2 * @brief Lightning memory-mapped database library
4 * @mainpage Lightning Memory-Mapped Database Manager (MDB)
6 * @section intro_sec Introduction
7 * MDB is a Btree-based database management library modeled loosely on the
8 * BerkeleyDB API, but much simplified. The entire database is exposed
9 * in a memory map, and all data fetches return data directly
10 * from the mapped memory, so no malloc's or memcpy's occur during
11 * data fetches. As such, the library is extremely simple because it
12 * requires no page caching layer of its own, and it is extremely high
13 * performance and memory-efficient. It is also fully transactional with
14 * full ACID semantics, and when the memory map is read-only, the
15 * database integrity cannot be corrupted by stray pointer writes from
18 * The library is fully thread-aware and supports concurrent read/write
19 * access from multiple processes and threads. Data pages use a copy-on-
20 * write strategy so no active data pages are ever overwritten, which
21 * also provides resistance to corruption and eliminates the need of any
22 * special recovery procedures after a system crash. Writes are fully
23 * serialized; only one write transaction may be active at a time, which
24 * guarantees that writers can never deadlock. The database structure is
25 * multi-versioned so readers run with no locks; writers cannot block
26 * readers, and readers don't block writers.
28 * Unlike other well-known database mechanisms which use either write-ahead
29 * transaction logs or append-only data writes, MDB requires no maintenance
30 * during operation. Both write-ahead loggers and append-only databases
31 * require periodic checkpointing and/or compaction of their log or database
32 * files otherwise they grow without bound. MDB tracks free pages within
33 * the database and re-uses them for new write operations, so the database
34 * size does not grow without bound in normal use.
36 * The memory map can be used as a read-only or read-write map. It is
37 * read-only by default as this provides total immunity to corruption.
38 * Using read-write mode offers much higher write performance, but adds
39 * the possibility for stray application writes thru pointers to silently
40 * corrupt the database. Of course if your application code is known to
41 * be bug-free (...) then this is not an issue.
43 * @section caveats_sec Caveats
44 * Troubleshooting the lock file, plus semaphores on BSD systems:
46 * - A broken lockfile can cause sync issues.
47 * Stale reader transactions left behind by an aborted program
48 * cause further writes to grow the database quickly, and
49 * stale locks can block further operation.
51 * Fix: Check for stale readers periodically, using the
52 * #mdb_reader_check function or the mdb_stat tool. Or just
53 * make all programs using the database close it; the lockfile
54 * is always reset on first open of the environment.
56 * - On BSD systems or others configured with MDB_USE_POSIX_SEM,
57 * startup can fail due to semaphores owned by another userid.
59 * Fix: Open and close the database as the user which owns the
60 * semaphores (likely last user) or as root, while no other
61 * process is using the database.
63 * Restrictions/caveats (in addition to those listed for some functions):
65 * - Only the database owner should normally use the database on
66 * BSD systems or when otherwise configured with MDB_USE_POSIX_SEM.
67 * Multiple users can cause startup to fail later, as noted above.
69 * - A thread can only use one transaction at a time, plus any child
70 * transactions. Each transaction belongs to one thread. See below.
71 * The #MDB_NOTLS flag changes this for read-only transactions.
73 * - Use an MDB_env* in the process which opened it, without fork()ing.
75 * - Do not have open an MDB database twice in the same process at
76 * the same time. Not even from a plain open() call - close()ing it
77 * breaks flock() advisory locking.
79 * - Avoid long-lived transactions. Read transactions prevent
80 * reuse of pages freed by newer write transactions, thus the
81 * database can grow quickly. Write transactions prevent
82 * other write transactions, since writes are serialized.
84 * - Avoid suspending a process with active transactions. These
85 * would then be "long-lived" as above. Also read transactions
86 * suspended when writers commit could sometimes see wrong data.
88 * ...when several processes can use a database concurrently:
90 * - Avoid aborting a process with an active transaction.
91 * The transaction becomes "long-lived" as above until a check
92 * for stale readers is performed or the lockfile is reset,
93 * since the process may not remove it from the lockfile.
95 * - If you do that anyway, do a periodic check for stale readers. Or
96 * close the environment once in a while, so the lockfile can get reset.
98 * - Do not use MDB databases on remote filesystems, even between
99 * processes on the same host. This breaks flock() on some OSes,
100 * possibly memory map sync, and certainly sync between programs
101 * on different hosts.
103 * - Opening a database can fail if another process is opening or
104 * closing it at exactly the same time.
106 * @author Howard Chu, Symas Corporation.
108 * @copyright Copyright 2011-2013 Howard Chu, Symas Corp. All rights reserved.
110 * Redistribution and use in source and binary forms, with or without
111 * modification, are permitted only as authorized by the OpenLDAP
114 * A copy of this license is available in the file LICENSE in the
115 * top-level directory of the distribution or, alternatively, at
116 * <http://www.OpenLDAP.org/license.html>.
119 * This code is derived from btree.c written by Martin Hedenfalk.
121 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
123 * Permission to use, copy, modify, and distribute this software for any
124 * purpose with or without fee is hereby granted, provided that the above
125 * copyright notice and this permission notice appear in all copies.
127 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
128 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
129 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
130 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
131 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
132 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
133 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
138 #include <sys/types.h>
144 /** Unix permissions for creating files, or dummy definition for Windows */
146 typedef int mdb_mode_t;
148 typedef mode_t mdb_mode_t;
151 /** An abstraction for a file handle.
152 * On POSIX systems file handles are small integers. On Windows
153 * they're opaque pointers.
156 typedef void *mdb_filehandle_t;
158 typedef int mdb_filehandle_t;
161 /** @defgroup mdb MDB API
163 * @brief OpenLDAP Lightning Memory-Mapped Database Manager
165 /** @defgroup Version Version Macros
168 /** Library major version */
169 #define MDB_VERSION_MAJOR 0
170 /** Library minor version */
171 #define MDB_VERSION_MINOR 9
172 /** Library patch version */
173 #define MDB_VERSION_PATCH 7
175 /** Combine args a,b,c into a single integer for easy version comparisons */
176 #define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
178 /** The full library version as a single integer */
179 #define MDB_VERSION_FULL \
180 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
182 /** The release date of this library version */
183 #define MDB_VERSION_DATE "January 10, 2013"
185 /** A stringifier for the version info */
186 #define MDB_VERSTR(a,b,c,d) "MDB " #a "." #b "." #c ": (" d ")"
188 /** A helper for the stringifier macro */
189 #define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d)
191 /** The full library version as a C string */
192 #define MDB_VERSION_STRING \
193 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
196 /** @brief Opaque structure for a database environment.
198 * A DB environment supports multiple databases, all residing in the same
201 typedef struct MDB_env MDB_env;
203 /** @brief Opaque structure for a transaction handle.
205 * All database operations require a transaction handle. Transactions may be
206 * read-only or read-write.
208 typedef struct MDB_txn MDB_txn;
210 /** @brief A handle for an individual database in the DB environment. */
211 typedef unsigned int MDB_dbi;
213 /** @brief Opaque structure for navigating through a database */
214 typedef struct MDB_cursor MDB_cursor;
216 /** @brief Generic structure used for passing keys and data in and out
219 * Key sizes must be between 1 and the liblmdb build-time constant
220 * #MDB_MAXKEYSIZE inclusive. This currently defaults to 511. The
221 * same applies to data sizes in databases with the #MDB_DUPSORT flag.
222 * Other data items can in theory be from 0 to 0xffffffff bytes long.
224 * Values returned from the database are valid only until a subsequent
225 * update operation, or the end of the transaction.
227 typedef struct MDB_val {
228 size_t mv_size; /**< size of the data item */
229 void *mv_data; /**< address of the data item */
232 /** @brief A callback function used to compare two keys in a database */
233 typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
235 /** @brief A callback function used to relocate a position-dependent data item
236 * in a fixed-address database.
238 * The \b newptr gives the item's desired address in
239 * the memory map, and \b oldptr gives its previous address. The item's actual
240 * data resides at the address in \b item. This callback is expected to walk
241 * through the fields of the record in \b item and modify any
242 * values based at the \b oldptr address to be relative to the \b newptr address.
243 * @param[in,out] item The item that is to be relocated.
244 * @param[in] oldptr The previous address.
245 * @param[in] newptr The new address to relocate to.
246 * @param[in] relctx An application-provided context, set by #mdb_set_relctx().
247 * @todo This feature is currently unimplemented.
249 typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
251 /** @defgroup mdb_env Environment Flags
253 * Values do not overlap Database Flags.
256 /** mmap at a fixed address (experimental) */
257 #define MDB_FIXEDMAP 0x01
258 /** no environment directory */
259 #define MDB_NOSUBDIR 0x4000
260 /** don't fsync after commit */
261 #define MDB_NOSYNC 0x10000
263 #define MDB_RDONLY 0x20000
264 /** don't fsync metapage after commit */
265 #define MDB_NOMETASYNC 0x40000
266 /** use writable mmap */
267 #define MDB_WRITEMAP 0x80000
268 /** use asynchronous msync when MDB_WRITEMAP is used */
269 #define MDB_MAPASYNC 0x100000
270 /** tie reader locktable slots to #MDB_txn objects instead of to threads */
271 #define MDB_NOTLS 0x200000
274 /** @defgroup mdb_dbi_open Database Flags
276 * Values do not overlap Environment Flags.
279 /** use reverse string keys */
280 #define MDB_REVERSEKEY 0x02
281 /** use sorted duplicates */
282 #define MDB_DUPSORT 0x04
283 /** numeric keys in native byte order.
284 * The keys must all be of the same size. */
285 #define MDB_INTEGERKEY 0x08
286 /** with #MDB_DUPSORT, sorted dup items have fixed size */
287 #define MDB_DUPFIXED 0x10
288 /** with #MDB_DUPSORT, dups are numeric in native byte order */
289 #define MDB_INTEGERDUP 0x20
290 /** with #MDB_DUPSORT, use reverse string dups */
291 #define MDB_REVERSEDUP 0x40
292 /** create DB if not already existing */
293 #define MDB_CREATE 0x40000
296 /** @defgroup mdb_put Write Flags
299 /** For put: Don't write if the key already exists. */
300 #define MDB_NOOVERWRITE 0x10
301 /** Only for #MDB_DUPSORT<br>
302 * For put: don't write if the key and data pair already exist.<br>
303 * For mdb_cursor_del: remove all duplicate data items.
305 #define MDB_NODUPDATA 0x20
306 /** For mdb_cursor_put: overwrite the current key/data pair */
307 #define MDB_CURRENT 0x40
308 /** For put: Just reserve space for data, don't copy it. Return a
309 * pointer to the reserved space.
311 #define MDB_RESERVE 0x10000
312 /** Data is being appended, don't split full pages. */
313 #define MDB_APPEND 0x20000
314 /** Duplicate data is being appended, don't split full pages. */
315 #define MDB_APPENDDUP 0x40000
316 /** Store multiple data items in one call. Only for #MDB_DUPFIXED. */
317 #define MDB_MULTIPLE 0x80000
320 /** @brief Cursor Get operations.
322 * This is the set of all operations for retrieving data
325 typedef enum MDB_cursor_op {
326 MDB_FIRST, /**< Position at first key/data item */
327 MDB_FIRST_DUP, /**< Position at first data item of current key.
328 Only for #MDB_DUPSORT */
329 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
330 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
331 MDB_GET_CURRENT, /**< Return key/data at current cursor position */
332 MDB_GET_MULTIPLE, /**< Return all the duplicate data items at the current
333 cursor position. Only for #MDB_DUPFIXED */
334 MDB_LAST, /**< Position at last key/data item */
335 MDB_LAST_DUP, /**< Position at last data item of current key.
336 Only for #MDB_DUPSORT */
337 MDB_NEXT, /**< Position at next data item */
338 MDB_NEXT_DUP, /**< Position at next data item of current key.
339 Only for #MDB_DUPSORT */
340 MDB_NEXT_MULTIPLE, /**< Return all duplicate data items at the next
341 cursor position. Only for #MDB_DUPFIXED */
342 MDB_NEXT_NODUP, /**< Position at first data item of next key */
343 MDB_PREV, /**< Position at previous data item */
344 MDB_PREV_DUP, /**< Position at previous data item of current key.
345 Only for #MDB_DUPSORT */
346 MDB_PREV_NODUP, /**< Position at last data item of previous key */
347 MDB_SET, /**< Position at specified key */
348 MDB_SET_KEY, /**< Position at specified key, return key + data */
349 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
352 /** @defgroup errors Return Codes
354 * BerkeleyDB uses -30800 to -30999, we'll go under them
357 /** Successful result */
358 #define MDB_SUCCESS 0
359 /** key/data pair already exists */
360 #define MDB_KEYEXIST (-30799)
361 /** key/data pair not found (EOF) */
362 #define MDB_NOTFOUND (-30798)
363 /** Requested page not found - this usually indicates corruption */
364 #define MDB_PAGE_NOTFOUND (-30797)
365 /** Located page was wrong type */
366 #define MDB_CORRUPTED (-30796)
367 /** Update of meta page failed, probably I/O error */
368 #define MDB_PANIC (-30795)
369 /** Environment version mismatch */
370 #define MDB_VERSION_MISMATCH (-30794)
371 /** File is not a valid MDB file */
372 #define MDB_INVALID (-30793)
373 /** Environment mapsize reached */
374 #define MDB_MAP_FULL (-30792)
375 /** Environment maxdbs reached */
376 #define MDB_DBS_FULL (-30791)
377 /** Environment maxreaders reached */
378 #define MDB_READERS_FULL (-30790)
379 /** Too many TLS keys in use - Windows only */
380 #define MDB_TLS_FULL (-30789)
381 /** Txn has too many dirty pages */
382 #define MDB_TXN_FULL (-30788)
383 /** Cursor stack too deep - internal error */
384 #define MDB_CURSOR_FULL (-30787)
385 /** Page has not enough space - internal error */
386 #define MDB_PAGE_FULL (-30786)
387 /** Database contents grew beyond environment mapsize */
388 #define MDB_MAP_RESIZED (-30785)
389 /** MDB_INCOMPATIBLE: Operation and DB incompatible, or DB flags changed */
390 #define MDB_INCOMPATIBLE (-30784)
391 /** Invalid reuse of reader locktable slot */
392 #define MDB_BAD_RSLOT (-30783)
393 /** Transaction cannot recover - it must be aborted */
394 #define MDB_BAD_TXN (-30782)
395 /** Too big key/data, key is empty, or wrong DUPFIXED size */
396 #define MDB_BAD_VALSIZE (-30781)
397 #define MDB_LAST_ERRCODE MDB_BAD_VALSIZE
400 /** @brief Statistics for a database in the environment */
401 typedef struct MDB_stat {
402 unsigned int ms_psize; /**< Size of a database page.
403 This is currently the same for all databases. */
404 unsigned int ms_depth; /**< Depth (height) of the B-tree */
405 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
406 size_t ms_leaf_pages; /**< Number of leaf pages */
407 size_t ms_overflow_pages; /**< Number of overflow pages */
408 size_t ms_entries; /**< Number of data items */
411 /** @brief Information about the environment */
412 typedef struct MDB_envinfo {
413 void *me_mapaddr; /**< Address of map, if fixed */
414 size_t me_mapsize; /**< Size of the data memory map */
415 size_t me_last_pgno; /**< ID of the last used page */
416 size_t me_last_txnid; /**< ID of the last committed transaction */
417 unsigned int me_maxreaders; /**< max reader slots in the environment */
418 unsigned int me_numreaders; /**< max reader slots used in the environment */
421 /** @brief Return the mdb library version information.
423 * @param[out] major if non-NULL, the library major version number is copied here
424 * @param[out] minor if non-NULL, the library minor version number is copied here
425 * @param[out] patch if non-NULL, the library patch version number is copied here
426 * @retval "version string" The library version as a string
428 char *mdb_version(int *major, int *minor, int *patch);
430 /** @brief Return a string describing a given error code.
432 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
433 * function. If the error code is greater than or equal to 0, then the string
434 * returned by the system function strerror(3) is returned. If the error code
435 * is less than 0, an error string corresponding to the MDB library error is
436 * returned. See @ref errors for a list of MDB-specific error codes.
437 * @param[in] err The error code
438 * @retval "error message" The description of the error
440 char *mdb_strerror(int err);
442 /** @brief Create an MDB environment handle.
444 * This function allocates memory for a #MDB_env structure. To release
445 * the allocated memory and discard the handle, call #mdb_env_close().
446 * Before the handle may be used, it must be opened using #mdb_env_open().
447 * Various other options may also need to be set before opening the handle,
448 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
449 * depending on usage requirements.
450 * @param[out] env The address where the new handle will be stored
451 * @return A non-zero error value on failure and 0 on success.
453 int mdb_env_create(MDB_env **env);
455 /** @brief Open an environment handle.
457 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
458 * @param[in] env An environment handle returned by #mdb_env_create()
459 * @param[in] path The directory in which the database files reside. This
460 * directory must already exist and be writable.
461 * @param[in] flags Special options for this environment. This parameter
462 * must be set to 0 or by bitwise OR'ing together one or more of the
463 * values described here.
464 * Flags set by mdb_env_set_flags() are also used.
467 * use a fixed address for the mmap region. This flag must be specified
468 * when creating the environment, and is stored persistently in the environment.
469 * If successful, the memory map will always reside at the same virtual address
470 * and pointers used to reference data items in the database will be constant
471 * across multiple invocations. This option may not always work, depending on
472 * how the operating system has allocated memory to shared libraries and other uses.
473 * The feature is highly experimental.
475 * By default, MDB creates its environment in a directory whose
476 * pathname is given in \b path, and creates its data and lock files
477 * under that directory. With this option, \b path is used as-is for
478 * the database main data file. The database lock file is the \b path
479 * with "-lock" appended.
481 * Open the environment in read-only mode. No write operations will be
482 * allowed. MDB will still modify the lock file - except on read-only
483 * filesystems, where MDB does not use locks.
485 * Use a writeable memory map unless MDB_RDONLY is set. This is faster
486 * and uses fewer mallocs, but loses protection from application bugs
487 * like wild pointer writes and other bad updates into the database.
488 * Incompatible with nested transactions.
489 * <li>#MDB_NOMETASYNC
490 * Flush system buffers to disk only once per transaction, omit the
491 * metadata flush. Defer that until the system flushes files to disk,
492 * or next non-MDB_RDONLY commit or #mdb_env_sync(). This optimization
493 * maintains database integrity, but a system crash may undo the last
494 * committed transaction. I.e. it preserves the ACI (atomicity,
495 * consistency, isolation) but not D (durability) database property.
496 * This flag may be changed at any time using #mdb_env_set_flags().
498 * Don't flush system buffers to disk when committing a transaction.
499 * This optimization means a system crash can corrupt the database or
500 * lose the last transactions if buffers are not yet flushed to disk.
501 * The risk is governed by how often the system flushes dirty buffers
502 * to disk and how often #mdb_env_sync() is called. However, if the
503 * filesystem preserves write order and the #MDB_WRITEMAP flag is not
504 * used, transactions exhibit ACI (atomicity, consistency, isolation)
505 * properties and only lose D (durability). I.e. database integrity
506 * is maintained, but a system crash may undo the final transactions.
507 * Note that (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no
508 * hint for when to write transactions to disk, unless #mdb_env_sync()
509 * is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable.
510 * This flag may be changed at any time using #mdb_env_set_flags().
512 * When using #MDB_WRITEMAP, use asynchronous flushes to disk.
513 * As with #MDB_NOSYNC, a system crash can then corrupt the
514 * database or lose the last transactions. Calling #mdb_env_sync()
515 * ensures on-disk database integrity until next commit.
516 * This flag may be changed at any time using #mdb_env_set_flags().
518 * Don't use Thread-Local Storage. Tie reader locktable slots to
519 * #MDB_txn objects instead of to threads. I.e. #mdb_txn_reset() keeps
520 * the slot reseved for the #MDB_txn object. A thread may use parallel
521 * read-only transactions. A read-only transaction may span threads if
522 * the user synchronizes its use. Applications that multiplex many
523 * user threads over individual OS threads need this option. Such an
524 * application must also serialize the write transactions in an OS
525 * thread, since MDB's write locking is unaware of the user threads.
527 * @param[in] mode The UNIX permissions to set on created files. This parameter
528 * is ignored on Windows.
529 * @return A non-zero error value on failure and 0 on success. Some possible
532 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
533 * version that created the database environment.
534 * <li>#MDB_INVALID - the environment file headers are corrupted.
535 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
536 * <li>EACCES - the user didn't have permission to access the environment files.
537 * <li>EAGAIN - the environment was locked by another process.
540 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode);
542 /** @brief Copy an MDB environment to the specified path.
544 * This function may be used to make a backup of an existing environment.
545 * No lockfile is created, since it gets recreated at need.
546 * @note This call can trigger significant file size growth if run in
547 * parallel with write transactions, because it employs a read-only
548 * transaction. See long-lived transactions under @ref caveats_sec.
549 * @param[in] env An environment handle returned by #mdb_env_create(). It
550 * must have already been opened successfully.
551 * @param[in] path The directory in which the copy will reside. This
552 * directory must already exist and be writable but must otherwise be
554 * @return A non-zero error value on failure and 0 on success.
556 int mdb_env_copy(MDB_env *env, const char *path);
558 /** @brief Copy an MDB environment to the specified file descriptor.
560 * This function may be used to make a backup of an existing environment.
561 * No lockfile is created, since it gets recreated at need.
562 * @note This call can trigger significant file size growth if run in
563 * parallel with write transactions, because it employs a read-only
564 * transaction. See long-lived transactions under @ref caveats_sec.
565 * @param[in] env An environment handle returned by #mdb_env_create(). It
566 * must have already been opened successfully.
567 * @param[in] fd The filedescriptor to write the copy to. It must
568 * have already been opened for Write access.
569 * @return A non-zero error value on failure and 0 on success.
571 int mdb_env_copyfd(MDB_env *env, mdb_filehandle_t fd);
573 /** @brief Return statistics about the MDB environment.
575 * @param[in] env An environment handle returned by #mdb_env_create()
576 * @param[out] stat The address of an #MDB_stat structure
577 * where the statistics will be copied
579 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
581 /** @brief Return information about the MDB environment.
583 * @param[in] env An environment handle returned by #mdb_env_create()
584 * @param[out] stat The address of an #MDB_envinfo structure
585 * where the information will be copied
587 int mdb_env_info(MDB_env *env, MDB_envinfo *stat);
589 /** @brief Flush the data buffers to disk.
591 * Data is always written to disk when #mdb_txn_commit() is called,
592 * but the operating system may keep it buffered. MDB always flushes
593 * the OS buffers upon commit as well, unless the environment was
594 * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC.
595 * @param[in] env An environment handle returned by #mdb_env_create()
596 * @param[in] force If non-zero, force a synchronous flush. Otherwise
597 * if the environment has the #MDB_NOSYNC flag set the flushes
598 * will be omitted, and with #MDB_MAPASYNC they will be asynchronous.
599 * @return A non-zero error value on failure and 0 on success. Some possible
602 * <li>EINVAL - an invalid parameter was specified.
603 * <li>EIO - an error occurred during synchronization.
606 int mdb_env_sync(MDB_env *env, int force);
608 /** @brief Close the environment and release the memory map.
610 * Only a single thread may call this function. All transactions, databases,
611 * and cursors must already be closed before calling this function. Attempts to
612 * use any such handles after calling this function will cause a SIGSEGV.
613 * The environment handle will be freed and must not be used again after this call.
614 * @param[in] env An environment handle returned by #mdb_env_create()
616 void mdb_env_close(MDB_env *env);
618 /** @brief Set environment flags.
620 * This may be used to set some flags in addition to those from
621 * #mdb_env_open(), or to unset these flags.
622 * @param[in] env An environment handle returned by #mdb_env_create()
623 * @param[in] flags The flags to change, bitwise OR'ed together
624 * @param[in] onoff A non-zero value sets the flags, zero clears them.
625 * @return A non-zero error value on failure and 0 on success. Some possible
628 * <li>EINVAL - an invalid parameter was specified.
631 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
633 /** @brief Get environment flags.
635 * @param[in] env An environment handle returned by #mdb_env_create()
636 * @param[out] flags The address of an integer to store the flags
637 * @return A non-zero error value on failure and 0 on success. Some possible
640 * <li>EINVAL - an invalid parameter was specified.
643 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
645 /** @brief Return the path that was used in #mdb_env_open().
647 * @param[in] env An environment handle returned by #mdb_env_create()
648 * @param[out] path Address of a string pointer to contain the path. This
649 * is the actual string in the environment, not a copy. It should not be
650 * altered in any way.
651 * @return A non-zero error value on failure and 0 on success. Some possible
654 * <li>EINVAL - an invalid parameter was specified.
657 int mdb_env_get_path(MDB_env *env, const char **path);
659 /** @brief Set the size of the memory map to use for this environment.
661 * The size should be a multiple of the OS page size. The default is
662 * 10485760 bytes. The size of the memory map is also the maximum size
663 * of the database. The value should be chosen as large as possible,
664 * to accommodate future growth of the database.
665 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
666 * The size may be changed by closing and reopening the environment.
667 * Any attempt to set a size smaller than the space already consumed
668 * by the environment will be silently changed to the current size of the used space.
669 * @param[in] env An environment handle returned by #mdb_env_create()
670 * @param[in] size The size in bytes
671 * @return A non-zero error value on failure and 0 on success. Some possible
674 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
677 int mdb_env_set_mapsize(MDB_env *env, size_t size);
679 /** @brief Set the maximum number of threads/reader slots for the environment.
681 * This defines the number of slots in the lock table that is used to track readers in the
682 * the environment. The default is 126.
683 * Starting a read-only transaction normally ties a lock table slot to the
684 * current thread until the environment closes or the thread exits. If
685 * MDB_NOTLS is in use, #mdb_txn_begin() instead ties the slot to the
686 * MDB_txn object until it or the #MDB_env object is destroyed.
687 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
688 * @param[in] env An environment handle returned by #mdb_env_create()
689 * @param[in] readers The maximum number of reader lock table slots
690 * @return A non-zero error value on failure and 0 on success. Some possible
693 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
696 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
698 /** @brief Get the maximum number of threads/reader slots for the environment.
700 * @param[in] env An environment handle returned by #mdb_env_create()
701 * @param[out] readers Address of an integer to store the number of readers
702 * @return A non-zero error value on failure and 0 on success. Some possible
705 * <li>EINVAL - an invalid parameter was specified.
708 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
710 /** @brief Set the maximum number of named databases for the environment.
712 * This function is only needed if multiple databases will be used in the
713 * environment. Simpler applications that use the environment as a single
714 * unnamed database can ignore this option.
715 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
716 * @param[in] env An environment handle returned by #mdb_env_create()
717 * @param[in] dbs The maximum number of databases
718 * @return A non-zero error value on failure and 0 on success. Some possible
721 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
724 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
726 /** @brief Get the maximum size of a key for the environment.
728 * @param[in] env An environment handle returned by #mdb_env_create()
729 * @return The maximum size of a key. (#MDB_MAXKEYSIZE)
731 int mdb_env_get_maxkeysize(MDB_env *env);
733 /** @brief Create a transaction for use with the environment.
735 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
736 * @note A transaction and its cursors must only be used by a single
737 * thread, and a thread may only have a single transaction at a time.
738 * If #MDB_NOTLS is in use, this does not apply to read-only transactions.
739 * @note Cursors may not span transactions.
740 * @param[in] env An environment handle returned by #mdb_env_create()
741 * @param[in] parent If this parameter is non-NULL, the new transaction
742 * will be a nested transaction, with the transaction indicated by \b parent
743 * as its parent. Transactions may be nested to any level. A parent
744 * transaction and its cursors may not issue any other operations than
745 * mdb_txn_commit and mdb_txn_abort while it has active child transactions.
746 * @param[in] flags Special options for this transaction. This parameter
747 * must be set to 0 or by bitwise OR'ing together one or more of the
748 * values described here.
751 * This transaction will not perform any write operations.
753 * @param[out] txn Address where the new #MDB_txn handle will be stored
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>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's
760 * mapsize and the environment must be shut down.
761 * <li>#MDB_READERS_FULL - a read-only transaction was requested and
762 * the reader lock table is full. See #mdb_env_set_maxreaders().
763 * <li>ENOMEM - out of memory.
766 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
768 /** @brief Returns the transaction's #MDB_env
770 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
772 MDB_env *mdb_txn_env(MDB_txn *txn);
774 /** @brief Commit all the operations of a transaction into the database.
776 * The transaction handle is freed. It and its cursors must not be used
777 * again after this call, except with #mdb_cursor_renew().
778 * @note Earlier documentation incorrectly said all cursors would be freed.
779 * Only write-transactions free cursors.
780 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
781 * @return A non-zero error value on failure and 0 on success. Some possible
784 * <li>EINVAL - an invalid parameter was specified.
785 * <li>ENOSPC - no more disk space.
786 * <li>EIO - a low-level I/O error occurred while writing.
787 * <li>ENOMEM - out of memory.
790 int mdb_txn_commit(MDB_txn *txn);
792 /** @brief Abandon all the operations of the transaction instead of saving them.
794 * The transaction handle is freed. It and its cursors must not be used
795 * again after this call, except with #mdb_cursor_renew().
796 * @note Earlier documentation incorrectly said all cursors would be freed.
797 * Only write-transactions free cursors.
798 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
800 void mdb_txn_abort(MDB_txn *txn);
802 /** @brief Reset a read-only transaction.
804 * Abort the transaction like #mdb_txn_abort(), but keep the transaction
805 * handle. #mdb_txn_renew() may reuse the handle. This saves allocation
806 * overhead if the process will start a new read-only transaction soon,
807 * and also locking overhead if #MDB_NOTLS is in use. The reader table
808 * lock is released, but the table slot stays tied to its thread or
809 * #MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free
810 * its lock table slot if MDB_NOTLS is in use.
811 * Cursors opened within the transaction must not be used
812 * again after this call, except with #mdb_cursor_renew().
813 * Reader locks generally don't interfere with writers, but they keep old
814 * versions of database pages allocated. Thus they prevent the old pages
815 * from being reused when writers commit new data, and so under heavy load
816 * the database size may grow much more rapidly than otherwise.
817 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
819 void mdb_txn_reset(MDB_txn *txn);
821 /** @brief Renew a read-only transaction.
823 * This acquires a new reader lock for a transaction handle that had been
824 * released by #mdb_txn_reset(). It must be called before a reset transaction
826 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
827 * @return A non-zero error value on failure and 0 on success. Some possible
830 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
832 * <li>EINVAL - an invalid parameter was specified.
835 int mdb_txn_renew(MDB_txn *txn);
837 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
838 #define mdb_open(txn,name,flags,dbi) mdb_dbi_open(txn,name,flags,dbi)
839 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
840 #define mdb_close(env,dbi) mdb_dbi_close(env,dbi)
842 /** @brief Open a database in the environment.
844 * A database handle denotes the name and parameters of a database,
845 * independently of whether such a database exists.
846 * The database handle may be discarded by calling #mdb_dbi_close().
847 * The old database handle is returned if the database was already open.
848 * The handle must only be closed once.
849 * The database handle will be private to the current transaction until
850 * the transaction is successfully committed. If the transaction is
851 * aborted the handle will be closed automatically.
852 * After a successful commit the
853 * handle will reside in the shared environment, and may be used
854 * by other transactions. This function must not be called from
855 * multiple concurrent transactions. A transaction that uses this function
856 * must finish (either commit or abort) before any other transaction may
859 * To use named databases (with name != NULL), #mdb_env_set_maxdbs()
860 * must be called before opening the environment.
861 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
862 * @param[in] name The name of the database to open. If only a single
863 * database is needed in the environment, this value may be NULL.
864 * @param[in] flags Special options for this database. This parameter
865 * must be set to 0 or by bitwise OR'ing together one or more of the
866 * values described here.
868 * <li>#MDB_REVERSEKEY
869 * Keys are strings to be compared in reverse order, from the end
870 * of the strings to the beginning. By default, Keys are treated as strings and
871 * compared from beginning to end.
873 * Duplicate keys may be used in the database. (Or, from another perspective,
874 * keys may have multiple data items, stored in sorted order.) By default
875 * keys must be unique and may have only a single data item.
876 * <li>#MDB_INTEGERKEY
877 * Keys are binary integers in native byte order. Setting this option
878 * requires all keys to be the same size, typically sizeof(int)
881 * This flag may only be used in combination with #MDB_DUPSORT. This option
882 * tells the library that the data items for this database are all the same
883 * size, which allows further optimizations in storage and retrieval. When
884 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
885 * cursor operations may be used to retrieve multiple items at once.
886 * <li>#MDB_INTEGERDUP
887 * This option specifies that duplicate data items are also integers, and
888 * should be sorted as such.
889 * <li>#MDB_REVERSEDUP
890 * This option specifies that duplicate data items should be compared as
891 * strings in reverse order.
893 * Create the named database if it doesn't exist. This option is not
894 * allowed in a read-only transaction or a read-only environment.
896 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
897 * @return A non-zero error value on failure and 0 on success. Some possible
900 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
901 * and #MDB_CREATE was not specified.
902 * <li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs().
905 int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
907 /** @brief Retrieve statistics for a database.
909 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
910 * @param[in] dbi A database handle returned by #mdb_dbi_open()
911 * @param[out] stat The address of an #MDB_stat structure
912 * where the statistics will be copied
913 * @return A non-zero error value on failure and 0 on success. Some possible
916 * <li>EINVAL - an invalid parameter was specified.
919 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
921 /** @brief Retrieve the DB flags for a database handle.
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[out] flags Address where the flags will be returned.
926 * @return A non-zero error value on failure and 0 on success.
928 int mdb_dbi_flags(MDB_txn *txn, MDB_dbi dbi, unsigned int *flags);
930 /** @brief Close a database handle.
932 * This call is not mutex protected. Handles should only be closed by
933 * a single thread, and only if no other threads are going to reference
934 * the database handle or one of its cursors any further. Do not close
935 * a handle if an existing transaction has modified its database.
936 * @param[in] env An environment handle returned by #mdb_env_create()
937 * @param[in] dbi A database handle returned by #mdb_dbi_open()
939 void mdb_dbi_close(MDB_env *env, MDB_dbi dbi);
941 /** @brief Empty or delete+close a database.
943 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
944 * @param[in] dbi A database handle returned by #mdb_dbi_open()
945 * @param[in] del 0 to empty the DB, 1 to delete it from the
946 * environment and close the DB handle.
947 * @return A non-zero error value on failure and 0 on success.
949 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
951 /** @brief Set a custom key comparison function for a database.
953 * The comparison function is called whenever it is necessary to compare a
954 * key specified by the application with a key currently stored in the database.
955 * If no comparison function is specified, and no special key flags were specified
956 * with #mdb_dbi_open(), the keys are compared lexically, with shorter keys collating
957 * before longer keys.
958 * @warning This function must be called before any data access functions are used,
959 * otherwise data corruption may occur. The same comparison function must be used by every
960 * program accessing the database, every time the database is used.
961 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
962 * @param[in] dbi A database handle returned by #mdb_dbi_open()
963 * @param[in] cmp A #MDB_cmp_func function
964 * @return A non-zero error value on failure and 0 on success. Some possible
967 * <li>EINVAL - an invalid parameter was specified.
970 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
972 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
974 * This comparison function is called whenever it is necessary to compare a data
975 * item specified by the application with a data item currently stored in the database.
976 * This function only takes effect if the database was opened with the #MDB_DUPSORT
978 * If no comparison function is specified, and no special key flags were specified
979 * with #mdb_dbi_open(), the data items are compared lexically, with shorter items collating
980 * before longer items.
981 * @warning This function must be called before any data access functions are used,
982 * otherwise data corruption may occur. The same comparison function must be used by every
983 * program accessing the database, every time the database is used.
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] cmp A #MDB_cmp_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_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
995 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
997 * @todo The relocation function is called whenever it is necessary to move the data
998 * of an item to a different position in the database (e.g. through tree
999 * balancing operations, shifts as a result of adds or deletes, etc.). It is
1000 * intended to allow address/position-dependent data items to be stored in
1001 * a database in an environment opened with the #MDB_FIXEDMAP option.
1002 * Currently the relocation feature is unimplemented and setting
1003 * this function has no effect.
1004 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1005 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1006 * @param[in] rel A #MDB_rel_func function
1007 * @return A non-zero error value on failure and 0 on success. Some possible
1010 * <li>EINVAL - an invalid parameter was specified.
1013 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
1015 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
1017 * See #mdb_set_relfunc and #MDB_rel_func for more details.
1018 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1019 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1020 * @param[in] ctx An arbitrary pointer for whatever the application needs.
1021 * It will be passed to the callback function set by #mdb_set_relfunc
1022 * as its \b relctx parameter whenever the callback is invoked.
1023 * @return A non-zero error value on failure and 0 on success. Some possible
1026 * <li>EINVAL - an invalid parameter was specified.
1029 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
1031 /** @brief Get items from a database.
1033 * This function retrieves key/data pairs from the database. The address
1034 * and length of the data associated with the specified \b key are returned
1035 * in the structure to which \b data refers.
1036 * If the database supports duplicate keys (#MDB_DUPSORT) then the
1037 * first data item for the key will be returned. Retrieval of other
1038 * items requires the use of #mdb_cursor_get().
1040 * @note The memory pointed to by the returned values is owned by the
1041 * database. The caller need not dispose of the memory, and may not
1042 * modify it in any way. For values returned in a read-only transaction
1043 * any modification attempts will cause a SIGSEGV.
1044 * @note Values returned from the database are valid only until a
1045 * subsequent update operation, or the end of the transaction.
1046 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1047 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1048 * @param[in] key The key to search for in the database
1049 * @param[out] data The data corresponding to the key
1050 * @return A non-zero error value on failure and 0 on success. Some possible
1053 * <li>#MDB_NOTFOUND - the key was not in the database.
1054 * <li>EINVAL - an invalid parameter was specified.
1057 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1059 /** @brief Store items into a database.
1061 * This function stores key/data pairs in the database. The default behavior
1062 * is to enter the new key/data pair, replacing any previously existing key
1063 * if duplicates are disallowed, or adding a duplicate data item if
1064 * duplicates are allowed (#MDB_DUPSORT).
1065 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1066 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1067 * @param[in] key The key to store in the database
1068 * @param[in,out] data The data to store
1069 * @param[in] flags Special options for this operation. This parameter
1070 * must be set to 0 or by bitwise OR'ing together one or more of the
1071 * values described here.
1073 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1074 * already appear in the database. This flag may only be specified
1075 * if the database was opened with #MDB_DUPSORT. The function will
1076 * return #MDB_KEYEXIST if the key/data pair already appears in the
1078 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1079 * does not already appear in the database. The function will return
1080 * #MDB_KEYEXIST if the key already appears in the database, even if
1081 * the database supports duplicates (#MDB_DUPSORT). The \b data
1082 * parameter will be set to point to the existing item.
1083 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1084 * don't copy the given data. Instead, return a pointer to the
1085 * reserved space, which the caller can fill in later - before
1086 * the next update operation or the transaction ends. This saves
1087 * an extra memcpy if the data is being generated later.
1088 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1089 * database. No key comparisons are performed. This option allows
1090 * fast bulk loading when keys are already known to be in the
1091 * correct order. Loading unsorted keys with this flag will cause
1093 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1095 * @return A non-zero error value on failure and 0 on success. Some possible
1098 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1099 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1100 * <li>EACCES - an attempt was made to write in a read-only transaction.
1101 * <li>EINVAL - an invalid parameter was specified.
1104 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
1105 unsigned int flags);
1107 /** @brief Delete items from a database.
1109 * This function removes key/data pairs from the database.
1110 * If the database does not support sorted duplicate data items
1111 * (#MDB_DUPSORT) the data parameter is ignored.
1112 * If the database supports sorted duplicates and the data parameter
1113 * is NULL, all of the duplicate data items for the key will be
1114 * deleted. Otherwise, if the data parameter is non-NULL
1115 * only the matching data item will be deleted.
1116 * This function will return #MDB_NOTFOUND if the specified key/data
1117 * pair is not in the database.
1118 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1119 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1120 * @param[in] key The key to delete from the database
1121 * @param[in] data The data to delete
1122 * @return A non-zero error value on failure and 0 on success. Some possible
1125 * <li>EACCES - an attempt was made to write in a read-only transaction.
1126 * <li>EINVAL - an invalid parameter was specified.
1129 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1131 /** @brief Create a cursor handle.
1133 * A cursor is associated with a specific transaction and database.
1134 * A cursor cannot be used when its database handle is closed. Nor
1135 * when its transaction has ended, except with #mdb_cursor_renew().
1136 * It can be discarded with #mdb_cursor_close().
1137 * A cursor in a write-transaction can be closed before its transaction
1138 * ends, and will otherwise be closed when its transaction ends.
1139 * A cursor in a read-only transaction must be closed explicitly, before
1140 * or after its transaction ends. It can be reused with
1141 * #mdb_cursor_renew() before finally closing it.
1142 * @note Earlier documentation said that cursors in every transaction
1143 * were closed when the transaction committed or aborted.
1144 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1145 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1146 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
1147 * @return A non-zero error value on failure and 0 on success. Some possible
1150 * <li>EINVAL - an invalid parameter was specified.
1153 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
1155 /** @brief Close a cursor handle.
1157 * The cursor handle will be freed and must not be used again after this call.
1158 * Its transaction must still be live if it is a write-transaction.
1159 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1161 void mdb_cursor_close(MDB_cursor *cursor);
1163 /** @brief Renew a cursor handle.
1165 * A cursor is associated with a specific transaction and database.
1166 * Cursors that are only used in read-only
1167 * transactions may be re-used, to avoid unnecessary malloc/free overhead.
1168 * The cursor may be associated with a new read-only transaction, and
1169 * referencing the same database handle as it was created with.
1170 * This may be done whether the previous transaction is live or dead.
1171 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1172 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1173 * @return A non-zero error value on failure and 0 on success. Some possible
1176 * <li>EINVAL - an invalid parameter was specified.
1179 int mdb_cursor_renew(MDB_txn *txn, MDB_cursor *cursor);
1181 /** @brief Return the cursor's transaction handle.
1183 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1185 MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
1187 /** @brief Return the cursor's database handle.
1189 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1191 MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor);
1193 /** @brief Retrieve by cursor.
1195 * This function retrieves key/data pairs from the database. The address and length
1196 * of the key are returned in the object to which \b key refers (except for the
1197 * case of the #MDB_SET option, in which the \b key object is unchanged), and
1198 * the address and length of the data are returned in the object to which \b data
1200 * See #mdb_get() for restrictions on using the output values.
1201 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1202 * @param[in,out] key The key for a retrieved item
1203 * @param[in,out] data The data of a retrieved item
1204 * @param[in] op A cursor operation #MDB_cursor_op
1205 * @return A non-zero error value on failure and 0 on success. Some possible
1208 * <li>#MDB_NOTFOUND - no matching key found.
1209 * <li>EINVAL - an invalid parameter was specified.
1212 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1215 /** @brief Store by cursor.
1217 * This function stores key/data pairs into the database.
1218 * If the function fails for any reason, the state of the cursor will be
1219 * unchanged. If the function succeeds and an item is inserted into the
1220 * database, the cursor is always positioned to refer to the newly inserted item.
1221 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1222 * @param[in] key The key operated on.
1223 * @param[in] data The data operated on.
1224 * @param[in] flags Options for this operation. This parameter
1225 * must be set to 0 or one of the values described here.
1227 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which
1228 * the cursor refers with the specified data item. The \b key
1229 * parameter is ignored.
1230 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1231 * already appear in the database. This flag may only be specified
1232 * if the database was opened with #MDB_DUPSORT. The function will
1233 * return #MDB_KEYEXIST if the key/data pair already appears in the
1235 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1236 * does not already appear in the database. The function will return
1237 * #MDB_KEYEXIST if the key already appears in the database, even if
1238 * the database supports duplicates (#MDB_DUPSORT).
1239 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1240 * don't copy the given data. Instead, return a pointer to the
1241 * reserved space, which the caller can fill in later. This saves
1242 * an extra memcpy if the data is being generated later.
1243 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1244 * database. No key comparisons are performed. This option allows
1245 * fast bulk loading when keys are already known to be in the
1246 * correct order. Loading unsorted keys with this flag will cause
1248 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1249 * <li>#MDB_MULTIPLE - store multiple contiguous data elements in a
1250 * single request. This flag may only be specified if the database
1251 * was opened with #MDB_DUPFIXED. The \b data argument must be an
1252 * array of two MDB_vals. The mv_size of the first MDB_val must be
1253 * the size of a single data element. The mv_data of the first MDB_val
1254 * must point to the beginning of the array of contiguous data elements.
1255 * The mv_size of the second MDB_val must be the count of the number
1256 * of data elements to store. On return this field will be set to
1257 * the count of the number of elements actually written. The mv_data
1258 * of the second MDB_val is unused.
1260 * @return A non-zero error value on failure and 0 on success. Some possible
1263 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1264 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
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_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1270 unsigned int flags);
1272 /** @brief Delete current key/data pair
1274 * This function deletes the key/data pair to which the cursor refers.
1275 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1276 * @param[in] flags Options for this operation. This parameter
1277 * must be set to 0 or one of the values described here.
1279 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
1280 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
1282 * @return A non-zero error value on failure and 0 on success. Some possible
1285 * <li>EACCES - an attempt was made to modify a read-only database.
1286 * <li>EINVAL - an invalid parameter was specified.
1289 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
1291 /** @brief Return count of duplicates for current key.
1293 * This call is only valid on databases that support sorted duplicate
1294 * data items #MDB_DUPSORT.
1295 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1296 * @param[out] countp Address where the count will be stored
1297 * @return A non-zero error value on failure and 0 on success. Some possible
1300 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
1303 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
1305 /** @brief Compare two data items according to a particular database.
1307 * This returns a comparison as if the two data items were keys in the
1308 * specified database.
1309 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1310 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1311 * @param[in] a The first item to compare
1312 * @param[in] b The second item to compare
1313 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1315 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1317 /** @brief Compare two data items according to a particular database.
1319 * This returns a comparison as if the two items were data items of
1320 * the specified database. The database must have the #MDB_DUPSORT flag.
1321 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1322 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1323 * @param[in] a The first item to compare
1324 * @param[in] b The second item to compare
1325 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1327 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1329 /** @brief A callback function used to print a message from the library.
1331 * @param[in] msg The string to be printed.
1332 * @param[in] ctx An arbitrary context pointer for the callback.
1333 * @return < 0 on failure, 0 on success.
1335 typedef int (MDB_msg_func)(const char *msg, void *ctx);
1337 /** @brief Dump the entries in the reader lock table.
1339 * @param[in] env An environment handle returned by #mdb_env_create()
1340 * @param[in] func A #MDB_msg_func function
1341 * @param[in] ctx Anything the message function needs
1342 * @return < 0 on failure, 0 on success.
1344 int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx);
1346 /** @brief Check for stale entries in the reader lock table.
1348 * @param[in] env An environment handle returned by #mdb_env_create()
1349 * @param[out] dead Number of stale slots that were cleared
1350 * @return 0 on success, non-zero on failure.
1352 int mdb_reader_check(MDB_env *env, int *dead);
1358 #endif /* _LMDB_H_ */