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.
70 * - Use an MDB_env* in the process which opened it, without fork()ing.
72 * - Do not have open an MDB database twice in the same process at
73 * the same time. Not even from a plain open() call - close()ing it
74 * breaks flock() advisory locking.
76 * - Avoid long-lived transactions. Read transactions prevent
77 * reuse of pages freed by newer write transactions, thus the
78 * database can grow quickly. Write transactions prevent
79 * other write transactions, since writes are serialized.
81 * - Avoid suspending a process with active transactions. These
82 * would then be "long-lived" as above. Also read transactions
83 * suspended when writers commit could sometimes see wrong data.
85 * ...when several processes can use a database concurrently:
87 * - Avoid aborting a process with an active transaction.
88 * The transaction becomes "long-lived" as above until the lockfile
89 * is reset, since the process may not remove it from the lockfile.
91 * - If you do that anyway, close the environment once in a while,
92 * so the lockfile can get reset.
94 * - Do not use MDB databases on remote filesystems, even between
95 * processes on the same host. This breaks flock() on some OSes,
96 * possibly memory map sync, and certainly sync between programs
99 * - Opening a database can fail if another process is opening or
100 * closing it at exactly the same time.
102 * @author Howard Chu, Symas Corporation.
104 * @copyright Copyright 2011-2013 Howard Chu, Symas Corp. All rights reserved.
106 * Redistribution and use in source and binary forms, with or without
107 * modification, are permitted only as authorized by the OpenLDAP
110 * A copy of this license is available in the file LICENSE in the
111 * top-level directory of the distribution or, alternatively, at
112 * <http://www.OpenLDAP.org/license.html>.
115 * This code is derived from btree.c written by Martin Hedenfalk.
117 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
119 * Permission to use, copy, modify, and distribute this software for any
120 * purpose with or without fee is hereby granted, provided that the above
121 * copyright notice and this permission notice appear in all copies.
123 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
124 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
125 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
126 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
127 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
128 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
129 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
134 #include <sys/types.h>
141 typedef int mdb_mode_t;
143 typedef mode_t mdb_mode_t;
146 /** @defgroup mdb MDB API
148 * @brief OpenLDAP Lightning Memory-Mapped Database Manager
150 /** @defgroup Version Version Macros
153 /** Library major version */
154 #define MDB_VERSION_MAJOR 0
155 /** Library minor version */
156 #define MDB_VERSION_MINOR 9
157 /** Library patch version */
158 #define MDB_VERSION_PATCH 6
160 /** Combine args a,b,c into a single integer for easy version comparisons */
161 #define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
163 /** The full library version as a single integer */
164 #define MDB_VERSION_FULL \
165 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
167 /** The release date of this library version */
168 #define MDB_VERSION_DATE "January 10, 2013"
170 /** A stringifier for the version info */
171 #define MDB_VERSTR(a,b,c,d) "MDB " #a "." #b "." #c ": (" d ")"
173 /** A helper for the stringifier macro */
174 #define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d)
176 /** The full library version as a C string */
177 #define MDB_VERSION_STRING \
178 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
181 /** @brief Opaque structure for a database environment.
183 * A DB environment supports multiple databases, all residing in the same
186 typedef struct MDB_env MDB_env;
188 /** @brief Opaque structure for a transaction handle.
190 * All database operations require a transaction handle. Transactions may be
191 * read-only or read-write.
193 typedef struct MDB_txn MDB_txn;
195 /** @brief A handle for an individual database in the DB environment. */
196 typedef unsigned int MDB_dbi;
198 /** @brief Opaque structure for navigating through a database */
199 typedef struct MDB_cursor MDB_cursor;
201 /** @brief Generic structure used for passing keys and data in and out
204 * Key sizes must be between 1 and the liblmdb build-time constant
205 * #MDB_MAXKEYSIZE inclusive. This currently defaults to 511. The
206 * same applies to data sizes in databases with the #MDB_DUPSORT flag.
207 * Other data items can in theory be from 0 to 0xffffffff bytes long.
209 typedef struct MDB_val {
210 size_t mv_size; /**< size of the data item */
211 void *mv_data; /**< address of the data item */
214 /** @brief A callback function used to compare two keys in a database */
215 typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
217 /** @brief A callback function used to relocate a position-dependent data item
218 * in a fixed-address database.
220 * The \b newptr gives the item's desired address in
221 * the memory map, and \b oldptr gives its previous address. The item's actual
222 * data resides at the address in \b item. This callback is expected to walk
223 * through the fields of the record in \b item and modify any
224 * values based at the \b oldptr address to be relative to the \b newptr address.
225 * @param[in,out] item The item that is to be relocated.
226 * @param[in] oldptr The previous address.
227 * @param[in] newptr The new address to relocate to.
228 * @param[in] relctx An application-provided context, set by #mdb_set_relctx().
229 * @todo This feature is currently unimplemented.
231 typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
233 /** @defgroup mdb_env Environment Flags
235 * Values do not overlap Database Flags.
238 /** mmap at a fixed address (experimental) */
239 #define MDB_FIXEDMAP 0x01
240 /** no environment directory */
241 #define MDB_NOSUBDIR 0x4000
242 /** don't fsync after commit */
243 #define MDB_NOSYNC 0x10000
245 #define MDB_RDONLY 0x20000
246 /** don't fsync metapage after commit */
247 #define MDB_NOMETASYNC 0x40000
248 /** use writable mmap */
249 #define MDB_WRITEMAP 0x80000
250 /** use asynchronous msync when MDB_WRITEMAP is used */
251 #define MDB_MAPASYNC 0x100000
254 /** @defgroup mdb_dbi_open Database Flags
256 * Values do not overlap Environment Flags.
259 /** use reverse string keys */
260 #define MDB_REVERSEKEY 0x02
261 /** use sorted duplicates */
262 #define MDB_DUPSORT 0x04
263 /** numeric keys in native byte order.
264 * The keys must all be of the same size. */
265 #define MDB_INTEGERKEY 0x08
266 /** with #MDB_DUPSORT, sorted dup items have fixed size */
267 #define MDB_DUPFIXED 0x10
268 /** with #MDB_DUPSORT, dups are numeric in native byte order */
269 #define MDB_INTEGERDUP 0x20
270 /** with #MDB_DUPSORT, use reverse string dups */
271 #define MDB_REVERSEDUP 0x40
272 /** create DB if not already existing */
273 #define MDB_CREATE 0x40000
276 /** @defgroup mdb_put Write Flags
279 /** For put: Don't write if the key already exists. */
280 #define MDB_NOOVERWRITE 0x10
281 /** Only for #MDB_DUPSORT<br>
282 * For put: don't write if the key and data pair already exist.<br>
283 * For mdb_cursor_del: remove all duplicate data items.
285 #define MDB_NODUPDATA 0x20
286 /** For mdb_cursor_put: overwrite the current key/data pair */
287 #define MDB_CURRENT 0x40
288 /** For put: Just reserve space for data, don't copy it. Return a
289 * pointer to the reserved space.
291 #define MDB_RESERVE 0x10000
292 /** Data is being appended, don't split full pages. */
293 #define MDB_APPEND 0x20000
294 /** Duplicate data is being appended, don't split full pages. */
295 #define MDB_APPENDDUP 0x40000
296 /** Store multiple data items in one call. */
297 #define MDB_MULTIPLE 0x80000
300 /** @brief Cursor Get operations.
302 * This is the set of all operations for retrieving data
305 typedef enum MDB_cursor_op {
306 MDB_FIRST, /**< Position at first key/data item */
307 MDB_FIRST_DUP, /**< Position at first data item of current key.
308 Only for #MDB_DUPSORT */
309 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
310 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
311 MDB_GET_CURRENT, /**< Return key/data at current cursor position */
312 MDB_GET_MULTIPLE, /**< Return all the duplicate data items at the current
313 cursor position. Only for #MDB_DUPFIXED */
314 MDB_LAST, /**< Position at last key/data item */
315 MDB_LAST_DUP, /**< Position at last data item of current key.
316 Only for #MDB_DUPSORT */
317 MDB_NEXT, /**< Position at next data item */
318 MDB_NEXT_DUP, /**< Position at next data item of current key.
319 Only for #MDB_DUPSORT */
320 MDB_NEXT_MULTIPLE, /**< Return all duplicate data items at the next
321 cursor position. Only for #MDB_DUPFIXED */
322 MDB_NEXT_NODUP, /**< Position at first data item of next key.
323 Only for #MDB_DUPSORT */
324 MDB_PREV, /**< Position at previous data item */
325 MDB_PREV_DUP, /**< Position at previous data item of current key.
326 Only for #MDB_DUPSORT */
327 MDB_PREV_NODUP, /**< Position at last data item of previous key.
328 Only for #MDB_DUPSORT */
329 MDB_SET, /**< Position at specified key */
330 MDB_SET_KEY, /**< Position at specified key, return key + data */
331 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
334 /** @defgroup errors Return Codes
336 * BerkeleyDB uses -30800 to -30999, we'll go under them
339 /** Successful result */
340 #define MDB_SUCCESS 0
341 /** key/data pair already exists */
342 #define MDB_KEYEXIST (-30799)
343 /** key/data pair not found (EOF) */
344 #define MDB_NOTFOUND (-30798)
345 /** Requested page not found - this usually indicates corruption */
346 #define MDB_PAGE_NOTFOUND (-30797)
347 /** Located page was wrong type */
348 #define MDB_CORRUPTED (-30796)
349 /** Update of meta page failed, probably I/O error */
350 #define MDB_PANIC (-30795)
351 /** Environment version mismatch */
352 #define MDB_VERSION_MISMATCH (-30794)
353 /** File is not a valid MDB file */
354 #define MDB_INVALID (-30793)
355 /** Environment mapsize reached */
356 #define MDB_MAP_FULL (-30792)
357 /** Environment maxdbs reached */
358 #define MDB_DBS_FULL (-30791)
359 /** Environment maxreaders reached */
360 #define MDB_READERS_FULL (-30790)
361 /** Too many TLS keys in use - Windows only */
362 #define MDB_TLS_FULL (-30789)
363 /** Txn has too many dirty pages */
364 #define MDB_TXN_FULL (-30788)
365 /** Cursor stack too deep - internal error */
366 #define MDB_CURSOR_FULL (-30787)
367 /** Page has not enough space - internal error */
368 #define MDB_PAGE_FULL (-30786)
369 /** Database contents grew beyond environment mapsize */
370 #define MDB_MAP_RESIZED (-30785)
371 /** Database flags changed or would change */
372 #define MDB_INCOMPATIBLE (-30784)
373 /** Invalid reuse of reader locktable slot */
374 #define MDB_BAD_RSLOT (-30783)
375 #define MDB_LAST_ERRCODE MDB_BAD_RSLOT
378 /** @brief Statistics for a database in the environment */
379 typedef struct MDB_stat {
380 unsigned int ms_psize; /**< Size of a database page.
381 This is currently the same for all databases. */
382 unsigned int ms_depth; /**< Depth (height) of the B-tree */
383 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
384 size_t ms_leaf_pages; /**< Number of leaf pages */
385 size_t ms_overflow_pages; /**< Number of overflow pages */
386 size_t ms_entries; /**< Number of data items */
389 /** @brief Information about the environment */
390 typedef struct MDB_envinfo {
391 void *me_mapaddr; /**< Address of map, if fixed */
392 size_t me_mapsize; /**< Size of the data memory map */
393 size_t me_last_pgno; /**< ID of the last used page */
394 size_t me_last_txnid; /**< ID of the last committed transaction */
395 unsigned int me_maxreaders; /**< maximum number of threads for the environment */
396 unsigned int me_numreaders; /**< maximum number of threads used in the environment */
399 /** @brief Return the mdb library version information.
401 * @param[out] major if non-NULL, the library major version number is copied here
402 * @param[out] minor if non-NULL, the library minor version number is copied here
403 * @param[out] patch if non-NULL, the library patch version number is copied here
404 * @retval "version string" The library version as a string
406 char *mdb_version(int *major, int *minor, int *patch);
408 /** @brief Return a string describing a given error code.
410 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
411 * function. If the error code is greater than or equal to 0, then the string
412 * returned by the system function strerror(3) is returned. If the error code
413 * is less than 0, an error string corresponding to the MDB library error is
414 * returned. See @ref errors for a list of MDB-specific error codes.
415 * @param[in] err The error code
416 * @retval "error message" The description of the error
418 char *mdb_strerror(int err);
420 /** @brief Create an MDB environment handle.
422 * This function allocates memory for a #MDB_env structure. To release
423 * the allocated memory and discard the handle, call #mdb_env_close().
424 * Before the handle may be used, it must be opened using #mdb_env_open().
425 * Various other options may also need to be set before opening the handle,
426 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
427 * depending on usage requirements.
428 * @param[out] env The address where the new handle will be stored
429 * @return A non-zero error value on failure and 0 on success.
431 int mdb_env_create(MDB_env **env);
433 /** @brief Open an environment handle.
435 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
436 * @param[in] env An environment handle returned by #mdb_env_create()
437 * @param[in] path The directory in which the database files reside. This
438 * directory must already exist and be writable.
439 * @param[in] flags Special options for this environment. This parameter
440 * must be set to 0 or by bitwise OR'ing together one or more of the
441 * values described here.
442 * Flags set by mdb_env_set_flags() are also used.
445 * use a fixed address for the mmap region. This flag must be specified
446 * when creating the environment, and is stored persistently in the environment.
447 * If successful, the memory map will always reside at the same virtual address
448 * and pointers used to reference data items in the database will be constant
449 * across multiple invocations. This option may not always work, depending on
450 * how the operating system has allocated memory to shared libraries and other uses.
451 * The feature is highly experimental.
453 * By default, MDB creates its environment in a directory whose
454 * pathname is given in \b path, and creates its data and lock files
455 * under that directory. With this option, \b path is used as-is for
456 * the database main data file. The database lock file is the \b path
457 * with "-lock" appended.
459 * Open the environment in read-only mode. No write operations will be
460 * allowed. MDB will still modify the lock file - except on read-only
461 * filesystems, where MDB does not use locks.
463 * Use a writeable memory map unless MDB_RDONLY is set. This is faster
464 * and uses fewer mallocs, but loses protection from application bugs
465 * like wild pointer writes and other bad updates into the database.
466 * Incompatible with nested transactions.
467 * <li>#MDB_NOMETASYNC
468 * Flush system buffers to disk only once per transaction, omit the
469 * metadata flush. Defer that until the system flushes files to disk,
470 * or next non-MDB_RDONLY commit or #mdb_env_sync(). This optimization
471 * maintains database integrity, but a system crash may undo the last
472 * committed transaction. I.e. it preserves the ACI (atomicity,
473 * consistency, isolation) but not D (durability) database property.
474 * This flag may be changed at any time using #mdb_env_set_flags().
476 * Don't flush system buffers to disk when committing a transaction.
477 * This optimization means a system crash can corrupt the database or
478 * lose the last transactions if buffers are not yet flushed to disk.
479 * The risk is governed by how often the system flushes dirty buffers
480 * to disk and how often #mdb_env_sync() is called. However, if the
481 * filesystem preserves write order and the #MDB_WRITEMAP flag is not
482 * used, transactions exhibit ACI (atomicity, consistency, isolation)
483 * properties and only lose D (durability). I.e. database integrity
484 * is maintained, but a system crash may undo the final transactions.
485 * Note that (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no
486 * hint for when to write transactions to disk, unless #mdb_env_sync()
487 * is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable.
488 * This flag may be changed at any time using #mdb_env_set_flags().
490 * When using #MDB_WRITEMAP, use asynchronous flushes to disk.
491 * As with #MDB_NOSYNC, a system crash can then corrupt the
492 * database or lose the last transactions. Calling #mdb_env_sync()
493 * ensures on-disk database integrity until next commit.
494 * This flag may be changed at any time using #mdb_env_set_flags().
496 * @param[in] mode The UNIX permissions to set on created files. This parameter
497 * is ignored on Windows.
498 * @return A non-zero error value on failure and 0 on success. Some possible
501 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
502 * version that created the database environment.
503 * <li>#MDB_INVALID - the environment file headers are corrupted.
504 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
505 * <li>EACCES - the user didn't have permission to access the environment files.
506 * <li>EAGAIN - the environment was locked by another process.
509 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode);
511 /** @brief Copy an MDB environment to the specified path.
513 * This function may be used to make a backup of an existing environment.
514 * @param[in] env An environment handle returned by #mdb_env_create(). It
515 * must have already been opened successfully.
516 * @param[in] path The directory in which the copy will reside. This
517 * directory must already exist and be writable but must otherwise be
519 * @return A non-zero error value on failure and 0 on success.
521 int mdb_env_copy(MDB_env *env, const char *path);
523 /** @brief Return statistics about the MDB environment.
525 * @param[in] env An environment handle returned by #mdb_env_create()
526 * @param[out] stat The address of an #MDB_stat structure
527 * where the statistics will be copied
529 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
531 /** @brief Return information about the MDB environment.
533 * @param[in] env An environment handle returned by #mdb_env_create()
534 * @param[out] stat The address of an #MDB_envinfo structure
535 * where the information will be copied
537 int mdb_env_info(MDB_env *env, MDB_envinfo *stat);
539 /** @brief Flush the data buffers to disk.
541 * Data is always written to disk when #mdb_txn_commit() is called,
542 * but the operating system may keep it buffered. MDB always flushes
543 * the OS buffers upon commit as well, unless the environment was
544 * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC.
545 * @param[in] env An environment handle returned by #mdb_env_create()
546 * @param[in] force If non-zero, force a synchronous flush. Otherwise
547 * if the environment has the #MDB_NOSYNC flag set the flushes
548 * will be omitted, and with #MDB_MAPASYNC they will be asynchronous.
549 * @return A non-zero error value on failure and 0 on success. Some possible
552 * <li>EINVAL - an invalid parameter was specified.
553 * <li>EIO - an error occurred during synchronization.
556 int mdb_env_sync(MDB_env *env, int force);
558 /** @brief Close the environment and release the memory map.
560 * Only a single thread may call this function. All transactions, databases,
561 * and cursors must already be closed before calling this function. Attempts to
562 * use any such handles after calling this function will cause a SIGSEGV.
563 * The environment handle will be freed and must not be used again after this call.
564 * @param[in] env An environment handle returned by #mdb_env_create()
566 void mdb_env_close(MDB_env *env);
568 /** @brief Set environment flags.
570 * This may be used to set some flags in addition to those from
571 * #mdb_env_open(), or to unset these flags.
572 * @param[in] env An environment handle returned by #mdb_env_create()
573 * @param[in] flags The flags to change, bitwise OR'ed together
574 * @param[in] onoff A non-zero value sets the flags, zero clears them.
575 * @return A non-zero error value on failure and 0 on success. Some possible
578 * <li>EINVAL - an invalid parameter was specified.
581 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
583 /** @brief Get environment flags.
585 * @param[in] env An environment handle returned by #mdb_env_create()
586 * @param[out] flags The address of an integer to store the flags
587 * @return A non-zero error value on failure and 0 on success. Some possible
590 * <li>EINVAL - an invalid parameter was specified.
593 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
595 /** @brief Return the path that was used in #mdb_env_open().
597 * @param[in] env An environment handle returned by #mdb_env_create()
598 * @param[out] path Address of a string pointer to contain the path. This
599 * is the actual string in the environment, not a copy. It should not be
600 * altered in any way.
601 * @return A non-zero error value on failure and 0 on success. Some possible
604 * <li>EINVAL - an invalid parameter was specified.
607 int mdb_env_get_path(MDB_env *env, const char **path);
609 /** @brief Set the size of the memory map to use for this environment.
611 * The size should be a multiple of the OS page size. The default is
612 * 10485760 bytes. The size of the memory map is also the maximum size
613 * of the database. The value should be chosen as large as possible,
614 * to accommodate future growth of the database.
615 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
616 * The size may be changed by closing and reopening the environment.
617 * Any attempt to set a size smaller than the space already consumed
618 * by the environment will be silently changed to the current size of the used space.
619 * @param[in] env An environment handle returned by #mdb_env_create()
620 * @param[in] size The size in bytes
621 * @return A non-zero error value on failure and 0 on success. Some possible
624 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
627 int mdb_env_set_mapsize(MDB_env *env, size_t size);
629 /** @brief Set the maximum number of threads for the environment.
631 * This defines the number of slots in the lock table that is used to track readers in the
632 * the environment. The default is 126.
633 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
634 * @param[in] env An environment handle returned by #mdb_env_create()
635 * @param[in] readers The maximum number of threads
636 * @return A non-zero error value on failure and 0 on success. Some possible
639 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
642 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
644 /** @brief Get the maximum number of threads for the environment.
646 * @param[in] env An environment handle returned by #mdb_env_create()
647 * @param[out] readers Address of an integer to store the number of readers
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_get_maxreaders(MDB_env *env, unsigned int *readers);
656 /** @brief Set the maximum number of named databases for the environment.
658 * This function is only needed if multiple databases will be used in the
659 * environment. Simpler applications that use the environment as a single
660 * unnamed database can ignore this option.
661 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
662 * @param[in] env An environment handle returned by #mdb_env_create()
663 * @param[in] dbs The maximum number of databases
664 * @return A non-zero error value on failure and 0 on success. Some possible
667 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
670 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
672 /** @brief Create a transaction for use with the environment.
674 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
675 * @note Transactions may not span threads; a transaction must only be used by a
676 * single thread. Also, a thread may only have a single transaction.
677 * @note Cursors may not span transactions; each cursor must be opened and closed
678 * within a single transaction.
679 * @param[in] env An environment handle returned by #mdb_env_create()
680 * @param[in] parent If this parameter is non-NULL, the new transaction
681 * will be a nested transaction, with the transaction indicated by \b parent
682 * as its parent. Transactions may be nested to any level. A parent
683 * transaction may not issue any other operations besides mdb_txn_begin,
684 * mdb_txn_abort, or mdb_txn_commit while it has active child transactions.
685 * @param[in] flags Special options for this transaction. This parameter
686 * must be set to 0 or by bitwise OR'ing together one or more of the
687 * values described here.
690 * This transaction will not perform any write operations.
692 * @param[out] txn Address where the new #MDB_txn handle will be stored
693 * @return A non-zero error value on failure and 0 on success. Some possible
696 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
697 - * must be shut down.
698 * <li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's
699 * mapsize and the environment must be shut down.
700 * <li>#MDB_READERS_FULL - a read-only transaction was requested and
701 * the reader lock table is full. See #mdb_env_set_maxreaders().
702 * <li>ENOMEM - out of memory.
705 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
707 /** @brief Commit all the operations of a transaction into the database.
709 * All cursors opened within the transaction will be closed by this call. The cursors
710 * and transaction handle will be freed and must not be used again after this call.
711 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
712 * @return A non-zero error value on failure and 0 on success. Some possible
715 * <li>EINVAL - an invalid parameter was specified.
716 * <li>ENOSPC - no more disk space.
717 * <li>EIO - a low-level I/O error occurred while writing.
718 * <li>ENOMEM - out of memory.
721 int mdb_txn_commit(MDB_txn *txn);
723 /** @brief Abandon all the operations of the transaction instead of saving them.
725 * All cursors opened within the transaction will be closed by this call. The cursors
726 * and transaction handle will be freed and must not be used again after this call.
727 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
729 void mdb_txn_abort(MDB_txn *txn);
731 /** @brief Reset a read-only transaction.
733 * This releases the current reader lock but doesn't free the
734 * transaction handle, allowing it to be used again later by #mdb_txn_renew().
735 * It otherwise has the same effect as #mdb_txn_abort() but saves some memory
736 * allocation/deallocation overhead if a thread is going to start a new
737 * read-only transaction again soon.
738 * All cursors opened within the transaction must be closed before the transaction
740 * Reader locks generally don't interfere with writers, but they keep old
741 * versions of database pages allocated. Thus they prevent the old pages
742 * from being reused when writers commit new data, and so under heavy load
743 * the database size may grow much more rapidly than otherwise.
744 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
746 void mdb_txn_reset(MDB_txn *txn);
748 /** @brief Renew a read-only transaction.
750 * This acquires a new reader lock for a transaction handle that had been
751 * released by #mdb_txn_reset(). It must be called before a reset transaction
753 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
754 * @return A non-zero error value on failure and 0 on success. Some possible
757 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
759 * <li>EINVAL - an invalid parameter was specified.
762 int mdb_txn_renew(MDB_txn *txn);
764 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
765 #define mdb_open(txn,name,flags,dbi) mdb_dbi_open(txn,name,flags,dbi)
766 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
767 #define mdb_close(env,dbi) mdb_dbi_close(env,dbi)
769 /** @brief Open a database in the environment.
771 * The database handle may be discarded by calling #mdb_dbi_close().
772 * The old database handle is returned if the database was already open.
773 * The handle must only be closed once.
774 * The database handle will be private to the current transaction until
775 * the transaction is successfully committed. If the transaction is
776 * aborted the handle will be closed automatically.
777 * After a successful commit the
778 * handle will reside in the shared environment, and may be used
779 * by other transactions. This function must not be called from
780 * multiple concurrent transactions. A transaction that uses this function
781 * must finish (either commit or abort) before any other transaction may
784 * To use named databases (with name != NULL), #mdb_env_set_maxdbs()
785 * must be called before opening the environment.
786 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
787 * @param[in] name The name of the database to open. If only a single
788 * database is needed in the environment, this value may be NULL.
789 * @param[in] flags Special options for this database. This parameter
790 * must be set to 0 or by bitwise OR'ing together one or more of the
791 * values described here.
793 * <li>#MDB_REVERSEKEY
794 * Keys are strings to be compared in reverse order, from the end
795 * of the strings to the beginning. By default, Keys are treated as strings and
796 * compared from beginning to end.
798 * Duplicate keys may be used in the database. (Or, from another perspective,
799 * keys may have multiple data items, stored in sorted order.) By default
800 * keys must be unique and may have only a single data item.
801 * <li>#MDB_INTEGERKEY
802 * Keys are binary integers in native byte order. Setting this option
803 * requires all keys to be the same size, typically sizeof(int)
806 * This flag may only be used in combination with #MDB_DUPSORT. This option
807 * tells the library that the data items for this database are all the same
808 * size, which allows further optimizations in storage and retrieval. When
809 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
810 * cursor operations may be used to retrieve multiple items at once.
811 * <li>#MDB_INTEGERDUP
812 * This option specifies that duplicate data items are also integers, and
813 * should be sorted as such.
814 * <li>#MDB_REVERSEDUP
815 * This option specifies that duplicate data items should be compared as
816 * strings in reverse order.
818 * Create the named database if it doesn't exist. This option is not
819 * allowed in a read-only transaction or a read-only environment.
821 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
822 * @return A non-zero error value on failure and 0 on success. Some possible
825 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
826 * and #MDB_CREATE was not specified.
827 * <li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs().
830 int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
832 /** @brief Retrieve statistics for a database.
834 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
835 * @param[in] dbi A database handle returned by #mdb_dbi_open()
836 * @param[out] stat The address of an #MDB_stat structure
837 * where the statistics will be copied
838 * @return A non-zero error value on failure and 0 on success. Some possible
841 * <li>EINVAL - an invalid parameter was specified.
844 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
846 /** @brief Close a database handle.
848 * This call is not mutex protected. Handles should only be closed by
849 * a single thread, and only if no other threads are going to reference
850 * the database handle or one of its cursors any further. Do not close
851 * a handle if an existing transaction has modified its database.
852 * @param[in] env An environment handle returned by #mdb_env_create()
853 * @param[in] dbi A database handle returned by #mdb_dbi_open()
855 void mdb_dbi_close(MDB_env *env, MDB_dbi dbi);
857 /** @brief Delete a database and/or free all its pages.
859 * If the \b del parameter is 1, the DB handle will be closed
860 * and the DB will be deleted.
861 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
862 * @param[in] dbi A database handle returned by #mdb_dbi_open()
863 * @param[in] del 1 to delete the DB from the environment,
864 * 0 to just free its pages.
865 * @return A non-zero error value on failure and 0 on success.
867 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
869 /** @brief Set a custom key comparison function for a database.
871 * The comparison function is called whenever it is necessary to compare a
872 * key specified by the application with a key currently stored in the database.
873 * If no comparison function is specified, and no special key flags were specified
874 * with #mdb_dbi_open(), the keys are compared lexically, with shorter keys collating
875 * before longer keys.
876 * @warning This function must be called before any data access functions are used,
877 * otherwise data corruption may occur. The same comparison function must be used by every
878 * program accessing the database, every time the database is used.
879 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
880 * @param[in] dbi A database handle returned by #mdb_dbi_open()
881 * @param[in] cmp A #MDB_cmp_func function
882 * @return A non-zero error value on failure and 0 on success. Some possible
885 * <li>EINVAL - an invalid parameter was specified.
888 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
890 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
892 * This comparison function is called whenever it is necessary to compare a data
893 * item specified by the application with a data item currently stored in the database.
894 * This function only takes effect if the database was opened with the #MDB_DUPSORT
896 * If no comparison function is specified, and no special key flags were specified
897 * with #mdb_dbi_open(), the data items are compared lexically, with shorter items collating
898 * before longer items.
899 * @warning This function must be called before any data access functions are used,
900 * otherwise data corruption may occur. The same comparison function must be used by every
901 * program accessing the database, every time the database is used.
902 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
903 * @param[in] dbi A database handle returned by #mdb_dbi_open()
904 * @param[in] cmp A #MDB_cmp_func function
905 * @return A non-zero error value on failure and 0 on success. Some possible
908 * <li>EINVAL - an invalid parameter was specified.
911 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
913 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
915 * @todo The relocation function is called whenever it is necessary to move the data
916 * of an item to a different position in the database (e.g. through tree
917 * balancing operations, shifts as a result of adds or deletes, etc.). It is
918 * intended to allow address/position-dependent data items to be stored in
919 * a database in an environment opened with the #MDB_FIXEDMAP option.
920 * Currently the relocation feature is unimplemented and setting
921 * this function has no effect.
922 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
923 * @param[in] dbi A database handle returned by #mdb_dbi_open()
924 * @param[in] rel A #MDB_rel_func function
925 * @return A non-zero error value on failure and 0 on success. Some possible
928 * <li>EINVAL - an invalid parameter was specified.
931 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
933 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
935 * See #mdb_set_relfunc and #MDB_rel_func for more details.
936 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
937 * @param[in] dbi A database handle returned by #mdb_dbi_open()
938 * @param[in] ctx An arbitrary pointer for whatever the application needs.
939 * It will be passed to the callback function set by #mdb_set_relfunc
940 * as its \b relctx parameter whenever the callback is invoked.
941 * @return A non-zero error value on failure and 0 on success. Some possible
944 * <li>EINVAL - an invalid parameter was specified.
947 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
949 /** @brief Get items from a database.
951 * This function retrieves key/data pairs from the database. The address
952 * and length of the data associated with the specified \b key are returned
953 * in the structure to which \b data refers.
954 * If the database supports duplicate keys (#MDB_DUPSORT) then the
955 * first data item for the key will be returned. Retrieval of other
956 * items requires the use of #mdb_cursor_get().
958 * @note The memory pointed to by the returned values is owned by the
959 * database. The caller need not dispose of the memory, and may not
960 * modify it in any way. For values returned in a read-only transaction
961 * any modification attempts will cause a SIGSEGV.
962 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
963 * @param[in] dbi A database handle returned by #mdb_dbi_open()
964 * @param[in] key The key to search for in the database
965 * @param[out] data The data corresponding to the key
966 * @return A non-zero error value on failure and 0 on success. Some possible
969 * <li>#MDB_NOTFOUND - the key was not in the database.
970 * <li>EINVAL - an invalid parameter was specified.
973 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
975 /** @brief Store items into a database.
977 * This function stores key/data pairs in the database. The default behavior
978 * is to enter the new key/data pair, replacing any previously existing key
979 * if duplicates are disallowed, or adding a duplicate data item if
980 * duplicates are allowed (#MDB_DUPSORT).
981 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
982 * @param[in] dbi A database handle returned by #mdb_dbi_open()
983 * @param[in] key The key to store in the database
984 * @param[in,out] data The data to store
985 * @param[in] flags Special options for this operation. This parameter
986 * must be set to 0 or by bitwise OR'ing together one or more of the
987 * values described here.
989 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
990 * already appear in the database. This flag may only be specified
991 * if the database was opened with #MDB_DUPSORT. The function will
992 * return #MDB_KEYEXIST if the key/data pair already appears in the
994 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
995 * does not already appear in the database. The function will return
996 * #MDB_KEYEXIST if the key already appears in the database, even if
997 * the database supports duplicates (#MDB_DUPSORT). The \b data
998 * parameter will be set to point to the existing item.
999 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1000 * don't copy the given data. Instead, return a pointer to the
1001 * reserved space, which the caller can fill in later. This saves
1002 * an extra memcpy if the data is being generated later.
1003 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1004 * database. No key comparisons are performed. This option allows
1005 * fast bulk loading when keys are already known to be in the
1006 * correct order. Loading unsorted keys with this flag will cause
1008 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1010 * @return A non-zero error value on failure and 0 on success. Some possible
1013 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1014 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1015 * <li>EACCES - an attempt was made to write in a read-only transaction.
1016 * <li>EINVAL - an invalid parameter was specified.
1019 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
1020 unsigned int flags);
1022 /** @brief Delete items from a database.
1024 * This function removes key/data pairs from the database.
1025 * If the database does not support sorted duplicate data items
1026 * (#MDB_DUPSORT) the data parameter is ignored.
1027 * If the database supports sorted duplicates and the data parameter
1028 * is NULL, all of the duplicate data items for the key will be
1029 * deleted. Otherwise, if the data parameter is non-NULL
1030 * only the matching data item will be deleted.
1031 * This function will return #MDB_NOTFOUND if the specified key/data
1032 * pair is not in the database.
1033 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1034 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1035 * @param[in] key The key to delete from the database
1036 * @param[in] data The data to delete
1037 * @return A non-zero error value on failure and 0 on success. Some possible
1040 * <li>EACCES - an attempt was made to write in a read-only transaction.
1041 * <li>EINVAL - an invalid parameter was specified.
1044 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1046 /** @brief Create a cursor handle.
1048 * Cursors are associated with a specific transaction and database and
1049 * may not span threads.
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[out] cursor Address where the new #MDB_cursor handle will be stored
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_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
1061 /** @brief Close a cursor handle.
1063 * The cursor handle will be freed and must not be used again after this call.
1064 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1066 void mdb_cursor_close(MDB_cursor *cursor);
1068 /** @brief Renew a cursor handle.
1070 * Cursors are associated with a specific transaction and database and
1071 * may not span threads. Cursors that are only used in read-only
1072 * transactions may be re-used, to avoid unnecessary malloc/free overhead.
1073 * The cursor may be associated with a new read-only transaction, and
1074 * referencing the same database handle as it was created with.
1075 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1076 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1077 * @return A non-zero error value on failure and 0 on success. Some possible
1080 * <li>EINVAL - an invalid parameter was specified.
1083 int mdb_cursor_renew(MDB_txn *txn, MDB_cursor *cursor);
1085 /** @brief Return the cursor's transaction handle.
1087 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1089 MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
1091 /** @brief Return the cursor's database handle.
1093 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1095 MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor);
1097 /** @brief Retrieve by cursor.
1099 * This function retrieves key/data pairs from the database. The address and length
1100 * of the key are returned in the object to which \b key refers (except for the
1101 * case of the #MDB_SET option, in which the \b key object is unchanged), and
1102 * the address and length of the data are returned in the object to which \b data
1104 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1105 * @param[in,out] key The key for a retrieved item
1106 * @param[in,out] data The data of a retrieved item
1107 * @param[in] op A cursor operation #MDB_cursor_op
1108 * @return A non-zero error value on failure and 0 on success. Some possible
1111 * <li>#MDB_NOTFOUND - no matching key found.
1112 * <li>EINVAL - an invalid parameter was specified.
1115 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1118 /** @brief Store by cursor.
1120 * This function stores key/data pairs into the database.
1121 * If the function fails for any reason, the state of the cursor will be
1122 * unchanged. If the function succeeds and an item is inserted into the
1123 * database, the cursor is always positioned to refer to the newly inserted item.
1124 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1125 * @param[in] key The key operated on.
1126 * @param[in] data The data operated on.
1127 * @param[in] flags Options for this operation. This parameter
1128 * must be set to 0 or one of the values described here.
1130 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which
1131 * the cursor refers with the specified data item. The \b key
1132 * parameter is ignored.
1133 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1134 * already appear in the database. This flag may only be specified
1135 * if the database was opened with #MDB_DUPSORT. The function will
1136 * return #MDB_KEYEXIST if the key/data pair already appears in the
1138 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1139 * does not already appear in the database. The function will return
1140 * #MDB_KEYEXIST if the key already appears in the database, even if
1141 * the database supports duplicates (#MDB_DUPSORT).
1142 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1143 * don't copy the given data. Instead, return a pointer to the
1144 * reserved space, which the caller can fill in later. This saves
1145 * an extra memcpy if the data is being generated later.
1146 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1147 * database. No key comparisons are performed. This option allows
1148 * fast bulk loading when keys are already known to be in the
1149 * correct order. Loading unsorted keys with this flag will cause
1151 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1153 * @return A non-zero error value on failure and 0 on success. Some possible
1156 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1157 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1158 * <li>EACCES - an attempt was made to modify a read-only database.
1159 * <li>EINVAL - an invalid parameter was specified.
1162 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1163 unsigned int flags);
1165 /** @brief Delete current key/data pair
1167 * This function deletes the key/data pair to which the cursor refers.
1168 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1169 * @param[in] flags Options for this operation. This parameter
1170 * must be set to 0 or one of the values described here.
1172 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
1173 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
1175 * @return A non-zero error value on failure and 0 on success. Some possible
1178 * <li>EACCES - an attempt was made to modify a read-only database.
1179 * <li>EINVAL - an invalid parameter was specified.
1182 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
1184 /** @brief Return count of duplicates for current key.
1186 * This call is only valid on databases that support sorted duplicate
1187 * data items #MDB_DUPSORT.
1188 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1189 * @param[out] countp Address where the count will be stored
1190 * @return A non-zero error value on failure and 0 on success. Some possible
1193 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
1196 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
1198 /** @brief Compare two data items according to a particular database.
1200 * This returns a comparison as if the two data items were keys in the
1201 * specified database.
1202 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1203 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1204 * @param[in] a The first item to compare
1205 * @param[in] b The second item to compare
1206 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1208 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1210 /** @brief Compare two data items according to a particular database.
1212 * This returns a comparison as if the two items were data items of
1213 * a sorted duplicates #MDB_DUPSORT database.
1214 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1215 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1216 * @param[in] a The first item to compare
1217 * @param[in] b The second item to compare
1218 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1220 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1226 #endif /* _LMDB_H_ */