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: Check for stale readers periodically, using the
52 * #mdb_reader_check function or the mdb_stat tool. Or just
53 * make all programs using the database close it; the lockfile
54 * is always reset on first open of the environment.
56 * - On BSD systems or others configured with MDB_USE_POSIX_SEM,
57 * startup can fail due to semaphores owned by another userid.
59 * Fix: Open and close the database as the user which owns the
60 * semaphores (likely last user) or as root, while no other
61 * process is using the database.
63 * Restrictions/caveats (in addition to those listed for some functions):
65 * - Only the database owner should normally use the database on
66 * BSD systems or when otherwise configured with MDB_USE_POSIX_SEM.
67 * Multiple users can cause startup to fail later, as noted above.
69 * - There is normally no pure read-only mode, since readers need write
70 * access to locks and lock file. Exceptions: On read-only filesystems
71 * or with the #MDB_NOLOCK flag described under #mdb_env_open().
73 * - A thread can only use one transaction at a time, plus any child
74 * transactions. Each transaction belongs to one thread. See below.
75 * The #MDB_NOTLS flag changes this for read-only transactions.
77 * - Use an MDB_env* in the process which opened it, without fork()ing.
79 * - Do not have open an MDB database twice in the same process at
80 * the same time. Not even from a plain open() call - close()ing it
81 * breaks flock() advisory locking.
83 * - Avoid long-lived transactions. Read transactions prevent
84 * reuse of pages freed by newer write transactions, thus the
85 * database can grow quickly. Write transactions prevent
86 * other write transactions, since writes are serialized.
88 * - Avoid suspending a process with active transactions. These
89 * would then be "long-lived" as above. Also read transactions
90 * suspended when writers commit could sometimes see wrong data.
92 * ...when several processes can use a database concurrently:
94 * - Avoid aborting a process with an active transaction.
95 * The transaction becomes "long-lived" as above until a check
96 * for stale readers is performed or the lockfile is reset,
97 * since the process may not remove it from the lockfile.
99 * - If you do that anyway, do a periodic check for stale readers. Or
100 * close the environment once in a while, so the lockfile can get reset.
102 * - Do not use MDB databases on remote filesystems, even between
103 * processes on the same host. This breaks flock() on some OSes,
104 * possibly memory map sync, and certainly sync between programs
105 * on different hosts.
107 * - Opening a database can fail if another process is opening or
108 * closing it at exactly the same time.
110 * @author Howard Chu, Symas Corporation.
112 * @copyright Copyright 2011-2013 Howard Chu, Symas Corp. All rights reserved.
114 * Redistribution and use in source and binary forms, with or without
115 * modification, are permitted only as authorized by the OpenLDAP
118 * A copy of this license is available in the file LICENSE in the
119 * top-level directory of the distribution or, alternatively, at
120 * <http://www.OpenLDAP.org/license.html>.
123 * This code is derived from btree.c written by Martin Hedenfalk.
125 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
127 * Permission to use, copy, modify, and distribute this software for any
128 * purpose with or without fee is hereby granted, provided that the above
129 * copyright notice and this permission notice appear in all copies.
131 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
132 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
133 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
134 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
135 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
136 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
137 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
142 #include <sys/types.h>
148 /** Unix permissions for creating files, or dummy definition for Windows */
150 typedef int mdb_mode_t;
152 typedef mode_t mdb_mode_t;
155 /** An abstraction for a file handle.
156 * On POSIX systems file handles are small integers. On Windows
157 * they're opaque pointers.
160 typedef void *mdb_filehandle_t;
162 typedef int mdb_filehandle_t;
165 /** @defgroup mdb MDB API
167 * @brief OpenLDAP Lightning Memory-Mapped Database Manager
169 /** @defgroup Version Version Macros
172 /** Library major version */
173 #define MDB_VERSION_MAJOR 0
174 /** Library minor version */
175 #define MDB_VERSION_MINOR 9
176 /** Library patch version */
177 #define MDB_VERSION_PATCH 8
179 /** Combine args a,b,c into a single integer for easy version comparisons */
180 #define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
182 /** The full library version as a single integer */
183 #define MDB_VERSION_FULL \
184 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
186 /** The release date of this library version */
187 #define MDB_VERSION_DATE "September 9, 2013"
189 /** A stringifier for the version info */
190 #define MDB_VERSTR(a,b,c,d) "MDB " #a "." #b "." #c ": (" d ")"
192 /** A helper for the stringifier macro */
193 #define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d)
195 /** The full library version as a C string */
196 #define MDB_VERSION_STRING \
197 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
200 /** @brief Opaque structure for a database environment.
202 * A DB environment supports multiple databases, all residing in the same
205 typedef struct MDB_env MDB_env;
207 /** @brief Opaque structure for a transaction handle.
209 * All database operations require a transaction handle. Transactions may be
210 * read-only or read-write.
212 typedef struct MDB_txn MDB_txn;
214 /** @brief A handle for an individual database in the DB environment. */
215 typedef unsigned int MDB_dbi;
217 /** @brief Opaque structure for navigating through a database */
218 typedef struct MDB_cursor MDB_cursor;
220 /** @brief Generic structure used for passing keys and data in and out
223 * Values returned from the database are valid only until a subsequent
224 * update operation, or the end of the transaction. Do not modify or
225 * free them, they commonly point into the database itself.
227 * Key sizes must be between 1 and #mdb_env_get_maxkeysize() inclusive.
228 * The same applies to data sizes in databases with the #MDB_DUPSORT flag.
229 * Other data items can in theory be from 0 to 0xffffffff bytes long.
231 typedef struct MDB_val {
232 size_t mv_size; /**< size of the data item */
233 void *mv_data; /**< address of the data item */
236 /** @brief A callback function used to compare two keys in a database */
237 typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
239 /** @brief A callback function used to relocate a position-dependent data item
240 * in a fixed-address database.
242 * The \b newptr gives the item's desired address in
243 * the memory map, and \b oldptr gives its previous address. The item's actual
244 * data resides at the address in \b item. This callback is expected to walk
245 * through the fields of the record in \b item and modify any
246 * values based at the \b oldptr address to be relative to the \b newptr address.
247 * @param[in,out] item The item that is to be relocated.
248 * @param[in] oldptr The previous address.
249 * @param[in] newptr The new address to relocate to.
250 * @param[in] relctx An application-provided context, set by #mdb_set_relctx().
251 * @todo This feature is currently unimplemented.
253 typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
255 /** @defgroup mdb_env Environment Flags
257 * Values do not overlap Database Flags.
260 /** mmap at a fixed address (experimental) */
261 #define MDB_FIXEDMAP 0x01
262 /** no environment directory */
263 #define MDB_NOSUBDIR 0x4000
264 /** don't fsync after commit */
265 #define MDB_NOSYNC 0x10000
267 #define MDB_RDONLY 0x20000
268 /** don't fsync metapage after commit */
269 #define MDB_NOMETASYNC 0x40000
270 /** use writable mmap */
271 #define MDB_WRITEMAP 0x80000
272 /** use asynchronous msync when #MDB_WRITEMAP is used */
273 #define MDB_MAPASYNC 0x100000
274 /** tie reader locktable slots to #MDB_txn objects instead of to threads */
275 #define MDB_NOTLS 0x200000
276 /** don't do any locking, caller must manage their own locks */
277 #define MDB_NOLOCK 0x400000
278 /** don't do readahead (no effect on Windows) */
279 #define MDB_NORDAHEAD 0x800000
282 /** @defgroup mdb_dbi_open Database Flags
284 * Values do not overlap Environment Flags.
287 /** use reverse string keys */
288 #define MDB_REVERSEKEY 0x02
289 /** use sorted duplicates */
290 #define MDB_DUPSORT 0x04
291 /** numeric keys in native byte order.
292 * The keys must all be of the same size. */
293 #define MDB_INTEGERKEY 0x08
294 /** with #MDB_DUPSORT, sorted dup items have fixed size */
295 #define MDB_DUPFIXED 0x10
296 /** with #MDB_DUPSORT, dups are numeric in native byte order */
297 #define MDB_INTEGERDUP 0x20
298 /** with #MDB_DUPSORT, use reverse string dups */
299 #define MDB_REVERSEDUP 0x40
300 /** create DB if not already existing */
301 #define MDB_CREATE 0x40000
304 /** @defgroup mdb_put Write Flags
307 /** For put: Don't write if the key already exists. */
308 #define MDB_NOOVERWRITE 0x10
309 /** Only for #MDB_DUPSORT<br>
310 * For put: don't write if the key and data pair already exist.<br>
311 * For mdb_cursor_del: remove all duplicate data items.
313 #define MDB_NODUPDATA 0x20
314 /** For mdb_cursor_put: overwrite the current key/data pair */
315 #define MDB_CURRENT 0x40
316 /** For put: Just reserve space for data, don't copy it. Return a
317 * pointer to the reserved space.
319 #define MDB_RESERVE 0x10000
320 /** Data is being appended, don't split full pages. */
321 #define MDB_APPEND 0x20000
322 /** Duplicate data is being appended, don't split full pages. */
323 #define MDB_APPENDDUP 0x40000
324 /** Store multiple data items in one call. Only for #MDB_DUPFIXED. */
325 #define MDB_MULTIPLE 0x80000
328 /** @brief Cursor Get operations.
330 * This is the set of all operations for retrieving data
333 typedef enum MDB_cursor_op {
334 MDB_FIRST, /**< Position at first key/data item */
335 MDB_FIRST_DUP, /**< Position at first data item of current key.
336 Only for #MDB_DUPSORT */
337 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
338 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
339 MDB_GET_CURRENT, /**< Return key/data at current cursor position */
340 MDB_GET_MULTIPLE, /**< Return all the duplicate data items at the current
341 cursor position. Only for #MDB_DUPFIXED */
342 MDB_LAST, /**< Position at last key/data item */
343 MDB_LAST_DUP, /**< Position at last data item of current key.
344 Only for #MDB_DUPSORT */
345 MDB_NEXT, /**< Position at next data item */
346 MDB_NEXT_DUP, /**< Position at next data item of current key.
347 Only for #MDB_DUPSORT */
348 MDB_NEXT_MULTIPLE, /**< Return all duplicate data items at the next
349 cursor position. Only for #MDB_DUPFIXED */
350 MDB_NEXT_NODUP, /**< Position at first data item of next key */
351 MDB_PREV, /**< Position at previous data item */
352 MDB_PREV_DUP, /**< Position at previous data item of current key.
353 Only for #MDB_DUPSORT */
354 MDB_PREV_NODUP, /**< Position at last data item of previous key */
355 MDB_SET, /**< Position at specified key */
356 MDB_SET_KEY, /**< Position at specified key, return key + data */
357 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
360 /** @defgroup errors Return Codes
362 * BerkeleyDB uses -30800 to -30999, we'll go under them
365 /** Successful result */
366 #define MDB_SUCCESS 0
367 /** key/data pair already exists */
368 #define MDB_KEYEXIST (-30799)
369 /** key/data pair not found (EOF) */
370 #define MDB_NOTFOUND (-30798)
371 /** Requested page not found - this usually indicates corruption */
372 #define MDB_PAGE_NOTFOUND (-30797)
373 /** Located page was wrong type */
374 #define MDB_CORRUPTED (-30796)
375 /** Update of meta page failed, probably I/O error */
376 #define MDB_PANIC (-30795)
377 /** Environment version mismatch */
378 #define MDB_VERSION_MISMATCH (-30794)
379 /** File is not a valid MDB file */
380 #define MDB_INVALID (-30793)
381 /** Environment mapsize reached */
382 #define MDB_MAP_FULL (-30792)
383 /** Environment maxdbs reached */
384 #define MDB_DBS_FULL (-30791)
385 /** Environment maxreaders reached */
386 #define MDB_READERS_FULL (-30790)
387 /** Too many TLS keys in use - Windows only */
388 #define MDB_TLS_FULL (-30789)
389 /** Txn has too many dirty pages */
390 #define MDB_TXN_FULL (-30788)
391 /** Cursor stack too deep - internal error */
392 #define MDB_CURSOR_FULL (-30787)
393 /** Page has not enough space - internal error */
394 #define MDB_PAGE_FULL (-30786)
395 /** Database contents grew beyond environment mapsize */
396 #define MDB_MAP_RESIZED (-30785)
397 /** MDB_INCOMPATIBLE: Operation and DB incompatible, or DB flags changed */
398 #define MDB_INCOMPATIBLE (-30784)
399 /** Invalid reuse of reader locktable slot */
400 #define MDB_BAD_RSLOT (-30783)
401 /** Transaction cannot recover - it must be aborted */
402 #define MDB_BAD_TXN (-30782)
403 /** Too big key/data, key is empty, or wrong DUPFIXED size */
404 #define MDB_BAD_VALSIZE (-30781)
405 #define MDB_LAST_ERRCODE MDB_BAD_VALSIZE
408 /** @brief Statistics for a database in the environment */
409 typedef struct MDB_stat {
410 unsigned int ms_psize; /**< Size of a database page.
411 This is currently the same for all databases. */
412 unsigned int ms_depth; /**< Depth (height) of the B-tree */
413 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
414 size_t ms_leaf_pages; /**< Number of leaf pages */
415 size_t ms_overflow_pages; /**< Number of overflow pages */
416 size_t ms_entries; /**< Number of data items */
419 /** @brief Information about the environment */
420 typedef struct MDB_envinfo {
421 void *me_mapaddr; /**< Address of map, if fixed */
422 size_t me_mapsize; /**< Size of the data memory map */
423 size_t me_last_pgno; /**< ID of the last used page */
424 size_t me_last_txnid; /**< ID of the last committed transaction */
425 unsigned int me_maxreaders; /**< max reader slots in the environment */
426 unsigned int me_numreaders; /**< max reader slots used in the environment */
429 /** @brief Return the mdb library version information.
431 * @param[out] major if non-NULL, the library major version number is copied here
432 * @param[out] minor if non-NULL, the library minor version number is copied here
433 * @param[out] patch if non-NULL, the library patch version number is copied here
434 * @retval "version string" The library version as a string
436 char *mdb_version(int *major, int *minor, int *patch);
438 /** @brief Return a string describing a given error code.
440 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
441 * function. If the error code is greater than or equal to 0, then the string
442 * returned by the system function strerror(3) is returned. If the error code
443 * is less than 0, an error string corresponding to the MDB library error is
444 * returned. See @ref errors for a list of MDB-specific error codes.
445 * @param[in] err The error code
446 * @retval "error message" The description of the error
448 char *mdb_strerror(int err);
450 /** @brief Create an MDB environment handle.
452 * This function allocates memory for a #MDB_env structure. To release
453 * the allocated memory and discard the handle, call #mdb_env_close().
454 * Before the handle may be used, it must be opened using #mdb_env_open().
455 * Various other options may also need to be set before opening the handle,
456 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
457 * depending on usage requirements.
458 * @param[out] env The address where the new handle will be stored
459 * @return A non-zero error value on failure and 0 on success.
461 int mdb_env_create(MDB_env **env);
463 /** @brief Open an environment handle.
465 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
466 * @param[in] env An environment handle returned by #mdb_env_create()
467 * @param[in] path The directory in which the database files reside. This
468 * directory must already exist and be writable.
469 * @param[in] flags Special options for this environment. This parameter
470 * must be set to 0 or by bitwise OR'ing together one or more of the
471 * values described here.
472 * Flags set by mdb_env_set_flags() are also used.
475 * use a fixed address for the mmap region. This flag must be specified
476 * when creating the environment, and is stored persistently in the environment.
477 * If successful, the memory map will always reside at the same virtual address
478 * and pointers used to reference data items in the database will be constant
479 * across multiple invocations. This option may not always work, depending on
480 * how the operating system has allocated memory to shared libraries and other uses.
481 * The feature is highly experimental.
483 * By default, MDB creates its environment in a directory whose
484 * pathname is given in \b path, and creates its data and lock files
485 * under that directory. With this option, \b path is used as-is for
486 * the database main data file. The database lock file is the \b path
487 * with "-lock" appended.
489 * Open the environment in read-only mode. No write operations will be
490 * allowed. MDB will still modify the lock file - except on read-only
491 * filesystems, where MDB does not use locks.
493 * Use a writeable memory map unless MDB_RDONLY is set. This is faster
494 * and uses fewer mallocs, but loses protection from application bugs
495 * like wild pointer writes and other bad updates into the database.
496 * Incompatible with nested transactions.
497 * Processes with and without MDB_WRITEMAP on the same environment do
498 * not cooperate well.
499 * <li>#MDB_NOMETASYNC
500 * Flush system buffers to disk only once per transaction, omit the
501 * metadata flush. Defer that until the system flushes files to disk,
502 * or next non-MDB_RDONLY commit or #mdb_env_sync(). This optimization
503 * maintains database integrity, but a system crash may undo the last
504 * committed transaction. I.e. it preserves the ACI (atomicity,
505 * consistency, isolation) but not D (durability) database property.
506 * This flag may be changed at any time using #mdb_env_set_flags().
508 * Don't flush system buffers to disk when committing a transaction.
509 * This optimization means a system crash can corrupt the database or
510 * lose the last transactions if buffers are not yet flushed to disk.
511 * The risk is governed by how often the system flushes dirty buffers
512 * to disk and how often #mdb_env_sync() is called. However, if the
513 * filesystem preserves write order and the #MDB_WRITEMAP flag is not
514 * used, transactions exhibit ACI (atomicity, consistency, isolation)
515 * properties and only lose D (durability). I.e. database integrity
516 * is maintained, but a system crash may undo the final transactions.
517 * Note that (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no
518 * hint for when to write transactions to disk, unless #mdb_env_sync()
519 * is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable.
520 * This flag may be changed at any time using #mdb_env_set_flags().
522 * When using #MDB_WRITEMAP, use asynchronous flushes to disk.
523 * As with #MDB_NOSYNC, a system crash can then corrupt the
524 * database or lose the last transactions. Calling #mdb_env_sync()
525 * ensures on-disk database integrity until next commit.
526 * This flag may be changed at any time using #mdb_env_set_flags().
528 * Don't use Thread-Local Storage. Tie reader locktable slots to
529 * #MDB_txn objects instead of to threads. I.e. #mdb_txn_reset() keeps
530 * the slot reseved for the #MDB_txn object. A thread may use parallel
531 * read-only transactions. A read-only transaction may span threads if
532 * the user synchronizes its use. Applications that multiplex many
533 * user threads over individual OS threads need this option. Such an
534 * application must also serialize the write transactions in an OS
535 * thread, since MDB's write locking is unaware of the user threads.
537 * Don't do any locking. If concurrent access is anticipated, the
538 * caller must manage all concurrency itself. For proper operation
539 * the caller must enforce single-writer semantics, and must ensure
540 * that no readers are using old transactions while a writer is
541 * active. The simplest approach is to use an exclusive lock so that
542 * no readers may be active at all when a writer begins.
544 * Turn off readahead. Most operating systems perform readahead on
545 * read requests by default. This option turns it off if the OS
546 * supports it. Turning it off may help random read performance
547 * when the DB is larger than RAM and system RAM is full.
548 * The option is not implemented on Windows.
550 * @param[in] mode The UNIX permissions to set on created files. This parameter
551 * is ignored on Windows.
552 * @return A non-zero error value on failure and 0 on success. Some possible
555 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
556 * version that created the database environment.
557 * <li>#MDB_INVALID - the environment file headers are corrupted.
558 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
559 * <li>EACCES - the user didn't have permission to access the environment files.
560 * <li>EAGAIN - the environment was locked by another process.
563 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode);
565 /** @brief Copy an MDB environment to the specified path.
567 * This function may be used to make a backup of an existing environment.
568 * No lockfile is created, since it gets recreated at need.
569 * @note This call can trigger significant file size growth if run in
570 * parallel with write transactions, because it employs a read-only
571 * transaction. See long-lived transactions under @ref caveats_sec.
572 * @param[in] env An environment handle returned by #mdb_env_create(). It
573 * must have already been opened successfully.
574 * @param[in] path The directory in which the copy will reside. This
575 * directory must already exist and be writable but must otherwise be
577 * @return A non-zero error value on failure and 0 on success.
579 int mdb_env_copy(MDB_env *env, const char *path);
581 /** @brief Copy an MDB environment to the specified file descriptor.
583 * This function may be used to make a backup of an existing environment.
584 * No lockfile is created, since it gets recreated at need.
585 * @note This call can trigger significant file size growth if run in
586 * parallel with write transactions, because it employs a read-only
587 * transaction. See long-lived transactions under @ref caveats_sec.
588 * @param[in] env An environment handle returned by #mdb_env_create(). It
589 * must have already been opened successfully.
590 * @param[in] fd The filedescriptor to write the copy to. It must
591 * have already been opened for Write access.
592 * @return A non-zero error value on failure and 0 on success.
594 int mdb_env_copyfd(MDB_env *env, mdb_filehandle_t fd);
596 /** @brief Return statistics about the MDB environment.
598 * @param[in] env An environment handle returned by #mdb_env_create()
599 * @param[out] stat The address of an #MDB_stat structure
600 * where the statistics will be copied
602 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
604 /** @brief Return information about the MDB environment.
606 * @param[in] env An environment handle returned by #mdb_env_create()
607 * @param[out] stat The address of an #MDB_envinfo structure
608 * where the information will be copied
610 int mdb_env_info(MDB_env *env, MDB_envinfo *stat);
612 /** @brief Flush the data buffers to disk.
614 * Data is always written to disk when #mdb_txn_commit() is called,
615 * but the operating system may keep it buffered. MDB always flushes
616 * the OS buffers upon commit as well, unless the environment was
617 * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC.
618 * @param[in] env An environment handle returned by #mdb_env_create()
619 * @param[in] force If non-zero, force a synchronous flush. Otherwise
620 * if the environment has the #MDB_NOSYNC flag set the flushes
621 * will be omitted, and with #MDB_MAPASYNC they will be asynchronous.
622 * @return A non-zero error value on failure and 0 on success. Some possible
625 * <li>EINVAL - an invalid parameter was specified.
626 * <li>EIO - an error occurred during synchronization.
629 int mdb_env_sync(MDB_env *env, int force);
631 /** @brief Close the environment and release the memory map.
633 * Only a single thread may call this function. All transactions, databases,
634 * and cursors must already be closed before calling this function. Attempts to
635 * use any such handles after calling this function will cause a SIGSEGV.
636 * The environment handle will be freed and must not be used again after this call.
637 * @param[in] env An environment handle returned by #mdb_env_create()
639 void mdb_env_close(MDB_env *env);
641 /** @brief Set environment flags.
643 * This may be used to set some flags in addition to those from
644 * #mdb_env_open(), or to unset these flags.
645 * @param[in] env An environment handle returned by #mdb_env_create()
646 * @param[in] flags The flags to change, bitwise OR'ed together
647 * @param[in] onoff A non-zero value sets the flags, zero clears them.
648 * @return A non-zero error value on failure and 0 on success. Some possible
651 * <li>EINVAL - an invalid parameter was specified.
654 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
656 /** @brief Get environment flags.
658 * @param[in] env An environment handle returned by #mdb_env_create()
659 * @param[out] flags The address of an integer to store the flags
660 * @return A non-zero error value on failure and 0 on success. Some possible
663 * <li>EINVAL - an invalid parameter was specified.
666 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
668 /** @brief Return the path that was used in #mdb_env_open().
670 * @param[in] env An environment handle returned by #mdb_env_create()
671 * @param[out] path Address of a string pointer to contain the path. This
672 * is the actual string in the environment, not a copy. It should not be
673 * altered in any way.
674 * @return A non-zero error value on failure and 0 on success. Some possible
677 * <li>EINVAL - an invalid parameter was specified.
680 int mdb_env_get_path(MDB_env *env, const char **path);
682 /** @brief Return the filedescriptor for the given environment.
684 * @param[in] env An environment handle returned by #mdb_env_create()
685 * @param[out] fd Address of a mdb_filehandle_t to contain the descriptor.
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_fd(MDB_env *env, mdb_filehandle_t *fd);
694 /** @brief Set the size of the memory map to use for this environment.
696 * The size should be a multiple of the OS page size. The default is
697 * 10485760 bytes. The size of the memory map is also the maximum size
698 * of the database. The value should be chosen as large as possible,
699 * to accommodate future growth of the database.
700 * This function should be called after #mdb_env_create() and before #mdb_env_open().
701 * It may be called at later times if no transactions are active in
702 * this process. Note that the library does not check for this condition,
703 * the caller must ensure it explicitly.
705 * If the mapsize is changed by another process, #mdb_txn_begin() will
706 * return #MDB_MAP_RESIZED. This function may be called with a size
707 * of zero to adopt the new size.
709 * Any attempt to set a size smaller than the space already consumed
710 * by the environment will be silently changed to the current size of the used space.
711 * @param[in] env An environment handle returned by #mdb_env_create()
712 * @param[in] size The size in bytes
713 * @return A non-zero error value on failure and 0 on success. Some possible
716 * <li>EINVAL - an invalid parameter was specified, or the environment has
717 * an active write transaction.
720 int mdb_env_set_mapsize(MDB_env *env, size_t size);
722 /** @brief Set the maximum number of threads/reader slots for the environment.
724 * This defines the number of slots in the lock table that is used to track readers in the
725 * the environment. The default is 126.
726 * Starting a read-only transaction normally ties a lock table slot to the
727 * current thread until the environment closes or the thread exits. If
728 * MDB_NOTLS is in use, #mdb_txn_begin() instead ties the slot to the
729 * MDB_txn object until it or the #MDB_env object is destroyed.
730 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
731 * @param[in] env An environment handle returned by #mdb_env_create()
732 * @param[in] readers The maximum number of reader lock table slots
733 * @return A non-zero error value on failure and 0 on success. Some possible
736 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
739 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
741 /** @brief Get the maximum number of threads/reader slots for the environment.
743 * @param[in] env An environment handle returned by #mdb_env_create()
744 * @param[out] readers Address of an integer to store the number of readers
745 * @return A non-zero error value on failure and 0 on success. Some possible
748 * <li>EINVAL - an invalid parameter was specified.
751 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
753 /** @brief Set the maximum number of named databases for the environment.
755 * This function is only needed if multiple databases will be used in the
756 * environment. Simpler applications that use the environment as a single
757 * unnamed database can ignore this option.
758 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
759 * @param[in] env An environment handle returned by #mdb_env_create()
760 * @param[in] dbs The maximum number of databases
761 * @return A non-zero error value on failure and 0 on success. Some possible
764 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
767 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
769 /** @brief Get the maximum size of a key for the environment.
771 * This is the compile-time constant #MDB_MAXKEYSIZE, default 511.
773 * @param[in] env An environment handle returned by #mdb_env_create()
774 * @return The maximum size of a key
776 int mdb_env_get_maxkeysize(MDB_env *env);
778 /** @brief Create a transaction for use with the environment.
780 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
781 * @note A transaction and its cursors must only be used by a single
782 * thread, and a thread may only have a single transaction at a time.
783 * If #MDB_NOTLS is in use, this does not apply to read-only transactions.
784 * @note Cursors may not span transactions.
785 * @param[in] env An environment handle returned by #mdb_env_create()
786 * @param[in] parent If this parameter is non-NULL, the new transaction
787 * will be a nested transaction, with the transaction indicated by \b parent
788 * as its parent. Transactions may be nested to any level. A parent
789 * transaction and its cursors may not issue any other operations than
790 * mdb_txn_commit and mdb_txn_abort while it has active child transactions.
791 * @param[in] flags Special options for this transaction. This parameter
792 * must be set to 0 or by bitwise OR'ing together one or more of the
793 * values described here.
796 * This transaction will not perform any write operations.
798 * @param[out] txn Address where the new #MDB_txn handle will be stored
799 * @return A non-zero error value on failure and 0 on success. Some possible
802 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
804 * <li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's
805 * mapsize and this environment's map must be resized as well.
806 * See #mdb_env_set_mapsize().
807 * <li>#MDB_READERS_FULL - a read-only transaction was requested and
808 * the reader lock table is full. See #mdb_env_set_maxreaders().
809 * <li>ENOMEM - out of memory.
812 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
814 /** @brief Returns the transaction's #MDB_env
816 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
818 MDB_env *mdb_txn_env(MDB_txn *txn);
820 /** @brief Commit all the operations of a transaction into the database.
822 * The transaction handle is freed. It and its cursors must not be used
823 * again after this call, except with #mdb_cursor_renew().
824 * @note Earlier documentation incorrectly said all cursors would be freed.
825 * Only write-transactions free cursors.
826 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
827 * @return A non-zero error value on failure and 0 on success. Some possible
830 * <li>EINVAL - an invalid parameter was specified.
831 * <li>ENOSPC - no more disk space.
832 * <li>EIO - a low-level I/O error occurred while writing.
833 * <li>ENOMEM - out of memory.
836 int mdb_txn_commit(MDB_txn *txn);
838 /** @brief Abandon all the operations of the transaction instead of saving them.
840 * The transaction handle is freed. It and its cursors must not be used
841 * again after this call, except with #mdb_cursor_renew().
842 * @note Earlier documentation incorrectly said all cursors would be freed.
843 * Only write-transactions free cursors.
844 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
846 void mdb_txn_abort(MDB_txn *txn);
848 /** @brief Reset a read-only transaction.
850 * Abort the transaction like #mdb_txn_abort(), but keep the transaction
851 * handle. #mdb_txn_renew() may reuse the handle. This saves allocation
852 * overhead if the process will start a new read-only transaction soon,
853 * and also locking overhead if #MDB_NOTLS is in use. The reader table
854 * lock is released, but the table slot stays tied to its thread or
855 * #MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free
856 * its lock table slot if MDB_NOTLS is in use.
857 * Cursors opened within the transaction must not be used
858 * again after this call, except with #mdb_cursor_renew().
859 * Reader locks generally don't interfere with writers, but they keep old
860 * versions of database pages allocated. Thus they prevent the old pages
861 * from being reused when writers commit new data, and so under heavy load
862 * the database size may grow much more rapidly than otherwise.
863 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
865 void mdb_txn_reset(MDB_txn *txn);
867 /** @brief Renew a read-only transaction.
869 * This acquires a new reader lock for a transaction handle that had been
870 * released by #mdb_txn_reset(). It must be called before a reset transaction
872 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
873 * @return A non-zero error value on failure and 0 on success. Some possible
876 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
878 * <li>EINVAL - an invalid parameter was specified.
881 int mdb_txn_renew(MDB_txn *txn);
883 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
884 #define mdb_open(txn,name,flags,dbi) mdb_dbi_open(txn,name,flags,dbi)
885 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
886 #define mdb_close(env,dbi) mdb_dbi_close(env,dbi)
888 /** @brief Open a database in the environment.
890 * A database handle denotes the name and parameters of a database,
891 * independently of whether such a database exists.
892 * The database handle may be discarded by calling #mdb_dbi_close().
893 * The old database handle is returned if the database was already open.
894 * The handle must only be closed once.
895 * The database handle will be private to the current transaction until
896 * the transaction is successfully committed. If the transaction is
897 * aborted the handle will be closed automatically.
898 * After a successful commit the
899 * handle will reside in the shared environment, and may be used
900 * by other transactions. This function must not be called from
901 * multiple concurrent transactions. A transaction that uses this function
902 * must finish (either commit or abort) before any other transaction may
905 * To use named databases (with name != NULL), #mdb_env_set_maxdbs()
906 * must be called before opening the environment.
907 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
908 * @param[in] name The name of the database to open. If only a single
909 * database is needed in the environment, this value may be NULL.
910 * @param[in] flags Special options for this database. This parameter
911 * must be set to 0 or by bitwise OR'ing together one or more of the
912 * values described here.
914 * <li>#MDB_REVERSEKEY
915 * Keys are strings to be compared in reverse order, from the end
916 * of the strings to the beginning. By default, Keys are treated as strings and
917 * compared from beginning to end.
919 * Duplicate keys may be used in the database. (Or, from another perspective,
920 * keys may have multiple data items, stored in sorted order.) By default
921 * keys must be unique and may have only a single data item.
922 * <li>#MDB_INTEGERKEY
923 * Keys are binary integers in native byte order. Setting this option
924 * requires all keys to be the same size, typically sizeof(int)
927 * This flag may only be used in combination with #MDB_DUPSORT. This option
928 * tells the library that the data items for this database are all the same
929 * size, which allows further optimizations in storage and retrieval. When
930 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
931 * cursor operations may be used to retrieve multiple items at once.
932 * <li>#MDB_INTEGERDUP
933 * This option specifies that duplicate data items are also integers, and
934 * should be sorted as such.
935 * <li>#MDB_REVERSEDUP
936 * This option specifies that duplicate data items should be compared as
937 * strings in reverse order.
939 * Create the named database if it doesn't exist. This option is not
940 * allowed in a read-only transaction or a read-only environment.
942 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
943 * @return A non-zero error value on failure and 0 on success. Some possible
946 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
947 * and #MDB_CREATE was not specified.
948 * <li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs().
951 int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
953 /** @brief Retrieve statistics for a database.
955 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
956 * @param[in] dbi A database handle returned by #mdb_dbi_open()
957 * @param[out] stat The address of an #MDB_stat structure
958 * where the statistics will be copied
959 * @return A non-zero error value on failure and 0 on success. Some possible
962 * <li>EINVAL - an invalid parameter was specified.
965 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
967 /** @brief Retrieve the DB flags for a database handle.
969 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
970 * @param[in] dbi A database handle returned by #mdb_dbi_open()
971 * @param[out] flags Address where the flags will be returned.
972 * @return A non-zero error value on failure and 0 on success.
974 int mdb_dbi_flags(MDB_txn *txn, MDB_dbi dbi, unsigned int *flags);
976 /** @brief Close a database handle.
978 * This call is not mutex protected. Handles should only be closed by
979 * a single thread, and only if no other threads are going to reference
980 * the database handle or one of its cursors any further. Do not close
981 * a handle if an existing transaction has modified its database.
982 * @param[in] env An environment handle returned by #mdb_env_create()
983 * @param[in] dbi A database handle returned by #mdb_dbi_open()
985 void mdb_dbi_close(MDB_env *env, MDB_dbi dbi);
987 /** @brief Empty or delete+close a database.
989 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
990 * @param[in] dbi A database handle returned by #mdb_dbi_open()
991 * @param[in] del 0 to empty the DB, 1 to delete it from the
992 * environment and close the DB handle.
993 * @return A non-zero error value on failure and 0 on success.
995 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
997 /** @brief Set a custom key comparison function for a database.
999 * The comparison function is called whenever it is necessary to compare a
1000 * key specified by the application with a key currently stored in the database.
1001 * If no comparison function is specified, and no special key flags were specified
1002 * with #mdb_dbi_open(), the keys are compared lexically, with shorter keys collating
1003 * before longer keys.
1004 * @warning This function must be called before any data access functions are used,
1005 * otherwise data corruption may occur. The same comparison function must be used by every
1006 * program accessing the database, every time the database is used.
1007 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1008 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1009 * @param[in] cmp A #MDB_cmp_func function
1010 * @return A non-zero error value on failure and 0 on success. Some possible
1013 * <li>EINVAL - an invalid parameter was specified.
1016 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
1018 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
1020 * This comparison function is called whenever it is necessary to compare a data
1021 * item specified by the application with a data item currently stored in the database.
1022 * This function only takes effect if the database was opened with the #MDB_DUPSORT
1024 * If no comparison function is specified, and no special key flags were specified
1025 * with #mdb_dbi_open(), the data items are compared lexically, with shorter items collating
1026 * before longer items.
1027 * @warning This function must be called before any data access functions are used,
1028 * otherwise data corruption may occur. The same comparison function must be used by every
1029 * program accessing the database, every time the database is used.
1030 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1031 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1032 * @param[in] cmp A #MDB_cmp_func function
1033 * @return A non-zero error value on failure and 0 on success. Some possible
1036 * <li>EINVAL - an invalid parameter was specified.
1039 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
1041 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
1043 * @todo The relocation function is called whenever it is necessary to move the data
1044 * of an item to a different position in the database (e.g. through tree
1045 * balancing operations, shifts as a result of adds or deletes, etc.). It is
1046 * intended to allow address/position-dependent data items to be stored in
1047 * a database in an environment opened with the #MDB_FIXEDMAP option.
1048 * Currently the relocation feature is unimplemented and setting
1049 * this function has no effect.
1050 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1051 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1052 * @param[in] rel A #MDB_rel_func function
1053 * @return A non-zero error value on failure and 0 on success. Some possible
1056 * <li>EINVAL - an invalid parameter was specified.
1059 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
1061 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
1063 * See #mdb_set_relfunc and #MDB_rel_func for more details.
1064 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1065 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1066 * @param[in] ctx An arbitrary pointer for whatever the application needs.
1067 * It will be passed to the callback function set by #mdb_set_relfunc
1068 * as its \b relctx parameter whenever the callback is invoked.
1069 * @return A non-zero error value on failure and 0 on success. Some possible
1072 * <li>EINVAL - an invalid parameter was specified.
1075 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
1077 /** @brief Get items from a database.
1079 * This function retrieves key/data pairs from the database. The address
1080 * and length of the data associated with the specified \b key are returned
1081 * in the structure to which \b data refers.
1082 * If the database supports duplicate keys (#MDB_DUPSORT) then the
1083 * first data item for the key will be returned. Retrieval of other
1084 * items requires the use of #mdb_cursor_get().
1086 * @note The memory pointed to by the returned values is owned by the
1087 * database. The caller need not dispose of the memory, and may not
1088 * modify it in any way. For values returned in a read-only transaction
1089 * any modification attempts will cause a SIGSEGV.
1090 * @note Values returned from the database are valid only until a
1091 * subsequent update operation, or the end of the transaction.
1092 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1093 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1094 * @param[in] key The key to search for in the database
1095 * @param[out] data The data corresponding to the key
1096 * @return A non-zero error value on failure and 0 on success. Some possible
1099 * <li>#MDB_NOTFOUND - the key was not in the database.
1100 * <li>EINVAL - an invalid parameter was specified.
1103 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1105 /** @brief Store items into a database.
1107 * This function stores key/data pairs in the database. The default behavior
1108 * is to enter the new key/data pair, replacing any previously existing key
1109 * if duplicates are disallowed, or adding a duplicate data item if
1110 * duplicates are allowed (#MDB_DUPSORT).
1111 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1112 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1113 * @param[in] key The key to store in the database
1114 * @param[in,out] data The data to store
1115 * @param[in] flags Special options for this operation. This parameter
1116 * must be set to 0 or by bitwise OR'ing together one or more of the
1117 * values described here.
1119 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1120 * already appear in the database. This flag may only be specified
1121 * if the database was opened with #MDB_DUPSORT. The function will
1122 * return #MDB_KEYEXIST if the key/data pair already appears in the
1124 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1125 * does not already appear in the database. The function will return
1126 * #MDB_KEYEXIST if the key already appears in the database, even if
1127 * the database supports duplicates (#MDB_DUPSORT). The \b data
1128 * parameter will be set to point to the existing item.
1129 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1130 * don't copy the given data. Instead, return a pointer to the
1131 * reserved space, which the caller can fill in later - before
1132 * the next update operation or the transaction ends. This saves
1133 * an extra memcpy if the data is being generated later.
1134 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1135 * database. No key comparisons are performed. This option allows
1136 * fast bulk loading when keys are already known to be in the
1137 * correct order. Loading unsorted keys with this flag will cause
1139 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1141 * @return A non-zero error value on failure and 0 on success. Some possible
1144 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1145 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1146 * <li>EACCES - an attempt was made to write in a read-only transaction.
1147 * <li>EINVAL - an invalid parameter was specified.
1150 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
1151 unsigned int flags);
1153 /** @brief Delete items from a database.
1155 * This function removes key/data pairs from the database.
1156 * If the database does not support sorted duplicate data items
1157 * (#MDB_DUPSORT) the data parameter is ignored.
1158 * If the database supports sorted duplicates and the data parameter
1159 * is NULL, all of the duplicate data items for the key will be
1160 * deleted. Otherwise, if the data parameter is non-NULL
1161 * only the matching data item will be deleted.
1162 * This function will return #MDB_NOTFOUND if the specified key/data
1163 * pair is not in the database.
1164 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1165 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1166 * @param[in] key The key to delete from the database
1167 * @param[in] data The data to delete
1168 * @return A non-zero error value on failure and 0 on success. Some possible
1171 * <li>EACCES - an attempt was made to write in a read-only transaction.
1172 * <li>EINVAL - an invalid parameter was specified.
1175 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1177 /** @brief Create a cursor handle.
1179 * A cursor is associated with a specific transaction and database.
1180 * A cursor cannot be used when its database handle is closed. Nor
1181 * when its transaction has ended, except with #mdb_cursor_renew().
1182 * It can be discarded with #mdb_cursor_close().
1183 * A cursor in a write-transaction can be closed before its transaction
1184 * ends, and will otherwise be closed when its transaction ends.
1185 * A cursor in a read-only transaction must be closed explicitly, before
1186 * or after its transaction ends. It can be reused with
1187 * #mdb_cursor_renew() before finally closing it.
1188 * @note Earlier documentation said that cursors in every transaction
1189 * were closed when the transaction committed or aborted.
1190 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1191 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1192 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
1193 * @return A non-zero error value on failure and 0 on success. Some possible
1196 * <li>EINVAL - an invalid parameter was specified.
1199 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
1201 /** @brief Close a cursor handle.
1203 * The cursor handle will be freed and must not be used again after this call.
1204 * Its transaction must still be live if it is a write-transaction.
1205 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1207 void mdb_cursor_close(MDB_cursor *cursor);
1209 /** @brief Renew a cursor handle.
1211 * A cursor is associated with a specific transaction and database.
1212 * Cursors that are only used in read-only
1213 * transactions may be re-used, to avoid unnecessary malloc/free overhead.
1214 * The cursor may be associated with a new read-only transaction, and
1215 * referencing the same database handle as it was created with.
1216 * This may be done whether the previous transaction is live or dead.
1217 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1218 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1219 * @return A non-zero error value on failure and 0 on success. Some possible
1222 * <li>EINVAL - an invalid parameter was specified.
1225 int mdb_cursor_renew(MDB_txn *txn, MDB_cursor *cursor);
1227 /** @brief Return the cursor's transaction handle.
1229 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1231 MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
1233 /** @brief Return the cursor's database handle.
1235 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1237 MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor);
1239 /** @brief Retrieve by cursor.
1241 * This function retrieves key/data pairs from the database. The address and length
1242 * of the key are returned in the object to which \b key refers (except for the
1243 * case of the #MDB_SET option, in which the \b key object is unchanged), and
1244 * the address and length of the data are returned in the object to which \b data
1246 * See #mdb_get() for restrictions on using the output values.
1247 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1248 * @param[in,out] key The key for a retrieved item
1249 * @param[in,out] data The data of a retrieved item
1250 * @param[in] op A cursor operation #MDB_cursor_op
1251 * @return A non-zero error value on failure and 0 on success. Some possible
1254 * <li>#MDB_NOTFOUND - no matching key found.
1255 * <li>EINVAL - an invalid parameter was specified.
1258 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1261 /** @brief Store by cursor.
1263 * This function stores key/data pairs into the database.
1264 * If the function fails for any reason, the state of the cursor will be
1265 * unchanged. If the function succeeds and an item is inserted into the
1266 * database, the cursor is always positioned to refer to the newly inserted item.
1267 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1268 * @param[in] key The key operated on.
1269 * @param[in] data The data operated on.
1270 * @param[in] flags Options for this operation. This parameter
1271 * must be set to 0 or one of the values described here.
1273 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which
1274 * the cursor refers with the specified data item. The \b key
1275 * parameter is ignored.
1276 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1277 * already appear in the database. This flag may only be specified
1278 * if the database was opened with #MDB_DUPSORT. The function will
1279 * return #MDB_KEYEXIST if the key/data pair already appears in the
1281 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1282 * does not already appear in the database. The function will return
1283 * #MDB_KEYEXIST if the key already appears in the database, even if
1284 * the database supports duplicates (#MDB_DUPSORT).
1285 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1286 * don't copy the given data. Instead, return a pointer to the
1287 * reserved space, which the caller can fill in later. This saves
1288 * an extra memcpy if the data is being generated later.
1289 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1290 * database. No key comparisons are performed. This option allows
1291 * fast bulk loading when keys are already known to be in the
1292 * correct order. Loading unsorted keys with this flag will cause
1294 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1295 * <li>#MDB_MULTIPLE - store multiple contiguous data elements in a
1296 * single request. This flag may only be specified if the database
1297 * was opened with #MDB_DUPFIXED. The \b data argument must be an
1298 * array of two MDB_vals. The mv_size of the first MDB_val must be
1299 * the size of a single data element. The mv_data of the first MDB_val
1300 * must point to the beginning of the array of contiguous data elements.
1301 * The mv_size of the second MDB_val must be the count of the number
1302 * of data elements to store. On return this field will be set to
1303 * the count of the number of elements actually written. The mv_data
1304 * of the second MDB_val is unused.
1306 * @return A non-zero error value on failure and 0 on success. Some possible
1309 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1310 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1311 * <li>EACCES - an attempt was made to modify a read-only database.
1312 * <li>EINVAL - an invalid parameter was specified.
1315 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1316 unsigned int flags);
1318 /** @brief Delete current key/data pair
1320 * This function deletes the key/data pair to which the cursor refers.
1321 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1322 * @param[in] flags Options for this operation. This parameter
1323 * must be set to 0 or one of the values described here.
1325 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
1326 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
1328 * @return A non-zero error value on failure and 0 on success. Some possible
1331 * <li>EACCES - an attempt was made to modify a read-only database.
1332 * <li>EINVAL - an invalid parameter was specified.
1335 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
1337 /** @brief Return count of duplicates for current key.
1339 * This call is only valid on databases that support sorted duplicate
1340 * data items #MDB_DUPSORT.
1341 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1342 * @param[out] countp Address where the count will be stored
1343 * @return A non-zero error value on failure and 0 on success. Some possible
1346 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
1349 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
1351 /** @brief Compare two data items according to a particular database.
1353 * This returns a comparison as if the two data items were keys in the
1354 * specified database.
1355 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1356 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1357 * @param[in] a The first item to compare
1358 * @param[in] b The second item to compare
1359 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1361 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1363 /** @brief Compare two data items according to a particular database.
1365 * This returns a comparison as if the two items were data items of
1366 * the specified database. The database must have the #MDB_DUPSORT flag.
1367 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1368 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1369 * @param[in] a The first item to compare
1370 * @param[in] b The second item to compare
1371 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1373 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1375 /** @brief A callback function used to print a message from the library.
1377 * @param[in] msg The string to be printed.
1378 * @param[in] ctx An arbitrary context pointer for the callback.
1379 * @return < 0 on failure, 0 on success.
1381 typedef int (MDB_msg_func)(const char *msg, void *ctx);
1383 /** @brief Dump the entries in the reader lock table.
1385 * @param[in] env An environment handle returned by #mdb_env_create()
1386 * @param[in] func A #MDB_msg_func function
1387 * @param[in] ctx Anything the message function needs
1388 * @return < 0 on failure, 0 on success.
1390 int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx);
1392 /** @brief Check for stale entries in the reader lock table.
1394 * @param[in] env An environment handle returned by #mdb_env_create()
1395 * @param[out] dead Number of stale slots that were cleared
1396 * @return 0 on success, non-zero on failure.
1398 int mdb_reader_check(MDB_env *env, int *dead);
1404 #endif /* _LMDB_H_ */