2 * @brief Lightning memory-mapped database library
4 * @mainpage Lightning Memory-Mapped Database Manager (MDB)
6 * @section intro_sec Introduction
7 * MDB 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, MDB 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. MDB 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: Terminate all programs using the database, or make
52 * them close it. Next database user will reset the lockfile.
54 * - On BSD systems or others configured with MDB_USE_POSIX_SEM,
55 * startup can fail due to semaphores owned by another userid.
57 * Fix: Open and close the database as the user which owns the
58 * semaphores (likely last user) or as root, while no other
59 * process is using the database.
61 * Restrictions/caveats (in addition to those listed for some functions):
63 * - Only the database owner should normally use the database on
64 * BSD systems or when otherwise configured with MDB_USE_POSIX_SEM.
65 * Multiple users can cause startup to fail later, as noted above.
67 * - A thread can only use one transaction at a time, plus any child
68 * transactions. Each transaction belongs to one thread. See below.
69 * The #MDB_NOTLS flag changes this for read-only transactions.
71 * - Use an MDB_env* in the process which opened it, without fork()ing.
73 * - Do not have open an MDB database twice in the same process at
74 * the same time. Not even from a plain open() call - close()ing it
75 * breaks flock() advisory locking.
77 * - Avoid long-lived transactions. Read transactions prevent
78 * reuse of pages freed by newer write transactions, thus the
79 * database can grow quickly. Write transactions prevent
80 * other write transactions, since writes are serialized.
82 * - Avoid suspending a process with active transactions. These
83 * would then be "long-lived" as above. Also read transactions
84 * suspended when writers commit could sometimes see wrong data.
86 * ...when several processes can use a database concurrently:
88 * - Avoid aborting a process with an active transaction.
89 * The transaction becomes "long-lived" as above until the lockfile
90 * is reset, since the process may not remove it from the lockfile.
92 * - If you do that anyway, close the environment once in a while,
93 * so the lockfile can get reset.
95 * - Do not use MDB databases on remote filesystems, even between
96 * processes on the same host. This breaks flock() on some OSes,
97 * possibly memory map sync, and certainly sync between programs
100 * - Opening a database can fail if another process is opening or
101 * closing it at exactly the same time.
103 * @author Howard Chu, Symas Corporation.
105 * @copyright Copyright 2011-2013 Howard Chu, Symas Corp. All rights reserved.
107 * Redistribution and use in source and binary forms, with or without
108 * modification, are permitted only as authorized by the OpenLDAP
111 * A copy of this license is available in the file LICENSE in the
112 * top-level directory of the distribution or, alternatively, at
113 * <http://www.OpenLDAP.org/license.html>.
116 * This code is derived from btree.c written by Martin Hedenfalk.
118 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
120 * Permission to use, copy, modify, and distribute this software for any
121 * purpose with or without fee is hereby granted, provided that the above
122 * copyright notice and this permission notice appear in all copies.
124 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
125 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
126 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
127 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
128 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
129 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
130 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
135 #include <sys/types.h>
142 typedef int mdb_mode_t;
144 typedef mode_t mdb_mode_t;
147 /** An abstraction for a file handle.
148 * On POSIX systems file handles are small integers. On Windows
149 * they're opaque pointers.
152 typedef void *mdb_filehandle_t;
154 typedef int mdb_filehandle_t;
157 /** @defgroup mdb MDB API
159 * @brief OpenLDAP Lightning Memory-Mapped Database Manager
161 /** @defgroup Version Version Macros
164 /** Library major version */
165 #define MDB_VERSION_MAJOR 0
166 /** Library minor version */
167 #define MDB_VERSION_MINOR 9
168 /** Library patch version */
169 #define MDB_VERSION_PATCH 7
171 /** Combine args a,b,c into a single integer for easy version comparisons */
172 #define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
174 /** The full library version as a single integer */
175 #define MDB_VERSION_FULL \
176 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
178 /** The release date of this library version */
179 #define MDB_VERSION_DATE "January 10, 2013"
181 /** A stringifier for the version info */
182 #define MDB_VERSTR(a,b,c,d) "MDB " #a "." #b "." #c ": (" d ")"
184 /** A helper for the stringifier macro */
185 #define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d)
187 /** The full library version as a C string */
188 #define MDB_VERSION_STRING \
189 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
192 /** @brief Opaque structure for a database environment.
194 * A DB environment supports multiple databases, all residing in the same
197 typedef struct MDB_env MDB_env;
199 /** @brief Opaque structure for a transaction handle.
201 * All database operations require a transaction handle. Transactions may be
202 * read-only or read-write.
204 typedef struct MDB_txn MDB_txn;
206 /** @brief A handle for an individual database in the DB environment. */
207 typedef unsigned int MDB_dbi;
209 /** @brief Opaque structure for navigating through a database */
210 typedef struct MDB_cursor MDB_cursor;
212 /** @brief Generic structure used for passing keys and data in and out
215 * Key sizes must be between 1 and the liblmdb build-time constant
216 * #MDB_MAXKEYSIZE inclusive. This currently defaults to 511. The
217 * same applies to data sizes in databases with the #MDB_DUPSORT flag.
218 * Other data items can in theory be from 0 to 0xffffffff bytes long.
220 * Values returned from the database are valid only until a subsequent
221 * update operation, or the end of the transaction.
223 typedef struct MDB_val {
224 size_t mv_size; /**< size of the data item */
225 void *mv_data; /**< address of the data item */
228 /** @brief A callback function used to compare two keys in a database */
229 typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
231 /** @brief A callback function used to relocate a position-dependent data item
232 * in a fixed-address database.
234 * The \b newptr gives the item's desired address in
235 * the memory map, and \b oldptr gives its previous address. The item's actual
236 * data resides at the address in \b item. This callback is expected to walk
237 * through the fields of the record in \b item and modify any
238 * values based at the \b oldptr address to be relative to the \b newptr address.
239 * @param[in,out] item The item that is to be relocated.
240 * @param[in] oldptr The previous address.
241 * @param[in] newptr The new address to relocate to.
242 * @param[in] relctx An application-provided context, set by #mdb_set_relctx().
243 * @todo This feature is currently unimplemented.
245 typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
247 /** @defgroup mdb_env Environment Flags
249 * Values do not overlap Database Flags.
252 /** mmap at a fixed address (experimental) */
253 #define MDB_FIXEDMAP 0x01
254 /** no environment directory */
255 #define MDB_NOSUBDIR 0x4000
256 /** don't fsync after commit */
257 #define MDB_NOSYNC 0x10000
259 #define MDB_RDONLY 0x20000
260 /** don't fsync metapage after commit */
261 #define MDB_NOMETASYNC 0x40000
262 /** use writable mmap */
263 #define MDB_WRITEMAP 0x80000
264 /** use asynchronous msync when MDB_WRITEMAP is used */
265 #define MDB_MAPASYNC 0x100000
266 /** tie reader locktable slots to #MDB_txn objects instead of to threads */
267 #define MDB_NOTLS 0x200000
270 /** @defgroup mdb_dbi_open Database Flags
272 * Values do not overlap Environment Flags.
275 /** use reverse string keys */
276 #define MDB_REVERSEKEY 0x02
277 /** use sorted duplicates */
278 #define MDB_DUPSORT 0x04
279 /** numeric keys in native byte order.
280 * The keys must all be of the same size. */
281 #define MDB_INTEGERKEY 0x08
282 /** with #MDB_DUPSORT, sorted dup items have fixed size */
283 #define MDB_DUPFIXED 0x10
284 /** with #MDB_DUPSORT, dups are numeric in native byte order */
285 #define MDB_INTEGERDUP 0x20
286 /** with #MDB_DUPSORT, use reverse string dups */
287 #define MDB_REVERSEDUP 0x40
288 /** create DB if not already existing */
289 #define MDB_CREATE 0x40000
292 /** @defgroup mdb_put Write Flags
295 /** For put: Don't write if the key already exists. */
296 #define MDB_NOOVERWRITE 0x10
297 /** Only for #MDB_DUPSORT<br>
298 * For put: don't write if the key and data pair already exist.<br>
299 * For mdb_cursor_del: remove all duplicate data items.
301 #define MDB_NODUPDATA 0x20
302 /** For mdb_cursor_put: overwrite the current key/data pair */
303 #define MDB_CURRENT 0x40
304 /** For put: Just reserve space for data, don't copy it. Return a
305 * pointer to the reserved space.
307 #define MDB_RESERVE 0x10000
308 /** Data is being appended, don't split full pages. */
309 #define MDB_APPEND 0x20000
310 /** Duplicate data is being appended, don't split full pages. */
311 #define MDB_APPENDDUP 0x40000
312 /** Store multiple data items in one call. Only for #MDB_DUPFIXED. */
313 #define MDB_MULTIPLE 0x80000
316 /** @brief Cursor Get operations.
318 * This is the set of all operations for retrieving data
321 typedef enum MDB_cursor_op {
322 MDB_FIRST, /**< Position at first key/data item */
323 MDB_FIRST_DUP, /**< Position at first data item of current key.
324 Only for #MDB_DUPSORT */
325 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
326 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
327 MDB_GET_CURRENT, /**< Return key/data at current cursor position */
328 MDB_GET_MULTIPLE, /**< Return all the duplicate data items at the current
329 cursor position. Only for #MDB_DUPFIXED */
330 MDB_LAST, /**< Position at last key/data item */
331 MDB_LAST_DUP, /**< Position at last data item of current key.
332 Only for #MDB_DUPSORT */
333 MDB_NEXT, /**< Position at next data item */
334 MDB_NEXT_DUP, /**< Position at next data item of current key.
335 Only for #MDB_DUPSORT */
336 MDB_NEXT_MULTIPLE, /**< Return all duplicate data items at the next
337 cursor position. Only for #MDB_DUPFIXED */
338 MDB_NEXT_NODUP, /**< Position at first data item of next key */
339 MDB_PREV, /**< Position at previous data item */
340 MDB_PREV_DUP, /**< Position at previous data item of current key.
341 Only for #MDB_DUPSORT */
342 MDB_PREV_NODUP, /**< Position at last data item of previous key */
343 MDB_SET, /**< Position at specified key */
344 MDB_SET_KEY, /**< Position at specified key, return key + data */
345 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
348 /** @defgroup errors Return Codes
350 * BerkeleyDB uses -30800 to -30999, we'll go under them
353 /** Successful result */
354 #define MDB_SUCCESS 0
355 /** key/data pair already exists */
356 #define MDB_KEYEXIST (-30799)
357 /** key/data pair not found (EOF) */
358 #define MDB_NOTFOUND (-30798)
359 /** Requested page not found - this usually indicates corruption */
360 #define MDB_PAGE_NOTFOUND (-30797)
361 /** Located page was wrong type */
362 #define MDB_CORRUPTED (-30796)
363 /** Update of meta page failed, probably I/O error */
364 #define MDB_PANIC (-30795)
365 /** Environment version mismatch */
366 #define MDB_VERSION_MISMATCH (-30794)
367 /** File is not a valid MDB file */
368 #define MDB_INVALID (-30793)
369 /** Environment mapsize reached */
370 #define MDB_MAP_FULL (-30792)
371 /** Environment maxdbs reached */
372 #define MDB_DBS_FULL (-30791)
373 /** Environment maxreaders reached */
374 #define MDB_READERS_FULL (-30790)
375 /** Too many TLS keys in use - Windows only */
376 #define MDB_TLS_FULL (-30789)
377 /** Txn has too many dirty pages */
378 #define MDB_TXN_FULL (-30788)
379 /** Cursor stack too deep - internal error */
380 #define MDB_CURSOR_FULL (-30787)
381 /** Page has not enough space - internal error */
382 #define MDB_PAGE_FULL (-30786)
383 /** Database contents grew beyond environment mapsize */
384 #define MDB_MAP_RESIZED (-30785)
385 /** Database flags changed or would change */
386 #define MDB_INCOMPATIBLE (-30784)
387 /** Invalid reuse of reader locktable slot */
388 #define MDB_BAD_RSLOT (-30783)
389 #define MDB_LAST_ERRCODE MDB_BAD_RSLOT
392 /** @brief Statistics for a database in the environment */
393 typedef struct MDB_stat {
394 unsigned int ms_psize; /**< Size of a database page.
395 This is currently the same for all databases. */
396 unsigned int ms_depth; /**< Depth (height) of the B-tree */
397 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
398 size_t ms_leaf_pages; /**< Number of leaf pages */
399 size_t ms_overflow_pages; /**< Number of overflow pages */
400 size_t ms_entries; /**< Number of data items */
403 /** @brief Information about the environment */
404 typedef struct MDB_envinfo {
405 void *me_mapaddr; /**< Address of map, if fixed */
406 size_t me_mapsize; /**< Size of the data memory map */
407 size_t me_last_pgno; /**< ID of the last used page */
408 size_t me_last_txnid; /**< ID of the last committed transaction */
409 unsigned int me_maxreaders; /**< max reader slots in the environment */
410 unsigned int me_numreaders; /**< max reader slots used in the environment */
413 /** @brief Return the mdb library version information.
415 * @param[out] major if non-NULL, the library major version number is copied here
416 * @param[out] minor if non-NULL, the library minor version number is copied here
417 * @param[out] patch if non-NULL, the library patch version number is copied here
418 * @retval "version string" The library version as a string
420 char *mdb_version(int *major, int *minor, int *patch);
422 /** @brief Return a string describing a given error code.
424 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
425 * function. If the error code is greater than or equal to 0, then the string
426 * returned by the system function strerror(3) is returned. If the error code
427 * is less than 0, an error string corresponding to the MDB library error is
428 * returned. See @ref errors for a list of MDB-specific error codes.
429 * @param[in] err The error code
430 * @retval "error message" The description of the error
432 char *mdb_strerror(int err);
434 /** @brief Create an MDB environment handle.
436 * This function allocates memory for a #MDB_env structure. To release
437 * the allocated memory and discard the handle, call #mdb_env_close().
438 * Before the handle may be used, it must be opened using #mdb_env_open().
439 * Various other options may also need to be set before opening the handle,
440 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
441 * depending on usage requirements.
442 * @param[out] env The address where the new handle will be stored
443 * @return A non-zero error value on failure and 0 on success.
445 int mdb_env_create(MDB_env **env);
447 /** @brief Open an environment handle.
449 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
450 * @param[in] env An environment handle returned by #mdb_env_create()
451 * @param[in] path The directory in which the database files reside. This
452 * directory must already exist and be writable.
453 * @param[in] flags Special options for this environment. This parameter
454 * must be set to 0 or by bitwise OR'ing together one or more of the
455 * values described here.
456 * Flags set by mdb_env_set_flags() are also used.
459 * use a fixed address for the mmap region. This flag must be specified
460 * when creating the environment, and is stored persistently in the environment.
461 * If successful, the memory map will always reside at the same virtual address
462 * and pointers used to reference data items in the database will be constant
463 * across multiple invocations. This option may not always work, depending on
464 * how the operating system has allocated memory to shared libraries and other uses.
465 * The feature is highly experimental.
467 * By default, MDB creates its environment in a directory whose
468 * pathname is given in \b path, and creates its data and lock files
469 * under that directory. With this option, \b path is used as-is for
470 * the database main data file. The database lock file is the \b path
471 * with "-lock" appended.
473 * Open the environment in read-only mode. No write operations will be
474 * allowed. MDB will still modify the lock file - except on read-only
475 * filesystems, where MDB does not use locks.
477 * Use a writeable memory map unless MDB_RDONLY is set. This is faster
478 * and uses fewer mallocs, but loses protection from application bugs
479 * like wild pointer writes and other bad updates into the database.
480 * Incompatible with nested transactions.
481 * <li>#MDB_NOMETASYNC
482 * Flush system buffers to disk only once per transaction, omit the
483 * metadata flush. Defer that until the system flushes files to disk,
484 * or next non-MDB_RDONLY commit or #mdb_env_sync(). This optimization
485 * maintains database integrity, but a system crash may undo the last
486 * committed transaction. I.e. it preserves the ACI (atomicity,
487 * consistency, isolation) but not D (durability) database property.
488 * This flag may be changed at any time using #mdb_env_set_flags().
490 * Don't flush system buffers to disk when committing a transaction.
491 * This optimization means a system crash can corrupt the database or
492 * lose the last transactions if buffers are not yet flushed to disk.
493 * The risk is governed by how often the system flushes dirty buffers
494 * to disk and how often #mdb_env_sync() is called. However, if the
495 * filesystem preserves write order and the #MDB_WRITEMAP flag is not
496 * used, transactions exhibit ACI (atomicity, consistency, isolation)
497 * properties and only lose D (durability). I.e. database integrity
498 * is maintained, but a system crash may undo the final transactions.
499 * Note that (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no
500 * hint for when to write transactions to disk, unless #mdb_env_sync()
501 * is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable.
502 * This flag may be changed at any time using #mdb_env_set_flags().
504 * When using #MDB_WRITEMAP, use asynchronous flushes to disk.
505 * As with #MDB_NOSYNC, a system crash can then corrupt the
506 * database or lose the last transactions. Calling #mdb_env_sync()
507 * ensures on-disk database integrity until next commit.
508 * This flag may be changed at any time using #mdb_env_set_flags().
510 * Don't use Thread-Local Storage. Tie reader locktable slots to
511 * #MDB_txn objects instead of to threads. I.e. #mdb_txn_reset() keeps
512 * the slot reseved for the #MDB_txn object. A thread may use parallel
513 * read-only transactions. A read-only transaction may span threads if
514 * the user synchronizes its use. Applications that multiplex many
515 * user threads over individual OS threads need this option. Such an
516 * application must also serialize the write transactions in an OS
517 * thread, since MDB's write locking is unaware of the user threads.
519 * @param[in] mode The UNIX permissions to set on created files. This parameter
520 * is ignored on Windows.
521 * @return A non-zero error value on failure and 0 on success. Some possible
524 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
525 * version that created the database environment.
526 * <li>#MDB_INVALID - the environment file headers are corrupted.
527 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
528 * <li>EACCES - the user didn't have permission to access the environment files.
529 * <li>EAGAIN - the environment was locked by another process.
532 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode);
534 /** @brief Copy an MDB environment to the specified path.
536 * This function may be used to make a backup of an existing environment.
537 * @param[in] env An environment handle returned by #mdb_env_create(). It
538 * must have already been opened successfully.
539 * @param[in] path The directory in which the copy will reside. This
540 * directory must already exist and be writable but must otherwise be
542 * @return A non-zero error value on failure and 0 on success.
544 int mdb_env_copy(MDB_env *env, const char *path);
546 /** @brief Copy an MDB environment to the specified file descriptor.
548 * This function may be used to make a backup of an existing environment.
549 * @param[in] env An environment handle returned by #mdb_env_create(). It
550 * must have already been opened successfully.
551 * @param[in] fd The filedescriptor to write the copy to. It must
552 * have already been opened for Write access.
553 * @return A non-zero error value on failure and 0 on success.
555 int mdb_env_copyfd(MDB_env *env, mdb_filehandle_t fd);
557 /** @brief Return statistics about the MDB environment.
559 * @param[in] env An environment handle returned by #mdb_env_create()
560 * @param[out] stat The address of an #MDB_stat structure
561 * where the statistics will be copied
563 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
565 /** @brief Return information about the MDB environment.
567 * @param[in] env An environment handle returned by #mdb_env_create()
568 * @param[out] stat The address of an #MDB_envinfo structure
569 * where the information will be copied
571 int mdb_env_info(MDB_env *env, MDB_envinfo *stat);
573 /** @brief Flush the data buffers to disk.
575 * Data is always written to disk when #mdb_txn_commit() is called,
576 * but the operating system may keep it buffered. MDB always flushes
577 * the OS buffers upon commit as well, unless the environment was
578 * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC.
579 * @param[in] env An environment handle returned by #mdb_env_create()
580 * @param[in] force If non-zero, force a synchronous flush. Otherwise
581 * if the environment has the #MDB_NOSYNC flag set the flushes
582 * will be omitted, and with #MDB_MAPASYNC they will be asynchronous.
583 * @return A non-zero error value on failure and 0 on success. Some possible
586 * <li>EINVAL - an invalid parameter was specified.
587 * <li>EIO - an error occurred during synchronization.
590 int mdb_env_sync(MDB_env *env, int force);
592 /** @brief Close the environment and release the memory map.
594 * Only a single thread may call this function. All transactions, databases,
595 * and cursors must already be closed before calling this function. Attempts to
596 * use any such handles after calling this function will cause a SIGSEGV.
597 * The environment handle will be freed and must not be used again after this call.
598 * @param[in] env An environment handle returned by #mdb_env_create()
600 void mdb_env_close(MDB_env *env);
602 /** @brief Set environment flags.
604 * This may be used to set some flags in addition to those from
605 * #mdb_env_open(), or to unset these flags.
606 * @param[in] env An environment handle returned by #mdb_env_create()
607 * @param[in] flags The flags to change, bitwise OR'ed together
608 * @param[in] onoff A non-zero value sets the flags, zero clears them.
609 * @return A non-zero error value on failure and 0 on success. Some possible
612 * <li>EINVAL - an invalid parameter was specified.
615 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
617 /** @brief Get environment flags.
619 * @param[in] env An environment handle returned by #mdb_env_create()
620 * @param[out] flags The address of an integer to store the flags
621 * @return A non-zero error value on failure and 0 on success. Some possible
624 * <li>EINVAL - an invalid parameter was specified.
627 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
629 /** @brief Return the path that was used in #mdb_env_open().
631 * @param[in] env An environment handle returned by #mdb_env_create()
632 * @param[out] path Address of a string pointer to contain the path. This
633 * is the actual string in the environment, not a copy. It should not be
634 * altered in any way.
635 * @return A non-zero error value on failure and 0 on success. Some possible
638 * <li>EINVAL - an invalid parameter was specified.
641 int mdb_env_get_path(MDB_env *env, const char **path);
643 /** @brief Set the size of the memory map to use for this environment.
645 * The size should be a multiple of the OS page size. The default is
646 * 10485760 bytes. The size of the memory map is also the maximum size
647 * of the database. The value should be chosen as large as possible,
648 * to accommodate future growth of the database.
649 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
650 * The size may be changed by closing and reopening the environment.
651 * Any attempt to set a size smaller than the space already consumed
652 * by the environment will be silently changed to the current size of the used space.
653 * @param[in] env An environment handle returned by #mdb_env_create()
654 * @param[in] size The size in bytes
655 * @return A non-zero error value on failure and 0 on success. Some possible
658 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
661 int mdb_env_set_mapsize(MDB_env *env, size_t size);
663 /** @brief Set the maximum number of threads/reader slots for the environment.
665 * This defines the number of slots in the lock table that is used to track readers in the
666 * the environment. The default is 126.
667 * Starting a read-only transaction normally ties a lock table slot to the
668 * current thread until the environment closes or the thread exits. If
669 * MDB_NOTLS is in use, #mdb_txn_begin() instead ties the slot to the
670 * MDB_txn object until it or the #MDB_env object is destroyed.
671 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
672 * @param[in] env An environment handle returned by #mdb_env_create()
673 * @param[in] readers The maximum number of reader lock table slots
674 * @return A non-zero error value on failure and 0 on success. Some possible
677 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
680 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
682 /** @brief Get the maximum number of threads/reader slots for the environment.
684 * @param[in] env An environment handle returned by #mdb_env_create()
685 * @param[out] readers Address of an integer to store the number of readers
686 * @return A non-zero error value on failure and 0 on success. Some possible
689 * <li>EINVAL - an invalid parameter was specified.
692 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
694 /** @brief Set the maximum number of named databases for the environment.
696 * This function is only needed if multiple databases will be used in the
697 * environment. Simpler applications that use the environment as a single
698 * unnamed database can ignore this option.
699 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
700 * @param[in] env An environment handle returned by #mdb_env_create()
701 * @param[in] dbs The maximum number of databases
702 * @return A non-zero error value on failure and 0 on success. Some possible
705 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
708 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
710 /** @brief Create a transaction for use with the environment.
712 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
713 * @note A transaction and its cursors must only be used by a single
714 * thread, and a thread may only have a single transaction at a time.
715 * If #MDB_NOTLS is in use, this does not apply to read-only transactions.
716 * @note Cursors may not span transactions.
717 * @param[in] env An environment handle returned by #mdb_env_create()
718 * @param[in] parent If this parameter is non-NULL, the new transaction
719 * will be a nested transaction, with the transaction indicated by \b parent
720 * as its parent. Transactions may be nested to any level. A parent
721 * transaction may not issue any other operations besides mdb_txn_begin,
722 * mdb_txn_abort, or mdb_txn_commit while it has active child transactions.
723 * @param[in] flags Special options for this transaction. This parameter
724 * must be set to 0 or by bitwise OR'ing together one or more of the
725 * values described here.
728 * This transaction will not perform any write operations.
730 * @param[out] txn Address where the new #MDB_txn handle will be stored
731 * @return A non-zero error value on failure and 0 on success. Some possible
734 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
736 * <li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's
737 * mapsize and the environment must be shut down.
738 * <li>#MDB_READERS_FULL - a read-only transaction was requested and
739 * the reader lock table is full. See #mdb_env_set_maxreaders().
740 * <li>ENOMEM - out of memory.
743 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
745 /** @brief Commit all the operations of a transaction into the database.
747 * The transaction handle is freed. It and its cursors must not be used
748 * again after this call, except with #mdb_cursor_renew().
749 * @note Earlier documentation incorrectly said all cursors would be freed.
750 * Only write-transactions free cursors.
751 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
752 * @return A non-zero error value on failure and 0 on success. Some possible
755 * <li>EINVAL - an invalid parameter was specified.
756 * <li>ENOSPC - no more disk space.
757 * <li>EIO - a low-level I/O error occurred while writing.
758 * <li>ENOMEM - out of memory.
761 int mdb_txn_commit(MDB_txn *txn);
763 /** @brief Abandon all the operations of the transaction instead of saving them.
765 * The transaction handle is freed. It and its cursors must not be used
766 * again after this call, except with #mdb_cursor_renew().
767 * @note Earlier documentation incorrectly said all cursors would be freed.
768 * Only write-transactions free cursors.
769 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
771 void mdb_txn_abort(MDB_txn *txn);
773 /** @brief Reset a read-only transaction.
775 * Abort the transaction like #mdb_txn_abort(), but keep the transaction
776 * handle. #mdb_txn_renew() may reuse the handle. This saves allocation
777 * overhead if the process will start a new read-only transaction soon,
778 * and also locking overhead if #MDB_NOTLS is in use. The reader table
779 * lock is released, but the table slot stays tied to its thread or
780 * #MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free
781 * its lock table slot if MDB_NOTLS is in use.
782 * Cursors opened within the transaction must not be used
783 * again after this call, except with #mdb_cursor_renew().
784 * Reader locks generally don't interfere with writers, but they keep old
785 * versions of database pages allocated. Thus they prevent the old pages
786 * from being reused when writers commit new data, and so under heavy load
787 * the database size may grow much more rapidly than otherwise.
788 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
790 void mdb_txn_reset(MDB_txn *txn);
792 /** @brief Renew a read-only transaction.
794 * This acquires a new reader lock for a transaction handle that had been
795 * released by #mdb_txn_reset(). It must be called before a reset transaction
797 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
798 * @return A non-zero error value on failure and 0 on success. Some possible
801 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
803 * <li>EINVAL - an invalid parameter was specified.
806 int mdb_txn_renew(MDB_txn *txn);
808 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
809 #define mdb_open(txn,name,flags,dbi) mdb_dbi_open(txn,name,flags,dbi)
810 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
811 #define mdb_close(env,dbi) mdb_dbi_close(env,dbi)
813 /** @brief Open a database in the environment.
815 * A database handle denotes the name and parameters of a database,
816 * independently of whether such a database exists.
817 * The database handle may be discarded by calling #mdb_dbi_close().
818 * The old database handle is returned if the database was already open.
819 * The handle must only be closed once.
820 * The database handle will be private to the current transaction until
821 * the transaction is successfully committed. If the transaction is
822 * aborted the handle will be closed automatically.
823 * After a successful commit the
824 * handle will reside in the shared environment, and may be used
825 * by other transactions. This function must not be called from
826 * multiple concurrent transactions. A transaction that uses this function
827 * must finish (either commit or abort) before any other transaction may
830 * To use named databases (with name != NULL), #mdb_env_set_maxdbs()
831 * must be called before opening the environment.
832 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
833 * @param[in] name The name of the database to open. If only a single
834 * database is needed in the environment, this value may be NULL.
835 * @param[in] flags Special options for this database. This parameter
836 * must be set to 0 or by bitwise OR'ing together one or more of the
837 * values described here.
839 * <li>#MDB_REVERSEKEY
840 * Keys are strings to be compared in reverse order, from the end
841 * of the strings to the beginning. By default, Keys are treated as strings and
842 * compared from beginning to end.
844 * Duplicate keys may be used in the database. (Or, from another perspective,
845 * keys may have multiple data items, stored in sorted order.) By default
846 * keys must be unique and may have only a single data item.
847 * <li>#MDB_INTEGERKEY
848 * Keys are binary integers in native byte order. Setting this option
849 * requires all keys to be the same size, typically sizeof(int)
852 * This flag may only be used in combination with #MDB_DUPSORT. This option
853 * tells the library that the data items for this database are all the same
854 * size, which allows further optimizations in storage and retrieval. When
855 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
856 * cursor operations may be used to retrieve multiple items at once.
857 * <li>#MDB_INTEGERDUP
858 * This option specifies that duplicate data items are also integers, and
859 * should be sorted as such.
860 * <li>#MDB_REVERSEDUP
861 * This option specifies that duplicate data items should be compared as
862 * strings in reverse order.
864 * Create the named database if it doesn't exist. This option is not
865 * allowed in a read-only transaction or a read-only environment.
867 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
868 * @return A non-zero error value on failure and 0 on success. Some possible
871 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
872 * and #MDB_CREATE was not specified.
873 * <li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs().
876 int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
878 /** @brief Retrieve statistics for a database.
880 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
881 * @param[in] dbi A database handle returned by #mdb_dbi_open()
882 * @param[out] stat The address of an #MDB_stat structure
883 * where the statistics will be copied
884 * @return A non-zero error value on failure and 0 on success. Some possible
887 * <li>EINVAL - an invalid parameter was specified.
890 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
892 /** @brief Retrieve the DB flags for a database handle.
894 * @param[in] env An environment handle returned by #mdb_env_create()
895 * @param[in] dbi A database handle returned by #mdb_dbi_open()
896 * @param[out] flags Address where the flags will be returned.
897 * @return A non-zero error value on failure and 0 on success.
899 int mdb_dbi_flags(MDB_env *env, MDB_dbi dbi, unsigned int *flags);
901 /** @brief Close a database handle.
903 * This call is not mutex protected. Handles should only be closed by
904 * a single thread, and only if no other threads are going to reference
905 * the database handle or one of its cursors any further. Do not close
906 * a handle if an existing transaction has modified its database.
907 * @param[in] env An environment handle returned by #mdb_env_create()
908 * @param[in] dbi A database handle returned by #mdb_dbi_open()
910 void mdb_dbi_close(MDB_env *env, MDB_dbi dbi);
912 /** @brief Delete a database and/or free all its pages.
914 * If the \b del parameter is 1, the DB handle will be closed
915 * and the DB will be deleted.
916 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
917 * @param[in] dbi A database handle returned by #mdb_dbi_open()
918 * @param[in] del 1 to delete the DB from the environment,
919 * 0 to just free its pages.
920 * @return A non-zero error value on failure and 0 on success.
922 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
924 /** @brief Set a custom key comparison function for a database.
926 * The comparison function is called whenever it is necessary to compare a
927 * key specified by the application with a key currently stored in the database.
928 * If no comparison function is specified, and no special key flags were specified
929 * with #mdb_dbi_open(), the keys are compared lexically, with shorter keys collating
930 * before longer keys.
931 * @warning This function must be called before any data access functions are used,
932 * otherwise data corruption may occur. The same comparison function must be used by every
933 * program accessing the database, every time the database is used.
934 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
935 * @param[in] dbi A database handle returned by #mdb_dbi_open()
936 * @param[in] cmp A #MDB_cmp_func function
937 * @return A non-zero error value on failure and 0 on success. Some possible
940 * <li>EINVAL - an invalid parameter was specified.
943 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
945 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
947 * This comparison function is called whenever it is necessary to compare a data
948 * item specified by the application with a data item currently stored in the database.
949 * This function only takes effect if the database was opened with the #MDB_DUPSORT
951 * If no comparison function is specified, and no special key flags were specified
952 * with #mdb_dbi_open(), the data items are compared lexically, with shorter items collating
953 * before longer items.
954 * @warning This function must be called before any data access functions are used,
955 * otherwise data corruption may occur. The same comparison function must be used by every
956 * program accessing the database, every time the database is used.
957 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
958 * @param[in] dbi A database handle returned by #mdb_dbi_open()
959 * @param[in] cmp A #MDB_cmp_func function
960 * @return A non-zero error value on failure and 0 on success. Some possible
963 * <li>EINVAL - an invalid parameter was specified.
966 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
968 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
970 * @todo The relocation function is called whenever it is necessary to move the data
971 * of an item to a different position in the database (e.g. through tree
972 * balancing operations, shifts as a result of adds or deletes, etc.). It is
973 * intended to allow address/position-dependent data items to be stored in
974 * a database in an environment opened with the #MDB_FIXEDMAP option.
975 * Currently the relocation feature is unimplemented and setting
976 * this function has no effect.
977 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
978 * @param[in] dbi A database handle returned by #mdb_dbi_open()
979 * @param[in] rel A #MDB_rel_func function
980 * @return A non-zero error value on failure and 0 on success. Some possible
983 * <li>EINVAL - an invalid parameter was specified.
986 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
988 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
990 * See #mdb_set_relfunc and #MDB_rel_func for more details.
991 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
992 * @param[in] dbi A database handle returned by #mdb_dbi_open()
993 * @param[in] ctx An arbitrary pointer for whatever the application needs.
994 * It will be passed to the callback function set by #mdb_set_relfunc
995 * as its \b relctx parameter whenever the callback is invoked.
996 * @return A non-zero error value on failure and 0 on success. Some possible
999 * <li>EINVAL - an invalid parameter was specified.
1002 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
1004 /** @brief Get items from a database.
1006 * This function retrieves key/data pairs from the database. The address
1007 * and length of the data associated with the specified \b key are returned
1008 * in the structure to which \b data refers.
1009 * If the database supports duplicate keys (#MDB_DUPSORT) then the
1010 * first data item for the key will be returned. Retrieval of other
1011 * items requires the use of #mdb_cursor_get().
1013 * @note The memory pointed to by the returned values is owned by the
1014 * database. The caller need not dispose of the memory, and may not
1015 * modify it in any way. For values returned in a read-only transaction
1016 * any modification attempts will cause a SIGSEGV.
1017 * @note Values returned from the database are valid only until a
1018 * subsequent update operation, or the end of the transaction.
1019 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1020 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1021 * @param[in] key The key to search for in the database
1022 * @param[out] data The data corresponding to the key
1023 * @return A non-zero error value on failure and 0 on success. Some possible
1026 * <li>#MDB_NOTFOUND - the key was not in the database.
1027 * <li>EINVAL - an invalid parameter was specified.
1030 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1032 /** @brief Store items into a database.
1034 * This function stores key/data pairs in the database. The default behavior
1035 * is to enter the new key/data pair, replacing any previously existing key
1036 * if duplicates are disallowed, or adding a duplicate data item if
1037 * duplicates are allowed (#MDB_DUPSORT).
1038 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1039 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1040 * @param[in] key The key to store in the database
1041 * @param[in,out] data The data to store
1042 * @param[in] flags Special options for this operation. This parameter
1043 * must be set to 0 or by bitwise OR'ing together one or more of the
1044 * values described here.
1046 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1047 * already appear in the database. This flag may only be specified
1048 * if the database was opened with #MDB_DUPSORT. The function will
1049 * return #MDB_KEYEXIST if the key/data pair already appears in the
1051 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1052 * does not already appear in the database. The function will return
1053 * #MDB_KEYEXIST if the key already appears in the database, even if
1054 * the database supports duplicates (#MDB_DUPSORT). The \b data
1055 * parameter will be set to point to the existing item.
1056 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1057 * don't copy the given data. Instead, return a pointer to the
1058 * reserved space, which the caller can fill in later - before
1059 * the next update operation or the transaction ends. This saves
1060 * an extra memcpy if the data is being generated later.
1061 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1062 * database. No key comparisons are performed. This option allows
1063 * fast bulk loading when keys are already known to be in the
1064 * correct order. Loading unsorted keys with this flag will cause
1066 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1068 * @return A non-zero error value on failure and 0 on success. Some possible
1071 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1072 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1073 * <li>EACCES - an attempt was made to write in a read-only transaction.
1074 * <li>EINVAL - an invalid parameter was specified.
1077 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
1078 unsigned int flags);
1080 /** @brief Delete items from a database.
1082 * This function removes key/data pairs from the database.
1083 * If the database does not support sorted duplicate data items
1084 * (#MDB_DUPSORT) the data parameter is ignored.
1085 * If the database supports sorted duplicates and the data parameter
1086 * is NULL, all of the duplicate data items for the key will be
1087 * deleted. Otherwise, if the data parameter is non-NULL
1088 * only the matching data item will be deleted.
1089 * This function will return #MDB_NOTFOUND if the specified key/data
1090 * pair is not in the database.
1091 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1092 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1093 * @param[in] key The key to delete from the database
1094 * @param[in] data The data to delete
1095 * @return A non-zero error value on failure and 0 on success. Some possible
1098 * <li>EACCES - an attempt was made to write in a read-only transaction.
1099 * <li>EINVAL - an invalid parameter was specified.
1102 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1104 /** @brief Create a cursor handle.
1106 * A cursor is associated with a specific transaction and database.
1107 * A cursor cannot be used when its database handle is closed. Nor
1108 * when its transaction has ended, except with #mdb_cursor_renew().
1109 * It can be discarded with #mdb_cursor_close().
1110 * A cursor in a write-transaction can be closed before its transaction
1111 * ends, and will otherwise be closed when its transaction ends.
1112 * A cursor in a read-only transaction must be closed explicitly, before
1113 * or after its transaction ends. It can be reused with
1114 * #mdb_cursor_renew() before finally closing it.
1115 * @note Earlier documentation said that cursors in every transaction
1116 * were closed when the transaction committed or aborted.
1117 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1118 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1119 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
1120 * @return A non-zero error value on failure and 0 on success. Some possible
1123 * <li>EINVAL - an invalid parameter was specified.
1126 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
1128 /** @brief Close a cursor handle.
1130 * The cursor handle will be freed and must not be used again after this call.
1131 * Its transaction must still be live if it is a write-transaction.
1132 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1134 void mdb_cursor_close(MDB_cursor *cursor);
1136 /** @brief Renew a cursor handle.
1138 * A cursor is associated with a specific transaction and database.
1139 * Cursors that are only used in read-only
1140 * transactions may be re-used, to avoid unnecessary malloc/free overhead.
1141 * The cursor may be associated with a new read-only transaction, and
1142 * referencing the same database handle as it was created with.
1143 * This may be done whether the previous transaction is live or dead.
1144 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1145 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1146 * @return A non-zero error value on failure and 0 on success. Some possible
1149 * <li>EINVAL - an invalid parameter was specified.
1152 int mdb_cursor_renew(MDB_txn *txn, MDB_cursor *cursor);
1154 /** @brief Return the cursor's transaction handle.
1156 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1158 MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
1160 /** @brief Return the cursor's database handle.
1162 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1164 MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor);
1166 /** @brief Retrieve by cursor.
1168 * This function retrieves key/data pairs from the database. The address and length
1169 * of the key are returned in the object to which \b key refers (except for the
1170 * case of the #MDB_SET option, in which the \b key object is unchanged), and
1171 * the address and length of the data are returned in the object to which \b data
1173 * See #mdb_get() for restrictions on using the output values.
1174 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1175 * @param[in,out] key The key for a retrieved item
1176 * @param[in,out] data The data of a retrieved item
1177 * @param[in] op A cursor operation #MDB_cursor_op
1178 * @return A non-zero error value on failure and 0 on success. Some possible
1181 * <li>#MDB_NOTFOUND - no matching key found.
1182 * <li>EINVAL - an invalid parameter was specified.
1185 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1188 /** @brief Store by cursor.
1190 * This function stores key/data pairs into the database.
1191 * If the function fails for any reason, the state of the cursor will be
1192 * unchanged. If the function succeeds and an item is inserted into the
1193 * database, the cursor is always positioned to refer to the newly inserted item.
1194 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1195 * @param[in] key The key operated on.
1196 * @param[in] data The data operated on.
1197 * @param[in] flags Options for this operation. This parameter
1198 * must be set to 0 or one of the values described here.
1200 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which
1201 * the cursor refers with the specified data item. The \b key
1202 * parameter is ignored.
1203 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1204 * already appear in the database. This flag may only be specified
1205 * if the database was opened with #MDB_DUPSORT. The function will
1206 * return #MDB_KEYEXIST if the key/data pair already appears in the
1208 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1209 * does not already appear in the database. The function will return
1210 * #MDB_KEYEXIST if the key already appears in the database, even if
1211 * the database supports duplicates (#MDB_DUPSORT).
1212 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1213 * don't copy the given data. Instead, return a pointer to the
1214 * reserved space, which the caller can fill in later. This saves
1215 * an extra memcpy if the data is being generated later.
1216 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1217 * database. No key comparisons are performed. This option allows
1218 * fast bulk loading when keys are already known to be in the
1219 * correct order. Loading unsorted keys with this flag will cause
1221 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1222 * <li>#MDB_MULTIPLE - store multiple contiguous data elements in a
1223 * single request. This flag may only be specified if the database
1224 * was opened with #MDB_DUPFIXED. The \b data argument must be an
1225 * array of two MDB_vals. The mv_size of the first MDB_val must be
1226 * the size of a single data element. The mv_data of the first MDB_val
1227 * must point to the beginning of the array of contiguous data elements.
1228 * The mv_size of the second MDB_val must be the count of the number
1229 * of data elements to store. On return this field will be set to
1230 * the count of the number of elements actually written. The mv_data
1231 * of the second MDB_val is unused.
1233 * @return A non-zero error value on failure and 0 on success. Some possible
1236 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1237 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1238 * <li>EACCES - an attempt was made to modify a read-only database.
1239 * <li>EINVAL - an invalid parameter was specified.
1242 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1243 unsigned int flags);
1245 /** @brief Delete current key/data pair
1247 * This function deletes the key/data pair to which the cursor refers.
1248 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1249 * @param[in] flags Options for this operation. This parameter
1250 * must be set to 0 or one of the values described here.
1252 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
1253 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
1255 * @return A non-zero error value on failure and 0 on success. Some possible
1258 * <li>EACCES - an attempt was made to modify a read-only database.
1259 * <li>EINVAL - an invalid parameter was specified.
1262 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
1264 /** @brief Return count of duplicates for current key.
1266 * This call is only valid on databases that support sorted duplicate
1267 * data items #MDB_DUPSORT.
1268 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1269 * @param[out] countp Address where the count will be stored
1270 * @return A non-zero error value on failure and 0 on success. Some possible
1273 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
1276 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
1278 /** @brief Compare two data items according to a particular database.
1280 * This returns a comparison as if the two data items were keys in the
1281 * specified database.
1282 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1283 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1284 * @param[in] a The first item to compare
1285 * @param[in] b The second item to compare
1286 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1288 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1290 /** @brief Compare two data items according to a particular database.
1292 * This returns a comparison as if the two items were data items of
1293 * the specified database. The database must have the #MDB_DUPSORT flag.
1294 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1295 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1296 * @param[in] a The first item to compare
1297 * @param[in] b The second item to compare
1298 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1300 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1302 /** @brief A callback function used to print a message from the library.
1304 * @param[in] msg The string to be printed.
1305 * @param[in] ctx An arbitrary context pointer for the callback.
1306 * @return < 0 on failure, 0 on success.
1308 typedef int (MDB_msg_func)(const char *msg, void *ctx);
1310 /** @brief Dump the entries in the reader lock table.
1312 * @param[in] env An environment handle returned by #mdb_env_create()
1313 * @param[in] func A #MDB_msg_func function
1314 * @param[in] ctx Anything the message function needs
1315 * @return < 0 on failure, 0 on success.
1317 int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx);
1319 /** @brief Check for stale entries in the reader lock table.
1321 * @param[in] env An environment handle returned by #mdb_env_create()
1322 * @param[out] dead Number of stale slots that were cleared
1323 * @return 0 on success, non-zero on failure.
1325 int mdb_reader_check(MDB_env *env, int *dead);
1331 #endif /* _LMDB_H_ */