2 * @brief Lightning memory-mapped database library
4 * @mainpage Lightning Memory-Mapped Database Manager (MDB)
6 * @section intro_sec Introduction
7 * MDB is a Btree-based database management library modeled loosely on the
8 * BerkeleyDB API, but much simplified. The entire database is exposed
9 * in a memory map, and all data fetches return data directly
10 * from the mapped memory, so no malloc's or memcpy's occur during
11 * data fetches. As such, the library is extremely simple because it
12 * requires no page caching layer of its own, and it is extremely high
13 * performance and memory-efficient. It is also fully transactional with
14 * full ACID semantics, and when the memory map is read-only, the
15 * database integrity cannot be corrupted by stray pointer writes from
18 * The library is fully thread-aware and supports concurrent read/write
19 * access from multiple processes and threads. Data pages use a copy-on-
20 * write strategy so no active data pages are ever overwritten, which
21 * also provides resistance to corruption and eliminates the need of any
22 * special recovery procedures after a system crash. Writes are fully
23 * serialized; only one write transaction may be active at a time, which
24 * guarantees that writers can never deadlock. The database structure is
25 * multi-versioned so readers run with no locks; writers cannot block
26 * readers, and readers don't block writers.
28 * Unlike other well-known database mechanisms which use either write-ahead
29 * transaction logs or append-only data writes, MDB requires no maintenance
30 * during operation. Both write-ahead loggers and append-only databases
31 * require periodic checkpointing and/or compaction of their log or database
32 * files otherwise they grow without bound. MDB tracks free pages within
33 * the database and re-uses them for new write operations, so the database
34 * size does not grow without bound in normal use.
36 * The memory map can be used as a read-only or read-write map. It is
37 * read-only by default as this provides total immunity to corruption.
38 * Using read-write mode offers much higher write performance, but adds
39 * the possibility for stray application writes thru pointers to silently
40 * corrupt the database. Of course if your application code is known to
41 * be bug-free (...) then this is not an issue.
43 * @section caveats_sec Caveats
44 * Troubleshooting the lock file, plus semaphores on BSD systems:
46 * - A broken lockfile can cause sync issues.
47 * Stale reader transactions left behind by an aborted program
48 * cause further writes to grow the database quickly, and
49 * stale locks can block further operation.
51 * Fix: Terminate all programs using the database, or make
52 * them close it. Next database user will reset the lockfile.
54 * - On BSD systems or others configured with MDB_USE_POSIX_SEM,
55 * startup can fail due to semaphores owned by another userid.
57 * Fix: Open and close the database as the user which owns the
58 * semaphores (likely last user) or as root, while no other
59 * process is using the database.
61 * Restrictions/caveats (in addition to those listed for some functions):
63 * - Only the database owner should normally use the database on
64 * BSD systems or when otherwise configured with MDB_USE_POSIX_SEM.
65 * Multiple users can cause startup to fail later, as noted above.
67 * - A thread can only use one transaction at a time, plus any child
68 * transactions. Each transaction belongs to one thread. See below.
69 * The #MDB_NOTLS flag changes this for read-only transactions.
71 * - Use an MDB_env* in the process which opened it, without fork()ing.
73 * - Do not have open an MDB database twice in the same process at
74 * the same time. Not even from a plain open() call - close()ing it
75 * breaks flock() advisory locking.
77 * - Avoid long-lived transactions. Read transactions prevent
78 * reuse of pages freed by newer write transactions, thus the
79 * database can grow quickly. Write transactions prevent
80 * other write transactions, since writes are serialized.
82 * - Avoid suspending a process with active transactions. These
83 * would then be "long-lived" as above. Also read transactions
84 * suspended when writers commit could sometimes see wrong data.
86 * ...when several processes can use a database concurrently:
88 * - Avoid aborting a process with an active transaction.
89 * The transaction becomes "long-lived" as above until the lockfile
90 * is reset, since the process may not remove it from the lockfile.
92 * - If you do that anyway, close the environment once in a while,
93 * so the lockfile can get reset.
95 * - Do not use MDB databases on remote filesystems, even between
96 * processes on the same host. This breaks flock() on some OSes,
97 * possibly memory map sync, and certainly sync between programs
100 * - Opening a database can fail if another process is opening or
101 * closing it at exactly the same time.
103 * @author Howard Chu, Symas Corporation.
105 * @copyright Copyright 2011-2013 Howard Chu, Symas Corp. All rights reserved.
107 * Redistribution and use in source and binary forms, with or without
108 * modification, are permitted only as authorized by the OpenLDAP
111 * A copy of this license is available in the file LICENSE in the
112 * top-level directory of the distribution or, alternatively, at
113 * <http://www.OpenLDAP.org/license.html>.
116 * This code is derived from btree.c written by Martin Hedenfalk.
118 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
120 * Permission to use, copy, modify, and distribute this software for any
121 * purpose with or without fee is hereby granted, provided that the above
122 * copyright notice and this permission notice appear in all copies.
124 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
125 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
126 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
127 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
128 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
129 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
130 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
135 #include <sys/types.h>
142 typedef int mdb_mode_t;
144 typedef mode_t mdb_mode_t;
147 /** @defgroup mdb MDB API
149 * @brief OpenLDAP Lightning Memory-Mapped Database Manager
151 /** @defgroup Version Version Macros
154 /** Library major version */
155 #define MDB_VERSION_MAJOR 0
156 /** Library minor version */
157 #define MDB_VERSION_MINOR 9
158 /** Library patch version */
159 #define MDB_VERSION_PATCH 6
161 /** Combine args a,b,c into a single integer for easy version comparisons */
162 #define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
164 /** The full library version as a single integer */
165 #define MDB_VERSION_FULL \
166 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
168 /** The release date of this library version */
169 #define MDB_VERSION_DATE "January 10, 2013"
171 /** A stringifier for the version info */
172 #define MDB_VERSTR(a,b,c,d) "MDB " #a "." #b "." #c ": (" d ")"
174 /** A helper for the stringifier macro */
175 #define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d)
177 /** The full library version as a C string */
178 #define MDB_VERSION_STRING \
179 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
182 /** @brief Opaque structure for a database environment.
184 * A DB environment supports multiple databases, all residing in the same
187 typedef struct MDB_env MDB_env;
189 /** @brief Opaque structure for a transaction handle.
191 * All database operations require a transaction handle. Transactions may be
192 * read-only or read-write.
194 typedef struct MDB_txn MDB_txn;
196 /** @brief A handle for an individual database in the DB environment. */
197 typedef unsigned int MDB_dbi;
199 /** @brief Opaque structure for navigating through a database */
200 typedef struct MDB_cursor MDB_cursor;
202 /** @brief Generic structure used for passing keys and data in and out
205 * Key sizes must be between 1 and the liblmdb build-time constant
206 * #MDB_MAXKEYSIZE inclusive. This currently defaults to 511. The
207 * same applies to data sizes in databases with the #MDB_DUPSORT flag.
208 * Other data items can in theory be from 0 to 0xffffffff bytes long.
210 * Values returned from the database are valid only until a subsequent
211 * update operation, or the end of the transaction.
213 typedef struct MDB_val {
214 size_t mv_size; /**< size of the data item */
215 void *mv_data; /**< address of the data item */
218 /** @brief A callback function used to compare two keys in a database */
219 typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
221 /** @brief A callback function used to relocate a position-dependent data item
222 * in a fixed-address database.
224 * The \b newptr gives the item's desired address in
225 * the memory map, and \b oldptr gives its previous address. The item's actual
226 * data resides at the address in \b item. This callback is expected to walk
227 * through the fields of the record in \b item and modify any
228 * values based at the \b oldptr address to be relative to the \b newptr address.
229 * @param[in,out] item The item that is to be relocated.
230 * @param[in] oldptr The previous address.
231 * @param[in] newptr The new address to relocate to.
232 * @param[in] relctx An application-provided context, set by #mdb_set_relctx().
233 * @todo This feature is currently unimplemented.
235 typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
237 /** @defgroup mdb_env Environment Flags
239 * Values do not overlap Database Flags.
242 /** mmap at a fixed address (experimental) */
243 #define MDB_FIXEDMAP 0x01
244 /** no environment directory */
245 #define MDB_NOSUBDIR 0x4000
246 /** don't fsync after commit */
247 #define MDB_NOSYNC 0x10000
249 #define MDB_RDONLY 0x20000
250 /** don't fsync metapage after commit */
251 #define MDB_NOMETASYNC 0x40000
252 /** use writable mmap */
253 #define MDB_WRITEMAP 0x80000
254 /** use asynchronous msync when MDB_WRITEMAP is used */
255 #define MDB_MAPASYNC 0x100000
256 /** tie reader locktable slots to #MDB_txn objects instead of to threads */
257 #define MDB_NOTLS 0x200000
260 /** @defgroup mdb_dbi_open Database Flags
262 * Values do not overlap Environment Flags.
265 /** use reverse string keys */
266 #define MDB_REVERSEKEY 0x02
267 /** use sorted duplicates */
268 #define MDB_DUPSORT 0x04
269 /** numeric keys in native byte order.
270 * The keys must all be of the same size. */
271 #define MDB_INTEGERKEY 0x08
272 /** with #MDB_DUPSORT, sorted dup items have fixed size */
273 #define MDB_DUPFIXED 0x10
274 /** with #MDB_DUPSORT, dups are numeric in native byte order */
275 #define MDB_INTEGERDUP 0x20
276 /** with #MDB_DUPSORT, use reverse string dups */
277 #define MDB_REVERSEDUP 0x40
278 /** create DB if not already existing */
279 #define MDB_CREATE 0x40000
282 /** @defgroup mdb_put Write Flags
285 /** For put: Don't write if the key already exists. */
286 #define MDB_NOOVERWRITE 0x10
287 /** Only for #MDB_DUPSORT<br>
288 * For put: don't write if the key and data pair already exist.<br>
289 * For mdb_cursor_del: remove all duplicate data items.
291 #define MDB_NODUPDATA 0x20
292 /** For mdb_cursor_put: overwrite the current key/data pair */
293 #define MDB_CURRENT 0x40
294 /** For put: Just reserve space for data, don't copy it. Return a
295 * pointer to the reserved space.
297 #define MDB_RESERVE 0x10000
298 /** Data is being appended, don't split full pages. */
299 #define MDB_APPEND 0x20000
300 /** Duplicate data is being appended, don't split full pages. */
301 #define MDB_APPENDDUP 0x40000
302 /** Store multiple data items in one call. */
303 #define MDB_MULTIPLE 0x80000
306 /** @brief Cursor Get operations.
308 * This is the set of all operations for retrieving data
311 typedef enum MDB_cursor_op {
312 MDB_FIRST, /**< Position at first key/data item */
313 MDB_FIRST_DUP, /**< Position at first data item of current key.
314 Only for #MDB_DUPSORT */
315 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
316 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
317 MDB_GET_CURRENT, /**< Return key/data at current cursor position */
318 MDB_GET_MULTIPLE, /**< Return all the duplicate data items at the current
319 cursor position. Only for #MDB_DUPFIXED */
320 MDB_LAST, /**< Position at last key/data item */
321 MDB_LAST_DUP, /**< Position at last data item of current key.
322 Only for #MDB_DUPSORT */
323 MDB_NEXT, /**< Position at next data item */
324 MDB_NEXT_DUP, /**< Position at next data item of current key.
325 Only for #MDB_DUPSORT */
326 MDB_NEXT_MULTIPLE, /**< Return all duplicate data items at the next
327 cursor position. Only for #MDB_DUPFIXED */
328 MDB_NEXT_NODUP, /**< Position at first data item of next key */
329 MDB_PREV, /**< Position at previous data item */
330 MDB_PREV_DUP, /**< Position at previous data item of current key.
331 Only for #MDB_DUPSORT */
332 MDB_PREV_NODUP, /**< Position at last data item of previous key */
333 MDB_SET, /**< Position at specified key */
334 MDB_SET_KEY, /**< Position at specified key, return key + data */
335 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
338 /** @defgroup errors Return Codes
340 * BerkeleyDB uses -30800 to -30999, we'll go under them
343 /** Successful result */
344 #define MDB_SUCCESS 0
345 /** key/data pair already exists */
346 #define MDB_KEYEXIST (-30799)
347 /** key/data pair not found (EOF) */
348 #define MDB_NOTFOUND (-30798)
349 /** Requested page not found - this usually indicates corruption */
350 #define MDB_PAGE_NOTFOUND (-30797)
351 /** Located page was wrong type */
352 #define MDB_CORRUPTED (-30796)
353 /** Update of meta page failed, probably I/O error */
354 #define MDB_PANIC (-30795)
355 /** Environment version mismatch */
356 #define MDB_VERSION_MISMATCH (-30794)
357 /** File is not a valid MDB file */
358 #define MDB_INVALID (-30793)
359 /** Environment mapsize reached */
360 #define MDB_MAP_FULL (-30792)
361 /** Environment maxdbs reached */
362 #define MDB_DBS_FULL (-30791)
363 /** Environment maxreaders reached */
364 #define MDB_READERS_FULL (-30790)
365 /** Too many TLS keys in use - Windows only */
366 #define MDB_TLS_FULL (-30789)
367 /** Txn has too many dirty pages */
368 #define MDB_TXN_FULL (-30788)
369 /** Cursor stack too deep - internal error */
370 #define MDB_CURSOR_FULL (-30787)
371 /** Page has not enough space - internal error */
372 #define MDB_PAGE_FULL (-30786)
373 /** Database contents grew beyond environment mapsize */
374 #define MDB_MAP_RESIZED (-30785)
375 /** Database flags changed or would change */
376 #define MDB_INCOMPATIBLE (-30784)
377 /** Invalid reuse of reader locktable slot */
378 #define MDB_BAD_RSLOT (-30783)
379 #define MDB_LAST_ERRCODE MDB_BAD_RSLOT
382 /** @brief Statistics for a database in the environment */
383 typedef struct MDB_stat {
384 unsigned int ms_psize; /**< Size of a database page.
385 This is currently the same for all databases. */
386 unsigned int ms_depth; /**< Depth (height) of the B-tree */
387 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
388 size_t ms_leaf_pages; /**< Number of leaf pages */
389 size_t ms_overflow_pages; /**< Number of overflow pages */
390 size_t ms_entries; /**< Number of data items */
393 /** @brief Information about the environment */
394 typedef struct MDB_envinfo {
395 void *me_mapaddr; /**< Address of map, if fixed */
396 size_t me_mapsize; /**< Size of the data memory map */
397 size_t me_last_pgno; /**< ID of the last used page */
398 size_t me_last_txnid; /**< ID of the last committed transaction */
399 unsigned int me_maxreaders; /**< max reader slots in the environment */
400 unsigned int me_numreaders; /**< max reader slots used in the environment */
403 /** @brief Return the mdb library version information.
405 * @param[out] major if non-NULL, the library major version number is copied here
406 * @param[out] minor if non-NULL, the library minor version number is copied here
407 * @param[out] patch if non-NULL, the library patch version number is copied here
408 * @retval "version string" The library version as a string
410 char *mdb_version(int *major, int *minor, int *patch);
412 /** @brief Return a string describing a given error code.
414 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
415 * function. If the error code is greater than or equal to 0, then the string
416 * returned by the system function strerror(3) is returned. If the error code
417 * is less than 0, an error string corresponding to the MDB library error is
418 * returned. See @ref errors for a list of MDB-specific error codes.
419 * @param[in] err The error code
420 * @retval "error message" The description of the error
422 char *mdb_strerror(int err);
424 /** @brief Create an MDB environment handle.
426 * This function allocates memory for a #MDB_env structure. To release
427 * the allocated memory and discard the handle, call #mdb_env_close().
428 * Before the handle may be used, it must be opened using #mdb_env_open().
429 * Various other options may also need to be set before opening the handle,
430 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
431 * depending on usage requirements.
432 * @param[out] env The address where the new handle will be stored
433 * @return A non-zero error value on failure and 0 on success.
435 int mdb_env_create(MDB_env **env);
437 /** @brief Open an environment handle.
439 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
440 * @param[in] env An environment handle returned by #mdb_env_create()
441 * @param[in] path The directory in which the database files reside. This
442 * directory must already exist and be writable.
443 * @param[in] flags Special options for this environment. This parameter
444 * must be set to 0 or by bitwise OR'ing together one or more of the
445 * values described here.
446 * Flags set by mdb_env_set_flags() are also used.
449 * use a fixed address for the mmap region. This flag must be specified
450 * when creating the environment, and is stored persistently in the environment.
451 * If successful, the memory map will always reside at the same virtual address
452 * and pointers used to reference data items in the database will be constant
453 * across multiple invocations. This option may not always work, depending on
454 * how the operating system has allocated memory to shared libraries and other uses.
455 * The feature is highly experimental.
457 * By default, MDB creates its environment in a directory whose
458 * pathname is given in \b path, and creates its data and lock files
459 * under that directory. With this option, \b path is used as-is for
460 * the database main data file. The database lock file is the \b path
461 * with "-lock" appended.
463 * Open the environment in read-only mode. No write operations will be
464 * allowed. MDB will still modify the lock file - except on read-only
465 * filesystems, where MDB does not use locks.
467 * Use a writeable memory map unless MDB_RDONLY is set. This is faster
468 * and uses fewer mallocs, but loses protection from application bugs
469 * like wild pointer writes and other bad updates into the database.
470 * Incompatible with nested transactions.
471 * <li>#MDB_NOMETASYNC
472 * Flush system buffers to disk only once per transaction, omit the
473 * metadata flush. Defer that until the system flushes files to disk,
474 * or next non-MDB_RDONLY commit or #mdb_env_sync(). This optimization
475 * maintains database integrity, but a system crash may undo the last
476 * committed transaction. I.e. it preserves the ACI (atomicity,
477 * consistency, isolation) but not D (durability) database property.
478 * This flag may be changed at any time using #mdb_env_set_flags().
480 * Don't flush system buffers to disk when committing a transaction.
481 * This optimization means a system crash can corrupt the database or
482 * lose the last transactions if buffers are not yet flushed to disk.
483 * The risk is governed by how often the system flushes dirty buffers
484 * to disk and how often #mdb_env_sync() is called. However, if the
485 * filesystem preserves write order and the #MDB_WRITEMAP flag is not
486 * used, transactions exhibit ACI (atomicity, consistency, isolation)
487 * properties and only lose D (durability). I.e. database integrity
488 * is maintained, but a system crash may undo the final transactions.
489 * Note that (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no
490 * hint for when to write transactions to disk, unless #mdb_env_sync()
491 * is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable.
492 * This flag may be changed at any time using #mdb_env_set_flags().
494 * When using #MDB_WRITEMAP, use asynchronous flushes to disk.
495 * As with #MDB_NOSYNC, a system crash can then corrupt the
496 * database or lose the last transactions. Calling #mdb_env_sync()
497 * ensures on-disk database integrity until next commit.
498 * This flag may be changed at any time using #mdb_env_set_flags().
500 * Don't use Thread-Local Storage. Tie reader locktable slots to
501 * #MDB_txn objects instead of to threads. I.e. #mdb_txn_reset() keeps
502 * the slot reseved for the #MDB_txn object. A thread may use parallel
503 * read-only transactions. A read-only transaction may span threads if
504 * the user synchronizes its use. Applications that multiplex many
505 * user threads over individual OS threads need this option. Such an
506 * application must also serialize the write transactions in an OS
507 * thread, since MDB's write locking is unaware of the user threads.
509 * @param[in] mode The UNIX permissions to set on created files. This parameter
510 * is ignored on Windows.
511 * @return A non-zero error value on failure and 0 on success. Some possible
514 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
515 * version that created the database environment.
516 * <li>#MDB_INVALID - the environment file headers are corrupted.
517 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
518 * <li>EACCES - the user didn't have permission to access the environment files.
519 * <li>EAGAIN - the environment was locked by another process.
522 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode);
524 /** @brief Copy an MDB environment to the specified path.
526 * This function may be used to make a backup of an existing environment.
527 * @param[in] env An environment handle returned by #mdb_env_create(). It
528 * must have already been opened successfully.
529 * @param[in] path The directory in which the copy will reside. This
530 * directory must already exist and be writable but must otherwise be
532 * @return A non-zero error value on failure and 0 on success.
534 int mdb_env_copy(MDB_env *env, const char *path);
536 /** @brief Return statistics about the MDB environment.
538 * @param[in] env An environment handle returned by #mdb_env_create()
539 * @param[out] stat The address of an #MDB_stat structure
540 * where the statistics will be copied
542 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
544 /** @brief Return information about the MDB environment.
546 * @param[in] env An environment handle returned by #mdb_env_create()
547 * @param[out] stat The address of an #MDB_envinfo structure
548 * where the information will be copied
550 int mdb_env_info(MDB_env *env, MDB_envinfo *stat);
552 /** @brief Flush the data buffers to disk.
554 * Data is always written to disk when #mdb_txn_commit() is called,
555 * but the operating system may keep it buffered. MDB always flushes
556 * the OS buffers upon commit as well, unless the environment was
557 * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC.
558 * @param[in] env An environment handle returned by #mdb_env_create()
559 * @param[in] force If non-zero, force a synchronous flush. Otherwise
560 * if the environment has the #MDB_NOSYNC flag set the flushes
561 * will be omitted, and with #MDB_MAPASYNC they will be asynchronous.
562 * @return A non-zero error value on failure and 0 on success. Some possible
565 * <li>EINVAL - an invalid parameter was specified.
566 * <li>EIO - an error occurred during synchronization.
569 int mdb_env_sync(MDB_env *env, int force);
571 /** @brief Close the environment and release the memory map.
573 * Only a single thread may call this function. All transactions, databases,
574 * and cursors must already be closed before calling this function. Attempts to
575 * use any such handles after calling this function will cause a SIGSEGV.
576 * The environment handle will be freed and must not be used again after this call.
577 * @param[in] env An environment handle returned by #mdb_env_create()
579 void mdb_env_close(MDB_env *env);
581 /** @brief Set environment flags.
583 * This may be used to set some flags in addition to those from
584 * #mdb_env_open(), or to unset these flags.
585 * @param[in] env An environment handle returned by #mdb_env_create()
586 * @param[in] flags The flags to change, bitwise OR'ed together
587 * @param[in] onoff A non-zero value sets the flags, zero clears them.
588 * @return A non-zero error value on failure and 0 on success. Some possible
591 * <li>EINVAL - an invalid parameter was specified.
594 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
596 /** @brief Get environment flags.
598 * @param[in] env An environment handle returned by #mdb_env_create()
599 * @param[out] flags The address of an integer to store the flags
600 * @return A non-zero error value on failure and 0 on success. Some possible
603 * <li>EINVAL - an invalid parameter was specified.
606 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
608 /** @brief Return the path that was used in #mdb_env_open().
610 * @param[in] env An environment handle returned by #mdb_env_create()
611 * @param[out] path Address of a string pointer to contain the path. This
612 * is the actual string in the environment, not a copy. It should not be
613 * altered in any way.
614 * @return A non-zero error value on failure and 0 on success. Some possible
617 * <li>EINVAL - an invalid parameter was specified.
620 int mdb_env_get_path(MDB_env *env, const char **path);
622 /** @brief Set the size of the memory map to use for this environment.
624 * The size should be a multiple of the OS page size. The default is
625 * 10485760 bytes. The size of the memory map is also the maximum size
626 * of the database. The value should be chosen as large as possible,
627 * to accommodate future growth of the database.
628 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
629 * The size may be changed by closing and reopening the environment.
630 * Any attempt to set a size smaller than the space already consumed
631 * by the environment will be silently changed to the current size of the used space.
632 * @param[in] env An environment handle returned by #mdb_env_create()
633 * @param[in] size The size in bytes
634 * @return A non-zero error value on failure and 0 on success. Some possible
637 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
640 int mdb_env_set_mapsize(MDB_env *env, size_t size);
642 /** @brief Set the maximum number of threads/reader slots for the environment.
644 * This defines the number of slots in the lock table that is used to track readers in the
645 * the environment. The default is 126.
646 * Starting a read-only transaction normally ties a lock table slot to the
647 * current thread until the environment closes or the thread exits. If
648 * MDB_NOTLS is in use, #mdb_txn_begin() instead ties the slot to the
649 * MDB_txn object until it or the #MDB_env object is destroyed.
650 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
651 * @param[in] env An environment handle returned by #mdb_env_create()
652 * @param[in] readers The maximum number of reader lock table slots
653 * @return A non-zero error value on failure and 0 on success. Some possible
656 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
659 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
661 /** @brief Get the maximum number of threads/reader slots for the environment.
663 * @param[in] env An environment handle returned by #mdb_env_create()
664 * @param[out] readers Address of an integer to store the number of readers
665 * @return A non-zero error value on failure and 0 on success. Some possible
668 * <li>EINVAL - an invalid parameter was specified.
671 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
673 /** @brief Set the maximum number of named databases for the environment.
675 * This function is only needed if multiple databases will be used in the
676 * environment. Simpler applications that use the environment as a single
677 * unnamed database can ignore this option.
678 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
679 * @param[in] env An environment handle returned by #mdb_env_create()
680 * @param[in] dbs The maximum number of databases
681 * @return A non-zero error value on failure and 0 on success. Some possible
684 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
687 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
689 /** @brief Create a transaction for use with the environment.
691 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
692 * @note A transaction and its cursors must only be used by a single
693 * thread, and a thread may only have a single transaction at a time.
694 * If #MDB_NOTLS is in use, this does not apply to read-only transactions.
695 * @note Cursors may not span transactions.
696 * @param[in] env An environment handle returned by #mdb_env_create()
697 * @param[in] parent If this parameter is non-NULL, the new transaction
698 * will be a nested transaction, with the transaction indicated by \b parent
699 * as its parent. Transactions may be nested to any level. A parent
700 * transaction may not issue any other operations besides mdb_txn_begin,
701 * mdb_txn_abort, or mdb_txn_commit while it has active child transactions.
702 * @param[in] flags Special options for this transaction. This parameter
703 * must be set to 0 or by bitwise OR'ing together one or more of the
704 * values described here.
707 * This transaction will not perform any write operations.
709 * @param[out] txn Address where the new #MDB_txn handle will be stored
710 * @return A non-zero error value on failure and 0 on success. Some possible
713 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
715 * <li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's
716 * mapsize and the environment must be shut down.
717 * <li>#MDB_READERS_FULL - a read-only transaction was requested and
718 * the reader lock table is full. See #mdb_env_set_maxreaders().
719 * <li>ENOMEM - out of memory.
722 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
724 /** @brief Commit all the operations of a transaction into the database.
726 * The transaction handle is freed. It and its cursors must not be used
727 * again after this call, except with #mdb_cursor_renew().
728 * @note Earlier documentation incorrectly said all cursors would be freed.
729 * Only write-transactions free cursors.
730 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
731 * @return A non-zero error value on failure and 0 on success. Some possible
734 * <li>EINVAL - an invalid parameter was specified.
735 * <li>ENOSPC - no more disk space.
736 * <li>EIO - a low-level I/O error occurred while writing.
737 * <li>ENOMEM - out of memory.
740 int mdb_txn_commit(MDB_txn *txn);
742 /** @brief Abandon all the operations of the transaction instead of saving them.
744 * The transaction handle is freed. It and its cursors must not be used
745 * again after this call, except with #mdb_cursor_renew().
746 * @note Earlier documentation incorrectly said all cursors would be freed.
747 * Only write-transactions free cursors.
748 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
750 void mdb_txn_abort(MDB_txn *txn);
752 /** @brief Reset a read-only transaction.
754 * Abort the transaction like #mdb_txn_abort(), but keep the transaction
755 * handle. #mdb_txn_renew() may reuse the handle. This saves allocation
756 * overhead if the process will start a new read-only transaction soon,
757 * and also locking overhead if #MDB_NOTLS is in use. The reader table
758 * lock is released, but the table slot stays tied to its thread or
759 * #MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free
760 * its lock table slot if MDB_NOTLS is in use.
761 * Cursors opened within the transaction must not be used
762 * again after this call, except with #mdb_cursor_renew().
763 * Reader locks generally don't interfere with writers, but they keep old
764 * versions of database pages allocated. Thus they prevent the old pages
765 * from being reused when writers commit new data, and so under heavy load
766 * the database size may grow much more rapidly than otherwise.
767 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
769 void mdb_txn_reset(MDB_txn *txn);
771 /** @brief Renew a read-only transaction.
773 * This acquires a new reader lock for a transaction handle that had been
774 * released by #mdb_txn_reset(). It must be called before a reset transaction
776 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
777 * @return A non-zero error value on failure and 0 on success. Some possible
780 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
782 * <li>EINVAL - an invalid parameter was specified.
785 int mdb_txn_renew(MDB_txn *txn);
787 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
788 #define mdb_open(txn,name,flags,dbi) mdb_dbi_open(txn,name,flags,dbi)
789 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
790 #define mdb_close(env,dbi) mdb_dbi_close(env,dbi)
792 /** @brief Open a database in the environment.
794 * A database handle denotes the name and parameters of a database,
795 * independently of whether such a database exists.
796 * The database handle may be discarded by calling #mdb_dbi_close().
797 * The old database handle is returned if the database was already open.
798 * The handle must only be closed once.
799 * The database handle will be private to the current transaction until
800 * the transaction is successfully committed. If the transaction is
801 * aborted the handle will be closed automatically.
802 * After a successful commit the
803 * handle will reside in the shared environment, and may be used
804 * by other transactions. This function must not be called from
805 * multiple concurrent transactions. A transaction that uses this function
806 * must finish (either commit or abort) before any other transaction may
809 * To use named databases (with name != NULL), #mdb_env_set_maxdbs()
810 * must be called before opening the environment.
811 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
812 * @param[in] name The name of the database to open. If only a single
813 * database is needed in the environment, this value may be NULL.
814 * @param[in] flags Special options for this database. This parameter
815 * must be set to 0 or by bitwise OR'ing together one or more of the
816 * values described here.
818 * <li>#MDB_REVERSEKEY
819 * Keys are strings to be compared in reverse order, from the end
820 * of the strings to the beginning. By default, Keys are treated as strings and
821 * compared from beginning to end.
823 * Duplicate keys may be used in the database. (Or, from another perspective,
824 * keys may have multiple data items, stored in sorted order.) By default
825 * keys must be unique and may have only a single data item.
826 * <li>#MDB_INTEGERKEY
827 * Keys are binary integers in native byte order. Setting this option
828 * requires all keys to be the same size, typically sizeof(int)
831 * This flag may only be used in combination with #MDB_DUPSORT. This option
832 * tells the library that the data items for this database are all the same
833 * size, which allows further optimizations in storage and retrieval. When
834 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
835 * cursor operations may be used to retrieve multiple items at once.
836 * <li>#MDB_INTEGERDUP
837 * This option specifies that duplicate data items are also integers, and
838 * should be sorted as such.
839 * <li>#MDB_REVERSEDUP
840 * This option specifies that duplicate data items should be compared as
841 * strings in reverse order.
843 * Create the named database if it doesn't exist. This option is not
844 * allowed in a read-only transaction or a read-only environment.
846 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
847 * @return A non-zero error value on failure and 0 on success. Some possible
850 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
851 * and #MDB_CREATE was not specified.
852 * <li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs().
855 int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
857 /** @brief Retrieve statistics for a database.
859 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
860 * @param[in] dbi A database handle returned by #mdb_dbi_open()
861 * @param[out] stat The address of an #MDB_stat structure
862 * where the statistics will be copied
863 * @return A non-zero error value on failure and 0 on success. Some possible
866 * <li>EINVAL - an invalid parameter was specified.
869 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
871 /** @brief Close a database handle.
873 * This call is not mutex protected. Handles should only be closed by
874 * a single thread, and only if no other threads are going to reference
875 * the database handle or one of its cursors any further. Do not close
876 * a handle if an existing transaction has modified its database.
877 * @param[in] env An environment handle returned by #mdb_env_create()
878 * @param[in] dbi A database handle returned by #mdb_dbi_open()
880 void mdb_dbi_close(MDB_env *env, MDB_dbi dbi);
882 /** @brief Delete a database and/or free all its pages.
884 * If the \b del parameter is 1, the DB handle will be closed
885 * and the DB will be deleted.
886 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
887 * @param[in] dbi A database handle returned by #mdb_dbi_open()
888 * @param[in] del 1 to delete the DB from the environment,
889 * 0 to just free its pages.
890 * @return A non-zero error value on failure and 0 on success.
892 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
894 /** @brief Set a custom key comparison function for a database.
896 * The comparison function is called whenever it is necessary to compare a
897 * key specified by the application with a key currently stored in the database.
898 * If no comparison function is specified, and no special key flags were specified
899 * with #mdb_dbi_open(), the keys are compared lexically, with shorter keys collating
900 * before longer keys.
901 * @warning This function must be called before any data access functions are used,
902 * otherwise data corruption may occur. The same comparison function must be used by every
903 * program accessing the database, every time the database is used.
904 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
905 * @param[in] dbi A database handle returned by #mdb_dbi_open()
906 * @param[in] cmp A #MDB_cmp_func function
907 * @return A non-zero error value on failure and 0 on success. Some possible
910 * <li>EINVAL - an invalid parameter was specified.
913 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
915 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
917 * This comparison function is called whenever it is necessary to compare a data
918 * item specified by the application with a data item currently stored in the database.
919 * This function only takes effect if the database was opened with the #MDB_DUPSORT
921 * If no comparison function is specified, and no special key flags were specified
922 * with #mdb_dbi_open(), the data items are compared lexically, with shorter items collating
923 * before longer items.
924 * @warning This function must be called before any data access functions are used,
925 * otherwise data corruption may occur. The same comparison function must be used by every
926 * program accessing the database, every time the database is used.
927 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
928 * @param[in] dbi A database handle returned by #mdb_dbi_open()
929 * @param[in] cmp A #MDB_cmp_func function
930 * @return A non-zero error value on failure and 0 on success. Some possible
933 * <li>EINVAL - an invalid parameter was specified.
936 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
938 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
940 * @todo The relocation function is called whenever it is necessary to move the data
941 * of an item to a different position in the database (e.g. through tree
942 * balancing operations, shifts as a result of adds or deletes, etc.). It is
943 * intended to allow address/position-dependent data items to be stored in
944 * a database in an environment opened with the #MDB_FIXEDMAP option.
945 * Currently the relocation feature is unimplemented and setting
946 * this function has no effect.
947 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
948 * @param[in] dbi A database handle returned by #mdb_dbi_open()
949 * @param[in] rel A #MDB_rel_func function
950 * @return A non-zero error value on failure and 0 on success. Some possible
953 * <li>EINVAL - an invalid parameter was specified.
956 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
958 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
960 * See #mdb_set_relfunc and #MDB_rel_func for more details.
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] ctx An arbitrary pointer for whatever the application needs.
964 * It will be passed to the callback function set by #mdb_set_relfunc
965 * as its \b relctx parameter whenever the callback is invoked.
966 * @return A non-zero error value on failure and 0 on success. Some possible
969 * <li>EINVAL - an invalid parameter was specified.
972 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
974 /** @brief Get items from a database.
976 * This function retrieves key/data pairs from the database. The address
977 * and length of the data associated with the specified \b key are returned
978 * in the structure to which \b data refers.
979 * If the database supports duplicate keys (#MDB_DUPSORT) then the
980 * first data item for the key will be returned. Retrieval of other
981 * items requires the use of #mdb_cursor_get().
983 * @note The memory pointed to by the returned values is owned by the
984 * database. The caller need not dispose of the memory, and may not
985 * modify it in any way. For values returned in a read-only transaction
986 * any modification attempts will cause a SIGSEGV.
987 * @note Values returned from the database are valid only until a
988 * subsequent update operation, or the end of the transaction.
989 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
990 * @param[in] dbi A database handle returned by #mdb_dbi_open()
991 * @param[in] key The key to search for in the database
992 * @param[out] data The data corresponding to the key
993 * @return A non-zero error value on failure and 0 on success. Some possible
996 * <li>#MDB_NOTFOUND - the key was not in the database.
997 * <li>EINVAL - an invalid parameter was specified.
1000 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1002 /** @brief Store items into a database.
1004 * This function stores key/data pairs in the database. The default behavior
1005 * is to enter the new key/data pair, replacing any previously existing key
1006 * if duplicates are disallowed, or adding a duplicate data item if
1007 * duplicates are allowed (#MDB_DUPSORT).
1008 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1009 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1010 * @param[in] key The key to store in the database
1011 * @param[in,out] data The data to store
1012 * @param[in] flags Special options for this operation. This parameter
1013 * must be set to 0 or by bitwise OR'ing together one or more of the
1014 * values described here.
1016 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1017 * already appear in the database. This flag may only be specified
1018 * if the database was opened with #MDB_DUPSORT. The function will
1019 * return #MDB_KEYEXIST if the key/data pair already appears in the
1021 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1022 * does not already appear in the database. The function will return
1023 * #MDB_KEYEXIST if the key already appears in the database, even if
1024 * the database supports duplicates (#MDB_DUPSORT). The \b data
1025 * parameter will be set to point to the existing item.
1026 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1027 * don't copy the given data. Instead, return a pointer to the
1028 * reserved space, which the caller can fill in later - before
1029 * the next update operation or the transaction ends. This saves
1030 * an extra memcpy if the data is being generated later.
1031 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1032 * database. No key comparisons are performed. This option allows
1033 * fast bulk loading when keys are already known to be in the
1034 * correct order. Loading unsorted keys with this flag will cause
1036 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1038 * @return A non-zero error value on failure and 0 on success. Some possible
1041 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1042 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1043 * <li>EACCES - an attempt was made to write in a read-only transaction.
1044 * <li>EINVAL - an invalid parameter was specified.
1047 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
1048 unsigned int flags);
1050 /** @brief Delete items from a database.
1052 * This function removes key/data pairs from the database.
1053 * If the database does not support sorted duplicate data items
1054 * (#MDB_DUPSORT) the data parameter is ignored.
1055 * If the database supports sorted duplicates and the data parameter
1056 * is NULL, all of the duplicate data items for the key will be
1057 * deleted. Otherwise, if the data parameter is non-NULL
1058 * only the matching data item will be deleted.
1059 * This function will return #MDB_NOTFOUND if the specified key/data
1060 * pair is not in the database.
1061 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1062 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1063 * @param[in] key The key to delete from the database
1064 * @param[in] data The data to delete
1065 * @return A non-zero error value on failure and 0 on success. Some possible
1068 * <li>EACCES - an attempt was made to write in a read-only transaction.
1069 * <li>EINVAL - an invalid parameter was specified.
1072 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1074 /** @brief Create a cursor handle.
1076 * A cursor is associated with a specific transaction and database.
1077 * A cursor cannot be used when its database handle is closed. Nor
1078 * when its transaction has ended, except with #mdb_cursor_renew().
1079 * It can be discarded with #mdb_cursor_close().
1080 * A cursor in a write-transaction can be closed before its transaction
1081 * ends, and will otherwise be closed when its transaction ends.
1082 * A cursor in a read-only transaction must be closed explicitly, before
1083 * or after its transaction ends. It can be reused with
1084 * #mdb_cursor_renew() before finally closing it.
1085 * @note Earlier documentation said that cursors in every transaction
1086 * were closed when the transaction committed or aborted.
1087 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1088 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1089 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
1090 * @return A non-zero error value on failure and 0 on success. Some possible
1093 * <li>EINVAL - an invalid parameter was specified.
1096 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
1098 /** @brief Close a cursor handle.
1100 * The cursor handle will be freed and must not be used again after this call.
1101 * Its transaction must still be live if it is a write-transaction.
1102 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1104 void mdb_cursor_close(MDB_cursor *cursor);
1106 /** @brief Renew a cursor handle.
1108 * A cursor is associated with a specific transaction and database.
1109 * Cursors that are only used in read-only
1110 * transactions may be re-used, to avoid unnecessary malloc/free overhead.
1111 * The cursor may be associated with a new read-only transaction, and
1112 * referencing the same database handle as it was created with.
1113 * This may be done whether the previous transaction is live or dead.
1114 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1115 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1116 * @return A non-zero error value on failure and 0 on success. Some possible
1119 * <li>EINVAL - an invalid parameter was specified.
1122 int mdb_cursor_renew(MDB_txn *txn, MDB_cursor *cursor);
1124 /** @brief Return the cursor's transaction handle.
1126 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1128 MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
1130 /** @brief Return the cursor's database handle.
1132 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1134 MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor);
1136 /** @brief Retrieve by cursor.
1138 * This function retrieves key/data pairs from the database. The address and length
1139 * of the key are returned in the object to which \b key refers (except for the
1140 * case of the #MDB_SET option, in which the \b key object is unchanged), and
1141 * the address and length of the data are returned in the object to which \b data
1143 * See #mdb_get() for restrictions on using the output values.
1144 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1145 * @param[in,out] key The key for a retrieved item
1146 * @param[in,out] data The data of a retrieved item
1147 * @param[in] op A cursor operation #MDB_cursor_op
1148 * @return A non-zero error value on failure and 0 on success. Some possible
1151 * <li>#MDB_NOTFOUND - no matching key found.
1152 * <li>EINVAL - an invalid parameter was specified.
1155 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1158 /** @brief Store by cursor.
1160 * This function stores key/data pairs into the database.
1161 * If the function fails for any reason, the state of the cursor will be
1162 * unchanged. If the function succeeds and an item is inserted into the
1163 * database, the cursor is always positioned to refer to the newly inserted item.
1164 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1165 * @param[in] key The key operated on.
1166 * @param[in] data The data operated on.
1167 * @param[in] flags Options for this operation. This parameter
1168 * must be set to 0 or one of the values described here.
1170 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which
1171 * the cursor refers with the specified data item. The \b key
1172 * parameter is ignored.
1173 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1174 * already appear in the database. This flag may only be specified
1175 * if the database was opened with #MDB_DUPSORT. The function will
1176 * return #MDB_KEYEXIST if the key/data pair already appears in the
1178 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1179 * does not already appear in the database. The function will return
1180 * #MDB_KEYEXIST if the key already appears in the database, even if
1181 * the database supports duplicates (#MDB_DUPSORT).
1182 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1183 * don't copy the given data. Instead, return a pointer to the
1184 * reserved space, which the caller can fill in later. This saves
1185 * an extra memcpy if the data is being generated later.
1186 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1187 * database. No key comparisons are performed. This option allows
1188 * fast bulk loading when keys are already known to be in the
1189 * correct order. Loading unsorted keys with this flag will cause
1191 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1193 * @return A non-zero error value on failure and 0 on success. Some possible
1196 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1197 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1198 * <li>EACCES - an attempt was made to modify a read-only database.
1199 * <li>EINVAL - an invalid parameter was specified.
1202 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1203 unsigned int flags);
1205 /** @brief Delete current key/data pair
1207 * This function deletes the key/data pair to which the cursor refers.
1208 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1209 * @param[in] flags Options for this operation. This parameter
1210 * must be set to 0 or one of the values described here.
1212 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
1213 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
1215 * @return A non-zero error value on failure and 0 on success. Some possible
1218 * <li>EACCES - an attempt was made to modify a read-only database.
1219 * <li>EINVAL - an invalid parameter was specified.
1222 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
1224 /** @brief Return count of duplicates for current key.
1226 * This call is only valid on databases that support sorted duplicate
1227 * data items #MDB_DUPSORT.
1228 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1229 * @param[out] countp Address where the count will be stored
1230 * @return A non-zero error value on failure and 0 on success. Some possible
1233 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
1236 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
1238 /** @brief Compare two data items according to a particular database.
1240 * This returns a comparison as if the two data items were keys in the
1241 * specified database.
1242 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1243 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1244 * @param[in] a The first item to compare
1245 * @param[in] b The second item to compare
1246 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1248 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1250 /** @brief Compare two data items according to a particular database.
1252 * This returns a comparison as if the two items were data items of
1253 * the specified database. The database must have the #MDB_DUPSORT flag.
1254 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1255 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1256 * @param[in] a The first item to compare
1257 * @param[in] b The second item to compare
1258 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1260 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1266 #endif /* _LMDB_H_ */