2 * @brief Lightning memory-mapped database library
4 * @mainpage Lightning Memory-Mapped Database Manager (MDB)
6 * @section intro_sec Introduction
7 * MDB is a Btree-based database management library modeled loosely on the
8 * BerkeleyDB API, but much simplified. The entire database is exposed
9 * in a memory map, and all data fetches return data directly
10 * from the mapped memory, so no malloc's or memcpy's occur during
11 * data fetches. As such, the library is extremely simple because it
12 * requires no page caching layer of its own, and it is extremely high
13 * performance and memory-efficient. It is also fully transactional with
14 * full ACID semantics, and when the memory map is read-only, the
15 * database integrity cannot be corrupted by stray pointer writes from
18 * The library is fully thread-aware and supports concurrent read/write
19 * access from multiple processes and threads. Data pages use a copy-on-
20 * write strategy so no active data pages are ever overwritten, which
21 * also provides resistance to corruption and eliminates the need of any
22 * special recovery procedures after a system crash. Writes are fully
23 * serialized; only one write transaction may be active at a time, which
24 * guarantees that writers can never deadlock. The database structure is
25 * multi-versioned so readers run with no locks; writers cannot block
26 * readers, and readers don't block writers.
28 * Unlike other well-known database mechanisms which use either write-ahead
29 * transaction logs or append-only data writes, MDB requires no maintenance
30 * during operation. Both write-ahead loggers and append-only databases
31 * require periodic checkpointing and/or compaction of their log or database
32 * files otherwise they grow without bound. MDB tracks free pages within
33 * the database and re-uses them for new write operations, so the database
34 * size does not grow without bound in normal use.
36 * The memory map can be used as a read-only or read-write map. It is
37 * read-only by default as this provides total immunity to corruption.
38 * Using read-write mode offers much higher write performance, but adds
39 * the possibility for stray application writes thru pointers to silently
40 * corrupt the database. Of course if your application code is known to
41 * be bug-free (...) then this is not an issue.
43 * @section caveats_sec Caveats
44 * Troubleshooting the lock file, plus semaphores on BSD systems:
46 * - A broken lockfile can cause sync issues.
47 * Stale reader transactions left behind by an aborted program
48 * cause further writes to grow the database quickly, and
49 * stale locks can block further operation.
51 * Fix: Check for stale readers periodically, using the
52 * #mdb_reader_check function or the mdb_stat tool. Or just
53 * make all programs using the database close it; the lockfile
54 * is always reset on first open of the environment.
56 * - On BSD systems or others configured with MDB_USE_POSIX_SEM,
57 * startup can fail due to semaphores owned by another userid.
59 * Fix: Open and close the database as the user which owns the
60 * semaphores (likely last user) or as root, while no other
61 * process is using the database.
63 * Restrictions/caveats (in addition to those listed for some functions):
65 * - Only the database owner should normally use the database on
66 * BSD systems or when otherwise configured with MDB_USE_POSIX_SEM.
67 * Multiple users can cause startup to fail later, as noted above.
69 * - There is normally no pure read-only mode, since readers need write
70 * access to locks and lock file. Exceptions: On read-only filesystems
71 * or with the #MDB_NOLOCK flag described under #mdb_env_open().
73 * - A thread can only use one transaction at a time, plus any child
74 * transactions. Each transaction belongs to one thread. See below.
75 * The #MDB_NOTLS flag changes this for read-only transactions.
77 * - Use an MDB_env* in the process which opened it, without fork()ing.
79 * - Do not have open an MDB database twice in the same process at
80 * the same time. Not even from a plain open() call - close()ing it
81 * breaks flock() advisory locking.
83 * - Avoid long-lived transactions. Read transactions prevent
84 * reuse of pages freed by newer write transactions, thus the
85 * database can grow quickly. Write transactions prevent
86 * other write transactions, since writes are serialized.
88 * - Avoid suspending a process with active transactions. These
89 * would then be "long-lived" as above. Also read transactions
90 * suspended when writers commit could sometimes see wrong data.
92 * ...when several processes can use a database concurrently:
94 * - Avoid aborting a process with an active transaction.
95 * The transaction becomes "long-lived" as above until a check
96 * for stale readers is performed or the lockfile is reset,
97 * since the process may not remove it from the lockfile.
99 * - If you do that anyway, do a periodic check for stale readers. Or
100 * close the environment once in a while, so the lockfile can get reset.
102 * - Do not use MDB databases on remote filesystems, even between
103 * processes on the same host. This breaks flock() on some OSes,
104 * possibly memory map sync, and certainly sync between programs
105 * on different hosts.
107 * - Opening a database can fail if another process is opening or
108 * closing it at exactly the same time.
110 * @author Howard Chu, Symas Corporation.
112 * @copyright Copyright 2011-2013 Howard Chu, Symas Corp. All rights reserved.
114 * Redistribution and use in source and binary forms, with or without
115 * modification, are permitted only as authorized by the OpenLDAP
118 * A copy of this license is available in the file LICENSE in the
119 * top-level directory of the distribution or, alternatively, at
120 * <http://www.OpenLDAP.org/license.html>.
123 * This code is derived from btree.c written by Martin Hedenfalk.
125 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
127 * Permission to use, copy, modify, and distribute this software for any
128 * purpose with or without fee is hereby granted, provided that the above
129 * copyright notice and this permission notice appear in all copies.
131 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
132 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
133 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
134 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
135 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
136 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
137 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
142 #include <sys/types.h>
148 /** Unix permissions for creating files, or dummy definition for Windows */
150 typedef int mdb_mode_t;
152 typedef mode_t mdb_mode_t;
155 /** An abstraction for a file handle.
156 * On POSIX systems file handles are small integers. On Windows
157 * they're opaque pointers.
160 typedef void *mdb_filehandle_t;
162 typedef int mdb_filehandle_t;
165 /** @defgroup mdb MDB API
167 * @brief OpenLDAP Lightning Memory-Mapped Database Manager
169 /** @defgroup Version Version Macros
172 /** Library major version */
173 #define MDB_VERSION_MAJOR 0
174 /** Library minor version */
175 #define MDB_VERSION_MINOR 9
176 /** Library patch version */
177 #define MDB_VERSION_PATCH 8
179 /** Combine args a,b,c into a single integer for easy version comparisons */
180 #define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
182 /** The full library version as a single integer */
183 #define MDB_VERSION_FULL \
184 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
186 /** The release date of this library version */
187 #define MDB_VERSION_DATE "September 9, 2013"
189 /** A stringifier for the version info */
190 #define MDB_VERSTR(a,b,c,d) "MDB " #a "." #b "." #c ": (" d ")"
192 /** A helper for the stringifier macro */
193 #define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d)
195 /** The full library version as a C string */
196 #define MDB_VERSION_STRING \
197 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
200 /** @brief Opaque structure for a database environment.
202 * A DB environment supports multiple databases, all residing in the same
205 typedef struct MDB_env MDB_env;
207 /** @brief Opaque structure for a transaction handle.
209 * All database operations require a transaction handle. Transactions may be
210 * read-only or read-write.
212 typedef struct MDB_txn MDB_txn;
214 /** @brief A handle for an individual database in the DB environment. */
215 typedef unsigned int MDB_dbi;
217 /** @brief Opaque structure for navigating through a database */
218 typedef struct MDB_cursor MDB_cursor;
220 /** @brief Generic structure used for passing keys and data in and out
223 * Values returned from the database are valid only until a subsequent
224 * update operation, or the end of the transaction. Do not modify or
225 * free them, they commonly point into the database itself.
227 * Key sizes must be between 1 and #mdb_env_get_maxkeysize() inclusive.
228 * The same applies to data sizes in databases with the #MDB_DUPSORT flag.
229 * Other data items can in theory be from 0 to 0xffffffff bytes long.
231 typedef struct MDB_val {
232 size_t mv_size; /**< size of the data item */
233 void *mv_data; /**< address of the data item */
236 /** @brief A callback function used to compare two keys in a database */
237 typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
239 /** @brief A callback function used to relocate a position-dependent data item
240 * in a fixed-address database.
242 * The \b newptr gives the item's desired address in
243 * the memory map, and \b oldptr gives its previous address. The item's actual
244 * data resides at the address in \b item. This callback is expected to walk
245 * through the fields of the record in \b item and modify any
246 * values based at the \b oldptr address to be relative to the \b newptr address.
247 * @param[in,out] item The item that is to be relocated.
248 * @param[in] oldptr The previous address.
249 * @param[in] newptr The new address to relocate to.
250 * @param[in] relctx An application-provided context, set by #mdb_set_relctx().
251 * @todo This feature is currently unimplemented.
253 typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
255 /** @defgroup mdb_env Environment Flags
257 * Values do not overlap Database Flags.
260 /** mmap at a fixed address (experimental) */
261 #define MDB_FIXEDMAP 0x01
262 /** no environment directory */
263 #define MDB_NOSUBDIR 0x4000
264 /** don't fsync after commit */
265 #define MDB_NOSYNC 0x10000
267 #define MDB_RDONLY 0x20000
268 /** don't fsync metapage after commit */
269 #define MDB_NOMETASYNC 0x40000
270 /** use writable mmap */
271 #define MDB_WRITEMAP 0x80000
272 /** use asynchronous msync when #MDB_WRITEMAP is used */
273 #define MDB_MAPASYNC 0x100000
274 /** tie reader locktable slots to #MDB_txn objects instead of to threads */
275 #define MDB_NOTLS 0x200000
276 /** don't do any locking, caller must manage their own locks */
277 #define MDB_NOLOCK 0x400000
280 /** @defgroup mdb_dbi_open Database Flags
282 * Values do not overlap Environment Flags.
285 /** use reverse string keys */
286 #define MDB_REVERSEKEY 0x02
287 /** use sorted duplicates */
288 #define MDB_DUPSORT 0x04
289 /** numeric keys in native byte order.
290 * The keys must all be of the same size. */
291 #define MDB_INTEGERKEY 0x08
292 /** with #MDB_DUPSORT, sorted dup items have fixed size */
293 #define MDB_DUPFIXED 0x10
294 /** with #MDB_DUPSORT, dups are numeric in native byte order */
295 #define MDB_INTEGERDUP 0x20
296 /** with #MDB_DUPSORT, use reverse string dups */
297 #define MDB_REVERSEDUP 0x40
298 /** create DB if not already existing */
299 #define MDB_CREATE 0x40000
302 /** @defgroup mdb_put Write Flags
305 /** For put: Don't write if the key already exists. */
306 #define MDB_NOOVERWRITE 0x10
307 /** Only for #MDB_DUPSORT<br>
308 * For put: don't write if the key and data pair already exist.<br>
309 * For mdb_cursor_del: remove all duplicate data items.
311 #define MDB_NODUPDATA 0x20
312 /** For mdb_cursor_put: overwrite the current key/data pair */
313 #define MDB_CURRENT 0x40
314 /** For put: Just reserve space for data, don't copy it. Return a
315 * pointer to the reserved space.
317 #define MDB_RESERVE 0x10000
318 /** Data is being appended, don't split full pages. */
319 #define MDB_APPEND 0x20000
320 /** Duplicate data is being appended, don't split full pages. */
321 #define MDB_APPENDDUP 0x40000
322 /** Store multiple data items in one call. Only for #MDB_DUPFIXED. */
323 #define MDB_MULTIPLE 0x80000
326 /** @brief Cursor Get operations.
328 * This is the set of all operations for retrieving data
331 typedef enum MDB_cursor_op {
332 MDB_FIRST, /**< Position at first key/data item */
333 MDB_FIRST_DUP, /**< Position at first data item of current key.
334 Only for #MDB_DUPSORT */
335 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
336 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
337 MDB_GET_CURRENT, /**< Return key/data at current cursor position */
338 MDB_GET_MULTIPLE, /**< Return all the duplicate data items at the current
339 cursor position. Only for #MDB_DUPFIXED */
340 MDB_LAST, /**< Position at last key/data item */
341 MDB_LAST_DUP, /**< Position at last data item of current key.
342 Only for #MDB_DUPSORT */
343 MDB_NEXT, /**< Position at next data item */
344 MDB_NEXT_DUP, /**< Position at next data item of current key.
345 Only for #MDB_DUPSORT */
346 MDB_NEXT_MULTIPLE, /**< Return all duplicate data items at the next
347 cursor position. Only for #MDB_DUPFIXED */
348 MDB_NEXT_NODUP, /**< Position at first data item of next key */
349 MDB_PREV, /**< Position at previous data item */
350 MDB_PREV_DUP, /**< Position at previous data item of current key.
351 Only for #MDB_DUPSORT */
352 MDB_PREV_NODUP, /**< Position at last data item of previous key */
353 MDB_SET, /**< Position at specified key */
354 MDB_SET_KEY, /**< Position at specified key, return key + data */
355 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
358 /** @defgroup errors Return Codes
360 * BerkeleyDB uses -30800 to -30999, we'll go under them
363 /** Successful result */
364 #define MDB_SUCCESS 0
365 /** key/data pair already exists */
366 #define MDB_KEYEXIST (-30799)
367 /** key/data pair not found (EOF) */
368 #define MDB_NOTFOUND (-30798)
369 /** Requested page not found - this usually indicates corruption */
370 #define MDB_PAGE_NOTFOUND (-30797)
371 /** Located page was wrong type */
372 #define MDB_CORRUPTED (-30796)
373 /** Update of meta page failed, probably I/O error */
374 #define MDB_PANIC (-30795)
375 /** Environment version mismatch */
376 #define MDB_VERSION_MISMATCH (-30794)
377 /** File is not a valid MDB file */
378 #define MDB_INVALID (-30793)
379 /** Environment mapsize reached */
380 #define MDB_MAP_FULL (-30792)
381 /** Environment maxdbs reached */
382 #define MDB_DBS_FULL (-30791)
383 /** Environment maxreaders reached */
384 #define MDB_READERS_FULL (-30790)
385 /** Too many TLS keys in use - Windows only */
386 #define MDB_TLS_FULL (-30789)
387 /** Txn has too many dirty pages */
388 #define MDB_TXN_FULL (-30788)
389 /** Cursor stack too deep - internal error */
390 #define MDB_CURSOR_FULL (-30787)
391 /** Page has not enough space - internal error */
392 #define MDB_PAGE_FULL (-30786)
393 /** Database contents grew beyond environment mapsize */
394 #define MDB_MAP_RESIZED (-30785)
395 /** MDB_INCOMPATIBLE: Operation and DB incompatible, or DB flags changed */
396 #define MDB_INCOMPATIBLE (-30784)
397 /** Invalid reuse of reader locktable slot */
398 #define MDB_BAD_RSLOT (-30783)
399 /** Transaction cannot recover - it must be aborted */
400 #define MDB_BAD_TXN (-30782)
401 /** Too big key/data, key is empty, or wrong DUPFIXED size */
402 #define MDB_BAD_VALSIZE (-30781)
403 #define MDB_LAST_ERRCODE MDB_BAD_VALSIZE
406 /** @brief Statistics for a database in the environment */
407 typedef struct MDB_stat {
408 unsigned int ms_psize; /**< Size of a database page.
409 This is currently the same for all databases. */
410 unsigned int ms_depth; /**< Depth (height) of the B-tree */
411 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
412 size_t ms_leaf_pages; /**< Number of leaf pages */
413 size_t ms_overflow_pages; /**< Number of overflow pages */
414 size_t ms_entries; /**< Number of data items */
417 /** @brief Information about the environment */
418 typedef struct MDB_envinfo {
419 void *me_mapaddr; /**< Address of map, if fixed */
420 size_t me_mapsize; /**< Size of the data memory map */
421 size_t me_last_pgno; /**< ID of the last used page */
422 size_t me_last_txnid; /**< ID of the last committed transaction */
423 unsigned int me_maxreaders; /**< max reader slots in the environment */
424 unsigned int me_numreaders; /**< max reader slots used in the environment */
427 /** @brief Return the mdb library version information.
429 * @param[out] major if non-NULL, the library major version number is copied here
430 * @param[out] minor if non-NULL, the library minor version number is copied here
431 * @param[out] patch if non-NULL, the library patch version number is copied here
432 * @retval "version string" The library version as a string
434 char *mdb_version(int *major, int *minor, int *patch);
436 /** @brief Return a string describing a given error code.
438 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
439 * function. If the error code is greater than or equal to 0, then the string
440 * returned by the system function strerror(3) is returned. If the error code
441 * is less than 0, an error string corresponding to the MDB library error is
442 * returned. See @ref errors for a list of MDB-specific error codes.
443 * @param[in] err The error code
444 * @retval "error message" The description of the error
446 char *mdb_strerror(int err);
448 /** @brief Create an MDB environment handle.
450 * This function allocates memory for a #MDB_env structure. To release
451 * the allocated memory and discard the handle, call #mdb_env_close().
452 * Before the handle may be used, it must be opened using #mdb_env_open().
453 * Various other options may also need to be set before opening the handle,
454 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
455 * depending on usage requirements.
456 * @param[out] env The address where the new handle will be stored
457 * @return A non-zero error value on failure and 0 on success.
459 int mdb_env_create(MDB_env **env);
461 /** @brief Open an environment handle.
463 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
464 * @param[in] env An environment handle returned by #mdb_env_create()
465 * @param[in] path The directory in which the database files reside. This
466 * directory must already exist and be writable.
467 * @param[in] flags Special options for this environment. This parameter
468 * must be set to 0 or by bitwise OR'ing together one or more of the
469 * values described here.
470 * Flags set by mdb_env_set_flags() are also used.
473 * use a fixed address for the mmap region. This flag must be specified
474 * when creating the environment, and is stored persistently in the environment.
475 * If successful, the memory map will always reside at the same virtual address
476 * and pointers used to reference data items in the database will be constant
477 * across multiple invocations. This option may not always work, depending on
478 * how the operating system has allocated memory to shared libraries and other uses.
479 * The feature is highly experimental.
481 * By default, MDB creates its environment in a directory whose
482 * pathname is given in \b path, and creates its data and lock files
483 * under that directory. With this option, \b path is used as-is for
484 * the database main data file. The database lock file is the \b path
485 * with "-lock" appended.
487 * Open the environment in read-only mode. No write operations will be
488 * allowed. MDB will still modify the lock file - except on read-only
489 * filesystems, where MDB does not use locks.
491 * Use a writeable memory map unless MDB_RDONLY is set. This is faster
492 * and uses fewer mallocs, but loses protection from application bugs
493 * like wild pointer writes and other bad updates into the database.
494 * Incompatible with nested transactions.
495 * Processes with and without MDB_WRITEMAP on the same environment do
496 * not cooperate well.
497 * <li>#MDB_NOMETASYNC
498 * Flush system buffers to disk only once per transaction, omit the
499 * metadata flush. Defer that until the system flushes files to disk,
500 * or next non-MDB_RDONLY commit or #mdb_env_sync(). This optimization
501 * maintains database integrity, but a system crash may undo the last
502 * committed transaction. I.e. it preserves the ACI (atomicity,
503 * consistency, isolation) but not D (durability) database property.
504 * This flag may be changed at any time using #mdb_env_set_flags().
506 * Don't flush system buffers to disk when committing a transaction.
507 * This optimization means a system crash can corrupt the database or
508 * lose the last transactions if buffers are not yet flushed to disk.
509 * The risk is governed by how often the system flushes dirty buffers
510 * to disk and how often #mdb_env_sync() is called. However, if the
511 * filesystem preserves write order and the #MDB_WRITEMAP flag is not
512 * used, transactions exhibit ACI (atomicity, consistency, isolation)
513 * properties and only lose D (durability). I.e. database integrity
514 * is maintained, but a system crash may undo the final transactions.
515 * Note that (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no
516 * hint for when to write transactions to disk, unless #mdb_env_sync()
517 * is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable.
518 * This flag may be changed at any time using #mdb_env_set_flags().
520 * When using #MDB_WRITEMAP, use asynchronous flushes to disk.
521 * As with #MDB_NOSYNC, a system crash can then corrupt the
522 * database or lose the last transactions. Calling #mdb_env_sync()
523 * ensures on-disk database integrity until next commit.
524 * This flag may be changed at any time using #mdb_env_set_flags().
526 * Don't use Thread-Local Storage. Tie reader locktable slots to
527 * #MDB_txn objects instead of to threads. I.e. #mdb_txn_reset() keeps
528 * the slot reseved for the #MDB_txn object. A thread may use parallel
529 * read-only transactions. A read-only transaction may span threads if
530 * the user synchronizes its use. Applications that multiplex many
531 * user threads over individual OS threads need this option. Such an
532 * application must also serialize the write transactions in an OS
533 * thread, since MDB's write locking is unaware of the user threads.
535 * Don't do any locking. If concurrent access is anticipated, the
536 * caller must manage all concurrency itself. For proper operation
537 * the caller must enforce single-writer semantics, and must ensure
538 * that no readers are using old transactions while a writer is
539 * active. The simplest approach is to use an exclusive lock so that
540 * no readers may be active at all when a writer begins.
542 * @param[in] mode The UNIX permissions to set on created files. This parameter
543 * is ignored on Windows.
544 * @return A non-zero error value on failure and 0 on success. Some possible
547 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
548 * version that created the database environment.
549 * <li>#MDB_INVALID - the environment file headers are corrupted.
550 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
551 * <li>EACCES - the user didn't have permission to access the environment files.
552 * <li>EAGAIN - the environment was locked by another process.
555 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode);
557 /** @brief Copy an MDB environment to the specified path.
559 * This function may be used to make a backup of an existing environment.
560 * No lockfile is created, since it gets recreated at need.
561 * @note This call can trigger significant file size growth if run in
562 * parallel with write transactions, because it employs a read-only
563 * transaction. See long-lived transactions under @ref caveats_sec.
564 * @param[in] env An environment handle returned by #mdb_env_create(). It
565 * must have already been opened successfully.
566 * @param[in] path The directory in which the copy will reside. This
567 * directory must already exist and be writable but must otherwise be
569 * @return A non-zero error value on failure and 0 on success.
571 int mdb_env_copy(MDB_env *env, const char *path);
573 /** @brief Copy an MDB environment to the specified file descriptor.
575 * This function may be used to make a backup of an existing environment.
576 * No lockfile is created, since it gets recreated at need.
577 * @note This call can trigger significant file size growth if run in
578 * parallel with write transactions, because it employs a read-only
579 * transaction. See long-lived transactions under @ref caveats_sec.
580 * @param[in] env An environment handle returned by #mdb_env_create(). It
581 * must have already been opened successfully.
582 * @param[in] fd The filedescriptor to write the copy to. It must
583 * have already been opened for Write access.
584 * @return A non-zero error value on failure and 0 on success.
586 int mdb_env_copyfd(MDB_env *env, mdb_filehandle_t fd);
588 /** @brief Return statistics about the MDB environment.
590 * @param[in] env An environment handle returned by #mdb_env_create()
591 * @param[out] stat The address of an #MDB_stat structure
592 * where the statistics will be copied
594 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
596 /** @brief Return information about the MDB environment.
598 * @param[in] env An environment handle returned by #mdb_env_create()
599 * @param[out] stat The address of an #MDB_envinfo structure
600 * where the information will be copied
602 int mdb_env_info(MDB_env *env, MDB_envinfo *stat);
604 /** @brief Flush the data buffers to disk.
606 * Data is always written to disk when #mdb_txn_commit() is called,
607 * but the operating system may keep it buffered. MDB always flushes
608 * the OS buffers upon commit as well, unless the environment was
609 * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC.
610 * @param[in] env An environment handle returned by #mdb_env_create()
611 * @param[in] force If non-zero, force a synchronous flush. Otherwise
612 * if the environment has the #MDB_NOSYNC flag set the flushes
613 * will be omitted, and with #MDB_MAPASYNC they will be asynchronous.
614 * @return A non-zero error value on failure and 0 on success. Some possible
617 * <li>EINVAL - an invalid parameter was specified.
618 * <li>EIO - an error occurred during synchronization.
621 int mdb_env_sync(MDB_env *env, int force);
623 /** @brief Close the environment and release the memory map.
625 * Only a single thread may call this function. All transactions, databases,
626 * and cursors must already be closed before calling this function. Attempts to
627 * use any such handles after calling this function will cause a SIGSEGV.
628 * The environment handle will be freed and must not be used again after this call.
629 * @param[in] env An environment handle returned by #mdb_env_create()
631 void mdb_env_close(MDB_env *env);
633 /** @brief Set environment flags.
635 * This may be used to set some flags in addition to those from
636 * #mdb_env_open(), or to unset these flags.
637 * @param[in] env An environment handle returned by #mdb_env_create()
638 * @param[in] flags The flags to change, bitwise OR'ed together
639 * @param[in] onoff A non-zero value sets the flags, zero clears them.
640 * @return A non-zero error value on failure and 0 on success. Some possible
643 * <li>EINVAL - an invalid parameter was specified.
646 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
648 /** @brief Get environment flags.
650 * @param[in] env An environment handle returned by #mdb_env_create()
651 * @param[out] flags The address of an integer to store the flags
652 * @return A non-zero error value on failure and 0 on success. Some possible
655 * <li>EINVAL - an invalid parameter was specified.
658 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
660 /** @brief Return the path that was used in #mdb_env_open().
662 * @param[in] env An environment handle returned by #mdb_env_create()
663 * @param[out] path Address of a string pointer to contain the path. This
664 * is the actual string in the environment, not a copy. It should not be
665 * altered in any way.
666 * @return A non-zero error value on failure and 0 on success. Some possible
669 * <li>EINVAL - an invalid parameter was specified.
672 int mdb_env_get_path(MDB_env *env, const char **path);
674 /** @brief Set the size of the memory map to use for this environment.
676 * The size should be a multiple of the OS page size. The default is
677 * 10485760 bytes. The size of the memory map is also the maximum size
678 * of the database. The value should be chosen as large as possible,
679 * to accommodate future growth of the database.
680 * This function should be called after #mdb_env_create() and before #mdb_env_open().
681 * It may be called at later times if no transactions are active in
682 * this process. Note that the library does not check for this condition,
683 * the caller must ensure it explicitly.
685 * If the mapsize is changed by another process, #mdb_txn_begin() will
686 * return #MDB_MAP_RESIZED. This function may be called with a size
687 * of zero to adopt the new size.
689 * Any attempt to set a size smaller than the space already consumed
690 * by the environment will be silently changed to the current size of the used space.
691 * @param[in] env An environment handle returned by #mdb_env_create()
692 * @param[in] size The size in bytes
693 * @return A non-zero error value on failure and 0 on success. Some possible
696 * <li>EINVAL - an invalid parameter was specified, or the environment has
697 * an active write transaction.
700 int mdb_env_set_mapsize(MDB_env *env, size_t size);
702 /** @brief Set the maximum number of threads/reader slots for the environment.
704 * This defines the number of slots in the lock table that is used to track readers in the
705 * the environment. The default is 126.
706 * Starting a read-only transaction normally ties a lock table slot to the
707 * current thread until the environment closes or the thread exits. If
708 * MDB_NOTLS is in use, #mdb_txn_begin() instead ties the slot to the
709 * MDB_txn object until it or the #MDB_env object is destroyed.
710 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
711 * @param[in] env An environment handle returned by #mdb_env_create()
712 * @param[in] readers The maximum number of reader lock table slots
713 * @return A non-zero error value on failure and 0 on success. Some possible
716 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
719 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
721 /** @brief Get the maximum number of threads/reader slots for the environment.
723 * @param[in] env An environment handle returned by #mdb_env_create()
724 * @param[out] readers Address of an integer to store the number of readers
725 * @return A non-zero error value on failure and 0 on success. Some possible
728 * <li>EINVAL - an invalid parameter was specified.
731 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
733 /** @brief Set the maximum number of named databases for the environment.
735 * This function is only needed if multiple databases will be used in the
736 * environment. Simpler applications that use the environment as a single
737 * unnamed database can ignore this option.
738 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
739 * @param[in] env An environment handle returned by #mdb_env_create()
740 * @param[in] dbs The maximum number of databases
741 * @return A non-zero error value on failure and 0 on success. Some possible
744 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
747 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
749 /** @brief Get the maximum size of a key for the environment.
751 * This is the compile-time constant #MDB_MAXKEYSIZE, default 511.
753 * @param[in] env An environment handle returned by #mdb_env_create()
754 * @return The maximum size of a key
756 int mdb_env_get_maxkeysize(MDB_env *env);
758 /** @brief Create a transaction for use with the environment.
760 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
761 * @note A transaction and its cursors must only be used by a single
762 * thread, and a thread may only have a single transaction at a time.
763 * If #MDB_NOTLS is in use, this does not apply to read-only transactions.
764 * @note Cursors may not span transactions.
765 * @param[in] env An environment handle returned by #mdb_env_create()
766 * @param[in] parent If this parameter is non-NULL, the new transaction
767 * will be a nested transaction, with the transaction indicated by \b parent
768 * as its parent. Transactions may be nested to any level. A parent
769 * transaction and its cursors may not issue any other operations than
770 * mdb_txn_commit and mdb_txn_abort while it has active child transactions.
771 * @param[in] flags Special options for this transaction. This parameter
772 * must be set to 0 or by bitwise OR'ing together one or more of the
773 * values described here.
776 * This transaction will not perform any write operations.
778 * @param[out] txn Address where the new #MDB_txn handle will be stored
779 * @return A non-zero error value on failure and 0 on success. Some possible
782 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
784 * <li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's
785 * mapsize and this environment's map must be resized as well.
786 * See #mdb_env_set_mapsize().
787 * <li>#MDB_READERS_FULL - a read-only transaction was requested and
788 * the reader lock table is full. See #mdb_env_set_maxreaders().
789 * <li>ENOMEM - out of memory.
792 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
794 /** @brief Returns the transaction's #MDB_env
796 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
798 MDB_env *mdb_txn_env(MDB_txn *txn);
800 /** @brief Commit all the operations of a transaction into the database.
802 * The transaction handle is freed. It and its cursors must not be used
803 * again after this call, except with #mdb_cursor_renew().
804 * @note Earlier documentation incorrectly said all cursors would be freed.
805 * Only write-transactions free cursors.
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>EINVAL - an invalid parameter was specified.
811 * <li>ENOSPC - no more disk space.
812 * <li>EIO - a low-level I/O error occurred while writing.
813 * <li>ENOMEM - out of memory.
816 int mdb_txn_commit(MDB_txn *txn);
818 /** @brief Abandon all the operations of the transaction instead of saving them.
820 * The transaction handle is freed. It and its cursors must not be used
821 * again after this call, except with #mdb_cursor_renew().
822 * @note Earlier documentation incorrectly said all cursors would be freed.
823 * Only write-transactions free cursors.
824 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
826 void mdb_txn_abort(MDB_txn *txn);
828 /** @brief Reset a read-only transaction.
830 * Abort the transaction like #mdb_txn_abort(), but keep the transaction
831 * handle. #mdb_txn_renew() may reuse the handle. This saves allocation
832 * overhead if the process will start a new read-only transaction soon,
833 * and also locking overhead if #MDB_NOTLS is in use. The reader table
834 * lock is released, but the table slot stays tied to its thread or
835 * #MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free
836 * its lock table slot if MDB_NOTLS is in use.
837 * Cursors opened within the transaction must not be used
838 * again after this call, except with #mdb_cursor_renew().
839 * Reader locks generally don't interfere with writers, but they keep old
840 * versions of database pages allocated. Thus they prevent the old pages
841 * from being reused when writers commit new data, and so under heavy load
842 * the database size may grow much more rapidly than otherwise.
843 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
845 void mdb_txn_reset(MDB_txn *txn);
847 /** @brief Renew a read-only transaction.
849 * This acquires a new reader lock for a transaction handle that had been
850 * released by #mdb_txn_reset(). It must be called before a reset transaction
852 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
853 * @return A non-zero error value on failure and 0 on success. Some possible
856 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
858 * <li>EINVAL - an invalid parameter was specified.
861 int mdb_txn_renew(MDB_txn *txn);
863 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
864 #define mdb_open(txn,name,flags,dbi) mdb_dbi_open(txn,name,flags,dbi)
865 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
866 #define mdb_close(env,dbi) mdb_dbi_close(env,dbi)
868 /** @brief Open a database in the environment.
870 * A database handle denotes the name and parameters of a database,
871 * independently of whether such a database exists.
872 * The database handle may be discarded by calling #mdb_dbi_close().
873 * The old database handle is returned if the database was already open.
874 * The handle must only be closed once.
875 * The database handle will be private to the current transaction until
876 * the transaction is successfully committed. If the transaction is
877 * aborted the handle will be closed automatically.
878 * After a successful commit the
879 * handle will reside in the shared environment, and may be used
880 * by other transactions. This function must not be called from
881 * multiple concurrent transactions. A transaction that uses this function
882 * must finish (either commit or abort) before any other transaction may
885 * To use named databases (with name != NULL), #mdb_env_set_maxdbs()
886 * must be called before opening the environment.
887 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
888 * @param[in] name The name of the database to open. If only a single
889 * database is needed in the environment, this value may be NULL.
890 * @param[in] flags Special options for this database. This parameter
891 * must be set to 0 or by bitwise OR'ing together one or more of the
892 * values described here.
894 * <li>#MDB_REVERSEKEY
895 * Keys are strings to be compared in reverse order, from the end
896 * of the strings to the beginning. By default, Keys are treated as strings and
897 * compared from beginning to end.
899 * Duplicate keys may be used in the database. (Or, from another perspective,
900 * keys may have multiple data items, stored in sorted order.) By default
901 * keys must be unique and may have only a single data item.
902 * <li>#MDB_INTEGERKEY
903 * Keys are binary integers in native byte order. Setting this option
904 * requires all keys to be the same size, typically sizeof(int)
907 * This flag may only be used in combination with #MDB_DUPSORT. This option
908 * tells the library that the data items for this database are all the same
909 * size, which allows further optimizations in storage and retrieval. When
910 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
911 * cursor operations may be used to retrieve multiple items at once.
912 * <li>#MDB_INTEGERDUP
913 * This option specifies that duplicate data items are also integers, and
914 * should be sorted as such.
915 * <li>#MDB_REVERSEDUP
916 * This option specifies that duplicate data items should be compared as
917 * strings in reverse order.
919 * Create the named database if it doesn't exist. This option is not
920 * allowed in a read-only transaction or a read-only environment.
922 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
923 * @return A non-zero error value on failure and 0 on success. Some possible
926 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
927 * and #MDB_CREATE was not specified.
928 * <li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs().
931 int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
933 /** @brief Retrieve statistics for a database.
935 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
936 * @param[in] dbi A database handle returned by #mdb_dbi_open()
937 * @param[out] stat The address of an #MDB_stat structure
938 * where the statistics will be copied
939 * @return A non-zero error value on failure and 0 on success. Some possible
942 * <li>EINVAL - an invalid parameter was specified.
945 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
947 /** @brief Retrieve the DB flags for a database handle.
949 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
950 * @param[in] dbi A database handle returned by #mdb_dbi_open()
951 * @param[out] flags Address where the flags will be returned.
952 * @return A non-zero error value on failure and 0 on success.
954 int mdb_dbi_flags(MDB_txn *txn, MDB_dbi dbi, unsigned int *flags);
956 /** @brief Close a database handle.
958 * This call is not mutex protected. Handles should only be closed by
959 * a single thread, and only if no other threads are going to reference
960 * the database handle or one of its cursors any further. Do not close
961 * a handle if an existing transaction has modified its database.
962 * @param[in] env An environment handle returned by #mdb_env_create()
963 * @param[in] dbi A database handle returned by #mdb_dbi_open()
965 void mdb_dbi_close(MDB_env *env, MDB_dbi dbi);
967 /** @brief Empty or delete+close a database.
969 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
970 * @param[in] dbi A database handle returned by #mdb_dbi_open()
971 * @param[in] del 0 to empty the DB, 1 to delete it from the
972 * environment and close the DB handle.
973 * @return A non-zero error value on failure and 0 on success.
975 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
977 /** @brief Set a custom key comparison function for a database.
979 * The comparison function is called whenever it is necessary to compare a
980 * key specified by the application with a key currently stored in the database.
981 * If no comparison function is specified, and no special key flags were specified
982 * with #mdb_dbi_open(), the keys are compared lexically, with shorter keys collating
983 * before longer keys.
984 * @warning This function must be called before any data access functions are used,
985 * otherwise data corruption may occur. The same comparison function must be used by every
986 * program accessing the database, every time the database is used.
987 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
988 * @param[in] dbi A database handle returned by #mdb_dbi_open()
989 * @param[in] cmp A #MDB_cmp_func function
990 * @return A non-zero error value on failure and 0 on success. Some possible
993 * <li>EINVAL - an invalid parameter was specified.
996 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
998 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
1000 * This comparison function is called whenever it is necessary to compare a data
1001 * item specified by the application with a data item currently stored in the database.
1002 * This function only takes effect if the database was opened with the #MDB_DUPSORT
1004 * If no comparison function is specified, and no special key flags were specified
1005 * with #mdb_dbi_open(), the data items are compared lexically, with shorter items collating
1006 * before longer items.
1007 * @warning This function must be called before any data access functions are used,
1008 * otherwise data corruption may occur. The same comparison function must be used by every
1009 * program accessing the database, every time the database is used.
1010 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1011 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1012 * @param[in] cmp A #MDB_cmp_func function
1013 * @return A non-zero error value on failure and 0 on success. Some possible
1016 * <li>EINVAL - an invalid parameter was specified.
1019 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
1021 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
1023 * @todo The relocation function is called whenever it is necessary to move the data
1024 * of an item to a different position in the database (e.g. through tree
1025 * balancing operations, shifts as a result of adds or deletes, etc.). It is
1026 * intended to allow address/position-dependent data items to be stored in
1027 * a database in an environment opened with the #MDB_FIXEDMAP option.
1028 * Currently the relocation feature is unimplemented and setting
1029 * this function has no effect.
1030 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1031 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1032 * @param[in] rel A #MDB_rel_func function
1033 * @return A non-zero error value on failure and 0 on success. Some possible
1036 * <li>EINVAL - an invalid parameter was specified.
1039 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
1041 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
1043 * See #mdb_set_relfunc and #MDB_rel_func for more details.
1044 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1045 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1046 * @param[in] ctx An arbitrary pointer for whatever the application needs.
1047 * It will be passed to the callback function set by #mdb_set_relfunc
1048 * as its \b relctx parameter whenever the callback is invoked.
1049 * @return A non-zero error value on failure and 0 on success. Some possible
1052 * <li>EINVAL - an invalid parameter was specified.
1055 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
1057 /** @brief Get items from a database.
1059 * This function retrieves key/data pairs from the database. The address
1060 * and length of the data associated with the specified \b key are returned
1061 * in the structure to which \b data refers.
1062 * If the database supports duplicate keys (#MDB_DUPSORT) then the
1063 * first data item for the key will be returned. Retrieval of other
1064 * items requires the use of #mdb_cursor_get().
1066 * @note The memory pointed to by the returned values is owned by the
1067 * database. The caller need not dispose of the memory, and may not
1068 * modify it in any way. For values returned in a read-only transaction
1069 * any modification attempts will cause a SIGSEGV.
1070 * @note Values returned from the database are valid only until a
1071 * subsequent update operation, or the end of the transaction.
1072 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1073 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1074 * @param[in] key The key to search for in the database
1075 * @param[out] data The data corresponding to the key
1076 * @return A non-zero error value on failure and 0 on success. Some possible
1079 * <li>#MDB_NOTFOUND - the key was not in the database.
1080 * <li>EINVAL - an invalid parameter was specified.
1083 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1085 /** @brief Store items into a database.
1087 * This function stores key/data pairs in the database. The default behavior
1088 * is to enter the new key/data pair, replacing any previously existing key
1089 * if duplicates are disallowed, or adding a duplicate data item if
1090 * duplicates are allowed (#MDB_DUPSORT).
1091 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1092 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1093 * @param[in] key The key to store in the database
1094 * @param[in,out] data The data to store
1095 * @param[in] flags Special options for this operation. This parameter
1096 * must be set to 0 or by bitwise OR'ing together one or more of the
1097 * values described here.
1099 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1100 * already appear in the database. This flag may only be specified
1101 * if the database was opened with #MDB_DUPSORT. The function will
1102 * return #MDB_KEYEXIST if the key/data pair already appears in the
1104 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1105 * does not already appear in the database. The function will return
1106 * #MDB_KEYEXIST if the key already appears in the database, even if
1107 * the database supports duplicates (#MDB_DUPSORT). The \b data
1108 * parameter will be set to point to the existing item.
1109 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1110 * don't copy the given data. Instead, return a pointer to the
1111 * reserved space, which the caller can fill in later - before
1112 * the next update operation or the transaction ends. This saves
1113 * an extra memcpy if the data is being generated later.
1114 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1115 * database. No key comparisons are performed. This option allows
1116 * fast bulk loading when keys are already known to be in the
1117 * correct order. Loading unsorted keys with this flag will cause
1119 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1121 * @return A non-zero error value on failure and 0 on success. Some possible
1124 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1125 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1126 * <li>EACCES - an attempt was made to write in a read-only transaction.
1127 * <li>EINVAL - an invalid parameter was specified.
1130 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
1131 unsigned int flags);
1133 /** @brief Delete items from a database.
1135 * This function removes key/data pairs from the database.
1136 * If the database does not support sorted duplicate data items
1137 * (#MDB_DUPSORT) the data parameter is ignored.
1138 * If the database supports sorted duplicates and the data parameter
1139 * is NULL, all of the duplicate data items for the key will be
1140 * deleted. Otherwise, if the data parameter is non-NULL
1141 * only the matching data item will be deleted.
1142 * This function will return #MDB_NOTFOUND if the specified key/data
1143 * pair is not in the database.
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[in] key The key to delete from the database
1147 * @param[in] data The data to delete
1148 * @return A non-zero error value on failure and 0 on success. Some possible
1151 * <li>EACCES - an attempt was made to write in a read-only transaction.
1152 * <li>EINVAL - an invalid parameter was specified.
1155 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1157 /** @brief Create a cursor handle.
1159 * A cursor is associated with a specific transaction and database.
1160 * A cursor cannot be used when its database handle is closed. Nor
1161 * when its transaction has ended, except with #mdb_cursor_renew().
1162 * It can be discarded with #mdb_cursor_close().
1163 * A cursor in a write-transaction can be closed before its transaction
1164 * ends, and will otherwise be closed when its transaction ends.
1165 * A cursor in a read-only transaction must be closed explicitly, before
1166 * or after its transaction ends. It can be reused with
1167 * #mdb_cursor_renew() before finally closing it.
1168 * @note Earlier documentation said that cursors in every transaction
1169 * were closed when the transaction committed or aborted.
1170 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1171 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1172 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
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_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
1181 /** @brief Close a cursor handle.
1183 * The cursor handle will be freed and must not be used again after this call.
1184 * Its transaction must still be live if it is a write-transaction.
1185 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1187 void mdb_cursor_close(MDB_cursor *cursor);
1189 /** @brief Renew a cursor handle.
1191 * A cursor is associated with a specific transaction and database.
1192 * Cursors that are only used in read-only
1193 * transactions may be re-used, to avoid unnecessary malloc/free overhead.
1194 * The cursor may be associated with a new read-only transaction, and
1195 * referencing the same database handle as it was created with.
1196 * This may be done whether the previous transaction is live or dead.
1197 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1198 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1199 * @return A non-zero error value on failure and 0 on success. Some possible
1202 * <li>EINVAL - an invalid parameter was specified.
1205 int mdb_cursor_renew(MDB_txn *txn, MDB_cursor *cursor);
1207 /** @brief Return the cursor's transaction handle.
1209 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1211 MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
1213 /** @brief Return the cursor's database handle.
1215 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1217 MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor);
1219 /** @brief Retrieve by cursor.
1221 * This function retrieves key/data pairs from the database. The address and length
1222 * of the key are returned in the object to which \b key refers (except for the
1223 * case of the #MDB_SET option, in which the \b key object is unchanged), and
1224 * the address and length of the data are returned in the object to which \b data
1226 * See #mdb_get() for restrictions on using the output values.
1227 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1228 * @param[in,out] key The key for a retrieved item
1229 * @param[in,out] data The data of a retrieved item
1230 * @param[in] op A cursor operation #MDB_cursor_op
1231 * @return A non-zero error value on failure and 0 on success. Some possible
1234 * <li>#MDB_NOTFOUND - no matching key found.
1235 * <li>EINVAL - an invalid parameter was specified.
1238 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1241 /** @brief Store by cursor.
1243 * This function stores key/data pairs into the database.
1244 * If the function fails for any reason, the state of the cursor will be
1245 * unchanged. If the function succeeds and an item is inserted into the
1246 * database, the cursor is always positioned to refer to the newly inserted item.
1247 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1248 * @param[in] key The key operated on.
1249 * @param[in] data The data operated on.
1250 * @param[in] flags Options for this operation. This parameter
1251 * must be set to 0 or one of the values described here.
1253 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which
1254 * the cursor refers with the specified data item. The \b key
1255 * parameter is ignored.
1256 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1257 * already appear in the database. This flag may only be specified
1258 * if the database was opened with #MDB_DUPSORT. The function will
1259 * return #MDB_KEYEXIST if the key/data pair already appears in the
1261 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1262 * does not already appear in the database. The function will return
1263 * #MDB_KEYEXIST if the key already appears in the database, even if
1264 * the database supports duplicates (#MDB_DUPSORT).
1265 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1266 * don't copy the given data. Instead, return a pointer to the
1267 * reserved space, which the caller can fill in later. This saves
1268 * an extra memcpy if the data is being generated later.
1269 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1270 * database. No key comparisons are performed. This option allows
1271 * fast bulk loading when keys are already known to be in the
1272 * correct order. Loading unsorted keys with this flag will cause
1274 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1275 * <li>#MDB_MULTIPLE - store multiple contiguous data elements in a
1276 * single request. This flag may only be specified if the database
1277 * was opened with #MDB_DUPFIXED. The \b data argument must be an
1278 * array of two MDB_vals. The mv_size of the first MDB_val must be
1279 * the size of a single data element. The mv_data of the first MDB_val
1280 * must point to the beginning of the array of contiguous data elements.
1281 * The mv_size of the second MDB_val must be the count of the number
1282 * of data elements to store. On return this field will be set to
1283 * the count of the number of elements actually written. The mv_data
1284 * of the second MDB_val is unused.
1286 * @return A non-zero error value on failure and 0 on success. Some possible
1289 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1290 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1291 * <li>EACCES - an attempt was made to modify a read-only database.
1292 * <li>EINVAL - an invalid parameter was specified.
1295 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1296 unsigned int flags);
1298 /** @brief Delete current key/data pair
1300 * This function deletes the key/data pair to which the cursor refers.
1301 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1302 * @param[in] flags Options for this operation. This parameter
1303 * must be set to 0 or one of the values described here.
1305 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
1306 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
1308 * @return A non-zero error value on failure and 0 on success. Some possible
1311 * <li>EACCES - an attempt was made to modify a read-only database.
1312 * <li>EINVAL - an invalid parameter was specified.
1315 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
1317 /** @brief Return count of duplicates for current key.
1319 * This call is only valid on databases that support sorted duplicate
1320 * data items #MDB_DUPSORT.
1321 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1322 * @param[out] countp Address where the count will be stored
1323 * @return A non-zero error value on failure and 0 on success. Some possible
1326 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
1329 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
1331 /** @brief Compare two data items according to a particular database.
1333 * This returns a comparison as if the two data items were keys in the
1334 * specified database.
1335 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1336 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1337 * @param[in] a The first item to compare
1338 * @param[in] b The second item to compare
1339 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1341 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1343 /** @brief Compare two data items according to a particular database.
1345 * This returns a comparison as if the two items were data items of
1346 * the specified database. The database must have the #MDB_DUPSORT flag.
1347 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1348 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1349 * @param[in] a The first item to compare
1350 * @param[in] b The second item to compare
1351 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1353 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1355 /** @brief A callback function used to print a message from the library.
1357 * @param[in] msg The string to be printed.
1358 * @param[in] ctx An arbitrary context pointer for the callback.
1359 * @return < 0 on failure, 0 on success.
1361 typedef int (MDB_msg_func)(const char *msg, void *ctx);
1363 /** @brief Dump the entries in the reader lock table.
1365 * @param[in] env An environment handle returned by #mdb_env_create()
1366 * @param[in] func A #MDB_msg_func function
1367 * @param[in] ctx Anything the message function needs
1368 * @return < 0 on failure, 0 on success.
1370 int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx);
1372 /** @brief Check for stale entries in the reader lock table.
1374 * @param[in] env An environment handle returned by #mdb_env_create()
1375 * @param[out] dead Number of stale slots that were cleared
1376 * @return 0 on success, non-zero on failure.
1378 int mdb_reader_check(MDB_env *env, int *dead);
1384 #endif /* _LMDB_H_ */