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 Only for #MDB_DUPSORT */
330 MDB_PREV, /**< Position at previous data item */
331 MDB_PREV_DUP, /**< Position at previous data item of current key.
332 Only for #MDB_DUPSORT */
333 MDB_PREV_NODUP, /**< Position at last data item of previous key.
334 Only for #MDB_DUPSORT */
335 MDB_SET, /**< Position at specified key */
336 MDB_SET_KEY, /**< Position at specified key, return key + data */
337 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
340 /** @defgroup errors Return Codes
342 * BerkeleyDB uses -30800 to -30999, we'll go under them
345 /** Successful result */
346 #define MDB_SUCCESS 0
347 /** key/data pair already exists */
348 #define MDB_KEYEXIST (-30799)
349 /** key/data pair not found (EOF) */
350 #define MDB_NOTFOUND (-30798)
351 /** Requested page not found - this usually indicates corruption */
352 #define MDB_PAGE_NOTFOUND (-30797)
353 /** Located page was wrong type */
354 #define MDB_CORRUPTED (-30796)
355 /** Update of meta page failed, probably I/O error */
356 #define MDB_PANIC (-30795)
357 /** Environment version mismatch */
358 #define MDB_VERSION_MISMATCH (-30794)
359 /** File is not a valid MDB file */
360 #define MDB_INVALID (-30793)
361 /** Environment mapsize reached */
362 #define MDB_MAP_FULL (-30792)
363 /** Environment maxdbs reached */
364 #define MDB_DBS_FULL (-30791)
365 /** Environment maxreaders reached */
366 #define MDB_READERS_FULL (-30790)
367 /** Too many TLS keys in use - Windows only */
368 #define MDB_TLS_FULL (-30789)
369 /** Txn has too many dirty pages */
370 #define MDB_TXN_FULL (-30788)
371 /** Cursor stack too deep - internal error */
372 #define MDB_CURSOR_FULL (-30787)
373 /** Page has not enough space - internal error */
374 #define MDB_PAGE_FULL (-30786)
375 /** Database contents grew beyond environment mapsize */
376 #define MDB_MAP_RESIZED (-30785)
377 /** Database flags changed or would change */
378 #define MDB_INCOMPATIBLE (-30784)
379 /** Invalid reuse of reader locktable slot */
380 #define MDB_BAD_RSLOT (-30783)
381 #define MDB_LAST_ERRCODE MDB_BAD_RSLOT
384 /** @brief Statistics for a database in the environment */
385 typedef struct MDB_stat {
386 unsigned int ms_psize; /**< Size of a database page.
387 This is currently the same for all databases. */
388 unsigned int ms_depth; /**< Depth (height) of the B-tree */
389 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
390 size_t ms_leaf_pages; /**< Number of leaf pages */
391 size_t ms_overflow_pages; /**< Number of overflow pages */
392 size_t ms_entries; /**< Number of data items */
395 /** @brief Information about the environment */
396 typedef struct MDB_envinfo {
397 void *me_mapaddr; /**< Address of map, if fixed */
398 size_t me_mapsize; /**< Size of the data memory map */
399 size_t me_last_pgno; /**< ID of the last used page */
400 size_t me_last_txnid; /**< ID of the last committed transaction */
401 unsigned int me_maxreaders; /**< max reader slots in the environment */
402 unsigned int me_numreaders; /**< max reader slots used in the environment */
405 /** @brief Return the mdb library version information.
407 * @param[out] major if non-NULL, the library major version number is copied here
408 * @param[out] minor if non-NULL, the library minor version number is copied here
409 * @param[out] patch if non-NULL, the library patch version number is copied here
410 * @retval "version string" The library version as a string
412 char *mdb_version(int *major, int *minor, int *patch);
414 /** @brief Return a string describing a given error code.
416 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
417 * function. If the error code is greater than or equal to 0, then the string
418 * returned by the system function strerror(3) is returned. If the error code
419 * is less than 0, an error string corresponding to the MDB library error is
420 * returned. See @ref errors for a list of MDB-specific error codes.
421 * @param[in] err The error code
422 * @retval "error message" The description of the error
424 char *mdb_strerror(int err);
426 /** @brief Create an MDB environment handle.
428 * This function allocates memory for a #MDB_env structure. To release
429 * the allocated memory and discard the handle, call #mdb_env_close().
430 * Before the handle may be used, it must be opened using #mdb_env_open().
431 * Various other options may also need to be set before opening the handle,
432 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
433 * depending on usage requirements.
434 * @param[out] env The address where the new handle will be stored
435 * @return A non-zero error value on failure and 0 on success.
437 int mdb_env_create(MDB_env **env);
439 /** @brief Open an environment handle.
441 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
442 * @param[in] env An environment handle returned by #mdb_env_create()
443 * @param[in] path The directory in which the database files reside. This
444 * directory must already exist and be writable.
445 * @param[in] flags Special options for this environment. This parameter
446 * must be set to 0 or by bitwise OR'ing together one or more of the
447 * values described here.
448 * Flags set by mdb_env_set_flags() are also used.
451 * use a fixed address for the mmap region. This flag must be specified
452 * when creating the environment, and is stored persistently in the environment.
453 * If successful, the memory map will always reside at the same virtual address
454 * and pointers used to reference data items in the database will be constant
455 * across multiple invocations. This option may not always work, depending on
456 * how the operating system has allocated memory to shared libraries and other uses.
457 * The feature is highly experimental.
459 * By default, MDB creates its environment in a directory whose
460 * pathname is given in \b path, and creates its data and lock files
461 * under that directory. With this option, \b path is used as-is for
462 * the database main data file. The database lock file is the \b path
463 * with "-lock" appended.
465 * Open the environment in read-only mode. No write operations will be
466 * allowed. MDB will still modify the lock file - except on read-only
467 * filesystems, where MDB does not use locks.
469 * Use a writeable memory map unless MDB_RDONLY is set. This is faster
470 * and uses fewer mallocs, but loses protection from application bugs
471 * like wild pointer writes and other bad updates into the database.
472 * Incompatible with nested transactions.
473 * <li>#MDB_NOMETASYNC
474 * Flush system buffers to disk only once per transaction, omit the
475 * metadata flush. Defer that until the system flushes files to disk,
476 * or next non-MDB_RDONLY commit or #mdb_env_sync(). This optimization
477 * maintains database integrity, but a system crash may undo the last
478 * committed transaction. I.e. it preserves the ACI (atomicity,
479 * consistency, isolation) but not D (durability) database property.
480 * This flag may be changed at any time using #mdb_env_set_flags().
482 * Don't flush system buffers to disk when committing a transaction.
483 * This optimization means a system crash can corrupt the database or
484 * lose the last transactions if buffers are not yet flushed to disk.
485 * The risk is governed by how often the system flushes dirty buffers
486 * to disk and how often #mdb_env_sync() is called. However, if the
487 * filesystem preserves write order and the #MDB_WRITEMAP flag is not
488 * used, transactions exhibit ACI (atomicity, consistency, isolation)
489 * properties and only lose D (durability). I.e. database integrity
490 * is maintained, but a system crash may undo the final transactions.
491 * Note that (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no
492 * hint for when to write transactions to disk, unless #mdb_env_sync()
493 * is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable.
494 * This flag may be changed at any time using #mdb_env_set_flags().
496 * When using #MDB_WRITEMAP, use asynchronous flushes to disk.
497 * As with #MDB_NOSYNC, a system crash can then corrupt the
498 * database or lose the last transactions. Calling #mdb_env_sync()
499 * ensures on-disk database integrity until next commit.
500 * This flag may be changed at any time using #mdb_env_set_flags().
502 * Don't use Thread-Local Storage. Tie reader locktable slots to
503 * #MDB_txn objects instead of to threads. I.e. #mdb_txn_reset() keeps
504 * the slot reseved for the #MDB_txn object. A thread may use parallel
505 * read-only transactions. A read-only transaction may span threads if
506 * the user synchronizes its use. Applications that multiplex many
507 * user threads over individual OS threads need this option. Such an
508 * application must also serialize the write transactions in an OS
509 * thread, since MDB's write locking is unaware of the user threads.
511 * @param[in] mode The UNIX permissions to set on created files. This parameter
512 * is ignored on Windows.
513 * @return A non-zero error value on failure and 0 on success. Some possible
516 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
517 * version that created the database environment.
518 * <li>#MDB_INVALID - the environment file headers are corrupted.
519 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
520 * <li>EACCES - the user didn't have permission to access the environment files.
521 * <li>EAGAIN - the environment was locked by another process.
524 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode);
526 /** @brief Copy an MDB environment to the specified path.
528 * This function may be used to make a backup of an existing environment.
529 * @param[in] env An environment handle returned by #mdb_env_create(). It
530 * must have already been opened successfully.
531 * @param[in] path The directory in which the copy will reside. This
532 * directory must already exist and be writable but must otherwise be
534 * @return A non-zero error value on failure and 0 on success.
536 int mdb_env_copy(MDB_env *env, const char *path);
538 /** @brief Return statistics about the MDB environment.
540 * @param[in] env An environment handle returned by #mdb_env_create()
541 * @param[out] stat The address of an #MDB_stat structure
542 * where the statistics will be copied
544 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
546 /** @brief Return information about the MDB environment.
548 * @param[in] env An environment handle returned by #mdb_env_create()
549 * @param[out] stat The address of an #MDB_envinfo structure
550 * where the information will be copied
552 int mdb_env_info(MDB_env *env, MDB_envinfo *stat);
554 /** @brief Flush the data buffers to disk.
556 * Data is always written to disk when #mdb_txn_commit() is called,
557 * but the operating system may keep it buffered. MDB always flushes
558 * the OS buffers upon commit as well, unless the environment was
559 * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC.
560 * @param[in] env An environment handle returned by #mdb_env_create()
561 * @param[in] force If non-zero, force a synchronous flush. Otherwise
562 * if the environment has the #MDB_NOSYNC flag set the flushes
563 * will be omitted, and with #MDB_MAPASYNC they will be asynchronous.
564 * @return A non-zero error value on failure and 0 on success. Some possible
567 * <li>EINVAL - an invalid parameter was specified.
568 * <li>EIO - an error occurred during synchronization.
571 int mdb_env_sync(MDB_env *env, int force);
573 /** @brief Close the environment and release the memory map.
575 * Only a single thread may call this function. All transactions, databases,
576 * and cursors must already be closed before calling this function. Attempts to
577 * use any such handles after calling this function will cause a SIGSEGV.
578 * The environment handle will be freed and must not be used again after this call.
579 * @param[in] env An environment handle returned by #mdb_env_create()
581 void mdb_env_close(MDB_env *env);
583 /** @brief Set environment flags.
585 * This may be used to set some flags in addition to those from
586 * #mdb_env_open(), or to unset these flags.
587 * @param[in] env An environment handle returned by #mdb_env_create()
588 * @param[in] flags The flags to change, bitwise OR'ed together
589 * @param[in] onoff A non-zero value sets the flags, zero clears them.
590 * @return A non-zero error value on failure and 0 on success. Some possible
593 * <li>EINVAL - an invalid parameter was specified.
596 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
598 /** @brief Get environment flags.
600 * @param[in] env An environment handle returned by #mdb_env_create()
601 * @param[out] flags The address of an integer to store the flags
602 * @return A non-zero error value on failure and 0 on success. Some possible
605 * <li>EINVAL - an invalid parameter was specified.
608 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
610 /** @brief Return the path that was used in #mdb_env_open().
612 * @param[in] env An environment handle returned by #mdb_env_create()
613 * @param[out] path Address of a string pointer to contain the path. This
614 * is the actual string in the environment, not a copy. It should not be
615 * altered in any way.
616 * @return A non-zero error value on failure and 0 on success. Some possible
619 * <li>EINVAL - an invalid parameter was specified.
622 int mdb_env_get_path(MDB_env *env, const char **path);
624 /** @brief Set the size of the memory map to use for this environment.
626 * The size should be a multiple of the OS page size. The default is
627 * 10485760 bytes. The size of the memory map is also the maximum size
628 * of the database. The value should be chosen as large as possible,
629 * to accommodate future growth of the database.
630 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
631 * The size may be changed by closing and reopening the environment.
632 * Any attempt to set a size smaller than the space already consumed
633 * by the environment will be silently changed to the current size of the used space.
634 * @param[in] env An environment handle returned by #mdb_env_create()
635 * @param[in] size The size in bytes
636 * @return A non-zero error value on failure and 0 on success. Some possible
639 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
642 int mdb_env_set_mapsize(MDB_env *env, size_t size);
644 /** @brief Set the maximum number of threads/reader slots for the environment.
646 * This defines the number of slots in the lock table that is used to track readers in the
647 * the environment. The default is 126.
648 * Starting a read-only transaction normally ties a lock table slot to the
649 * current thread until the environment closes or the thread exits. If
650 * MDB_NOTLS is in use, #mdb_txn_begin() instead ties the slot to the
651 * MDB_txn object until it or the #MDB_env object is destroyed.
652 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
653 * @param[in] env An environment handle returned by #mdb_env_create()
654 * @param[in] readers The maximum number of reader lock table slots
655 * @return A non-zero error value on failure and 0 on success. Some possible
658 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
661 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
663 /** @brief Get the maximum number of threads/reader slots for the environment.
665 * @param[in] env An environment handle returned by #mdb_env_create()
666 * @param[out] readers Address of an integer to store the number of readers
667 * @return A non-zero error value on failure and 0 on success. Some possible
670 * <li>EINVAL - an invalid parameter was specified.
673 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
675 /** @brief Set the maximum number of named databases for the environment.
677 * This function is only needed if multiple databases will be used in the
678 * environment. Simpler applications that use the environment as a single
679 * unnamed database can ignore this option.
680 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
681 * @param[in] env An environment handle returned by #mdb_env_create()
682 * @param[in] dbs The maximum number of databases
683 * @return A non-zero error value on failure and 0 on success. Some possible
686 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
689 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
691 /** @brief Create a transaction for use with the environment.
693 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
694 * @note A transaction and its cursors must only be used by a single
695 * thread, and a thread may only have a single transaction at a time.
696 * If #MDB_NOTLS is in use, this does not apply to read-only transactions.
697 * @note Cursors may not span transactions.
698 * @param[in] env An environment handle returned by #mdb_env_create()
699 * @param[in] parent If this parameter is non-NULL, the new transaction
700 * will be a nested transaction, with the transaction indicated by \b parent
701 * as its parent. Transactions may be nested to any level. A parent
702 * transaction may not issue any other operations besides mdb_txn_begin,
703 * mdb_txn_abort, or mdb_txn_commit while it has active child transactions.
704 * @param[in] flags Special options for this transaction. This parameter
705 * must be set to 0 or by bitwise OR'ing together one or more of the
706 * values described here.
709 * This transaction will not perform any write operations.
711 * @param[out] txn Address where the new #MDB_txn handle will be stored
712 * @return A non-zero error value on failure and 0 on success. Some possible
715 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
717 * <li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's
718 * mapsize and the environment must be shut down.
719 * <li>#MDB_READERS_FULL - a read-only transaction was requested and
720 * the reader lock table is full. See #mdb_env_set_maxreaders().
721 * <li>ENOMEM - out of memory.
724 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
726 /** @brief Commit all the operations of a transaction into the database.
728 * The transaction handle is freed. It and its cursors must not be used
729 * again after this call, except with #mdb_cursor_renew().
730 * @note Earlier documentation incorrectly said all cursors would be freed.
731 * Only write-transactions free cursors.
732 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
733 * @return A non-zero error value on failure and 0 on success. Some possible
736 * <li>EINVAL - an invalid parameter was specified.
737 * <li>ENOSPC - no more disk space.
738 * <li>EIO - a low-level I/O error occurred while writing.
739 * <li>ENOMEM - out of memory.
742 int mdb_txn_commit(MDB_txn *txn);
744 /** @brief Abandon all the operations of the transaction instead of saving them.
746 * The transaction handle is freed. It and its cursors must not be used
747 * again after this call, except with #mdb_cursor_renew().
748 * @note Earlier documentation incorrectly said all cursors would be freed.
749 * Only write-transactions free cursors.
750 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
752 void mdb_txn_abort(MDB_txn *txn);
754 /** @brief Reset a read-only transaction.
756 * Abort the transaction like #mdb_txn_abort(), but keep the transaction
757 * handle. #mdb_txn_renew() may reuse the handle. This saves allocation
758 * overhead if the process will start a new read-only transaction soon,
759 * and also locking overhead if #MDB_NOTLS is in use. The reader table
760 * lock is released, but the table slot stays tied to its thread or
761 * #MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free
762 * its lock table slot if MDB_NOTLS is in use.
763 * Cursors opened within the transaction must not be used
764 * again after this call, except with #mdb_cursor_renew().
765 * Reader locks generally don't interfere with writers, but they keep old
766 * versions of database pages allocated. Thus they prevent the old pages
767 * from being reused when writers commit new data, and so under heavy load
768 * the database size may grow much more rapidly than otherwise.
769 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
771 void mdb_txn_reset(MDB_txn *txn);
773 /** @brief Renew a read-only transaction.
775 * This acquires a new reader lock for a transaction handle that had been
776 * released by #mdb_txn_reset(). It must be called before a reset transaction
778 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
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>EINVAL - an invalid parameter was specified.
787 int mdb_txn_renew(MDB_txn *txn);
789 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
790 #define mdb_open(txn,name,flags,dbi) mdb_dbi_open(txn,name,flags,dbi)
791 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
792 #define mdb_close(env,dbi) mdb_dbi_close(env,dbi)
794 /** @brief Open a database in the environment.
796 * A database handle denotes the name and parameters of a database,
797 * independently of whether such a database exists.
798 * The database handle may be discarded by calling #mdb_dbi_close().
799 * The old database handle is returned if the database was already open.
800 * The handle must only be closed once.
801 * The database handle will be private to the current transaction until
802 * the transaction is successfully committed. If the transaction is
803 * aborted the handle will be closed automatically.
804 * After a successful commit the
805 * handle will reside in the shared environment, and may be used
806 * by other transactions. This function must not be called from
807 * multiple concurrent transactions. A transaction that uses this function
808 * must finish (either commit or abort) before any other transaction may
811 * To use named databases (with name != NULL), #mdb_env_set_maxdbs()
812 * must be called before opening the environment.
813 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
814 * @param[in] name The name of the database to open. If only a single
815 * database is needed in the environment, this value may be NULL.
816 * @param[in] flags Special options for this database. This parameter
817 * must be set to 0 or by bitwise OR'ing together one or more of the
818 * values described here.
820 * <li>#MDB_REVERSEKEY
821 * Keys are strings to be compared in reverse order, from the end
822 * of the strings to the beginning. By default, Keys are treated as strings and
823 * compared from beginning to end.
825 * Duplicate keys may be used in the database. (Or, from another perspective,
826 * keys may have multiple data items, stored in sorted order.) By default
827 * keys must be unique and may have only a single data item.
828 * <li>#MDB_INTEGERKEY
829 * Keys are binary integers in native byte order. Setting this option
830 * requires all keys to be the same size, typically sizeof(int)
833 * This flag may only be used in combination with #MDB_DUPSORT. This option
834 * tells the library that the data items for this database are all the same
835 * size, which allows further optimizations in storage and retrieval. When
836 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
837 * cursor operations may be used to retrieve multiple items at once.
838 * <li>#MDB_INTEGERDUP
839 * This option specifies that duplicate data items are also integers, and
840 * should be sorted as such.
841 * <li>#MDB_REVERSEDUP
842 * This option specifies that duplicate data items should be compared as
843 * strings in reverse order.
845 * Create the named database if it doesn't exist. This option is not
846 * allowed in a read-only transaction or a read-only environment.
848 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
849 * @return A non-zero error value on failure and 0 on success. Some possible
852 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
853 * and #MDB_CREATE was not specified.
854 * <li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs().
857 int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
859 /** @brief Retrieve statistics for a database.
861 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
862 * @param[in] dbi A database handle returned by #mdb_dbi_open()
863 * @param[out] stat The address of an #MDB_stat structure
864 * where the statistics will be copied
865 * @return A non-zero error value on failure and 0 on success. Some possible
868 * <li>EINVAL - an invalid parameter was specified.
871 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
873 /** @brief Close a database handle.
875 * This call is not mutex protected. Handles should only be closed by
876 * a single thread, and only if no other threads are going to reference
877 * the database handle or one of its cursors any further. Do not close
878 * a handle if an existing transaction has modified its database.
879 * @param[in] env An environment handle returned by #mdb_env_create()
880 * @param[in] dbi A database handle returned by #mdb_dbi_open()
882 void mdb_dbi_close(MDB_env *env, MDB_dbi dbi);
884 /** @brief Delete a database and/or free all its pages.
886 * If the \b del parameter is 1, the DB handle will be closed
887 * and the DB will be deleted.
888 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
889 * @param[in] dbi A database handle returned by #mdb_dbi_open()
890 * @param[in] del 1 to delete the DB from the environment,
891 * 0 to just free its pages.
892 * @return A non-zero error value on failure and 0 on success.
894 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
896 /** @brief Set a custom key comparison function for a database.
898 * The comparison function is called whenever it is necessary to compare a
899 * key specified by the application with a key currently stored in the database.
900 * If no comparison function is specified, and no special key flags were specified
901 * with #mdb_dbi_open(), the keys are compared lexically, with shorter keys collating
902 * before longer keys.
903 * @warning This function must be called before any data access functions are used,
904 * otherwise data corruption may occur. The same comparison function must be used by every
905 * program accessing the database, every time the database is used.
906 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
907 * @param[in] dbi A database handle returned by #mdb_dbi_open()
908 * @param[in] cmp A #MDB_cmp_func function
909 * @return A non-zero error value on failure and 0 on success. Some possible
912 * <li>EINVAL - an invalid parameter was specified.
915 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
917 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
919 * This comparison function is called whenever it is necessary to compare a data
920 * item specified by the application with a data item currently stored in the database.
921 * This function only takes effect if the database was opened with the #MDB_DUPSORT
923 * If no comparison function is specified, and no special key flags were specified
924 * with #mdb_dbi_open(), the data items are compared lexically, with shorter items collating
925 * before longer items.
926 * @warning This function must be called before any data access functions are used,
927 * otherwise data corruption may occur. The same comparison function must be used by every
928 * program accessing the database, every time the database is used.
929 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
930 * @param[in] dbi A database handle returned by #mdb_dbi_open()
931 * @param[in] cmp A #MDB_cmp_func function
932 * @return A non-zero error value on failure and 0 on success. Some possible
935 * <li>EINVAL - an invalid parameter was specified.
938 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
940 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
942 * @todo The relocation function is called whenever it is necessary to move the data
943 * of an item to a different position in the database (e.g. through tree
944 * balancing operations, shifts as a result of adds or deletes, etc.). It is
945 * intended to allow address/position-dependent data items to be stored in
946 * a database in an environment opened with the #MDB_FIXEDMAP option.
947 * Currently the relocation feature is unimplemented and setting
948 * this function has no effect.
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[in] rel A #MDB_rel_func function
952 * @return A non-zero error value on failure and 0 on success. Some possible
955 * <li>EINVAL - an invalid parameter was specified.
958 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
960 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
962 * See #mdb_set_relfunc and #MDB_rel_func for more details.
963 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
964 * @param[in] dbi A database handle returned by #mdb_dbi_open()
965 * @param[in] ctx An arbitrary pointer for whatever the application needs.
966 * It will be passed to the callback function set by #mdb_set_relfunc
967 * as its \b relctx parameter whenever the callback is invoked.
968 * @return A non-zero error value on failure and 0 on success. Some possible
971 * <li>EINVAL - an invalid parameter was specified.
974 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
976 /** @brief Get items from a database.
978 * This function retrieves key/data pairs from the database. The address
979 * and length of the data associated with the specified \b key are returned
980 * in the structure to which \b data refers.
981 * If the database supports duplicate keys (#MDB_DUPSORT) then the
982 * first data item for the key will be returned. Retrieval of other
983 * items requires the use of #mdb_cursor_get().
985 * @note The memory pointed to by the returned values is owned by the
986 * database. The caller need not dispose of the memory, and may not
987 * modify it in any way. For values returned in a read-only transaction
988 * any modification attempts will cause a SIGSEGV.
989 * @note Values returned from the database are valid only until a
990 * subsequent update operation, or the end of the transaction.
991 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
992 * @param[in] dbi A database handle returned by #mdb_dbi_open()
993 * @param[in] key The key to search for in the database
994 * @param[out] data The data corresponding to the key
995 * @return A non-zero error value on failure and 0 on success. Some possible
998 * <li>#MDB_NOTFOUND - the key was not in the database.
999 * <li>EINVAL - an invalid parameter was specified.
1002 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1004 /** @brief Store items into a database.
1006 * This function stores key/data pairs in the database. The default behavior
1007 * is to enter the new key/data pair, replacing any previously existing key
1008 * if duplicates are disallowed, or adding a duplicate data item if
1009 * duplicates are allowed (#MDB_DUPSORT).
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] key The key to store in the database
1013 * @param[in,out] data The data to store
1014 * @param[in] flags Special options for this operation. This parameter
1015 * must be set to 0 or by bitwise OR'ing together one or more of the
1016 * values described here.
1018 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1019 * already appear in the database. This flag may only be specified
1020 * if the database was opened with #MDB_DUPSORT. The function will
1021 * return #MDB_KEYEXIST if the key/data pair already appears in the
1023 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1024 * does not already appear in the database. The function will return
1025 * #MDB_KEYEXIST if the key already appears in the database, even if
1026 * the database supports duplicates (#MDB_DUPSORT). The \b data
1027 * parameter will be set to point to the existing item.
1028 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1029 * don't copy the given data. Instead, return a pointer to the
1030 * reserved space, which the caller can fill in later - before
1031 * the next update operation or the transaction ends. This saves
1032 * an extra memcpy if the data is being generated later.
1033 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1034 * database. No key comparisons are performed. This option allows
1035 * fast bulk loading when keys are already known to be in the
1036 * correct order. Loading unsorted keys with this flag will cause
1038 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1040 * @return A non-zero error value on failure and 0 on success. Some possible
1043 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1044 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1045 * <li>EACCES - an attempt was made to write in a read-only transaction.
1046 * <li>EINVAL - an invalid parameter was specified.
1049 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
1050 unsigned int flags);
1052 /** @brief Delete items from a database.
1054 * This function removes key/data pairs from the database.
1055 * If the database does not support sorted duplicate data items
1056 * (#MDB_DUPSORT) the data parameter is ignored.
1057 * If the database supports sorted duplicates and the data parameter
1058 * is NULL, all of the duplicate data items for the key will be
1059 * deleted. Otherwise, if the data parameter is non-NULL
1060 * only the matching data item will be deleted.
1061 * This function will return #MDB_NOTFOUND if the specified key/data
1062 * pair is not in the database.
1063 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1064 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1065 * @param[in] key The key to delete from the database
1066 * @param[in] data The data to delete
1067 * @return A non-zero error value on failure and 0 on success. Some possible
1070 * <li>EACCES - an attempt was made to write in a read-only transaction.
1071 * <li>EINVAL - an invalid parameter was specified.
1074 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1076 /** @brief Create a cursor handle.
1078 * A cursor is associated with a specific transaction and database.
1079 * A cursor cannot be used when its database handle is closed. Nor
1080 * when its transaction has ended, except with #mdb_cursor_renew().
1081 * It can be discarded with #mdb_cursor_close().
1082 * A cursor in a write-transaction can be closed before its transaction
1083 * ends, and will otherwise be closed when its transaction ends.
1084 * A cursor in a read-only transaction must be closed explicitly, before
1085 * or after its transaction ends. It can be reused with
1086 * #mdb_cursor_renew() before finally closing it.
1087 * @note Earlier documentation said that cursors in every transaction
1088 * were closed when the transaction committed or aborted.
1089 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1090 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1091 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
1092 * @return A non-zero error value on failure and 0 on success. Some possible
1095 * <li>EINVAL - an invalid parameter was specified.
1098 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
1100 /** @brief Close a cursor handle.
1102 * The cursor handle will be freed and must not be used again after this call.
1103 * Its transaction must still be live if it is a write-transaction.
1104 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1106 void mdb_cursor_close(MDB_cursor *cursor);
1108 /** @brief Renew a cursor handle.
1110 * A cursor is associated with a specific transaction and database.
1111 * Cursors that are only used in read-only
1112 * transactions may be re-used, to avoid unnecessary malloc/free overhead.
1113 * The cursor may be associated with a new read-only transaction, and
1114 * referencing the same database handle as it was created with.
1115 * This may be done whether the previous transaction is live or dead.
1116 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1117 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1118 * @return A non-zero error value on failure and 0 on success. Some possible
1121 * <li>EINVAL - an invalid parameter was specified.
1124 int mdb_cursor_renew(MDB_txn *txn, MDB_cursor *cursor);
1126 /** @brief Return the cursor's transaction handle.
1128 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1130 MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
1132 /** @brief Return the cursor's database handle.
1134 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1136 MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor);
1138 /** @brief Retrieve by cursor.
1140 * This function retrieves key/data pairs from the database. The address and length
1141 * of the key are returned in the object to which \b key refers (except for the
1142 * case of the #MDB_SET option, in which the \b key object is unchanged), and
1143 * the address and length of the data are returned in the object to which \b data
1145 * See #mdb_get() for restrictions on using the output values.
1146 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1147 * @param[in,out] key The key for a retrieved item
1148 * @param[in,out] data The data of a retrieved item
1149 * @param[in] op A cursor operation #MDB_cursor_op
1150 * @return A non-zero error value on failure and 0 on success. Some possible
1153 * <li>#MDB_NOTFOUND - no matching key found.
1154 * <li>EINVAL - an invalid parameter was specified.
1157 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1160 /** @brief Store by cursor.
1162 * This function stores key/data pairs into the database.
1163 * If the function fails for any reason, the state of the cursor will be
1164 * unchanged. If the function succeeds and an item is inserted into the
1165 * database, the cursor is always positioned to refer to the newly inserted item.
1166 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1167 * @param[in] key The key operated on.
1168 * @param[in] data The data operated on.
1169 * @param[in] flags Options for this operation. This parameter
1170 * must be set to 0 or one of the values described here.
1172 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which
1173 * the cursor refers with the specified data item. The \b key
1174 * parameter is ignored.
1175 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1176 * already appear in the database. This flag may only be specified
1177 * if the database was opened with #MDB_DUPSORT. The function will
1178 * return #MDB_KEYEXIST if the key/data pair already appears in the
1180 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1181 * does not already appear in the database. The function will return
1182 * #MDB_KEYEXIST if the key already appears in the database, even if
1183 * the database supports duplicates (#MDB_DUPSORT).
1184 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1185 * don't copy the given data. Instead, return a pointer to the
1186 * reserved space, which the caller can fill in later. This saves
1187 * an extra memcpy if the data is being generated later.
1188 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1189 * database. No key comparisons are performed. This option allows
1190 * fast bulk loading when keys are already known to be in the
1191 * correct order. Loading unsorted keys with this flag will cause
1193 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1195 * @return A non-zero error value on failure and 0 on success. Some possible
1198 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1199 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1200 * <li>EACCES - an attempt was made to modify a read-only database.
1201 * <li>EINVAL - an invalid parameter was specified.
1204 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1205 unsigned int flags);
1207 /** @brief Delete current key/data pair
1209 * This function deletes the key/data pair to which the cursor refers.
1210 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1211 * @param[in] flags Options for this operation. This parameter
1212 * must be set to 0 or one of the values described here.
1214 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
1215 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
1217 * @return A non-zero error value on failure and 0 on success. Some possible
1220 * <li>EACCES - an attempt was made to modify a read-only database.
1221 * <li>EINVAL - an invalid parameter was specified.
1224 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
1226 /** @brief Return count of duplicates for current key.
1228 * This call is only valid on databases that support sorted duplicate
1229 * data items #MDB_DUPSORT.
1230 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1231 * @param[out] countp Address where the count will be stored
1232 * @return A non-zero error value on failure and 0 on success. Some possible
1235 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
1238 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
1240 /** @brief Compare two data items according to a particular database.
1242 * This returns a comparison as if the two data items were keys in the
1243 * specified database.
1244 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1245 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1246 * @param[in] a The first item to compare
1247 * @param[in] b The second item to compare
1248 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1250 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1252 /** @brief Compare two data items according to a particular database.
1254 * This returns a comparison as if the two items were data items of
1255 * the specified database. The database must have the #MDB_DUPSORT flag.
1256 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1257 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1258 * @param[in] a The first item to compare
1259 * @param[in] b The second item to compare
1260 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1262 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1268 #endif /* _LMDB_H_ */