_midl_append(mc->mc_txn->mt_free_pgs, mc->mc_pg[mc->mc_top]->mp_pgno);
                        mc->mc_snum = 0;
                } else if (IS_BRANCH(mc->mc_pg[mc->mc_top]) && NUMKEYS(mc->mc_pg[mc->mc_top]) == 1) {
                        DPUTS("collapsing root page!");
                        mdb_midl_append(mc->mc_txn->mt_free_pgs, mc->mc_pg[mc->mc_top]->mp_pgno);
                        mc->mc_db->md_root = NODEPGNO(NODEPTR(mc->mc_pg[mc->mc_top], 0));
                        if ((rc = mdb_page_get(mc->mc_txn, mc->mc_db->md_root,
                                &mc->mc_pg[mc->mc_top])))
                                return rc;
                        mc->mc_db->md_depth--;
                        mc->mc_db->md_branch_pages--;
                } 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;
        assert(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;

        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]);
                if ((rc = mdb_page_get(mc->mc_txn, NODEPGNO(node), &mn.mc_pg[mn.mc_top])))
                        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]);
                if ((rc = mdb_page_get(mc->mc_txn, NODEPGNO(node), &mn.mc_pg[mn.mc_top])))
                        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 %zu (%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 at least two
         * keys, move one key from it.
         *
         * Otherwise we should try to merge them.
         */
        if (PAGEFILL(mc->mc_txn->mt_env, mn.mc_pg[mn.mc_top]) >= FILL_THRESHOLD && NUMKEYS(mn.mc_pg[mn.mc_top]) >= 2)
                return mdb_node_move(&mn, mc);
        else { /* FIXME: if (has_enough_room()) */
                if (mc->mc_ki[ptop] == 0)
                        return mdb_page_merge(&mn, mc);
                else
                        return mdb_page_merge(mc, &mn);
        }
}

/** Complete a delete operation started by #mdb_cursor_del(). */
static int
mdb_cursor_del0(MDB_cursor *mc, MDB_node *leaf)
{
        int rc;

        /* add overflow pages to free list */
        if (!IS_LEAF2(mc->mc_pg[mc->mc_top]) && F_ISSET(leaf->mn_flags, F_BIGDATA)) {
                int i, ovpages;
                pgno_t pg;

                memcpy(&pg, NODEDATA(leaf), sizeof(pg));
                ovpages = OVPAGES(NODEDSZ(leaf), mc->mc_txn->mt_env->me_psize);
                for (i=0; i<ovpages; i++) {
                        DPRINTF("freed ov page %zu", pg);
                        mdb_midl_append(mc->mc_txn->mt_free_pgs, pg);
                        pg++;
                }
        }
        mdb_node_del(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], mc->mc_db->md_pad);
        mc->mc_db->md_entries--;
        rc = mdb_rebalance(mc);
        if (rc != MDB_SUCCESS)
                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)
{
        MDB_cursor mc;
        MDB_xcursor mx;
        MDB_cursor_op op;
        MDB_val rdata, *xdata;
        int              rc, exact;
        DKBUF;

        assert(key != NULL);

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

        if (txn == NULL || !dbi || dbi >= txn->mt_numdbs)
                return EINVAL;

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

        if (key->mv_size == 0 || key->mv_size > MAXKEYSIZE) {
                return EINVAL;
        }

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

        exact = 0;
        if (data) {
                op = MDB_GET_BOTH;
                rdata = *data;
                xdata = &rdata;
        } else {
                op = MDB_SET;
                xdata = NULL;
        }
        rc = mdb_cursor_set(&mc, key, xdata, op, &exact);
        if (rc == 0)
                rc = mdb_cursor_del(&mc, data ? 0 : MDB_NODUPDATA);
        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.
 * @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)
{
        uint8_t          flags;
        int              rc = MDB_SUCCESS, ins_new = 0;
        indx_t           newindx;
        pgno_t           pgno = 0;
        unsigned int     i, j, split_indx, nkeys, pmax;
        MDB_node        *node;
        MDB_val  sepkey, rkey, rdata;
        MDB_page        *copy;
        MDB_page        *mp, *rp, *pp;
        unsigned int ptop;
        MDB_cursor      mn;
        DKBUF;

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

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

        if (mc->mc_snum < 2) {
                if ((pp = mdb_page_new(mc, P_BRANCH, 1)) == NULL)
                        return ENOMEM;
                /* 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 = %zu", pp->mp_pgno);
                mc->mc_db->md_depth++;

                /* 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--;
                        return rc;
                }
                mc->mc_snum = 2;
                mc->mc_top = 1;
                ptop = 0;
        } else {
                ptop = mc->mc_top-1;
                DPRINTF("parent branch page is %zu", mc->mc_pg[ptop]->mp_pgno);
        }

        /* Create a right sibling. */
        if ((rp = mdb_page_new(mc, mp->mp_flags, 1)) == NULL)
                return ENOMEM;
        mdb_cursor_copy(mc, &mn);
        mn.mc_pg[mn.mc_top] = rp;
        mn.mc_ki[ptop] = mc->mc_ki[ptop]+1;
        DPRINTF("new right sibling: page %zu", rp->mp_pgno);

        nkeys = NUMKEYS(mp);
        split_indx = nkeys / 2 + 1;

        if (IS_LEAF2(rp)) {
                char *split, *ins;
                int x;
                unsigned int lsize, rsize, ksize;
                /* Move half of the keys to the right sibling */
                copy = NULL;
                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;
                }
                goto newsep;
        }

        /* For leaf pages, check the split point based on what
         * fits where, since otherwise add_node can fail.
         */
        if (IS_LEAF(mp)) {
                unsigned int psize, nsize;
                /* Maximum free space in an empty page */
                pmax = mc->mc_txn->mt_env->me_psize - PAGEHDRSZ;
                nsize = mdb_leaf_size(mc->mc_txn->mt_env, newkey, newdata);
                if (newindx < split_indx) {
                        psize = nsize;
                        for (i=0; i<split_indx; i++) {
                                node = NODEPTR(mp, i);
                                psize += NODESIZE + NODEKSZ(node) + sizeof(indx_t);
                                if (F_ISSET(node->mn_flags, F_BIGDATA))
                                        psize += sizeof(pgno_t);
                                else
                                        psize += NODEDSZ(node);
                                psize += psize & 1;
                                if (psize > pmax) {
                                        split_indx = i;
                                        break;
                                }
                        }
                } else {
                        psize = nsize;
                        for (i=nkeys-1; i>=split_indx; i--) {
                                node = NODEPTR(mp, i);
                                psize += NODESIZE + NODEKSZ(node) + sizeof(indx_t);
                                if (F_ISSET(node->mn_flags, F_BIGDATA))
                                        psize += sizeof(pgno_t);
                                else
                                        psize += NODEDSZ(node);
                                psize += psize & 1;
                                if (psize > pmax) {
                                        split_indx = i+1;
                                        break;
                                }
                        }
                }
        }

        /* First find the separating key between the split pages.
         */
        if (newindx == split_indx) {
                sepkey.mv_size = newkey->mv_size;
                sepkey.mv_data = newkey->mv_data;
        } else {
                node = NODEPTR(mp, split_indx);
                sepkey.mv_size = node->mn_ksize;
                sepkey.mv_data = NODEKEY(node);
        }

newsep:
        DPRINTF("separator is [%s]", DKEY(&sepkey));

        /* Copy separator key to the parent.
         */
        if (SIZELEFT(mn.mc_pg[ptop]) < mdb_branch_size(mc->mc_txn->mt_env, &sepkey)) {
                mn.mc_snum--;
                mn.mc_top--;
                rc = mdb_page_split(&mn, &sepkey, NULL, rp->mp_pgno);

                /* 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])) {
                        mc->mc_pg[ptop] = mn.mc_pg[ptop];
                        mc->mc_ki[ptop] = mn.mc_ki[ptop] - 1;
                }
        } else {
                mn.mc_top--;
                rc = mdb_node_add(&mn, mn.mc_ki[ptop], &sepkey, NULL, rp->mp_pgno, 0);
                mn.mc_top++;
        }
        if (IS_LEAF2(rp)) {
                return rc;
        }
        if (rc != MDB_SUCCESS) {
                return rc;
        }

        /* Move half of the keys to the right sibling. */

        /* grab a page to hold a temporary copy */
        if (mc->mc_txn->mt_env->me_dpages) {
                copy = mc->mc_txn->mt_env->me_dpages;
                mc->mc_txn->mt_env->me_dpages = copy->mp_next;
        } else {
                if ((copy = malloc(mc->mc_txn->mt_env->me_psize)) == NULL)
                        return ENOMEM;
        }

        copy->mp_pgno  = mp->mp_pgno;
        copy->mp_flags = mp->mp_flags;
        copy->mp_lower = PAGEHDRSZ;
        copy->mp_upper = mc->mc_txn->mt_env->me_psize;
        mc->mc_pg[mc->mc_top] = copy;
        for (i = j = 0; i <= nkeys; j++) {
                if (i == split_indx) {
                /* Insert in right sibling. */
                /* Reset insert index for right sibling. */
                        j = (i == newindx && ins_new);
                        mc->mc_pg[mc->mc_top] = rp;
                }

                if (i == newindx && !ins_new) {
                        /* Insert the original entry that caused the split. */
                        rkey.mv_data = newkey->mv_data;
                        rkey.mv_size = newkey->mv_size;
                        if (IS_LEAF(mp)) {
                                rdata.mv_data = newdata->mv_data;
                                rdata.mv_size = newdata->mv_size;
                        } else
                                pgno = newpgno;
                        flags = 0;

                        ins_new = 1;

                        /* Update page and index for the new key. */
                        mc->mc_ki[mc->mc_top] = j;
                } else if (i == nkeys) {
                        break;
                } else {
                        node = NODEPTR(mp, i);
                        rkey.mv_data = NODEKEY(node);
                        rkey.mv_size = node->mn_ksize;
                        if (IS_LEAF(mp)) {
                                rdata.mv_data = NODEDATA(node);
                                rdata.mv_size = NODEDSZ(node);
                        } else
                                pgno = NODEPGNO(node);
                        flags = node->mn_flags;

                        i++;
                }

                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);
        }

        /* reset back to original page */
        if (newindx < split_indx)
                mc->mc_pg[mc->mc_top] = mp;

        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),
                mc->mc_txn->mt_env->me_psize - copy->mp_upper);

        /* return tmp page to freelist */
        copy->mp_next = mc->mc_txn->mt_env->me_dpages;
        mc->mc_txn->mt_env->me_dpages = copy;
        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;

        assert(key != NULL);
        assert(data != NULL);

        if (txn == NULL || !dbi || dbi >= txn->mt_numdbs)
                return EINVAL;

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

        if (key->mv_size == 0 || key->mv_size > MAXKEYSIZE) {
                return EINVAL;
        }

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

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

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

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

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

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

        *arg = env->me_path;
        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
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
mdb_env_stat(MDB_env *env, MDB_stat *arg)
{
        int toggle;

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

        mdb_env_read_meta(env, &toggle);

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

/** 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_open()
 */
static void
mdb_default_cmp(MDB_txn *txn, MDB_dbi dbi)
{
        if (txn->mt_dbs[dbi].md_flags & MDB_REVERSEKEY)
                txn->mt_dbxs[dbi].md_cmp = mdb_cmp_memnr;
        else if (txn->mt_dbs[dbi].md_flags & MDB_INTEGERKEY)
                txn->mt_dbxs[dbi].md_cmp = mdb_cmp_cint;
        else
                txn->mt_dbxs[dbi].md_cmp = mdb_cmp_memn;

        if (txn->mt_dbs[dbi].md_flags & MDB_DUPSORT) {
                if (txn->mt_dbs[dbi].md_flags & MDB_INTEGERDUP) {
                        if (txn->mt_dbs[dbi].md_flags & MDB_DUPFIXED)
                                txn->mt_dbxs[dbi].md_dcmp = mdb_cmp_int;
                        else
                                txn->mt_dbxs[dbi].md_dcmp = mdb_cmp_cint;
                } else if (txn->mt_dbs[dbi].md_flags & MDB_REVERSEDUP) {
                        txn->mt_dbxs[dbi].md_dcmp = mdb_cmp_memnr;
                } else {
                        txn->mt_dbxs[dbi].md_dcmp = mdb_cmp_memn;
                }
        } else {
                txn->mt_dbxs[dbi].md_dcmp = NULL;
        }
}

int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi)
{
        MDB_val key, data;
        MDB_dbi i;
        int rc, dirty = 0;
        size_t len;

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

        /* main DB? */
        if (!name) {
                *dbi = MAIN_DBI;
                if (flags & (MDB_DUPSORT|MDB_REVERSEKEY|MDB_INTEGERKEY))
                        txn->mt_dbs[MAIN_DBI].md_flags |= (flags & (MDB_DUPSORT|MDB_REVERSEKEY|MDB_INTEGERKEY));
                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 (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 (txn->mt_numdbs >= txn->mt_env->me_maxdbs - 1)
                return ENFILE;

        /* Find the DB info */
        key.mv_size = len;
        key.mv_data = (void *)name;
        rc = mdb_get(txn, MAIN_DBI, &key, &data);

        /* Create if requested */
        if (rc == MDB_NOTFOUND && (flags & MDB_CREATE)) {
                MDB_cursor mc;
                MDB_db dummy;
                data.mv_size = sizeof(MDB_db);
                data.mv_data = &dummy;
                memset(&dummy, 0, sizeof(dummy));
                dummy.md_root = P_INVALID;
                dummy.md_flags = flags & 0xffff;
                mdb_cursor_init(&mc, txn, MAIN_DBI, NULL);
                rc = mdb_cursor_put(&mc, &key, &data, F_SUBDATA);
                dirty = 1;
        }

        /* OK, got info, add to table */
        if (rc == MDB_SUCCESS) {
                txn->mt_dbxs[txn->mt_numdbs].md_name.mv_data = strdup(name);
                txn->mt_dbxs[txn->mt_numdbs].md_name.mv_size = len;
                txn->mt_dbxs[txn->mt_numdbs].md_rel = NULL;
                txn->mt_dbxs[txn->mt_numdbs].md_parent = MAIN_DBI;
                txn->mt_dbxs[txn->mt_numdbs].md_dirty = dirty;
                memcpy(&txn->mt_dbs[txn->mt_numdbs], data.mv_data, sizeof(MDB_db));
                *dbi = txn->mt_numdbs;
                txn->mt_env->me_dbs[0][txn->mt_numdbs] = txn->mt_dbs[txn->mt_numdbs];
                txn->mt_env->me_dbs[1][txn->mt_numdbs] = txn->mt_dbs[txn->mt_numdbs];
                mdb_default_cmp(txn, txn->mt_numdbs);
                txn->mt_numdbs++;
        }

        return rc;
}

int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *arg)
{
        if (txn == NULL || arg == NULL || dbi >= txn->mt_numdbs)
                return EINVAL;

        return mdb_stat0(txn->mt_env, &txn->mt_dbs[dbi], arg);
}

void mdb_close(MDB_txn *txn, MDB_dbi dbi)
{
        char *ptr;
        if (dbi <= MAIN_DBI || dbi >= txn->mt_numdbs)
                return;
        ptr = txn->mt_dbxs[dbi].md_name.mv_data;
        txn->mt_dbxs[dbi].md_name.mv_data = NULL;
        txn->mt_dbxs[dbi].md_name.mv_size = 0;
        free(ptr);
}

int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp)
{
        if (txn == NULL || !dbi || dbi >= txn->mt_numdbs)
                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 (txn == NULL || !dbi || dbi >= txn->mt_numdbs)
                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 (txn == NULL || !dbi || dbi >= txn->mt_numdbs)
                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 (txn == NULL || !dbi || dbi >= txn->mt_numdbs)
                return EINVAL;

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

/** @} */