2 * @brief memory-mapped database library
4 * @mainpage MDB Memory-Mapped Database Manager
5 * MDB is a Btree-based database management library modeled loosely on the
6 * BerkeleyDB API, but much simplified. The entire database is exposed
7 * in a read-only memory map, and all data fetches return data directly
8 * from the mapped memory, so no malloc's or memcpy's occur during
9 * data fetches. As such, the library is extremely simple because it
10 * requires no page caching layer of its own, and it is extremely high
11 * performance and memory-efficient. It is also fully transactional with
12 * full ACID semantics, and because the memory map is read-only, the
13 * database integrity cannot be corrupted by stray pointer writes from
16 * The library is fully thread-aware and supports concurrent read/write
17 * access from multiple processes and threads. Data pages use a copy-on-
18 * write strategy so no active data pages are ever overwritten, which
19 * also provides resistance to corruption and eliminates the need of any
20 * special recovery procedures after a system crash. Writes are fully
21 * serialized; only one write transaction may be active at a time, which
22 * guarantees that writers can never deadlock. The database structure is
23 * multi-versioned so readers run with no locks; writers cannot block
24 * readers, and readers don't block writers.
26 * Unlike other well-known database mechanisms which use either write-ahead
27 * transaction logs or append-only data writes, MDB requires no maintenance
28 * during operation. Both write-ahead loggers and append-only databases
29 * require periodic checkpointing and/or compaction of their log or database
30 * files otherwise they grow without bound. MDB tracks free pages within
31 * the database and re-uses them for new write operations, so the database
32 * size does not grow without bound in normal use.
34 * @author Howard Chu, Symas Corporation.
36 * @copyright Copyright 2011 Howard Chu, Symas Corp. All rights reserved.
38 * Redistribution and use in source and binary forms, with or without
39 * modification, are permitted only as authorized by the OpenLDAP
42 * A copy of this license is available in the file LICENSE in the
43 * top-level directory of the distribution or, alternatively, at
44 * <http://www.OpenLDAP.org/license.html>.
47 * This code is derived from btree.c written by Martin Hedenfalk.
49 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
51 * Permission to use, copy, modify, and distribute this software for any
52 * purpose with or without fee is hereby granted, provided that the above
53 * copyright notice and this permission notice appear in all copies.
55 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
56 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
57 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
58 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
59 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
60 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
61 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
66 #include <sys/types.h>
68 /** @defgroup Version Version Macros
71 /** Library major version */
72 #define MDB_VERSION_MAJOR 0
73 /** Library minor version */
74 #define MDB_VERSION_MINOR 9
75 /** Library patch version */
76 #define MDB_VERSION_PATCH 0
78 /** Combine args a,b,c into a single integer for easy version comparisons */
79 #define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
81 /** The full library version as a single integer */
82 #define MDB_VERSION_FULL \
83 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
85 /** The release date of this library version */
86 #define MDB_VERSION_DATE "September 1, 2011"
88 /** A stringifier for the version info */
89 #define MDB_VERSTR(a,b,c,d) "MDB " #a "." #b "." #c ": (" #d ")"
91 /** A helper for the stringifier macro */
92 #define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d)
94 /** The full library version as a C string */
95 #define MDB_VERSION_STRING \
96 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
99 /** Opaque structure for a database environment. A DB environment supports multiple
100 * databases, all residing in the same shared-memory map.
102 typedef struct MDB_env MDB_env;
104 /** Opaque structure for a transaction handle. All database operations require
105 * a transaction handle. Transactions may be read-only or read-write.
107 typedef struct MDB_txn MDB_txn;
109 /** A handle for an individual database in the DB environment. */
110 typedef unsigned int MDB_dbi;
112 /** Opaque structure for navigating through a database */
113 typedef struct MDB_cursor MDB_cursor;
115 /** Generic structure used for passing keys and data in and out of the database. */
116 typedef struct MDB_val {
117 size_t mv_size; /**< size of the data item */
118 void *mv_data; /**< address of the data item */
121 /** A callback function used to compare two keys in a database */
122 typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
124 /** A callback function used to relocate a position-dependent data item
125 * in a fixed-address database. The \b newptr gives the item's current address in
126 * the memory map, and \b oldptr gives its previous address. This callback is
127 * expected to walk through the fields of the record in newptr and modify any
128 * values based at the \b oldptr address to be relative to the \b newptr address.
129 * @todo This feature is currently unimplemented.
131 typedef void (MDB_rel_func)(void *newptr, void *oldptr, size_t size);
133 /** @defgroup mdb_env environment flags
136 /** mmap at a fixed address */
137 #define MDB_FIXEDMAP 0x01
138 /** don't fsync after commit */
139 #define MDB_NOSYNC 0x10000
141 #define MDB_RDONLY 0x20000
144 /** @defgroup mdb_open database flags
147 /** use reverse string keys */
148 #define MDB_REVERSEKEY 0x02
149 /** use sorted duplicates */
150 #define MDB_DUPSORT 0x04
151 /** numeric keys in native byte order */
152 #define MDB_INTEGERKEY 0x08
153 /** with #MDB_DUPSORT, sorted dup items have fixed size */
154 #define MDB_DUPFIXED 0x10
155 /** with #MDB_DUPSORT, dups are numeric in native byte order */
156 #define MDB_INTEGERDUP 0x20
157 /** create DB if not already existing */
158 #define MDB_CREATE 0x40000
161 /** @defgroup mdb_put mdb_put flags
164 /** For mdb_put: don't write if the key already exists. */
165 #define MDB_NOOVERWRITE 0x10
166 /** For mdb_put: don't write if the key and data pair already exist.
167 * Only for #MDB_DUPSORT
169 #define MDB_NODUPDATA 0x20
172 /** Cursor operations */
173 typedef enum MDB_cursor_op {
174 MDB_FIRST, /**< Position at first key/data item */
175 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
176 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
177 MDB_GET_MULTIPLE, /**< Return all the duplicate data items at the current
178 cursor position. Only for #MDB_DUPFIXED */
179 MDB_LAST, /**< Position at last key/data item */
180 MDB_NEXT, /**< Position at next data item */
181 MDB_NEXT_DUP, /**< Position at next data item of current key.
182 Only for #MDB_DUPSORT */
183 MDB_NEXT_MULTIPLE, /**< Return all duplicate data items at the next
184 cursor position. Only for #MDB_DUPFIXED */
185 MDB_NEXT_NODUP, /**< Position at first data item of next key.
186 Only for #MDB_DUPSORT */
187 MDB_PREV, /**< Position at previous data item */
188 MDB_PREV_DUP, /**< Position at previous data item of current key.
189 Only for #MDB_DUPSORT */
190 MDB_PREV_NODUP, /**< Position at last data item of previous key.
191 only for #MDB_DUPSORT */
192 MDB_SET, /**< Position at specified key */
193 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
196 /** @defgroup errors Return Codes
198 * BerkeleyDB uses -30800 to -30999, we'll go under them
201 /** Successful result */
202 #define MDB_SUCCESS 0
203 /** key/data pair already exists */
204 #define MDB_KEYEXIST (-30799)
205 /** key/data pair not found (EOF) */
206 #define MDB_NOTFOUND (-30798)
207 /** Requested page not found - this usually indicates corruption */
208 #define MDB_PAGE_NOTFOUND (-30797)
209 /** Located page was wrong type */
210 #define MDB_CORRUPTED (-30796)
211 /** Update of meta page failed, probably I/O error */
212 #define MDB_PANIC (-30795)
213 /** Environment version mismatch */
214 #define MDB_VERSION_MISMATCH (-30794)
217 /** Statistics for a database in the environment */
218 typedef struct MDB_stat {
219 unsigned int ms_psize; /**< Size of a database page.
220 This is currently the same for all databases. */
221 unsigned int ms_depth; /**< Depth (height) of the B-tree */
222 unsigned long ms_branch_pages; /**< Number of internal (non-leaf) pages */
223 unsigned long ms_leaf_pages; /**< Number of leaf pages */
224 unsigned long ms_overflow_pages; /**< Number of overflow pages */
225 unsigned long ms_entries; /**< Number of data items */
228 /** Return the mdb library version information.
229 * @param[out] major if non-NULL, the library major version number is copied here
230 * @param[out] minor if non-NULL, the library minor version number is copied here
231 * @param[out] patch if non-NULL, the library patch version number is copied here
232 * @retval "version string" The library version as a string
234 char *mdb_version(int *major, int *minor, int *patch);
236 /** Return a string describing a given error code.
237 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
238 * function. If the error code is greater than or equal to 0, then the string
239 * returned by the system function strerror(3) is returned. If the error code
240 * is less than 0, an error string corresponding to the MDB library error is
241 * returned. See @ref errors for a list of MDB-specific error codes.
242 * @param[in] err The error code
243 * @retval "error message" The description of the error
245 char *mdb_strerror(int err);
247 /** Create an MDB environment handle.
248 * This function allocates memory for a #MDB_env structure. To release
249 * the allocated memory and discard the handle, call #mdb_env_close().
250 * Before the handle may be used, it must be opened using #mdb_env_open().
251 * Various other options may also need to be set before opening the handle,
252 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
253 * depending on usage requirements.
254 * @param[out] env The address where the new handle will be stored
255 * @return A non-zero error value on failure and 0 on success.
257 int mdb_env_create(MDB_env **env);
259 /** Open an environment handle.
260 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
261 * @param[in] env An environment handle returned by #mdb_env_create()
262 * @param[in] path The directory in which the database files reside. This
263 * directory must already exist and be writable.
264 * @param[in] flags Special options for this environment. This parameter
265 * must be set to 0 or by bitwise OR'ing together one or more of the
266 * values described here.
269 * use a fixed address for the mmap region. This flag must be specified
270 * when creating the environment, and is stored persistently in the environment.
271 * If successful, the memory map will always reside at the same virtual address
272 * and pointers used to reference data items in the database will be constant
273 * across multiple invocations. This option may not always work, depending on
274 * how the operating system has allocated memory to shared libraries and other uses.
275 * The feature is highly experimental.
277 * Don't perform a synchronous flush after committing a transaction. This means
278 * transactions will exhibit the ACI (atomicity, consistency, and isolation)
279 * properties, but not D (durability); that is database integrity will be
280 * maintained but it is possible some number of the most recently committed
281 * transactions may be undone after a system crash. The number of transactions
282 * at risk is governed by how often the system flushes dirty buffers to disk
283 * and how often #mdb_env_sync() is called. This flag may be changed
284 * at any time using #mdb_env_set_flags().
286 * Open the environment in read-only mode. No write operations will be allowed.
288 * @param[in] mode The UNIX permissions to set on created files. This parameter
289 * is ignored on Windows.
290 * @return A non-zero error value on failure and 0 on success. Some possible
293 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
294 * version that created the database environment.
295 * <li>EINVAL - the environment file headers are corrupted.
296 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
297 * <li>EACCES - the user didn't have permission to access the environment files.
298 * <li>EAGAIN - the environment was locked by another process.
301 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mode_t mode);
303 /** Return statistics about the MDB environment.
304 * @param[in] env An environment handle returned by #mdb_env_create()
305 * @param[out] stat The address of an #MDB_stat structure
306 * where the statistics will be copied
308 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
310 /** Flush the data buffers to disk.
311 * Data is always written to disk when #mdb_txn_commit() is called,
312 * but the operating system may keep it buffered. MDB always flushes
313 * the OS buffers upon commit as well, unless the environment was
314 * opened with #MDB_NOSYNC.
315 * @param[in] env An environment handle returned by #mdb_env_create()
316 * @param[in] force If non-zero, force the flush to occur. Otherwise
317 * if the environment has the #MDB_NOSYNC flag set the flushes
319 * @return A non-zero error value on failure and 0 on success. Some possible
322 * <li>EINVAL - an invalid parameter was specified.
323 * <li>EIO - an error occurred during synchronization.
326 int mdb_env_sync(MDB_env *env, int force);
328 /** Close the environment and release the memory map.
329 * Only a single thread may call this function. All transactions, databases,
330 * and cursors must already be closed before calling this function. Attempts to
331 * use any such handles after calling this function will cause a SIGSEGV.
332 * The environment handle will be freed and must not be used again after this call.
333 * @param[in] env An environment handle returned by #mdb_env_create()
335 void mdb_env_close(MDB_env *env);
337 /** Set environment flags.
338 * This may be used to set some flags that weren't already set during
339 * #mdb_env_open(), or to unset these flags. Currently only the
340 * #MDB_NOSYNC flag setting may be changed with this function.
341 * @param[in] env An environment handle returned by #mdb_env_create()
342 * @param[in] flags The flags to change, bitwise OR'ed together
343 * @param[in] onoff A non-zero value sets the flags, zero clears them.
344 * @return A non-zero error value on failure and 0 on success. Some possible
347 * <li>EINVAL - an invalid parameter was specified.
350 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
352 /** Get environment flags.
353 * @param[in] env An environment handle returned by #mdb_env_create()
354 * @param[out] flags The address of an integer to store the flags
355 * @return A non-zero error value on failure and 0 on success. Some possible
358 * <li>EINVAL - an invalid parameter was specified.
361 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
363 /** Return the path that was used in #mdb_env_open().
364 * @param[in] env An environment handle returned by #mdb_env_create()
365 * @param[out] path Address of a string pointer to contain the path. This
366 * is the actual string in the environment, not a copy. It should not be
367 * altered in any way.
368 * @return A non-zero error value on failure and 0 on success. Some possible
371 * <li>EINVAL - an invalid parameter was specified.
374 int mdb_env_get_path(MDB_env *env, const char **path);
376 /** Set the size of the memory map to use for this environment.
377 * The size should be a multiple of the OS page size. The default is
378 * 10485760 bytes. The size of the memory map is also the maximum size
379 * of the database. The value should be chosen as large as possible,
380 * to accomodate future growth of the database.
381 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
382 * @param[in] env An environment handle returned by #mdb_env_create()
383 * @param[in] size The size in bytes
384 * @return A non-zero error value on failure and 0 on success. Some possible
387 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
390 int mdb_env_set_mapsize(MDB_env *env, size_t size);
392 /** Set the maximum number of threads for the environment.
393 * This defines the number of slots in the lock table that is used to track readers in the
394 * the environment. The default is 126.
395 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
396 * @param[in] env An environment handle returned by #mdb_env_create()
397 * @param[in] readers The maximum number of threads
398 * @return A non-zero error value on failure and 0 on success. Some possible
401 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
404 int mdb_env_set_maxreaders(MDB_env *env, int readers);
406 /** Get the maximum number of threads for the environment.
407 * @param[in] env An environment handle returned by #mdb_env_create()
408 * @param[out] readers Address of an integer to store the number of readers
409 * @return A non-zero error value on failure and 0 on success. Some possible
412 * <li>EINVAL - an invalid parameter was specified.
415 int mdb_env_get_maxreaders(MDB_env *env, int *readers);
417 /** Set the maximum number of databases for the environment.
418 * This function is only needed if multiple databases will be used in the
419 * environment. Simpler applications that only use a single database can ignore
421 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
422 * @param[in] env An environment handle returned by #mdb_env_create()
423 * @param[in] dbs The maximum number of databases
424 * @return A non-zero error value on failure and 0 on success. Some possible
427 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
430 int mdb_env_set_maxdbs(MDB_env *env, int dbs);
432 /** Create a transaction for use with the environment.
433 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
434 * @note Transactions may not span threads, a transaction must only be used by a
436 * @note Cursors may not span transactions; each cursor must be opened and closed
437 * within a single transaction.
438 * @param[in] env An environment handle returned by #mdb_env_create()
439 * @param[in] flags Special options for this transaction. This parameter
440 * must be set to 0 or by bitwise OR'ing together one or more of the
441 * values described here.
444 * This transaction will not perform any write operations.
446 * @param[out] txn Address where the new #MDB_txn handle will be stored
447 * @return A non-zero error value on failure and 0 on success. Some possible
450 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
452 * <li>ENOMEM - out of memory, or a read-only transaction was requested and
453 * the reader lock table is full. See #mdb_env_set_maxreaders().
456 int mdb_txn_begin(MDB_env *env, unsigned int flags, MDB_txn **txn);
458 /** Commit all the operations of a transaction into the database.
459 * All cursors opened within the transaction must be closed before the transaction
461 * The transaction handle will be freed and must not be used again after this call.
462 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
463 * @return A non-zero error value on failure and 0 on success. Some possible
466 * <li>EINVAL - an invalid parameter was specified.
467 * <li>ENOSPC - no more disk space.
468 * <li>EIO - a low-level I/O error occurred while writing.
471 int mdb_txn_commit(MDB_txn *txn);
473 /** Abandon all the operations of the transaction instead of saving them.
474 * All cursors opened within the transaction must be closed before the transaction
476 * The transaction handle will be freed and must not be used again after this call.
477 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
479 void mdb_txn_abort(MDB_txn *txn);
481 /** Reset a read-only transaction.
482 * This releases the current reader lock but doesn't free the
483 * transaction handle, allowing it to be used again later by #mdb_txn_renew().
484 * It otherwise has the same affect as #mdb_txn_abort() but saves some memory
485 * allocation/deallocation overhead if a thread is going to start a new
486 * read-only transaction again soon.
487 * All cursors opened within the transaction must be closed before the transaction
489 * Reader locks generally don't interfere with writers, but they keep old
490 * versions of database pages allocated. Thus they prevent the old pages
491 * from being reused when writers commit new data, and so under heavy load
492 * the database size may grow much more rapidly than otherwise.
493 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
495 void mdb_txn_reset(MDB_txn *txn);
497 /** Renew a read-only transaction.
498 * This acquires a new reader lock for a transaction handle that had been
499 * released by #mdb_txn_reset(). It must be called before a reset transaction
501 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
502 * @return A non-zero error value on failure and 0 on success. Some possible
505 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
507 * <li>EINVAL - an invalid parameter was specified.
510 int mdb_txn_renew(MDB_txn *txn);
512 /** Open a database in the environment.
513 * The database handle may be discarded by calling #mdb_close().
514 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
515 * @param[in] name The name of the database to open. If only a single
516 * database is needed in the enviroment, this value may be NULL.
517 * @param[in] flags Special options for this database. This parameter
518 * must be set to 0 or by bitwise OR'ing together one or more of the
519 * values described here.
521 * <li>#MDB_REVERSEKEY
522 * Keys are strings to be compared in reverse order, from the end
523 * of the strings to the beginning. By default, Keys are treated as strings and
524 * compared from beginning to end.
526 * Duplicate keys may be used in the database. (Or, from another perspective,
527 * keys may have multiple data items, stored in sorted order.) By default
528 * keys must be unique and may have only a single data item.
529 * <li>#MDB_INTEGERKEY
530 * Keys are binary integers in native byte order. On Big-Endian systems
531 * this flag has no effect. On Little-Endian systems this flag behaves
532 * the same as #MDB_REVERSEKEY. This flag is simply provided as a
533 * convenience so that applications don't need to detect Endianness themselves
534 * when using integers as keys.
536 * This flag may only be used in combination with #MDB_DUPSORT. This option
537 * tells the library that the data items for this database are all the same
538 * size, which allows further optimizations in storage and retrieval. When
539 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
540 * cursor operations may be used to retrieve multiple items at once.
541 * <li>#MDB_INTEGERDUP
542 * This option specifies that duplicate data items are also integers, and
543 * should be sorted as such.
545 * Create the named database if it doesn't exist. This option is not
546 * allowed in a read-only transaction or a read-only environment.
548 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
549 * @return A non-zero error value on failure and 0 on success. Some possible
552 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
553 * and #MDB_CREATE was not specified.
554 * <li>ENFILE - too many databases have been opened. See #mdb_env_set_maxdbs().
557 int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
559 /** Retrieve statistics for a database.
560 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
561 * @param[in] dbi A database handle returned by #mdb_open()
562 * @param[out] stat The address of an #MDB_stat structure
563 * where the statistics will be copied
564 * @return A non-zero error value on failure and 0 on success. Some possible
567 * <li>EINVAL - an invalid parameter was specified.
570 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
572 /** Close a database handle.
573 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
574 * @param[in] dbi A database handle returned by #mdb_open()
576 void mdb_close(MDB_txn *txn, MDB_dbi dbi);
578 /** Set a custom key comparison function for a database.
579 * The comparison function is called whenever it is necessary to compare a
580 * key specified by the application with a key currently stored in the database.
581 * If no comparison function is specified, and no special key flags were specified
582 * with #mdb_open(), the keys are compared lexically, with shorter keys collating
583 * before longer keys.
584 * @warning This function must be called before any data access functions are used,
585 * otherwise data corruption may occur. The same function must be used by every
586 * process accessing the database, every time the database is used.
587 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
588 * @param[in] dbi A database handle returned by #mdb_open()
589 * @param[in] cmp A #MDB_cmp_func function
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_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
598 /** Set a custom data comparison function for a #MDB_DUPSORT database.
599 * This comparison function is called whenever it is necessary to compare a data
600 * item specified by the application with a data item currently stored in the database.
601 * This function only takes effect if the database was opened with the #MDB_DUPSORT
603 * If no comparison function is specified, and no special key flags were specified
604 * with #mdb_open(), the data items are compared lexically, with shorter items collating
605 * before longer items.
606 * @warning This function must be called before any data access functions are used,
607 * otherwise data corruption may occur. The same function must be used by every
608 * process accessing the database, every time the database is used.
609 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
610 * @param[in] dbi A database handle returned by #mdb_open()
611 * @param[in] cmp A #MDB_cmp_func function
612 * @return A non-zero error value on failure and 0 on success. Some possible
615 * <li>EINVAL - an invalid parameter was specified.
618 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
620 /** Set a relocation function for a #MDB_FIXEDMAP database.
621 * @todo The relocation function is called whenever it is necessary to move the data
622 * of an item to a different position in the database (e.g. through tree
623 * balancing operations, shifts as a result of adds or deletes, etc.). It is
624 * intended to allow address/position-dependent data items to be stored in
625 * a database in an environment opened with the #MDB_FIXEDMAP option.
626 * Currently the relocation feature is unimplemented and setting
627 * this function has no effect.
628 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
629 * @param[in] dbi A database handle returned by #mdb_open()
630 * @param[in] rel A #MDB_rel_func function
631 * @return A non-zero error value on failure and 0 on success. Some possible
634 * <li>EINVAL - an invalid parameter was specified.
637 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
639 /** Get items from a database.
640 * This function retrieves key/data pairs from the database. The address
641 * and length of the data associated with the specified \b key are returned
642 * in the structure to which \b data refers.
643 * If the database supports duplicate keys (#MDB_DUPSORT) then the
644 * first data item for the key will be returned. Retrieval of other
645 * items requires the use of #mdb_cursor_get().
646 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
647 * @param[in] dbi A database handle returned by #mdb_open()
648 * @param[in] key The key to search for in the database
649 * @param[out] data The data corresponding to the key
650 * @return A non-zero error value on failure and 0 on success. Some possible
653 * <li>#MDB_NOTFOUND - the key was not in the database.
654 * <li>EINVAL - an invalid parameter was specified.
657 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
659 /** Store items into a database.
660 * This function stores key/data pairs in the database. The default behavior
661 * is to enter the new key/data pair, replacing any previously existing key
662 * if duplicates are disallowed, or adding a duplicate data item if
663 * duplicates are allowed (#MDB_DUPSORT).
664 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
665 * @param[in] dbi A database handle returned by #mdb_open()
666 * @param[in] key The key to store in the database
667 * @param[in] data The data to store
668 * @param[in] flags Special options for this operation. This parameter
669 * must be set to 0 or by bitwise OR'ing together one or more of the
670 * values described here.
672 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
673 * already appear in the database. This flag may only be specified
674 * if the database was opened with #MDB_DUPSORT. The function will
675 * return #MDB_KEYEXIST if the key/data pair already appears in the
677 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
678 * does not already appear in the database. The function will return
679 * #MDB_KEYEXIST if the key already appears in the database, even if
680 * the database supports duplicates (#MDB_DUPSORT).
682 * @return A non-zero error value on failure and 0 on success. Some possible
685 * <li>EACCESS - an attempt was made to write in a read-only transaction.
686 * <li>EINVAL - an invalid parameter was specified.
687 * <li>ENOMEM - the database is full, see #mdb_env_set_mapsize().
690 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
693 /** Delete items from a database.
694 * This function removes key/data pairs from the database.
695 * If the database does not support sorted duplicate data items
696 * (#MDB_DUPSORT) the data parameter is ignored.
697 * If the database supports sorted duplicates and the data parameter
698 * is NULL, all of the duplicate data items for the key will be
699 * deleted. Otherwise, if the data parameter is non-NULL
700 * only the matching data item will be deleted.
701 * This function will return #MDB_NOTFOUND if the specified key/data
702 * pair is not in the database.
703 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
704 * @param[in] dbi A database handle returned by #mdb_open()
705 * @param[in] key The key to delete from the database
706 * @param[in] data The data to delete
707 * @return A non-zero error value on failure and 0 on success. Some possible
710 * <li>EACCESS - an attempt was made to write in a read-only transaction.
711 * <li>EINVAL - an invalid parameter was specified.
714 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
716 /** Create a cursor handle.
717 * Cursors are associated with a specific transaction and database and
718 * may not span threads.
719 * @todo Cursors only support read operations. Support for cursor_put() and
720 * cursor_del() needs to be added.
721 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
722 * @param[in] dbi A database handle returned by #mdb_open()
723 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
724 * @return A non-zero error value on failure and 0 on success. Some possible
727 * <li>EINVAL - an invalid parameter was specified.
730 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
732 /** Close a cursor handle.
733 * The cursor handle will be freed and must not be used again after this call.
734 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
736 void mdb_cursor_close(MDB_cursor *cursor);
738 /** Retrieve by cursor.
739 * This function retrieves key/data pairs from the database. The address and length
740 * of the key are returned in the object to which \b key refers (except for the
741 * case of the #MDB_SET option, in which the \b key object is unchanged), and
742 * the address and length of the data are returned in the object to which \b data
744 * @bug Cursors are not coordinated with write operations. If a cursor in a
745 * write transaction is performing a sequential scan while records are being
746 * inserted or deleted in the same transaction, the cursor will be corrupted.
747 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
748 * @param[in,out] key The key for a retrieved item
749 * @param[in,out] data The data of a retrieved item
750 * @param[in] op A cursor operation #MDB_cursor_op
751 * @return A non-zero error value on failure and 0 on success. Some possible
754 * <li>#MDB_NOTFOUND - no matching key found.
755 * <li>EINVAL - an invalid parameter was specified.
758 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
761 /** Return count of duplicates for current key.
762 * This call is only valid on databases that support sorted duplicate
763 * data items #MDB_DUPSORT.
764 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
765 * @param[out] countp Address where the count will be stored
766 * @return A non-zero error value on failure and 0 on success. Some possible
769 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
772 int mdb_cursor_count(MDB_cursor *cursor, unsigned long *countp);
774 /** Compare two data items according to a particular database.
775 * This returns a comparison as if the two data items were keys in the
776 * specified database.
777 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
778 * @param[in] dbi A database handle returned by #mdb_open()
779 * @param[in] a The first item to compare
780 * @param[in] b The second item to compare
781 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
783 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);