2 * @brief Lightning memory-mapped database library
4 * @mainpage Lightning Memory-Mapped Database Manager (MDB)
6 * @section intro_sec Introduction
7 * MDB is a Btree-based database management library modeled loosely on the
8 * BerkeleyDB API, but much simplified. The entire database is exposed
9 * in a memory map, and all data fetches return data directly
10 * from the mapped memory, so no malloc's or memcpy's occur during
11 * data fetches. As such, the library is extremely simple because it
12 * requires no page caching layer of its own, and it is extremely high
13 * performance and memory-efficient. It is also fully transactional with
14 * full ACID semantics, and when the memory map is read-only, the
15 * database integrity cannot be corrupted by stray pointer writes from
18 * The library is fully thread-aware and supports concurrent read/write
19 * access from multiple processes and threads. Data pages use a copy-on-
20 * write strategy so no active data pages are ever overwritten, which
21 * also provides resistance to corruption and eliminates the need of any
22 * special recovery procedures after a system crash. Writes are fully
23 * serialized; only one write transaction may be active at a time, which
24 * guarantees that writers can never deadlock. The database structure is
25 * multi-versioned so readers run with no locks; writers cannot block
26 * readers, and readers don't block writers.
28 * Unlike other well-known database mechanisms which use either write-ahead
29 * transaction logs or append-only data writes, MDB requires no maintenance
30 * during operation. Both write-ahead loggers and append-only databases
31 * require periodic checkpointing and/or compaction of their log or database
32 * files otherwise they grow without bound. MDB tracks free pages within
33 * the database and re-uses them for new write operations, so the database
34 * size does not grow without bound in normal use.
36 * The memory map can be used as a read-only or read-write map. It is
37 * read-only by default as this provides total immunity to corruption.
38 * Using read-write mode offers much higher write performance, but adds
39 * the possibility for stray application writes thru pointers to silently
40 * corrupt the database. Of course if your application code is known to
41 * be bug-free (...) then this is not an issue.
43 * @section caveats_sec Caveats
44 * Troubleshooting the lock file, plus semaphores on BSD systems:
46 * - A broken lockfile can cause sync issues.
47 * Stale reader transactions left behind by an aborted program
48 * cause further writes to grow the database quickly, and
49 * stale locks can block further operation.
51 * Fix: Terminate all programs using the database, or make
52 * them close it. Next database user will reset the lockfile.
54 * - On BSD systems or others configured with MDB_USE_POSIX_SEM,
55 * startup can fail due to semaphores owned by another userid.
57 * Fix: Open and close the database as the user which owns the
58 * semaphores (likely last user) or as root, while no other
59 * process is using the database.
61 * Restrictions/caveats (in addition to those listed for some functions):
63 * - Only the database owner should normally use the database on
64 * BSD systems or when otherwise configured with MDB_USE_POSIX_SEM.
65 * Multiple users can cause startup to fail later, as noted above.
67 * - A thread can only use one transaction at a time, plus any child
68 * transactions. Each transaction belongs to one thread. See below.
69 * The #MDB_NOTLS flag changes this for read-only transactions.
71 * - Use an MDB_env* in the process which opened it, without fork()ing.
73 * - Do not have open an MDB database twice in the same process at
74 * the same time. Not even from a plain open() call - close()ing it
75 * breaks flock() advisory locking.
77 * - Avoid long-lived transactions. Read transactions prevent
78 * reuse of pages freed by newer write transactions, thus the
79 * database can grow quickly. Write transactions prevent
80 * other write transactions, since writes are serialized.
82 * - Avoid suspending a process with active transactions. These
83 * would then be "long-lived" as above. Also read transactions
84 * suspended when writers commit could sometimes see wrong data.
86 * ...when several processes can use a database concurrently:
88 * - Avoid aborting a process with an active transaction.
89 * The transaction becomes "long-lived" as above until the lockfile
90 * is reset, since the process may not remove it from the lockfile.
92 * - If you do that anyway, close the environment once in a while,
93 * so the lockfile can get reset.
95 * - Do not use MDB databases on remote filesystems, even between
96 * processes on the same host. This breaks flock() on some OSes,
97 * possibly memory map sync, and certainly sync between programs
100 * - Opening a database can fail if another process is opening or
101 * closing it at exactly the same time.
103 * @author Howard Chu, Symas Corporation.
105 * @copyright Copyright 2011-2013 Howard Chu, Symas Corp. All rights reserved.
107 * Redistribution and use in source and binary forms, with or without
108 * modification, are permitted only as authorized by the OpenLDAP
111 * A copy of this license is available in the file LICENSE in the
112 * top-level directory of the distribution or, alternatively, at
113 * <http://www.OpenLDAP.org/license.html>.
116 * This code is derived from btree.c written by Martin Hedenfalk.
118 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
120 * Permission to use, copy, modify, and distribute this software for any
121 * purpose with or without fee is hereby granted, provided that the above
122 * copyright notice and this permission notice appear in all copies.
124 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
125 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
126 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
127 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
128 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
129 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
130 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
135 #include <sys/types.h>
141 /** Unix permissions for creating files, or dummy definition for Windows */
143 typedef int mdb_mode_t;
145 typedef mode_t mdb_mode_t;
148 /** An abstraction for a file handle.
149 * On POSIX systems file handles are small integers. On Windows
150 * they're opaque pointers.
153 typedef void *mdb_filehandle_t;
155 typedef int mdb_filehandle_t;
158 /** @defgroup mdb MDB API
160 * @brief OpenLDAP Lightning Memory-Mapped Database Manager
162 /** @defgroup Version Version Macros
165 /** Library major version */
166 #define MDB_VERSION_MAJOR 0
167 /** Library minor version */
168 #define MDB_VERSION_MINOR 9
169 /** Library patch version */
170 #define MDB_VERSION_PATCH 7
172 /** Combine args a,b,c into a single integer for easy version comparisons */
173 #define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
175 /** The full library version as a single integer */
176 #define MDB_VERSION_FULL \
177 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
179 /** The release date of this library version */
180 #define MDB_VERSION_DATE "January 10, 2013"
182 /** A stringifier for the version info */
183 #define MDB_VERSTR(a,b,c,d) "MDB " #a "." #b "." #c ": (" d ")"
185 /** A helper for the stringifier macro */
186 #define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d)
188 /** The full library version as a C string */
189 #define MDB_VERSION_STRING \
190 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
193 /** @brief Opaque structure for a database environment.
195 * A DB environment supports multiple databases, all residing in the same
198 typedef struct MDB_env MDB_env;
200 /** @brief Opaque structure for a transaction handle.
202 * All database operations require a transaction handle. Transactions may be
203 * read-only or read-write.
205 typedef struct MDB_txn MDB_txn;
207 /** @brief A handle for an individual database in the DB environment. */
208 typedef unsigned int MDB_dbi;
210 /** @brief Opaque structure for navigating through a database */
211 typedef struct MDB_cursor MDB_cursor;
213 /** @brief Generic structure used for passing keys and data in and out
216 * Key sizes must be between 1 and the liblmdb build-time constant
217 * #MDB_MAXKEYSIZE inclusive. This currently defaults to 511. The
218 * same applies to data sizes in databases with the #MDB_DUPSORT flag.
219 * Other data items can in theory be from 0 to 0xffffffff bytes long.
221 * Values returned from the database are valid only until a subsequent
222 * update operation, or the end of the transaction.
224 typedef struct MDB_val {
225 size_t mv_size; /**< size of the data item */
226 void *mv_data; /**< address of the data item */
229 /** @brief A callback function used to compare two keys in a database */
230 typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
232 /** @brief A callback function used to relocate a position-dependent data item
233 * in a fixed-address database.
235 * The \b newptr gives the item's desired address in
236 * the memory map, and \b oldptr gives its previous address. The item's actual
237 * data resides at the address in \b item. This callback is expected to walk
238 * through the fields of the record in \b item and modify any
239 * values based at the \b oldptr address to be relative to the \b newptr address.
240 * @param[in,out] item The item that is to be relocated.
241 * @param[in] oldptr The previous address.
242 * @param[in] newptr The new address to relocate to.
243 * @param[in] relctx An application-provided context, set by #mdb_set_relctx().
244 * @todo This feature is currently unimplemented.
246 typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
248 /** @defgroup mdb_env Environment Flags
250 * Values do not overlap Database Flags.
253 /** mmap at a fixed address (experimental) */
254 #define MDB_FIXEDMAP 0x01
255 /** no environment directory */
256 #define MDB_NOSUBDIR 0x4000
257 /** don't fsync after commit */
258 #define MDB_NOSYNC 0x10000
260 #define MDB_RDONLY 0x20000
261 /** don't fsync metapage after commit */
262 #define MDB_NOMETASYNC 0x40000
263 /** use writable mmap */
264 #define MDB_WRITEMAP 0x80000
265 /** use asynchronous msync when MDB_WRITEMAP is used */
266 #define MDB_MAPASYNC 0x100000
267 /** tie reader locktable slots to #MDB_txn objects instead of to threads */
268 #define MDB_NOTLS 0x200000
271 /** @defgroup mdb_dbi_open Database Flags
273 * Values do not overlap Environment Flags.
276 /** use reverse string keys */
277 #define MDB_REVERSEKEY 0x02
278 /** use sorted duplicates */
279 #define MDB_DUPSORT 0x04
280 /** numeric keys in native byte order.
281 * The keys must all be of the same size. */
282 #define MDB_INTEGERKEY 0x08
283 /** with #MDB_DUPSORT, sorted dup items have fixed size */
284 #define MDB_DUPFIXED 0x10
285 /** with #MDB_DUPSORT, dups are numeric in native byte order */
286 #define MDB_INTEGERDUP 0x20
287 /** with #MDB_DUPSORT, use reverse string dups */
288 #define MDB_REVERSEDUP 0x40
289 /** create DB if not already existing */
290 #define MDB_CREATE 0x40000
293 /** @defgroup mdb_put Write Flags
296 /** For put: Don't write if the key already exists. */
297 #define MDB_NOOVERWRITE 0x10
298 /** Only for #MDB_DUPSORT<br>
299 * For put: don't write if the key and data pair already exist.<br>
300 * For mdb_cursor_del: remove all duplicate data items.
302 #define MDB_NODUPDATA 0x20
303 /** For mdb_cursor_put: overwrite the current key/data pair */
304 #define MDB_CURRENT 0x40
305 /** For put: Just reserve space for data, don't copy it. Return a
306 * pointer to the reserved space.
308 #define MDB_RESERVE 0x10000
309 /** Data is being appended, don't split full pages. */
310 #define MDB_APPEND 0x20000
311 /** Duplicate data is being appended, don't split full pages. */
312 #define MDB_APPENDDUP 0x40000
313 /** Store multiple data items in one call. Only for #MDB_DUPFIXED. */
314 #define MDB_MULTIPLE 0x80000
317 /** @brief Cursor Get operations.
319 * This is the set of all operations for retrieving data
322 typedef enum MDB_cursor_op {
323 MDB_FIRST, /**< Position at first key/data item */
324 MDB_FIRST_DUP, /**< Position at first data item of current key.
325 Only for #MDB_DUPSORT */
326 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
327 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
328 MDB_GET_CURRENT, /**< Return key/data at current cursor position */
329 MDB_GET_MULTIPLE, /**< Return all the duplicate data items at the current
330 cursor position. Only for #MDB_DUPFIXED */
331 MDB_LAST, /**< Position at last key/data item */
332 MDB_LAST_DUP, /**< Position at last data item of current key.
333 Only for #MDB_DUPSORT */
334 MDB_NEXT, /**< Position at next data item */
335 MDB_NEXT_DUP, /**< Position at next data item of current key.
336 Only for #MDB_DUPSORT */
337 MDB_NEXT_MULTIPLE, /**< Return all duplicate data items at the next
338 cursor position. Only for #MDB_DUPFIXED */
339 MDB_NEXT_NODUP, /**< Position at first data item of next key */
340 MDB_PREV, /**< Position at previous data item */
341 MDB_PREV_DUP, /**< Position at previous data item of current key.
342 Only for #MDB_DUPSORT */
343 MDB_PREV_NODUP, /**< Position at last data item of previous key */
344 MDB_SET, /**< Position at specified key */
345 MDB_SET_KEY, /**< Position at specified key, return key + data */
346 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
349 /** @defgroup errors Return Codes
351 * BerkeleyDB uses -30800 to -30999, we'll go under them
354 /** Successful result */
355 #define MDB_SUCCESS 0
356 /** key/data pair already exists */
357 #define MDB_KEYEXIST (-30799)
358 /** key/data pair not found (EOF) */
359 #define MDB_NOTFOUND (-30798)
360 /** Requested page not found - this usually indicates corruption */
361 #define MDB_PAGE_NOTFOUND (-30797)
362 /** Located page was wrong type */
363 #define MDB_CORRUPTED (-30796)
364 /** Update of meta page failed, probably I/O error */
365 #define MDB_PANIC (-30795)
366 /** Environment version mismatch */
367 #define MDB_VERSION_MISMATCH (-30794)
368 /** File is not a valid MDB file */
369 #define MDB_INVALID (-30793)
370 /** Environment mapsize reached */
371 #define MDB_MAP_FULL (-30792)
372 /** Environment maxdbs reached */
373 #define MDB_DBS_FULL (-30791)
374 /** Environment maxreaders reached */
375 #define MDB_READERS_FULL (-30790)
376 /** Too many TLS keys in use - Windows only */
377 #define MDB_TLS_FULL (-30789)
378 /** Txn has too many dirty pages */
379 #define MDB_TXN_FULL (-30788)
380 /** Cursor stack too deep - internal error */
381 #define MDB_CURSOR_FULL (-30787)
382 /** Page has not enough space - internal error */
383 #define MDB_PAGE_FULL (-30786)
384 /** Database contents grew beyond environment mapsize */
385 #define MDB_MAP_RESIZED (-30785)
386 /** Database flags changed or would change */
387 #define MDB_INCOMPATIBLE (-30784)
388 /** Invalid reuse of reader locktable slot */
389 #define MDB_BAD_RSLOT (-30783)
390 #define MDB_LAST_ERRCODE MDB_BAD_RSLOT
393 /** @brief Statistics for a database in the environment */
394 typedef struct MDB_stat {
395 unsigned int ms_psize; /**< Size of a database page.
396 This is currently the same for all databases. */
397 unsigned int ms_depth; /**< Depth (height) of the B-tree */
398 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
399 size_t ms_leaf_pages; /**< Number of leaf pages */
400 size_t ms_overflow_pages; /**< Number of overflow pages */
401 size_t ms_entries; /**< Number of data items */
404 /** @brief Information about the environment */
405 typedef struct MDB_envinfo {
406 void *me_mapaddr; /**< Address of map, if fixed */
407 size_t me_mapsize; /**< Size of the data memory map */
408 size_t me_last_pgno; /**< ID of the last used page */
409 size_t me_last_txnid; /**< ID of the last committed transaction */
410 unsigned int me_maxreaders; /**< max reader slots in the environment */
411 unsigned int me_numreaders; /**< max reader slots used in the environment */
414 /** @brief Return the mdb library version information.
416 * @param[out] major if non-NULL, the library major version number is copied here
417 * @param[out] minor if non-NULL, the library minor version number is copied here
418 * @param[out] patch if non-NULL, the library patch version number is copied here
419 * @retval "version string" The library version as a string
421 char *mdb_version(int *major, int *minor, int *patch);
423 /** @brief Return a string describing a given error code.
425 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
426 * function. If the error code is greater than or equal to 0, then the string
427 * returned by the system function strerror(3) is returned. If the error code
428 * is less than 0, an error string corresponding to the MDB library error is
429 * returned. See @ref errors for a list of MDB-specific error codes.
430 * @param[in] err The error code
431 * @retval "error message" The description of the error
433 char *mdb_strerror(int err);
435 /** @brief Create an MDB environment handle.
437 * This function allocates memory for a #MDB_env structure. To release
438 * the allocated memory and discard the handle, call #mdb_env_close().
439 * Before the handle may be used, it must be opened using #mdb_env_open().
440 * Various other options may also need to be set before opening the handle,
441 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
442 * depending on usage requirements.
443 * @param[out] env The address where the new handle will be stored
444 * @return A non-zero error value on failure and 0 on success.
446 int mdb_env_create(MDB_env **env);
448 /** @brief Open an environment handle.
450 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
451 * @param[in] env An environment handle returned by #mdb_env_create()
452 * @param[in] path The directory in which the database files reside. This
453 * directory must already exist and be writable.
454 * @param[in] flags Special options for this environment. This parameter
455 * must be set to 0 or by bitwise OR'ing together one or more of the
456 * values described here.
457 * Flags set by mdb_env_set_flags() are also used.
460 * use a fixed address for the mmap region. This flag must be specified
461 * when creating the environment, and is stored persistently in the environment.
462 * If successful, the memory map will always reside at the same virtual address
463 * and pointers used to reference data items in the database will be constant
464 * across multiple invocations. This option may not always work, depending on
465 * how the operating system has allocated memory to shared libraries and other uses.
466 * The feature is highly experimental.
468 * By default, MDB creates its environment in a directory whose
469 * pathname is given in \b path, and creates its data and lock files
470 * under that directory. With this option, \b path is used as-is for
471 * the database main data file. The database lock file is the \b path
472 * with "-lock" appended.
474 * Open the environment in read-only mode. No write operations will be
475 * allowed. MDB will still modify the lock file - except on read-only
476 * filesystems, where MDB does not use locks.
478 * Use a writeable memory map unless MDB_RDONLY is set. This is faster
479 * and uses fewer mallocs, but loses protection from application bugs
480 * like wild pointer writes and other bad updates into the database.
481 * Incompatible with nested transactions.
482 * <li>#MDB_NOMETASYNC
483 * Flush system buffers to disk only once per transaction, omit the
484 * metadata flush. Defer that until the system flushes files to disk,
485 * or next non-MDB_RDONLY commit or #mdb_env_sync(). This optimization
486 * maintains database integrity, but a system crash may undo the last
487 * committed transaction. I.e. it preserves the ACI (atomicity,
488 * consistency, isolation) but not D (durability) database property.
489 * This flag may be changed at any time using #mdb_env_set_flags().
491 * Don't flush system buffers to disk when committing a transaction.
492 * This optimization means a system crash can corrupt the database or
493 * lose the last transactions if buffers are not yet flushed to disk.
494 * The risk is governed by how often the system flushes dirty buffers
495 * to disk and how often #mdb_env_sync() is called. However, if the
496 * filesystem preserves write order and the #MDB_WRITEMAP flag is not
497 * used, transactions exhibit ACI (atomicity, consistency, isolation)
498 * properties and only lose D (durability). I.e. database integrity
499 * is maintained, but a system crash may undo the final transactions.
500 * Note that (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no
501 * hint for when to write transactions to disk, unless #mdb_env_sync()
502 * is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable.
503 * This flag may be changed at any time using #mdb_env_set_flags().
505 * When using #MDB_WRITEMAP, use asynchronous flushes to disk.
506 * As with #MDB_NOSYNC, a system crash can then corrupt the
507 * database or lose the last transactions. Calling #mdb_env_sync()
508 * ensures on-disk database integrity until next commit.
509 * This flag may be changed at any time using #mdb_env_set_flags().
511 * Don't use Thread-Local Storage. Tie reader locktable slots to
512 * #MDB_txn objects instead of to threads. I.e. #mdb_txn_reset() keeps
513 * the slot reseved for the #MDB_txn object. A thread may use parallel
514 * read-only transactions. A read-only transaction may span threads if
515 * the user synchronizes its use. Applications that multiplex many
516 * user threads over individual OS threads need this option. Such an
517 * application must also serialize the write transactions in an OS
518 * thread, since MDB's write locking is unaware of the user threads.
520 * @param[in] mode The UNIX permissions to set on created files. This parameter
521 * is ignored on Windows.
522 * @return A non-zero error value on failure and 0 on success. Some possible
525 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
526 * version that created the database environment.
527 * <li>#MDB_INVALID - the environment file headers are corrupted.
528 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
529 * <li>EACCES - the user didn't have permission to access the environment files.
530 * <li>EAGAIN - the environment was locked by another process.
533 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode);
535 /** @brief Copy an MDB environment to the specified path.
537 * This function may be used to make a backup of an existing environment.
538 * No lockfile is created, since it gets recreated at need.
539 * @note This call can trigger significant file size growth if run in
540 * parallel with write transactions, because it employs a read-only
541 * transaction. See long-lived transactions under @ref caveats_sec.
542 * @param[in] env An environment handle returned by #mdb_env_create(). It
543 * must have already been opened successfully.
544 * @param[in] path The directory in which the copy will reside. This
545 * directory must already exist and be writable but must otherwise be
547 * @return A non-zero error value on failure and 0 on success.
549 int mdb_env_copy(MDB_env *env, const char *path);
551 /** @brief Copy an MDB environment to the specified file descriptor.
553 * This function may be used to make a backup of an existing environment.
554 * No lockfile is created, since it gets recreated at need.
555 * @note This call can trigger significant file size growth if run in
556 * parallel with write transactions, because it employs a read-only
557 * transaction. See long-lived transactions under @ref caveats_sec.
558 * @param[in] env An environment handle returned by #mdb_env_create(). It
559 * must have already been opened successfully.
560 * @param[in] fd The filedescriptor to write the copy to. It must
561 * have already been opened for Write access.
562 * @return A non-zero error value on failure and 0 on success.
564 int mdb_env_copyfd(MDB_env *env, mdb_filehandle_t fd);
566 /** @brief Return statistics about the MDB environment.
568 * @param[in] env An environment handle returned by #mdb_env_create()
569 * @param[out] stat The address of an #MDB_stat structure
570 * where the statistics will be copied
572 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
574 /** @brief Return information about the MDB environment.
576 * @param[in] env An environment handle returned by #mdb_env_create()
577 * @param[out] stat The address of an #MDB_envinfo structure
578 * where the information will be copied
580 int mdb_env_info(MDB_env *env, MDB_envinfo *stat);
582 /** @brief Flush the data buffers to disk.
584 * Data is always written to disk when #mdb_txn_commit() is called,
585 * but the operating system may keep it buffered. MDB always flushes
586 * the OS buffers upon commit as well, unless the environment was
587 * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC.
588 * @param[in] env An environment handle returned by #mdb_env_create()
589 * @param[in] force If non-zero, force a synchronous flush. Otherwise
590 * if the environment has the #MDB_NOSYNC flag set the flushes
591 * will be omitted, and with #MDB_MAPASYNC they will be asynchronous.
592 * @return A non-zero error value on failure and 0 on success. Some possible
595 * <li>EINVAL - an invalid parameter was specified.
596 * <li>EIO - an error occurred during synchronization.
599 int mdb_env_sync(MDB_env *env, int force);
601 /** @brief Close the environment and release the memory map.
603 * Only a single thread may call this function. All transactions, databases,
604 * and cursors must already be closed before calling this function. Attempts to
605 * use any such handles after calling this function will cause a SIGSEGV.
606 * The environment handle will be freed and must not be used again after this call.
607 * @param[in] env An environment handle returned by #mdb_env_create()
609 void mdb_env_close(MDB_env *env);
611 /** @brief Set environment flags.
613 * This may be used to set some flags in addition to those from
614 * #mdb_env_open(), or to unset these flags.
615 * @param[in] env An environment handle returned by #mdb_env_create()
616 * @param[in] flags The flags to change, bitwise OR'ed together
617 * @param[in] onoff A non-zero value sets the flags, zero clears them.
618 * @return A non-zero error value on failure and 0 on success. Some possible
621 * <li>EINVAL - an invalid parameter was specified.
624 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
626 /** @brief Get environment flags.
628 * @param[in] env An environment handle returned by #mdb_env_create()
629 * @param[out] flags The address of an integer to store the flags
630 * @return A non-zero error value on failure and 0 on success. Some possible
633 * <li>EINVAL - an invalid parameter was specified.
636 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
638 /** @brief Return the path that was used in #mdb_env_open().
640 * @param[in] env An environment handle returned by #mdb_env_create()
641 * @param[out] path Address of a string pointer to contain the path. This
642 * is the actual string in the environment, not a copy. It should not be
643 * altered in any way.
644 * @return A non-zero error value on failure and 0 on success. Some possible
647 * <li>EINVAL - an invalid parameter was specified.
650 int mdb_env_get_path(MDB_env *env, const char **path);
652 /** @brief Set the size of the memory map to use for this environment.
654 * The size should be a multiple of the OS page size. The default is
655 * 10485760 bytes. The size of the memory map is also the maximum size
656 * of the database. The value should be chosen as large as possible,
657 * to accommodate future growth of the database.
658 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
659 * The size may be changed by closing and reopening the environment.
660 * Any attempt to set a size smaller than the space already consumed
661 * by the environment will be silently changed to the current size of the used space.
662 * @param[in] env An environment handle returned by #mdb_env_create()
663 * @param[in] size The size in bytes
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_mapsize(MDB_env *env, size_t size);
672 /** @brief Set the maximum number of threads/reader slots for the environment.
674 * This defines the number of slots in the lock table that is used to track readers in the
675 * the environment. The default is 126.
676 * Starting a read-only transaction normally ties a lock table slot to the
677 * current thread until the environment closes or the thread exits. If
678 * MDB_NOTLS is in use, #mdb_txn_begin() instead ties the slot to the
679 * MDB_txn object until it or the #MDB_env object is destroyed.
680 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
681 * @param[in] env An environment handle returned by #mdb_env_create()
682 * @param[in] readers The maximum number of reader lock table slots
683 * @return A non-zero error value on failure and 0 on success. Some possible
686 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
689 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
691 /** @brief Get the maximum number of threads/reader slots for the environment.
693 * @param[in] env An environment handle returned by #mdb_env_create()
694 * @param[out] readers Address of an integer to store the number of readers
695 * @return A non-zero error value on failure and 0 on success. Some possible
698 * <li>EINVAL - an invalid parameter was specified.
701 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
703 /** @brief Set the maximum number of named databases for the environment.
705 * This function is only needed if multiple databases will be used in the
706 * environment. Simpler applications that use the environment as a single
707 * unnamed database can ignore this option.
708 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
709 * @param[in] env An environment handle returned by #mdb_env_create()
710 * @param[in] dbs The maximum number of databases
711 * @return A non-zero error value on failure and 0 on success. Some possible
714 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
717 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
719 /** @brief Create a transaction for use with the environment.
721 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
722 * @note A transaction and its cursors must only be used by a single
723 * thread, and a thread may only have a single transaction at a time.
724 * If #MDB_NOTLS is in use, this does not apply to read-only transactions.
725 * @note Cursors may not span transactions.
726 * @param[in] env An environment handle returned by #mdb_env_create()
727 * @param[in] parent If this parameter is non-NULL, the new transaction
728 * will be a nested transaction, with the transaction indicated by \b parent
729 * as its parent. Transactions may be nested to any level. A parent
730 * transaction and its cursors may not issue any other operations than
731 * mdb_txn_commit and mdb_txn_abort while it has active child transactions.
732 * @param[in] flags Special options for this transaction. This parameter
733 * must be set to 0 or by bitwise OR'ing together one or more of the
734 * values described here.
737 * This transaction will not perform any write operations.
739 * @param[out] txn Address where the new #MDB_txn handle will be stored
740 * @return A non-zero error value on failure and 0 on success. Some possible
743 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
745 * <li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's
746 * mapsize and the environment must be shut down.
747 * <li>#MDB_READERS_FULL - a read-only transaction was requested and
748 * the reader lock table is full. See #mdb_env_set_maxreaders().
749 * <li>ENOMEM - out of memory.
752 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
754 /** @brief Commit all the operations of a transaction into the database.
756 * The transaction handle is freed. It and its cursors must not be used
757 * again after this call, except with #mdb_cursor_renew().
758 * @note Earlier documentation incorrectly said all cursors would be freed.
759 * Only write-transactions free cursors.
760 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
761 * @return A non-zero error value on failure and 0 on success. Some possible
764 * <li>EINVAL - an invalid parameter was specified.
765 * <li>ENOSPC - no more disk space.
766 * <li>EIO - a low-level I/O error occurred while writing.
767 * <li>ENOMEM - out of memory.
770 int mdb_txn_commit(MDB_txn *txn);
772 /** @brief Abandon all the operations of the transaction instead of saving them.
774 * The transaction handle is freed. It and its cursors must not be used
775 * again after this call, except with #mdb_cursor_renew().
776 * @note Earlier documentation incorrectly said all cursors would be freed.
777 * Only write-transactions free cursors.
778 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
780 void mdb_txn_abort(MDB_txn *txn);
782 /** @brief Reset a read-only transaction.
784 * Abort the transaction like #mdb_txn_abort(), but keep the transaction
785 * handle. #mdb_txn_renew() may reuse the handle. This saves allocation
786 * overhead if the process will start a new read-only transaction soon,
787 * and also locking overhead if #MDB_NOTLS is in use. The reader table
788 * lock is released, but the table slot stays tied to its thread or
789 * #MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free
790 * its lock table slot if MDB_NOTLS is in use.
791 * Cursors opened within the transaction must not be used
792 * again after this call, except with #mdb_cursor_renew().
793 * Reader locks generally don't interfere with writers, but they keep old
794 * versions of database pages allocated. Thus they prevent the old pages
795 * from being reused when writers commit new data, and so under heavy load
796 * the database size may grow much more rapidly than otherwise.
797 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
799 void mdb_txn_reset(MDB_txn *txn);
801 /** @brief Renew a read-only transaction.
803 * This acquires a new reader lock for a transaction handle that had been
804 * released by #mdb_txn_reset(). It must be called before a reset transaction
806 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
807 * @return A non-zero error value on failure and 0 on success. Some possible
810 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
812 * <li>EINVAL - an invalid parameter was specified.
815 int mdb_txn_renew(MDB_txn *txn);
817 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
818 #define mdb_open(txn,name,flags,dbi) mdb_dbi_open(txn,name,flags,dbi)
819 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
820 #define mdb_close(env,dbi) mdb_dbi_close(env,dbi)
822 /** @brief Open a database in the environment.
824 * A database handle denotes the name and parameters of a database,
825 * independently of whether such a database exists.
826 * The database handle may be discarded by calling #mdb_dbi_close().
827 * The old database handle is returned if the database was already open.
828 * The handle must only be closed once.
829 * The database handle will be private to the current transaction until
830 * the transaction is successfully committed. If the transaction is
831 * aborted the handle will be closed automatically.
832 * After a successful commit the
833 * handle will reside in the shared environment, and may be used
834 * by other transactions. This function must not be called from
835 * multiple concurrent transactions. A transaction that uses this function
836 * must finish (either commit or abort) before any other transaction may
839 * To use named databases (with name != NULL), #mdb_env_set_maxdbs()
840 * must be called before opening the environment.
841 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
842 * @param[in] name The name of the database to open. If only a single
843 * database is needed in the environment, this value may be NULL.
844 * @param[in] flags Special options for this database. This parameter
845 * must be set to 0 or by bitwise OR'ing together one or more of the
846 * values described here.
848 * <li>#MDB_REVERSEKEY
849 * Keys are strings to be compared in reverse order, from the end
850 * of the strings to the beginning. By default, Keys are treated as strings and
851 * compared from beginning to end.
853 * Duplicate keys may be used in the database. (Or, from another perspective,
854 * keys may have multiple data items, stored in sorted order.) By default
855 * keys must be unique and may have only a single data item.
856 * <li>#MDB_INTEGERKEY
857 * Keys are binary integers in native byte order. Setting this option
858 * requires all keys to be the same size, typically sizeof(int)
861 * This flag may only be used in combination with #MDB_DUPSORT. This option
862 * tells the library that the data items for this database are all the same
863 * size, which allows further optimizations in storage and retrieval. When
864 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
865 * cursor operations may be used to retrieve multiple items at once.
866 * <li>#MDB_INTEGERDUP
867 * This option specifies that duplicate data items are also integers, and
868 * should be sorted as such.
869 * <li>#MDB_REVERSEDUP
870 * This option specifies that duplicate data items should be compared as
871 * strings in reverse order.
873 * Create the named database if it doesn't exist. This option is not
874 * allowed in a read-only transaction or a read-only environment.
876 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
877 * @return A non-zero error value on failure and 0 on success. Some possible
880 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
881 * and #MDB_CREATE was not specified.
882 * <li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs().
885 int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
887 /** @brief Retrieve statistics for a database.
889 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
890 * @param[in] dbi A database handle returned by #mdb_dbi_open()
891 * @param[out] stat The address of an #MDB_stat structure
892 * where the statistics will be copied
893 * @return A non-zero error value on failure and 0 on success. Some possible
896 * <li>EINVAL - an invalid parameter was specified.
899 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
901 /** @brief Retrieve the DB flags for a database handle.
903 * @param[in] env An environment handle returned by #mdb_env_create()
904 * @param[in] dbi A database handle returned by #mdb_dbi_open()
905 * @param[out] flags Address where the flags will be returned.
906 * @return A non-zero error value on failure and 0 on success.
908 int mdb_dbi_flags(MDB_env *env, MDB_dbi dbi, unsigned int *flags);
910 /** @brief Close a database handle.
912 * This call is not mutex protected. Handles should only be closed by
913 * a single thread, and only if no other threads are going to reference
914 * the database handle or one of its cursors any further. Do not close
915 * a handle if an existing transaction has modified its database.
916 * @param[in] env An environment handle returned by #mdb_env_create()
917 * @param[in] dbi A database handle returned by #mdb_dbi_open()
919 void mdb_dbi_close(MDB_env *env, MDB_dbi dbi);
921 /** @brief Empty or delete+close a database.
923 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
924 * @param[in] dbi A database handle returned by #mdb_dbi_open()
925 * @param[in] del 0 to empty the DB, 1 to delete it from the
926 * environment and close the DB handle.
927 * @return A non-zero error value on failure and 0 on success.
929 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
931 /** @brief Set a custom key comparison function for a database.
933 * The comparison function is called whenever it is necessary to compare a
934 * key specified by the application with a key currently stored in the database.
935 * If no comparison function is specified, and no special key flags were specified
936 * with #mdb_dbi_open(), the keys are compared lexically, with shorter keys collating
937 * before longer keys.
938 * @warning This function must be called before any data access functions are used,
939 * otherwise data corruption may occur. The same comparison function must be used by every
940 * program accessing the database, every time the database is used.
941 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
942 * @param[in] dbi A database handle returned by #mdb_dbi_open()
943 * @param[in] cmp A #MDB_cmp_func function
944 * @return A non-zero error value on failure and 0 on success. Some possible
947 * <li>EINVAL - an invalid parameter was specified.
950 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
952 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
954 * This comparison function is called whenever it is necessary to compare a data
955 * item specified by the application with a data item currently stored in the database.
956 * This function only takes effect if the database was opened with the #MDB_DUPSORT
958 * If no comparison function is specified, and no special key flags were specified
959 * with #mdb_dbi_open(), the data items are compared lexically, with shorter items collating
960 * before longer items.
961 * @warning This function must be called before any data access functions are used,
962 * otherwise data corruption may occur. The same comparison function must be used by every
963 * program accessing the database, every time the database is used.
964 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
965 * @param[in] dbi A database handle returned by #mdb_dbi_open()
966 * @param[in] cmp A #MDB_cmp_func function
967 * @return A non-zero error value on failure and 0 on success. Some possible
970 * <li>EINVAL - an invalid parameter was specified.
973 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
975 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
977 * @todo The relocation function is called whenever it is necessary to move the data
978 * of an item to a different position in the database (e.g. through tree
979 * balancing operations, shifts as a result of adds or deletes, etc.). It is
980 * intended to allow address/position-dependent data items to be stored in
981 * a database in an environment opened with the #MDB_FIXEDMAP option.
982 * Currently the relocation feature is unimplemented and setting
983 * this function has no effect.
984 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
985 * @param[in] dbi A database handle returned by #mdb_dbi_open()
986 * @param[in] rel A #MDB_rel_func function
987 * @return A non-zero error value on failure and 0 on success. Some possible
990 * <li>EINVAL - an invalid parameter was specified.
993 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
995 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
997 * See #mdb_set_relfunc and #MDB_rel_func for more details.
998 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
999 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1000 * @param[in] ctx An arbitrary pointer for whatever the application needs.
1001 * It will be passed to the callback function set by #mdb_set_relfunc
1002 * as its \b relctx parameter whenever the callback is invoked.
1003 * @return A non-zero error value on failure and 0 on success. Some possible
1006 * <li>EINVAL - an invalid parameter was specified.
1009 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
1011 /** @brief Get items from a database.
1013 * This function retrieves key/data pairs from the database. The address
1014 * and length of the data associated with the specified \b key are returned
1015 * in the structure to which \b data refers.
1016 * If the database supports duplicate keys (#MDB_DUPSORT) then the
1017 * first data item for the key will be returned. Retrieval of other
1018 * items requires the use of #mdb_cursor_get().
1020 * @note The memory pointed to by the returned values is owned by the
1021 * database. The caller need not dispose of the memory, and may not
1022 * modify it in any way. For values returned in a read-only transaction
1023 * any modification attempts will cause a SIGSEGV.
1024 * @note Values returned from the database are valid only until a
1025 * subsequent update operation, or the end of the transaction.
1026 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1027 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1028 * @param[in] key The key to search for in the database
1029 * @param[out] data The data corresponding to the key
1030 * @return A non-zero error value on failure and 0 on success. Some possible
1033 * <li>#MDB_NOTFOUND - the key was not in the database.
1034 * <li>EINVAL - an invalid parameter was specified.
1037 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1039 /** @brief Store items into a database.
1041 * This function stores key/data pairs in the database. The default behavior
1042 * is to enter the new key/data pair, replacing any previously existing key
1043 * if duplicates are disallowed, or adding a duplicate data item if
1044 * duplicates are allowed (#MDB_DUPSORT).
1045 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1046 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1047 * @param[in] key The key to store in the database
1048 * @param[in,out] data The data to store
1049 * @param[in] flags Special options for this operation. This parameter
1050 * must be set to 0 or by bitwise OR'ing together one or more of the
1051 * values described here.
1053 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1054 * already appear in the database. This flag may only be specified
1055 * if the database was opened with #MDB_DUPSORT. The function will
1056 * return #MDB_KEYEXIST if the key/data pair already appears in the
1058 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1059 * does not already appear in the database. The function will return
1060 * #MDB_KEYEXIST if the key already appears in the database, even if
1061 * the database supports duplicates (#MDB_DUPSORT). The \b data
1062 * parameter will be set to point to the existing item.
1063 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1064 * don't copy the given data. Instead, return a pointer to the
1065 * reserved space, which the caller can fill in later - before
1066 * the next update operation or the transaction ends. This saves
1067 * an extra memcpy if the data is being generated later.
1068 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1069 * database. No key comparisons are performed. This option allows
1070 * fast bulk loading when keys are already known to be in the
1071 * correct order. Loading unsorted keys with this flag will cause
1073 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1075 * @return A non-zero error value on failure and 0 on success. Some possible
1078 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1079 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1080 * <li>EACCES - an attempt was made to write in a read-only transaction.
1081 * <li>EINVAL - an invalid parameter was specified.
1084 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
1085 unsigned int flags);
1087 /** @brief Delete items from a database.
1089 * This function removes key/data pairs from the database.
1090 * If the database does not support sorted duplicate data items
1091 * (#MDB_DUPSORT) the data parameter is ignored.
1092 * If the database supports sorted duplicates and the data parameter
1093 * is NULL, all of the duplicate data items for the key will be
1094 * deleted. Otherwise, if the data parameter is non-NULL
1095 * only the matching data item will be deleted.
1096 * This function will return #MDB_NOTFOUND if the specified key/data
1097 * pair is not in the database.
1098 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1099 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1100 * @param[in] key The key to delete from the database
1101 * @param[in] data The data to delete
1102 * @return A non-zero error value on failure and 0 on success. Some possible
1105 * <li>EACCES - an attempt was made to write in a read-only transaction.
1106 * <li>EINVAL - an invalid parameter was specified.
1109 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1111 /** @brief Create a cursor handle.
1113 * A cursor is associated with a specific transaction and database.
1114 * A cursor cannot be used when its database handle is closed. Nor
1115 * when its transaction has ended, except with #mdb_cursor_renew().
1116 * It can be discarded with #mdb_cursor_close().
1117 * A cursor in a write-transaction can be closed before its transaction
1118 * ends, and will otherwise be closed when its transaction ends.
1119 * A cursor in a read-only transaction must be closed explicitly, before
1120 * or after its transaction ends. It can be reused with
1121 * #mdb_cursor_renew() before finally closing it.
1122 * @note Earlier documentation said that cursors in every transaction
1123 * were closed when the transaction committed or aborted.
1124 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1125 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1126 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
1127 * @return A non-zero error value on failure and 0 on success. Some possible
1130 * <li>EINVAL - an invalid parameter was specified.
1133 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
1135 /** @brief Close a cursor handle.
1137 * The cursor handle will be freed and must not be used again after this call.
1138 * Its transaction must still be live if it is a write-transaction.
1139 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1141 void mdb_cursor_close(MDB_cursor *cursor);
1143 /** @brief Renew a cursor handle.
1145 * A cursor is associated with a specific transaction and database.
1146 * Cursors that are only used in read-only
1147 * transactions may be re-used, to avoid unnecessary malloc/free overhead.
1148 * The cursor may be associated with a new read-only transaction, and
1149 * referencing the same database handle as it was created with.
1150 * This may be done whether the previous transaction is live or dead.
1151 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1152 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1153 * @return A non-zero error value on failure and 0 on success. Some possible
1156 * <li>EINVAL - an invalid parameter was specified.
1159 int mdb_cursor_renew(MDB_txn *txn, MDB_cursor *cursor);
1161 /** @brief Return the cursor's transaction handle.
1163 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1165 MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
1167 /** @brief Return the cursor's database handle.
1169 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1171 MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor);
1173 /** @brief Retrieve by cursor.
1175 * This function retrieves key/data pairs from the database. The address and length
1176 * of the key are returned in the object to which \b key refers (except for the
1177 * case of the #MDB_SET option, in which the \b key object is unchanged), and
1178 * the address and length of the data are returned in the object to which \b data
1180 * See #mdb_get() for restrictions on using the output values.
1181 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1182 * @param[in,out] key The key for a retrieved item
1183 * @param[in,out] data The data of a retrieved item
1184 * @param[in] op A cursor operation #MDB_cursor_op
1185 * @return A non-zero error value on failure and 0 on success. Some possible
1188 * <li>#MDB_NOTFOUND - no matching key found.
1189 * <li>EINVAL - an invalid parameter was specified.
1192 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1195 /** @brief Store by cursor.
1197 * This function stores key/data pairs into the database.
1198 * If the function fails for any reason, the state of the cursor will be
1199 * unchanged. If the function succeeds and an item is inserted into the
1200 * database, the cursor is always positioned to refer to the newly inserted item.
1201 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1202 * @param[in] key The key operated on.
1203 * @param[in] data The data operated on.
1204 * @param[in] flags Options for this operation. This parameter
1205 * must be set to 0 or one of the values described here.
1207 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which
1208 * the cursor refers with the specified data item. The \b key
1209 * parameter is ignored.
1210 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1211 * already appear in the database. This flag may only be specified
1212 * if the database was opened with #MDB_DUPSORT. The function will
1213 * return #MDB_KEYEXIST if the key/data pair already appears in the
1215 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1216 * does not already appear in the database. The function will return
1217 * #MDB_KEYEXIST if the key already appears in the database, even if
1218 * the database supports duplicates (#MDB_DUPSORT).
1219 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1220 * don't copy the given data. Instead, return a pointer to the
1221 * reserved space, which the caller can fill in later. This saves
1222 * an extra memcpy if the data is being generated later.
1223 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1224 * database. No key comparisons are performed. This option allows
1225 * fast bulk loading when keys are already known to be in the
1226 * correct order. Loading unsorted keys with this flag will cause
1228 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1229 * <li>#MDB_MULTIPLE - store multiple contiguous data elements in a
1230 * single request. This flag may only be specified if the database
1231 * was opened with #MDB_DUPFIXED. The \b data argument must be an
1232 * array of two MDB_vals. The mv_size of the first MDB_val must be
1233 * the size of a single data element. The mv_data of the first MDB_val
1234 * must point to the beginning of the array of contiguous data elements.
1235 * The mv_size of the second MDB_val must be the count of the number
1236 * of data elements to store. On return this field will be set to
1237 * the count of the number of elements actually written. The mv_data
1238 * of the second MDB_val is unused.
1240 * @return A non-zero error value on failure and 0 on success. Some possible
1243 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1244 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1245 * <li>EACCES - an attempt was made to modify a read-only database.
1246 * <li>EINVAL - an invalid parameter was specified.
1249 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1250 unsigned int flags);
1252 /** @brief Delete current key/data pair
1254 * This function deletes the key/data pair to which the cursor refers.
1255 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1256 * @param[in] flags Options for this operation. This parameter
1257 * must be set to 0 or one of the values described here.
1259 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
1260 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
1262 * @return A non-zero error value on failure and 0 on success. Some possible
1265 * <li>EACCES - an attempt was made to modify a read-only database.
1266 * <li>EINVAL - an invalid parameter was specified.
1269 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
1271 /** @brief Return count of duplicates for current key.
1273 * This call is only valid on databases that support sorted duplicate
1274 * data items #MDB_DUPSORT.
1275 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1276 * @param[out] countp Address where the count will be stored
1277 * @return A non-zero error value on failure and 0 on success. Some possible
1280 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
1283 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
1285 /** @brief Compare two data items according to a particular database.
1287 * This returns a comparison as if the two data items were keys in the
1288 * specified database.
1289 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1290 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1291 * @param[in] a The first item to compare
1292 * @param[in] b The second item to compare
1293 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1295 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1297 /** @brief Compare two data items according to a particular database.
1299 * This returns a comparison as if the two items were data items of
1300 * the specified database. The database must have the #MDB_DUPSORT flag.
1301 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1302 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1303 * @param[in] a The first item to compare
1304 * @param[in] b The second item to compare
1305 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1307 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1309 /** @brief A callback function used to print a message from the library.
1311 * @param[in] msg The string to be printed.
1312 * @param[in] ctx An arbitrary context pointer for the callback.
1313 * @return < 0 on failure, 0 on success.
1315 typedef int (MDB_msg_func)(const char *msg, void *ctx);
1317 /** @brief Dump the entries in the reader lock table.
1319 * @param[in] env An environment handle returned by #mdb_env_create()
1320 * @param[in] func A #MDB_msg_func function
1321 * @param[in] ctx Anything the message function needs
1322 * @return < 0 on failure, 0 on success.
1324 int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx);
1326 /** @brief Check for stale entries in the reader lock table.
1328 * @param[in] env An environment handle returned by #mdb_env_create()
1329 * @param[out] dead Number of stale slots that were cleared
1330 * @return 0 on success, non-zero on failure.
1332 int mdb_reader_check(MDB_env *env, int *dead);
1338 #endif /* _LMDB_H_ */