2 * @brief Lightning memory-mapped database library
4 * @mainpage Lightning Memory-Mapped Database Manager (LMDB)
6 * @section intro_sec Introduction
7 * LMDB is a Btree-based database management library modeled loosely on the
8 * BerkeleyDB API, but much simplified. The entire database is exposed
9 * in a memory map, and all data fetches return data directly
10 * from the mapped memory, so no malloc's or memcpy's occur during
11 * data fetches. As such, the library is extremely simple because it
12 * requires no page caching layer of its own, and it is extremely high
13 * performance and memory-efficient. It is also fully transactional with
14 * full ACID semantics, and when the memory map is read-only, the
15 * database integrity cannot be corrupted by stray pointer writes from
18 * The library is fully thread-aware and supports concurrent read/write
19 * access from multiple processes and threads. Data pages use a copy-on-
20 * write strategy so no active data pages are ever overwritten, which
21 * also provides resistance to corruption and eliminates the need of any
22 * special recovery procedures after a system crash. Writes are fully
23 * serialized; only one write transaction may be active at a time, which
24 * guarantees that writers can never deadlock. The database structure is
25 * multi-versioned so readers run with no locks; writers cannot block
26 * readers, and readers don't block writers.
28 * Unlike other well-known database mechanisms which use either write-ahead
29 * transaction logs or append-only data writes, LMDB requires no maintenance
30 * during operation. Both write-ahead loggers and append-only databases
31 * require periodic checkpointing and/or compaction of their log or database
32 * files otherwise they grow without bound. LMDB tracks free pages within
33 * the database and re-uses them for new write operations, so the database
34 * size does not grow without bound in normal use.
36 * The memory map can be used as a read-only or read-write map. It is
37 * read-only by default as this provides total immunity to corruption.
38 * Using read-write mode offers much higher write performance, but adds
39 * the possibility for stray application writes thru pointers to silently
40 * corrupt the database. Of course if your application code is known to
41 * be bug-free (...) then this is not an issue.
43 * @section caveats_sec Caveats
44 * Troubleshooting the lock file, plus semaphores on BSD systems:
46 * - A broken lockfile can cause sync issues.
47 * Stale reader transactions left behind by an aborted program
48 * cause further writes to grow the database quickly, and
49 * stale locks can block further operation.
51 * Fix: Check for stale readers periodically, using the
52 * #mdb_reader_check function or the \ref mdb_stat_1 "mdb_stat" tool.
53 * Stale writers will be cleared automatically on most systems:
54 * - Windows - automatic
55 * - BSD, systems using SysV semaphores - automatic
56 * - Linux, systems using POSIX mutexes with Robust option - automatic
57 * Otherwise just make all programs using the database close it;
58 * the lockfile is always reset on first open of the environment.
60 * - On BSD systems or others configured with MDB_USE_SYSV_SEM,
61 * startup can fail due to semaphores owned by another userid.
63 * Fix: Open and close the database as the user which owns the
64 * semaphores (likely last user) or as root, while no other
65 * process is using the database.
67 * Restrictions/caveats (in addition to those listed for some functions):
69 * - Only the database owner should normally use the database on
70 * BSD systems or when otherwise configured with MDB_USE_POSIX_SEM.
71 * Multiple users can cause startup to fail later, as noted above.
73 * - There is normally no pure read-only mode, since readers need write
74 * access to locks and lock file. Exceptions: On read-only filesystems
75 * or with the #MDB_NOLOCK flag described under #mdb_env_open().
77 * - By default, in versions before 0.9.10, unused portions of the data
78 * file might receive garbage data from memory freed by other code.
79 * (This does not happen when using the #MDB_WRITEMAP flag.) As of
80 * 0.9.10 the default behavior is to initialize such memory before
81 * writing to the data file. Since there may be a slight performance
82 * cost due to this initialization, applications may disable it using
83 * the #MDB_NOMEMINIT flag. Applications handling sensitive data
84 * which must not be written should not use this flag. This flag is
85 * irrelevant when using #MDB_WRITEMAP.
87 * - A thread can only use one transaction at a time, plus any child
88 * transactions. Each transaction belongs to one thread. See below.
89 * The #MDB_NOTLS flag changes this for read-only transactions.
91 * - Use an MDB_env* in the process which opened it, without fork()ing.
93 * - Do not have open an LMDB database twice in the same process at
94 * the same time. Not even from a plain open() call - close()ing it
95 * breaks flock() advisory locking.
97 * - Avoid long-lived transactions. Read transactions prevent
98 * reuse of pages freed by newer write transactions, thus the
99 * database can grow quickly. Write transactions prevent
100 * other write transactions, since writes are serialized.
102 * - Avoid suspending a process with active transactions. These
103 * would then be "long-lived" as above. Also read transactions
104 * suspended when writers commit could sometimes see wrong data.
106 * ...when several processes can use a database concurrently:
108 * - Avoid aborting a process with an active transaction.
109 * The transaction becomes "long-lived" as above until a check
110 * for stale readers is performed or the lockfile is reset,
111 * since the process may not remove it from the lockfile.
112 * Except write-transactions on Unix with MDB_ROBUST or on Windows.
114 * - If you do that anyway, do a periodic check for stale readers. Or
115 * close the environment once in a while, so the lockfile can get reset.
117 * - Do not use LMDB databases on remote filesystems, even between
118 * processes on the same host. This breaks flock() on some OSes,
119 * possibly memory map sync, and certainly sync between programs
120 * on different hosts.
122 * - Opening a database can fail if another process is opening or
123 * closing it at exactly the same time.
125 * @author Howard Chu, Symas Corporation.
127 * @copyright Copyright 2011-2014 Howard Chu, Symas Corp. All rights reserved.
129 * Redistribution and use in source and binary forms, with or without
130 * modification, are permitted only as authorized by the OpenLDAP
133 * A copy of this license is available in the file LICENSE in the
134 * top-level directory of the distribution or, alternatively, at
135 * <http://www.OpenLDAP.org/license.html>.
138 * This code is derived from btree.c written by Martin Hedenfalk.
140 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
142 * Permission to use, copy, modify, and distribute this software for any
143 * purpose with or without fee is hereby granted, provided that the above
144 * copyright notice and this permission notice appear in all copies.
146 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
147 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
148 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
149 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
150 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
151 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
152 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
157 #include <sys/types.h>
163 /** Unix permissions for creating files, or dummy definition for Windows */
165 typedef int mdb_mode_t;
167 typedef mode_t mdb_mode_t;
170 /** An abstraction for a file handle.
171 * On POSIX systems file handles are small integers. On Windows
172 * they're opaque pointers.
175 typedef void *mdb_filehandle_t;
177 typedef int mdb_filehandle_t;
180 /** @defgroup mdb LMDB API
182 * @brief OpenLDAP Lightning Memory-Mapped Database Manager
184 /** @defgroup Version Version Macros
187 /** Library major version */
188 #define MDB_VERSION_MAJOR 0
189 /** Library minor version */
190 #define MDB_VERSION_MINOR 9
191 /** Library patch version */
192 #define MDB_VERSION_PATCH 14
194 /** Combine args a,b,c into a single integer for easy version comparisons */
195 #define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
197 /** The full library version as a single integer */
198 #define MDB_VERSION_FULL \
199 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
201 /** The release date of this library version */
202 #define MDB_VERSION_DATE "September 20, 2014"
204 /** A stringifier for the version info */
205 #define MDB_VERSTR(a,b,c,d) "LMDB " #a "." #b "." #c ": (" d ")"
207 /** A helper for the stringifier macro */
208 #define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d)
210 /** The full library version as a C string */
211 #define MDB_VERSION_STRING \
212 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
215 /** @brief Opaque structure for a database environment.
217 * A DB environment supports multiple databases, all residing in the same
220 typedef struct MDB_env MDB_env;
222 /** @brief Opaque structure for a transaction handle.
224 * All database operations require a transaction handle. Transactions may be
225 * read-only or read-write.
227 typedef struct MDB_txn MDB_txn;
229 /** @brief A handle for an individual database in the DB environment. */
230 typedef unsigned int MDB_dbi;
232 /** @brief Opaque structure for navigating through a database */
233 typedef struct MDB_cursor MDB_cursor;
235 /** @brief Generic structure used for passing keys and data in and out
238 * Values returned from the database are valid only until a subsequent
239 * update operation, or the end of the transaction. Do not modify or
240 * free them, they commonly point into the database itself.
242 * Key sizes must be between 1 and #mdb_env_get_maxkeysize() inclusive.
243 * The same applies to data sizes in databases with the #MDB_DUPSORT flag.
244 * Other data items can in theory be from 0 to 0xffffffff bytes long.
246 typedef struct MDB_val {
247 size_t mv_size; /**< size of the data item */
248 void *mv_data; /**< address of the data item */
251 /** @brief A callback function used to compare two keys in a database */
252 typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
254 /** @brief A callback function used to relocate a position-dependent data item
255 * in a fixed-address database.
257 * The \b newptr gives the item's desired address in
258 * the memory map, and \b oldptr gives its previous address. The item's actual
259 * data resides at the address in \b item. This callback is expected to walk
260 * through the fields of the record in \b item and modify any
261 * values based at the \b oldptr address to be relative to the \b newptr address.
262 * @param[in,out] item The item that is to be relocated.
263 * @param[in] oldptr The previous address.
264 * @param[in] newptr The new address to relocate to.
265 * @param[in] relctx An application-provided context, set by #mdb_set_relctx().
266 * @todo This feature is currently unimplemented.
268 typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
270 /** @defgroup mdb_env Environment Flags
273 /** mmap at a fixed address (experimental) */
274 #define MDB_FIXEDMAP 0x01
275 /** no environment directory */
276 #define MDB_NOSUBDIR 0x4000
277 /** don't fsync after commit */
278 #define MDB_NOSYNC 0x10000
280 #define MDB_RDONLY 0x20000
281 /** don't fsync metapage after commit */
282 #define MDB_NOMETASYNC 0x40000
283 /** use writable mmap */
284 #define MDB_WRITEMAP 0x80000
285 /** use asynchronous msync when #MDB_WRITEMAP is used */
286 #define MDB_MAPASYNC 0x100000
287 /** tie reader locktable slots to #MDB_txn objects instead of to threads */
288 #define MDB_NOTLS 0x200000
289 /** don't do any locking, caller must manage their own locks */
290 #define MDB_NOLOCK 0x400000
291 /** don't do readahead (no effect on Windows) */
292 #define MDB_NORDAHEAD 0x800000
293 /** don't initialize malloc'd memory before writing to datafile */
294 #define MDB_NOMEMINIT 0x1000000
297 /** @defgroup mdb_dbi_open Database Flags
300 /** use reverse string keys */
301 #define MDB_REVERSEKEY 0x02
302 /** use sorted duplicates */
303 #define MDB_DUPSORT 0x04
304 /** numeric keys in native byte order.
305 * The keys must all be of the same size. */
306 #define MDB_INTEGERKEY 0x08
307 /** with #MDB_DUPSORT, sorted dup items have fixed size */
308 #define MDB_DUPFIXED 0x10
309 /** with #MDB_DUPSORT, dups are numeric in native byte order */
310 #define MDB_INTEGERDUP 0x20
311 /** with #MDB_DUPSORT, use reverse string dups */
312 #define MDB_REVERSEDUP 0x40
313 /** create DB if not already existing */
314 #define MDB_CREATE 0x40000
317 /** @defgroup mdb_put Write Flags
320 /** For put: Don't write if the key already exists. */
321 #define MDB_NOOVERWRITE 0x10
322 /** Only for #MDB_DUPSORT<br>
323 * For put: don't write if the key and data pair already exist.<br>
324 * For mdb_cursor_del: remove all duplicate data items.
326 #define MDB_NODUPDATA 0x20
327 /** For mdb_cursor_put: overwrite the current key/data pair */
328 #define MDB_CURRENT 0x40
329 /** For put: Just reserve space for data, don't copy it. Return a
330 * pointer to the reserved space.
332 #define MDB_RESERVE 0x10000
333 /** Data is being appended, don't split full pages. */
334 #define MDB_APPEND 0x20000
335 /** Duplicate data is being appended, don't split full pages. */
336 #define MDB_APPENDDUP 0x40000
337 /** Store multiple data items in one call. Only for #MDB_DUPFIXED. */
338 #define MDB_MULTIPLE 0x80000
341 /** @defgroup mdb_copy Copy Flags
344 /** Compacting copy: Omit free space from copy, and renumber all
345 * pages sequentially.
347 #define MDB_CP_COMPACT 0x01
350 /** @brief Cursor Get operations.
352 * This is the set of all operations for retrieving data
355 typedef enum MDB_cursor_op {
356 MDB_FIRST, /**< Position at first key/data item */
357 MDB_FIRST_DUP, /**< Position at first data item of current key.
358 Only for #MDB_DUPSORT */
359 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
360 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
361 MDB_GET_CURRENT, /**< Return key/data at current cursor position */
362 MDB_GET_MULTIPLE, /**< Return key and up to a page of duplicate data items
363 from current cursor position. Move cursor to prepare
364 for #MDB_NEXT_MULTIPLE. Only for #MDB_DUPFIXED */
365 MDB_LAST, /**< Position at last key/data item */
366 MDB_LAST_DUP, /**< Position at last data item of current key.
367 Only for #MDB_DUPSORT */
368 MDB_NEXT, /**< Position at next data item */
369 MDB_NEXT_DUP, /**< Position at next data item of current key.
370 Only for #MDB_DUPSORT */
371 MDB_NEXT_MULTIPLE, /**< Return key and up to a page of duplicate data items
372 from next cursor position. Move cursor to prepare
373 for #MDB_NEXT_MULTIPLE. Only for #MDB_DUPFIXED */
374 MDB_NEXT_NODUP, /**< Position at first data item of next key */
375 MDB_PREV, /**< Position at previous data item */
376 MDB_PREV_DUP, /**< Position at previous data item of current key.
377 Only for #MDB_DUPSORT */
378 MDB_PREV_NODUP, /**< Position at last data item of previous key */
379 MDB_SET, /**< Position at specified key */
380 MDB_SET_KEY, /**< Position at specified key, return key + data */
381 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
384 /** @defgroup errors Return Codes
386 * BerkeleyDB uses -30800 to -30999, we'll go under them
389 /** Successful result */
390 #define MDB_SUCCESS 0
391 /** key/data pair already exists */
392 #define MDB_KEYEXIST (-30799)
393 /** key/data pair not found (EOF) */
394 #define MDB_NOTFOUND (-30798)
395 /** Requested page not found - this usually indicates corruption */
396 #define MDB_PAGE_NOTFOUND (-30797)
397 /** Located page was wrong type */
398 #define MDB_CORRUPTED (-30796)
399 /** Update of meta page failed or environment had fatal error */
400 #define MDB_PANIC (-30795)
401 /** Environment version mismatch */
402 #define MDB_VERSION_MISMATCH (-30794)
403 /** File is not a valid LMDB file */
404 #define MDB_INVALID (-30793)
405 /** Environment mapsize reached */
406 #define MDB_MAP_FULL (-30792)
407 /** Environment maxdbs reached */
408 #define MDB_DBS_FULL (-30791)
409 /** Environment maxreaders reached */
410 #define MDB_READERS_FULL (-30790)
411 /** Too many TLS keys in use - Windows only */
412 #define MDB_TLS_FULL (-30789)
413 /** Txn has too many dirty pages */
414 #define MDB_TXN_FULL (-30788)
415 /** Cursor stack too deep - internal error */
416 #define MDB_CURSOR_FULL (-30787)
417 /** Page has not enough space - internal error */
418 #define MDB_PAGE_FULL (-30786)
419 /** Database contents grew beyond environment mapsize */
420 #define MDB_MAP_RESIZED (-30785)
421 /** MDB_INCOMPATIBLE: Operation and DB incompatible, or DB flags changed */
422 #define MDB_INCOMPATIBLE (-30784)
423 /** Invalid reuse of reader locktable slot */
424 #define MDB_BAD_RSLOT (-30783)
425 /** Transaction cannot recover - it must be aborted */
426 #define MDB_BAD_TXN (-30782)
427 /** Unsupported size of key/DB name/data, or wrong DUPFIXED size */
428 #define MDB_BAD_VALSIZE (-30781)
429 /** The specified DBI was changed unexpectedly */
430 #define MDB_BAD_DBI (-30780)
431 /** The last defined error code */
432 #define MDB_LAST_ERRCODE MDB_BAD_DBI
435 /** @brief Statistics for a database in the environment */
436 typedef struct MDB_stat {
437 unsigned int ms_psize; /**< Size of a database page.
438 This is currently the same for all databases. */
439 unsigned int ms_depth; /**< Depth (height) of the B-tree */
440 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
441 size_t ms_leaf_pages; /**< Number of leaf pages */
442 size_t ms_overflow_pages; /**< Number of overflow pages */
443 size_t ms_entries; /**< Number of data items */
446 /** @brief Information about the environment */
447 typedef struct MDB_envinfo {
448 void *me_mapaddr; /**< Address of map, if fixed */
449 size_t me_mapsize; /**< Size of the data memory map */
450 size_t me_last_pgno; /**< ID of the last used page */
451 size_t me_last_txnid; /**< ID of the last committed transaction */
452 unsigned int me_maxreaders; /**< max reader slots in the environment */
453 unsigned int me_numreaders; /**< max reader slots used in the environment */
456 /** @brief Return the LMDB library version information.
458 * @param[out] major if non-NULL, the library major version number is copied here
459 * @param[out] minor if non-NULL, the library minor version number is copied here
460 * @param[out] patch if non-NULL, the library patch version number is copied here
461 * @retval "version string" The library version as a string
463 char *mdb_version(int *major, int *minor, int *patch);
465 /** @brief Return a string describing a given error code.
467 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
468 * function. If the error code is greater than or equal to 0, then the string
469 * returned by the system function strerror(3) is returned. If the error code
470 * is less than 0, an error string corresponding to the LMDB library error is
471 * returned. See @ref errors for a list of LMDB-specific error codes.
472 * @param[in] err The error code
473 * @retval "error message" The description of the error
475 char *mdb_strerror(int err);
477 /** @brief Create an LMDB environment handle.
479 * This function allocates memory for a #MDB_env structure. To release
480 * the allocated memory and discard the handle, call #mdb_env_close().
481 * Before the handle may be used, it must be opened using #mdb_env_open().
482 * Various other options may also need to be set before opening the handle,
483 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
484 * depending on usage requirements.
485 * @param[out] env The address where the new handle will be stored
486 * @return A non-zero error value on failure and 0 on success.
488 int mdb_env_create(MDB_env **env);
490 /** @brief Open an environment handle.
492 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
493 * @param[in] env An environment handle returned by #mdb_env_create()
494 * @param[in] path The directory in which the database files reside. This
495 * directory must already exist and be writable.
496 * @param[in] flags Special options for this environment. This parameter
497 * must be set to 0 or by bitwise OR'ing together one or more of the
498 * values described here.
499 * Flags set by mdb_env_set_flags() are also used.
502 * use a fixed address for the mmap region. This flag must be specified
503 * when creating the environment, and is stored persistently in the environment.
504 * If successful, the memory map will always reside at the same virtual address
505 * and pointers used to reference data items in the database will be constant
506 * across multiple invocations. This option may not always work, depending on
507 * how the operating system has allocated memory to shared libraries and other uses.
508 * The feature is highly experimental.
510 * By default, LMDB creates its environment in a directory whose
511 * pathname is given in \b path, and creates its data and lock files
512 * under that directory. With this option, \b path is used as-is for
513 * the database main data file. The database lock file is the \b path
514 * with "-lock" appended.
516 * Open the environment in read-only mode. No write operations will be
517 * allowed. LMDB will still modify the lock file - except on read-only
518 * filesystems, where LMDB does not use locks.
520 * Use a writeable memory map unless MDB_RDONLY is set. This is faster
521 * and uses fewer mallocs, but loses protection from application bugs
522 * like wild pointer writes and other bad updates into the database.
523 * Incompatible with nested transactions.
524 * Processes with and without MDB_WRITEMAP on the same environment do
525 * not cooperate well.
526 * <li>#MDB_NOMETASYNC
527 * Flush system buffers to disk only once per transaction, omit the
528 * metadata flush. Defer that until the system flushes files to disk,
529 * or next non-MDB_RDONLY commit or #mdb_env_sync(). This optimization
530 * maintains database integrity, but a system crash may undo the last
531 * committed transaction. I.e. it preserves the ACI (atomicity,
532 * consistency, isolation) but not D (durability) database property.
533 * This flag may be changed at any time using #mdb_env_set_flags().
535 * Don't flush system buffers to disk when committing a transaction.
536 * This optimization means a system crash can corrupt the database or
537 * lose the last transactions if buffers are not yet flushed to disk.
538 * The risk is governed by how often the system flushes dirty buffers
539 * to disk and how often #mdb_env_sync() is called. However, if the
540 * filesystem preserves write order and the #MDB_WRITEMAP flag is not
541 * used, transactions exhibit ACI (atomicity, consistency, isolation)
542 * properties and only lose D (durability). I.e. database integrity
543 * is maintained, but a system crash may undo the final transactions.
544 * Note that (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no
545 * hint for when to write transactions to disk, unless #mdb_env_sync()
546 * is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable.
547 * This flag may be changed at any time using #mdb_env_set_flags().
549 * When using #MDB_WRITEMAP, use asynchronous flushes to disk.
550 * As with #MDB_NOSYNC, a system crash can then corrupt the
551 * database or lose the last transactions. Calling #mdb_env_sync()
552 * ensures on-disk database integrity until next commit.
553 * This flag may be changed at any time using #mdb_env_set_flags().
555 * Don't use Thread-Local Storage. Tie reader locktable slots to
556 * #MDB_txn objects instead of to threads. I.e. #mdb_txn_reset() keeps
557 * the slot reseved for the #MDB_txn object. A thread may use parallel
558 * read-only transactions. A read-only transaction may span threads if
559 * the user synchronizes its use. Applications that multiplex many
560 * user threads over individual OS threads need this option. Such an
561 * application must also serialize the write transactions in an OS
562 * thread, since LMDB's write locking is unaware of the user threads.
564 * Don't do any locking. If concurrent access is anticipated, the
565 * caller must manage all concurrency itself. For proper operation
566 * the caller must enforce single-writer semantics, and must ensure
567 * that no readers are using old transactions while a writer is
568 * active. The simplest approach is to use an exclusive lock so that
569 * no readers may be active at all when a writer begins.
571 * Turn off readahead. Most operating systems perform readahead on
572 * read requests by default. This option turns it off if the OS
573 * supports it. Turning it off may help random read performance
574 * when the DB is larger than RAM and system RAM is full.
575 * The option is not implemented on Windows.
577 * Don't initialize malloc'd memory before writing to unused spaces
578 * in the data file. By default, memory for pages written to the data
579 * file is obtained using malloc. While these pages may be reused in
580 * subsequent transactions, freshly malloc'd pages will be initialized
581 * to zeroes before use. This avoids persisting leftover data from other
582 * code (that used the heap and subsequently freed the memory) into the
583 * data file. Note that many other system libraries may allocate
584 * and free memory from the heap for arbitrary uses. E.g., stdio may
585 * use the heap for file I/O buffers. This initialization step has a
586 * modest performance cost so some applications may want to disable
587 * it using this flag. This option can be a problem for applications
588 * which handle sensitive data like passwords, and it makes memory
589 * checkers like Valgrind noisy. This flag is not needed with #MDB_WRITEMAP,
590 * which writes directly to the mmap instead of using malloc for pages. The
591 * initialization is also skipped if #MDB_RESERVE is used; the
592 * caller is expected to overwrite all of the memory that was
593 * reserved in that case.
594 * This flag may be changed at any time using #mdb_env_set_flags().
596 * @param[in] mode The UNIX permissions to set on created files. This parameter
597 * is ignored on Windows.
598 * @return A non-zero error value on failure and 0 on success. Some possible
601 * <li>#MDB_VERSION_MISMATCH - the version of the LMDB library doesn't match the
602 * version that created the database environment.
603 * <li>#MDB_INVALID - the environment file headers are corrupted.
604 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
605 * <li>EACCES - the user didn't have permission to access the environment files.
606 * <li>EAGAIN - the environment was locked by another process.
609 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode);
611 /** @brief Copy an LMDB environment to the specified path.
613 * This function may be used to make a backup of an existing environment.
614 * No lockfile is created, since it gets recreated at need.
615 * @note This call can trigger significant file size growth if run in
616 * parallel with write transactions, because it employs a read-only
617 * transaction. See long-lived transactions under @ref caveats_sec.
618 * @param[in] env An environment handle returned by #mdb_env_create(). It
619 * must have already been opened successfully.
620 * @param[in] path The directory in which the copy will reside. This
621 * directory must already exist and be writable but must otherwise be
623 * @return A non-zero error value on failure and 0 on success.
625 int mdb_env_copy(MDB_env *env, const char *path);
627 /** @brief Copy an LMDB environment to the specified file descriptor.
629 * This function may be used to make a backup of an existing environment.
630 * No lockfile is created, since it gets recreated at need.
631 * @note This call can trigger significant file size growth if run in
632 * parallel with write transactions, because it employs a read-only
633 * transaction. See long-lived transactions under @ref caveats_sec.
634 * @param[in] env An environment handle returned by #mdb_env_create(). It
635 * must have already been opened successfully.
636 * @param[in] fd The filedescriptor to write the copy to. It must
637 * have already been opened for Write access.
638 * @return A non-zero error value on failure and 0 on success.
640 int mdb_env_copyfd(MDB_env *env, mdb_filehandle_t fd);
642 /** @brief Copy an LMDB environment to the specified path, with options.
644 * This function may be used to make a backup of an existing environment.
645 * No lockfile is created, since it gets recreated at need.
646 * @note This call can trigger significant file size growth if run in
647 * parallel with write transactions, because it employs a read-only
648 * transaction. See long-lived transactions under @ref caveats_sec.
649 * @param[in] env An environment handle returned by #mdb_env_create(). It
650 * must have already been opened successfully.
651 * @param[in] path The directory in which the copy will reside. This
652 * directory must already exist and be writable but must otherwise be
654 * @param[in] flags Special options for this operation. This parameter
655 * must be set to 0 or by bitwise OR'ing together one or more of the
656 * values described here.
658 * <li>#MDB_CP_COMPACT - Perform compaction while copying: omit free
659 * pages and sequentially renumber all pages in output. This option
660 * consumes more CPU and runs more slowly than the default.
662 * @return A non-zero error value on failure and 0 on success.
664 int mdb_env_copy2(MDB_env *env, const char *path, unsigned int flags);
666 /** @brief Copy an LMDB environment to the specified file descriptor,
669 * This function may be used to make a backup of an existing environment.
670 * No lockfile is created, since it gets recreated at need. See
671 * #mdb_env_copy2() for further details.
672 * @note This call can trigger significant file size growth if run in
673 * parallel with write transactions, because it employs a read-only
674 * transaction. See long-lived transactions under @ref caveats_sec.
675 * @param[in] env An environment handle returned by #mdb_env_create(). It
676 * must have already been opened successfully.
677 * @param[in] fd The filedescriptor to write the copy to. It must
678 * have already been opened for Write access.
679 * @param[in] flags Special options for this operation.
680 * See #mdb_env_copy2() for options.
681 * @return A non-zero error value on failure and 0 on success.
683 int mdb_env_copyfd2(MDB_env *env, mdb_filehandle_t fd, unsigned int flags);
685 /** @brief Return statistics about the LMDB environment.
687 * @param[in] env An environment handle returned by #mdb_env_create()
688 * @param[out] stat The address of an #MDB_stat structure
689 * where the statistics will be copied
691 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
693 /** @brief Return information about the LMDB environment.
695 * @param[in] env An environment handle returned by #mdb_env_create()
696 * @param[out] stat The address of an #MDB_envinfo structure
697 * where the information will be copied
699 int mdb_env_info(MDB_env *env, MDB_envinfo *stat);
701 /** @brief Flush the data buffers to disk.
703 * Data is always written to disk when #mdb_txn_commit() is called,
704 * but the operating system may keep it buffered. LMDB always flushes
705 * the OS buffers upon commit as well, unless the environment was
706 * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC.
707 * @param[in] env An environment handle returned by #mdb_env_create()
708 * @param[in] force If non-zero, force a synchronous flush. Otherwise
709 * if the environment has the #MDB_NOSYNC flag set the flushes
710 * will be omitted, and with #MDB_MAPASYNC they will be asynchronous.
711 * @return A non-zero error value on failure and 0 on success. Some possible
714 * <li>EINVAL - an invalid parameter was specified.
715 * <li>EIO - an error occurred during synchronization.
718 int mdb_env_sync(MDB_env *env, int force);
720 /** @brief Close the environment and release the memory map.
722 * Only a single thread may call this function. All transactions, databases,
723 * and cursors must already be closed before calling this function. Attempts to
724 * use any such handles after calling this function will cause a SIGSEGV.
725 * The environment handle will be freed and must not be used again after this call.
726 * @param[in] env An environment handle returned by #mdb_env_create()
728 void mdb_env_close(MDB_env *env);
730 /** @brief Set environment flags.
732 * This may be used to set some flags in addition to those from
733 * #mdb_env_open(), or to unset these flags. If several threads
734 * change the flags at the same time, the result is undefined.
735 * Most flags cannot be changed after #mdb_env_open().
736 * @param[in] env An environment handle returned by #mdb_env_create()
737 * @param[in] flags The flags to change, bitwise OR'ed together
738 * @param[in] onoff A non-zero value sets the flags, zero clears them.
739 * @return A non-zero error value on failure and 0 on success. Some possible
742 * <li>EINVAL - an invalid parameter was specified.
745 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
747 /** @brief Get environment flags.
749 * @param[in] env An environment handle returned by #mdb_env_create()
750 * @param[out] flags The address of an integer to store the flags
751 * @return A non-zero error value on failure and 0 on success. Some possible
754 * <li>EINVAL - an invalid parameter was specified.
757 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
759 /** @brief Return the path that was used in #mdb_env_open().
761 * @param[in] env An environment handle returned by #mdb_env_create()
762 * @param[out] path Address of a string pointer to contain the path. This
763 * is the actual string in the environment, not a copy. It should not be
764 * altered in any way.
765 * @return A non-zero error value on failure and 0 on success. Some possible
768 * <li>EINVAL - an invalid parameter was specified.
771 int mdb_env_get_path(MDB_env *env, const char **path);
773 /** @brief Return the filedescriptor for the given environment.
775 * @param[in] env An environment handle returned by #mdb_env_create()
776 * @param[out] fd Address of a mdb_filehandle_t to contain the descriptor.
777 * @return A non-zero error value on failure and 0 on success. Some possible
780 * <li>EINVAL - an invalid parameter was specified.
783 int mdb_env_get_fd(MDB_env *env, mdb_filehandle_t *fd);
785 /** @brief Set the size of the memory map to use for this environment.
787 * The size should be a multiple of the OS page size. The default is
788 * 10485760 bytes. The size of the memory map is also the maximum size
789 * of the database. The value should be chosen as large as possible,
790 * to accommodate future growth of the database.
791 * This function should be called after #mdb_env_create() and before #mdb_env_open().
792 * It may be called at later times if no transactions are active in
793 * this process. Note that the library does not check for this condition,
794 * the caller must ensure it explicitly.
796 * The new size takes effect immediately for the current process but
797 * will not be persisted to any others until a write transaction has been
798 * committed by the current process. Also, only mapsize increases are
799 * persisted into the environment.
801 * If the mapsize is increased by another process, and data has grown
802 * beyond the range of the current mapsize, #mdb_txn_begin() will
803 * return #MDB_MAP_RESIZED. This function may be called with a size
804 * of zero to adopt the new size.
806 * Any attempt to set a size smaller than the space already consumed
807 * by the environment will be silently changed to the current size of the used space.
808 * @param[in] env An environment handle returned by #mdb_env_create()
809 * @param[in] size The size in bytes
810 * @return A non-zero error value on failure and 0 on success. Some possible
813 * <li>EINVAL - an invalid parameter was specified, or the environment has
814 * an active write transaction.
817 int mdb_env_set_mapsize(MDB_env *env, size_t size);
819 /** @brief Set the maximum number of threads/reader slots for the environment.
821 * This defines the number of slots in the lock table that is used to track readers in the
822 * the environment. The default is 126.
823 * Starting a read-only transaction normally ties a lock table slot to the
824 * current thread until the environment closes or the thread exits. If
825 * MDB_NOTLS is in use, #mdb_txn_begin() instead ties the slot to the
826 * MDB_txn object until it or the #MDB_env object is destroyed.
827 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
828 * @param[in] env An environment handle returned by #mdb_env_create()
829 * @param[in] readers The maximum number of reader lock table slots
830 * @return A non-zero error value on failure and 0 on success. Some possible
833 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
836 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
838 /** @brief Get the maximum number of threads/reader slots for the environment.
840 * @param[in] env An environment handle returned by #mdb_env_create()
841 * @param[out] readers Address of an integer to store the number of readers
842 * @return A non-zero error value on failure and 0 on success. Some possible
845 * <li>EINVAL - an invalid parameter was specified.
848 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
850 /** @brief Set the maximum number of named databases for the environment.
852 * This function is only needed if multiple databases will be used in the
853 * environment. Simpler applications that use the environment as a single
854 * unnamed database can ignore this option.
855 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
857 * Currently a moderate number of slots are cheap but a huge number gets
858 * expensive: 7-120 words per transaction, and every #mdb_dbi_open()
859 * does a linear search of the opened slots.
860 * @param[in] env An environment handle returned by #mdb_env_create()
861 * @param[in] dbs The maximum number of databases
862 * @return A non-zero error value on failure and 0 on success. Some possible
865 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
868 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
870 /** @brief Get the maximum size of keys and #MDB_DUPSORT data we can write.
872 * Depends on the compile-time constant #MDB_MAXKEYSIZE. Default 511.
874 * @param[in] env An environment handle returned by #mdb_env_create()
875 * @return The maximum size of a key we can write
877 int mdb_env_get_maxkeysize(MDB_env *env);
879 /** @brief Set application information associated with the #MDB_env.
881 * @param[in] env An environment handle returned by #mdb_env_create()
882 * @param[in] ctx An arbitrary pointer for whatever the application needs.
883 * @return A non-zero error value on failure and 0 on success.
885 int mdb_env_set_userctx(MDB_env *env, void *ctx);
887 /** @brief Get the application information associated with the #MDB_env.
889 * @param[in] env An environment handle returned by #mdb_env_create()
890 * @return The pointer set by #mdb_env_set_userctx().
892 void *mdb_env_get_userctx(MDB_env *env);
894 /** @brief A callback function for most LMDB assert() failures,
895 * called before printing the message and aborting.
897 * @param[in] env An environment handle returned by #mdb_env_create().
898 * @param[in] msg The assertion message, not including newline.
900 typedef void MDB_assert_func(MDB_env *env, const char *msg);
902 /** Set or reset the assert() callback of the environment.
903 * Disabled if liblmdb is buillt with NDEBUG.
904 * @note This hack should become obsolete as lmdb's error handling matures.
905 * @param[in] env An environment handle returned by #mdb_env_create().
906 * @param[in] func An #MDB_assert_func function, or 0.
907 * @return A non-zero error value on failure and 0 on success.
909 int mdb_env_set_assert(MDB_env *env, MDB_assert_func *func);
911 /** @brief Create a transaction for use with the environment.
913 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
914 * @note A transaction and its cursors must only be used by a single
915 * thread, and a thread may only have a single transaction at a time.
916 * If #MDB_NOTLS is in use, this does not apply to read-only transactions.
917 * @note Cursors may not span transactions.
918 * @param[in] env An environment handle returned by #mdb_env_create()
919 * @param[in] parent If this parameter is non-NULL, the new transaction
920 * will be a nested transaction, with the transaction indicated by \b parent
921 * as its parent. Transactions may be nested to any level. A parent
922 * transaction and its cursors may not issue any other operations than
923 * mdb_txn_commit and mdb_txn_abort while it has active child transactions.
924 * @param[in] flags Special options for this transaction. This parameter
925 * must be set to 0 or by bitwise OR'ing together one or more of the
926 * values described here.
929 * This transaction will not perform any write operations.
931 * @param[out] txn Address where the new #MDB_txn handle will be stored
932 * @return A non-zero error value on failure and 0 on success. Some possible
935 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
937 * <li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's
938 * mapsize and this environment's map must be resized as well.
939 * See #mdb_env_set_mapsize().
940 * <li>#MDB_READERS_FULL - a read-only transaction was requested and
941 * the reader lock table is full. See #mdb_env_set_maxreaders().
942 * <li>ENOMEM - out of memory.
945 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
947 /** @brief Returns the transaction's #MDB_env
949 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
951 MDB_env *mdb_txn_env(MDB_txn *txn);
953 /** @brief Commit all the operations of a transaction into the database.
955 * The transaction handle is freed. It and its cursors must not be used
956 * again after this call, except with #mdb_cursor_renew().
957 * @note Earlier documentation incorrectly said all cursors would be freed.
958 * Only write-transactions free cursors.
959 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
960 * @return A non-zero error value on failure and 0 on success. Some possible
963 * <li>EINVAL - an invalid parameter was specified.
964 * <li>ENOSPC - no more disk space.
965 * <li>EIO - a low-level I/O error occurred while writing.
966 * <li>ENOMEM - out of memory.
969 int mdb_txn_commit(MDB_txn *txn);
971 /** @brief Abandon all the operations of the transaction instead of saving them.
973 * The transaction handle is freed. It and its cursors must not be used
974 * again after this call, except with #mdb_cursor_renew().
975 * @note Earlier documentation incorrectly said all cursors would be freed.
976 * Only write-transactions free cursors.
977 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
979 void mdb_txn_abort(MDB_txn *txn);
981 /** @brief Reset a read-only transaction.
983 * Abort the transaction like #mdb_txn_abort(), but keep the transaction
984 * handle. #mdb_txn_renew() may reuse the handle. This saves allocation
985 * overhead if the process will start a new read-only transaction soon,
986 * and also locking overhead if #MDB_NOTLS is in use. The reader table
987 * lock is released, but the table slot stays tied to its thread or
988 * #MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free
989 * its lock table slot if MDB_NOTLS is in use.
990 * Cursors opened within the transaction must not be used
991 * again after this call, except with #mdb_cursor_renew().
992 * Reader locks generally don't interfere with writers, but they keep old
993 * versions of database pages allocated. Thus they prevent the old pages
994 * from being reused when writers commit new data, and so under heavy load
995 * the database size may grow much more rapidly than otherwise.
996 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
998 void mdb_txn_reset(MDB_txn *txn);
1000 /** @brief Renew a read-only transaction.
1002 * This acquires a new reader lock for a transaction handle that had been
1003 * released by #mdb_txn_reset(). It must be called before a reset transaction
1004 * may be used again.
1005 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1006 * @return A non-zero error value on failure and 0 on success. Some possible
1009 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
1010 * must be shut down.
1011 * <li>EINVAL - an invalid parameter was specified.
1014 int mdb_txn_renew(MDB_txn *txn);
1016 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
1017 #define mdb_open(txn,name,flags,dbi) mdb_dbi_open(txn,name,flags,dbi)
1018 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
1019 #define mdb_close(env,dbi) mdb_dbi_close(env,dbi)
1021 /** @brief Open a database in the environment.
1023 * A database handle denotes the name and parameters of a database,
1024 * independently of whether such a database exists.
1025 * The database handle may be discarded by calling #mdb_dbi_close().
1026 * The old database handle is returned if the database was already open.
1027 * The handle may only be closed once.
1028 * The database handle will be private to the current transaction until
1029 * the transaction is successfully committed. If the transaction is
1030 * aborted the handle will be closed automatically.
1031 * After a successful commit the
1032 * handle will reside in the shared environment, and may be used
1033 * by other transactions. This function must not be called from
1034 * multiple concurrent transactions. A transaction that uses this function
1035 * must finish (either commit or abort) before any other transaction may
1036 * use this function.
1038 * To use named databases (with name != NULL), #mdb_env_set_maxdbs()
1039 * must be called before opening the environment. Database names
1040 * are kept as keys in the unnamed database.
1041 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1042 * @param[in] name The name of the database to open. If only a single
1043 * database is needed in the environment, this value may be NULL.
1044 * @param[in] flags Special options for this database. This parameter
1045 * must be set to 0 or by bitwise OR'ing together one or more of the
1046 * values described here.
1048 * <li>#MDB_REVERSEKEY
1049 * Keys are strings to be compared in reverse order, from the end
1050 * of the strings to the beginning. By default, Keys are treated as strings and
1051 * compared from beginning to end.
1053 * Duplicate keys may be used in the database. (Or, from another perspective,
1054 * keys may have multiple data items, stored in sorted order.) By default
1055 * keys must be unique and may have only a single data item.
1056 * <li>#MDB_INTEGERKEY
1057 * Keys are binary integers in native byte order. Setting this option
1058 * requires all keys to be the same size, typically sizeof(int)
1059 * or sizeof(size_t).
1061 * This flag may only be used in combination with #MDB_DUPSORT. This option
1062 * tells the library that the data items for this database are all the same
1063 * size, which allows further optimizations in storage and retrieval. When
1064 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
1065 * cursor operations may be used to retrieve multiple items at once.
1066 * <li>#MDB_INTEGERDUP
1067 * This option specifies that duplicate data items are also integers, and
1068 * should be sorted as such.
1069 * <li>#MDB_REVERSEDUP
1070 * This option specifies that duplicate data items should be compared as
1071 * strings in reverse order.
1073 * Create the named database if it doesn't exist. This option is not
1074 * allowed in a read-only transaction or a read-only environment.
1076 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
1077 * @return A non-zero error value on failure and 0 on success. Some possible
1080 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
1081 * and #MDB_CREATE was not specified.
1082 * <li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs().
1085 int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
1087 /** @brief Retrieve statistics for a database.
1089 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1090 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1091 * @param[out] stat The address of an #MDB_stat structure
1092 * where the statistics will be copied
1093 * @return A non-zero error value on failure and 0 on success. Some possible
1096 * <li>EINVAL - an invalid parameter was specified.
1099 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
1101 /** @brief Retrieve the DB flags for a database handle.
1103 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1104 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1105 * @param[out] flags Address where the flags will be returned.
1106 * @return A non-zero error value on failure and 0 on success.
1108 int mdb_dbi_flags(MDB_txn *txn, MDB_dbi dbi, unsigned int *flags);
1110 /** @brief Close a database handle. Normally unnecessary. Use with care:
1112 * This call is not mutex protected. Handles should only be closed by
1113 * a single thread, and only if no other threads are going to reference
1114 * the database handle or one of its cursors any further. Do not close
1115 * a handle if an existing transaction has modified its database.
1116 * Doing so can cause misbehavior from database corruption to errors
1117 * like MDB_BAD_VALSIZE (since the DB name is gone).
1119 * Closing a database handle is not necessary, but lets #mdb_dbi_open()
1120 * reuse the handle value. Usually it's better to set a bigger
1121 * #mdb_env_set_maxdbs(), unless that value would be large.
1123 * @param[in] env An environment handle returned by #mdb_env_create()
1124 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1126 void mdb_dbi_close(MDB_env *env, MDB_dbi dbi);
1128 /** @brief Empty or delete+close a database.
1130 * See #mdb_dbi_close() for restrictions about closing the DB handle.
1131 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1132 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1133 * @param[in] del 0 to empty the DB, 1 to delete it from the
1134 * environment and close the DB handle.
1135 * @return A non-zero error value on failure and 0 on success.
1137 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
1139 /** @brief Set a custom key comparison function for a database.
1141 * The comparison function is called whenever it is necessary to compare a
1142 * key specified by the application with a key currently stored in the database.
1143 * If no comparison function is specified, and no special key flags were specified
1144 * with #mdb_dbi_open(), the keys are compared lexically, with shorter keys collating
1145 * before longer keys.
1146 * @warning This function must be called before any data access functions are used,
1147 * otherwise data corruption may occur. The same comparison function must be used by every
1148 * program accessing the database, every time the database is used.
1149 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1150 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1151 * @param[in] cmp A #MDB_cmp_func function
1152 * @return A non-zero error value on failure and 0 on success. Some possible
1155 * <li>EINVAL - an invalid parameter was specified.
1158 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
1160 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
1162 * This comparison function is called whenever it is necessary to compare a data
1163 * item specified by the application with a data item currently stored in the database.
1164 * This function only takes effect if the database was opened with the #MDB_DUPSORT
1166 * If no comparison function is specified, and no special key flags were specified
1167 * with #mdb_dbi_open(), the data items are compared lexically, with shorter items collating
1168 * before longer items.
1169 * @warning This function must be called before any data access functions are used,
1170 * otherwise data corruption may occur. The same comparison function must be used by every
1171 * program accessing the database, every time the database is used.
1172 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1173 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1174 * @param[in] cmp A #MDB_cmp_func function
1175 * @return A non-zero error value on failure and 0 on success. Some possible
1178 * <li>EINVAL - an invalid parameter was specified.
1181 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
1183 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
1185 * @todo The relocation function is called whenever it is necessary to move the data
1186 * of an item to a different position in the database (e.g. through tree
1187 * balancing operations, shifts as a result of adds or deletes, etc.). It is
1188 * intended to allow address/position-dependent data items to be stored in
1189 * a database in an environment opened with the #MDB_FIXEDMAP option.
1190 * Currently the relocation feature is unimplemented and setting
1191 * this function has no effect.
1192 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1193 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1194 * @param[in] rel A #MDB_rel_func function
1195 * @return A non-zero error value on failure and 0 on success. Some possible
1198 * <li>EINVAL - an invalid parameter was specified.
1201 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
1203 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
1205 * See #mdb_set_relfunc and #MDB_rel_func for more details.
1206 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1207 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1208 * @param[in] ctx An arbitrary pointer for whatever the application needs.
1209 * It will be passed to the callback function set by #mdb_set_relfunc
1210 * as its \b relctx parameter whenever the callback is invoked.
1211 * @return A non-zero error value on failure and 0 on success. Some possible
1214 * <li>EINVAL - an invalid parameter was specified.
1217 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
1219 /** @brief Get items from a database.
1221 * This function retrieves key/data pairs from the database. The address
1222 * and length of the data associated with the specified \b key are returned
1223 * in the structure to which \b data refers.
1224 * If the database supports duplicate keys (#MDB_DUPSORT) then the
1225 * first data item for the key will be returned. Retrieval of other
1226 * items requires the use of #mdb_cursor_get().
1228 * @note The memory pointed to by the returned values is owned by the
1229 * database. The caller need not dispose of the memory, and may not
1230 * modify it in any way. For values returned in a read-only transaction
1231 * any modification attempts will cause a SIGSEGV.
1232 * @note Values returned from the database are valid only until a
1233 * subsequent update operation, or the end of the transaction.
1234 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1235 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1236 * @param[in] key The key to search for in the database
1237 * @param[out] data The data corresponding to the key
1238 * @return A non-zero error value on failure and 0 on success. Some possible
1241 * <li>#MDB_NOTFOUND - the key was not in the database.
1242 * <li>EINVAL - an invalid parameter was specified.
1245 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1247 /** @brief Store items into a database.
1249 * This function stores key/data pairs in the database. The default behavior
1250 * is to enter the new key/data pair, replacing any previously existing key
1251 * if duplicates are disallowed, or adding a duplicate data item if
1252 * duplicates are allowed (#MDB_DUPSORT).
1253 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1254 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1255 * @param[in] key The key to store in the database
1256 * @param[in,out] data The data to store
1257 * @param[in] flags Special options for this operation. This parameter
1258 * must be set to 0 or by bitwise OR'ing together one or more of the
1259 * values described here.
1261 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1262 * already appear in the database. This flag may only be specified
1263 * if the database was opened with #MDB_DUPSORT. The function will
1264 * return #MDB_KEYEXIST if the key/data pair already appears in the
1266 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1267 * does not already appear in the database. The function will return
1268 * #MDB_KEYEXIST if the key already appears in the database, even if
1269 * the database supports duplicates (#MDB_DUPSORT). The \b data
1270 * parameter will be set to point to the existing item.
1271 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1272 * don't copy the given data. Instead, return a pointer to the
1273 * reserved space, which the caller can fill in later - before
1274 * the next update operation or the transaction ends. This saves
1275 * an extra memcpy if the data is being generated later.
1276 * LMDB does nothing else with this memory, the caller is expected
1277 * to modify all of the space requested.
1278 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1279 * database. No key comparisons are performed. This option allows
1280 * fast bulk loading when keys are already known to be in the
1281 * correct order. Loading unsorted keys with this flag will cause
1283 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1285 * @return A non-zero error value on failure and 0 on success. Some possible
1288 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1289 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1290 * <li>EACCES - an attempt was made to write in a read-only transaction.
1291 * <li>EINVAL - an invalid parameter was specified.
1294 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
1295 unsigned int flags);
1297 /** @brief Delete items from a database.
1299 * This function removes key/data pairs from the database.
1300 * If the database does not support sorted duplicate data items
1301 * (#MDB_DUPSORT) the data parameter is ignored.
1302 * If the database supports sorted duplicates and the data parameter
1303 * is NULL, all of the duplicate data items for the key will be
1304 * deleted. Otherwise, if the data parameter is non-NULL
1305 * only the matching data item will be deleted.
1306 * This function will return #MDB_NOTFOUND if the specified key/data
1307 * pair is not in the database.
1308 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1309 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1310 * @param[in] key The key to delete from the database
1311 * @param[in] data The data to delete
1312 * @return A non-zero error value on failure and 0 on success. Some possible
1315 * <li>EACCES - an attempt was made to write in a read-only transaction.
1316 * <li>EINVAL - an invalid parameter was specified.
1319 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1321 /** @brief Create a cursor handle.
1323 * A cursor is associated with a specific transaction and database.
1324 * A cursor cannot be used when its database handle is closed. Nor
1325 * when its transaction has ended, except with #mdb_cursor_renew().
1326 * It can be discarded with #mdb_cursor_close().
1327 * A cursor in a write-transaction can be closed before its transaction
1328 * ends, and will otherwise be closed when its transaction ends.
1329 * A cursor in a read-only transaction must be closed explicitly, before
1330 * or after its transaction ends. It can be reused with
1331 * #mdb_cursor_renew() before finally closing it.
1332 * @note Earlier documentation said that cursors in every transaction
1333 * were closed when the transaction committed or aborted.
1334 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1335 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1336 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
1337 * @return A non-zero error value on failure and 0 on success. Some possible
1340 * <li>EINVAL - an invalid parameter was specified.
1343 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
1345 /** @brief Close a cursor handle.
1347 * The cursor handle will be freed and must not be used again after this call.
1348 * Its transaction must still be live if it is a write-transaction.
1349 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1351 void mdb_cursor_close(MDB_cursor *cursor);
1353 /** @brief Renew a cursor handle.
1355 * A cursor is associated with a specific transaction and database.
1356 * Cursors that are only used in read-only
1357 * transactions may be re-used, to avoid unnecessary malloc/free overhead.
1358 * The cursor may be associated with a new read-only transaction, and
1359 * referencing the same database handle as it was created with.
1360 * This may be done whether the previous transaction is live or dead.
1361 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1362 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1363 * @return A non-zero error value on failure and 0 on success. Some possible
1366 * <li>EINVAL - an invalid parameter was specified.
1369 int mdb_cursor_renew(MDB_txn *txn, MDB_cursor *cursor);
1371 /** @brief Return the cursor's transaction handle.
1373 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1375 MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
1377 /** @brief Return the cursor's database handle.
1379 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1381 MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor);
1383 /** @brief Retrieve by cursor.
1385 * This function retrieves key/data pairs from the database. The address and length
1386 * of the key are returned in the object to which \b key refers (except for the
1387 * case of the #MDB_SET option, in which the \b key object is unchanged), and
1388 * the address and length of the data are returned in the object to which \b data
1390 * See #mdb_get() for restrictions on using the output values.
1391 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1392 * @param[in,out] key The key for a retrieved item
1393 * @param[in,out] data The data of a retrieved item
1394 * @param[in] op A cursor operation #MDB_cursor_op
1395 * @return A non-zero error value on failure and 0 on success. Some possible
1398 * <li>#MDB_NOTFOUND - no matching key found.
1399 * <li>EINVAL - an invalid parameter was specified.
1402 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1405 /** @brief Store by cursor.
1407 * This function stores key/data pairs into the database.
1408 * The cursor is positioned at the new item, or on failure usually near it.
1409 * @note Earlier documentation incorrectly said errors would leave the
1410 * state of the cursor unchanged.
1411 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1412 * @param[in] key The key operated on.
1413 * @param[in] data The data operated on.
1414 * @param[in] flags Options for this operation. This parameter
1415 * must be set to 0 or one of the values described here.
1417 * <li>#MDB_CURRENT - replace the item at the current cursor position.
1418 * The \b key parameter must still be provided, and must match it.
1419 * If using sorted duplicates (#MDB_DUPSORT) the data item must still
1420 * sort into the same place. This is intended to be used when the
1421 * new data is the same size as the old. Otherwise it will simply
1422 * perform a delete of the old record followed by an insert.
1423 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1424 * already appear in the database. This flag may only be specified
1425 * if the database was opened with #MDB_DUPSORT. The function will
1426 * return #MDB_KEYEXIST if the key/data pair already appears in the
1428 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1429 * does not already appear in the database. The function will return
1430 * #MDB_KEYEXIST if the key already appears in the database, even if
1431 * the database supports duplicates (#MDB_DUPSORT).
1432 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1433 * don't copy the given data. Instead, return a pointer to the
1434 * reserved space, which the caller can fill in later. This saves
1435 * an extra memcpy if the data is being generated later.
1436 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1437 * database. No key comparisons are performed. This option allows
1438 * fast bulk loading when keys are already known to be in the
1439 * correct order. Loading unsorted keys with this flag will cause
1441 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1442 * <li>#MDB_MULTIPLE - store multiple contiguous data elements in a
1443 * single request. This flag may only be specified if the database
1444 * was opened with #MDB_DUPFIXED. The \b data argument must be an
1445 * array of two MDB_vals. The mv_size of the first MDB_val must be
1446 * the size of a single data element. The mv_data of the first MDB_val
1447 * must point to the beginning of the array of contiguous data elements.
1448 * The mv_size of the second MDB_val must be the count of the number
1449 * of data elements to store. On return this field will be set to
1450 * the count of the number of elements actually written. The mv_data
1451 * of the second MDB_val is unused.
1453 * @return A non-zero error value on failure and 0 on success. Some possible
1456 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1457 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1458 * <li>EACCES - an attempt was made to modify a read-only database.
1459 * <li>EINVAL - an invalid parameter was specified.
1462 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1463 unsigned int flags);
1465 /** @brief Delete current key/data pair
1467 * This function deletes the key/data pair to which the cursor refers.
1468 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1469 * @param[in] flags Options for this operation. This parameter
1470 * must be set to 0 or one of the values described here.
1472 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
1473 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
1475 * @return A non-zero error value on failure and 0 on success. Some possible
1478 * <li>EACCES - an attempt was made to modify a read-only database.
1479 * <li>EINVAL - an invalid parameter was specified.
1482 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
1484 /** @brief Return count of duplicates for current key.
1486 * This call is only valid on databases that support sorted duplicate
1487 * data items #MDB_DUPSORT.
1488 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1489 * @param[out] countp Address where the count will be stored
1490 * @return A non-zero error value on failure and 0 on success. Some possible
1493 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
1496 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
1498 /** @brief Compare two data items according to a particular database.
1500 * This returns a comparison as if the two data items were keys in the
1501 * specified database.
1502 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1503 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1504 * @param[in] a The first item to compare
1505 * @param[in] b The second item to compare
1506 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1508 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1510 /** @brief Compare two data items according to a particular database.
1512 * This returns a comparison as if the two items were data items of
1513 * the specified database. The database must have the #MDB_DUPSORT flag.
1514 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1515 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1516 * @param[in] a The first item to compare
1517 * @param[in] b The second item to compare
1518 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1520 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1522 /** @brief A callback function used to print a message from the library.
1524 * @param[in] msg The string to be printed.
1525 * @param[in] ctx An arbitrary context pointer for the callback.
1526 * @return < 0 on failure, >= 0 on success.
1528 typedef int (MDB_msg_func)(const char *msg, void *ctx);
1530 /** @brief Dump the entries in the reader lock table.
1532 * @param[in] env An environment handle returned by #mdb_env_create()
1533 * @param[in] func A #MDB_msg_func function
1534 * @param[in] ctx Anything the message function needs
1535 * @return < 0 on failure, >= 0 on success.
1537 int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx);
1539 /** @brief Check for stale entries in the reader lock table.
1541 * @param[in] env An environment handle returned by #mdb_env_create()
1542 * @param[out] dead Number of stale slots that were cleared
1543 * @return 0 on success, non-zero on failure.
1545 int mdb_reader_check(MDB_env *env, int *dead);
1551 /** @page tools LMDB Command Line Tools
1552 The following describes the command line tools that are available for LMDB.
1559 #endif /* _LMDB_H_ */