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 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 when 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 * The memory map can be used as a read-only or read-write map. It is
35 * read-only by default as this provides total immunity to corruption.
36 * Using read-write mode offers much higher write performance, but adds
37 * the possibility for stray application writes thru pointers to silently
38 * corrupt the database. Of course if your application code is known to
39 * be bug-free (...) then this is not an issue.
41 * @author Howard Chu, Symas Corporation.
43 * @copyright Copyright 2011-2012 Howard Chu, Symas Corp. All rights reserved.
45 * Redistribution and use in source and binary forms, with or without
46 * modification, are permitted only as authorized by the OpenLDAP
49 * A copy of this license is available in the file LICENSE in the
50 * top-level directory of the distribution or, alternatively, at
51 * <http://www.OpenLDAP.org/license.html>.
54 * This code is derived from btree.c written by Martin Hedenfalk.
56 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
58 * Permission to use, copy, modify, and distribute this software for any
59 * purpose with or without fee is hereby granted, provided that the above
60 * copyright notice and this permission notice appear in all copies.
62 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
63 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
64 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
65 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
66 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
67 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
68 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
73 #include <sys/types.h>
79 /** @defgroup public Public API
82 /** @defgroup Version Version Macros
85 /** Library major version */
86 #define MDB_VERSION_MAJOR 0
87 /** Library minor version */
88 #define MDB_VERSION_MINOR 9
89 /** Library patch version */
90 #define MDB_VERSION_PATCH 4
92 /** Combine args a,b,c into a single integer for easy version comparisons */
93 #define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
95 /** The full library version as a single integer */
96 #define MDB_VERSION_FULL \
97 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
99 /** The release date of this library version */
100 #define MDB_VERSION_DATE "September 14, 2012"
102 /** A stringifier for the version info */
103 #define MDB_VERSTR(a,b,c,d) "MDB " #a "." #b "." #c ": (" d ")"
105 /** A helper for the stringifier macro */
106 #define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d)
108 /** The full library version as a C string */
109 #define MDB_VERSION_STRING \
110 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
113 /** @brief Opaque structure for a database environment.
115 * A DB environment supports multiple databases, all residing in the same
118 typedef struct MDB_env MDB_env;
120 /** @brief Opaque structure for a transaction handle.
122 * All database operations require a transaction handle. Transactions may be
123 * read-only or read-write.
125 typedef struct MDB_txn MDB_txn;
127 /** @brief A handle for an individual database in the DB environment. */
128 typedef unsigned int MDB_dbi;
130 /** @brief Opaque structure for navigating through a database */
131 typedef struct MDB_cursor MDB_cursor;
133 /** @brief Generic structure used for passing keys and data in and out of the database. */
134 typedef struct MDB_val {
135 size_t mv_size; /**< size of the data item */
136 void *mv_data; /**< address of the data item */
139 /** @brief A callback function used to compare two keys in a database */
140 typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
142 /** @brief A callback function used to relocate a position-dependent data item
143 * in a fixed-address database.
145 * The \b newptr gives the item's desired address in
146 * the memory map, and \b oldptr gives its previous address. The item's actual
147 * data resides at the address in \b item. This callback is expected to walk
148 * through the fields of the record in \b item and modify any
149 * values based at the \b oldptr address to be relative to the \b newptr address.
150 * @param[in,out] item The item that is to be relocated.
151 * @param[in] oldptr The previous address.
152 * @param[in] newptr The new address to relocate to.
153 * @param[in] relctx An application-provided context, set by #mdb_set_relctx().
154 * @todo This feature is currently unimplemented.
156 typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
158 /** @defgroup mdb_env Environment Flags
161 /** mmap at a fixed address */
162 #define MDB_FIXEDMAP 0x01
163 /** no environment directory */
164 #define MDB_NOSUBDIR 0x02
165 /** don't fsync after commit */
166 #define MDB_NOSYNC 0x10000
168 #define MDB_RDONLY 0x20000
169 /** don't fsync metapage after commit */
170 #define MDB_NOMETASYNC 0x40000
171 /** use writable mmap */
172 #define MDB_WRITEMAP 0x80000
173 /** use asynchronous msync */
174 #define MDB_MAPASYNC 0x100000
177 /** @defgroup mdb_open Database Flags
180 /** use reverse string keys */
181 #define MDB_REVERSEKEY 0x02
182 /** use sorted duplicates */
183 #define MDB_DUPSORT 0x04
184 /** numeric keys in native byte order.
185 * The keys must all be of the same size. */
186 #define MDB_INTEGERKEY 0x08
187 /** with #MDB_DUPSORT, sorted dup items have fixed size */
188 #define MDB_DUPFIXED 0x10
189 /** with #MDB_DUPSORT, dups are numeric in native byte order */
190 #define MDB_INTEGERDUP 0x20
191 /** with #MDB_DUPSORT, use reverse string dups */
192 #define MDB_REVERSEDUP 0x40
193 /** create DB if not already existing */
194 #define MDB_CREATE 0x40000
197 /** @defgroup mdb_put Write Flags
200 /** For put: Don't write if the key already exists. */
201 #define MDB_NOOVERWRITE 0x10
202 /** Only for #MDB_DUPSORT<br>
203 * For put: don't write if the key and data pair already exist.<br>
204 * For mdb_cursor_del: remove all duplicate data items.
206 #define MDB_NODUPDATA 0x20
207 /** For mdb_cursor_put: overwrite the current key/data pair */
208 #define MDB_CURRENT 0x40
209 /** For put: Just reserve space for data, don't copy it. Return a
210 * pointer to the reserved space.
212 #define MDB_RESERVE 0x10000
213 /** Data is being appended, don't split full pages. */
214 #define MDB_APPEND 0x20000
215 /** Duplicate data is being appended, don't split full pages. */
216 #define MDB_APPENDDUP 0x40000
217 /** Store multiple data items in one call. */
218 #define MDB_MULTIPLE 0x80000
221 /** @brief Cursor Get operations.
223 * This is the set of all operations for retrieving data
226 typedef enum MDB_cursor_op {
227 MDB_FIRST, /**< Position at first key/data item */
228 MDB_FIRST_DUP, /**< Position at first data item of current key.
229 Only for #MDB_DUPSORT */
230 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
231 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
232 MDB_GET_MULTIPLE, /**< Return all the duplicate data items at the current
233 cursor position. Only for #MDB_DUPFIXED */
234 MDB_LAST, /**< Position at last key/data item */
235 MDB_LAST_DUP, /**< Position at last data item of current key.
236 Only for #MDB_DUPSORT */
237 MDB_NEXT, /**< Position at next data item */
238 MDB_NEXT_DUP, /**< Position at next data item of current key.
239 Only for #MDB_DUPSORT */
240 MDB_NEXT_MULTIPLE, /**< Return all duplicate data items at the next
241 cursor position. Only for #MDB_DUPFIXED */
242 MDB_NEXT_NODUP, /**< Position at first data item of next key.
243 Only for #MDB_DUPSORT */
244 MDB_PREV, /**< Position at previous data item */
245 MDB_PREV_DUP, /**< Position at previous data item of current key.
246 Only for #MDB_DUPSORT */
247 MDB_PREV_NODUP, /**< Position at last data item of previous key.
248 Only for #MDB_DUPSORT */
249 MDB_SET, /**< Position at specified key */
250 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
253 /** @defgroup errors Return Codes
255 * BerkeleyDB uses -30800 to -30999, we'll go under them
258 /** Successful result */
259 #define MDB_SUCCESS 0
260 /** key/data pair already exists */
261 #define MDB_KEYEXIST (-30799)
262 /** key/data pair not found (EOF) */
263 #define MDB_NOTFOUND (-30798)
264 /** Requested page not found - this usually indicates corruption */
265 #define MDB_PAGE_NOTFOUND (-30797)
266 /** Located page was wrong type */
267 #define MDB_CORRUPTED (-30796)
268 /** Update of meta page failed, probably I/O error */
269 #define MDB_PANIC (-30795)
270 /** Environment version mismatch */
271 #define MDB_VERSION_MISMATCH (-30794)
272 /** File is not a valid MDB file */
273 #define MDB_INVALID (-30793)
274 /** Environment mapsize reached */
275 #define MDB_MAP_FULL (-30792)
276 /** Environment maxdbs reached */
277 #define MDB_DBS_FULL (-30791)
278 /** Environment maxreaders reached */
279 #define MDB_READERS_FULL (-30790)
280 /** Too many TLS keys in use - Windows only */
281 #define MDB_TLS_FULL (-30789)
282 /** Nested txn has too many dirty pages */
283 #define MDB_TXN_FULL (-30788)
284 /** Cursor stack too deep - internal error */
285 #define MDB_CURSOR_FULL (-30787)
286 /** Page has not enough space - internal error */
287 #define MDB_PAGE_FULL (-30786)
290 /** @brief Statistics for a database in the environment */
291 typedef struct MDB_stat {
292 unsigned int ms_psize; /**< Size of a database page.
293 This is currently the same for all databases. */
294 unsigned int ms_depth; /**< Depth (height) of the B-tree */
295 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
296 size_t ms_leaf_pages; /**< Number of leaf pages */
297 size_t ms_overflow_pages; /**< Number of overflow pages */
298 size_t ms_entries; /**< Number of data items */
301 /** @brief Return the mdb library version information.
303 * @param[out] major if non-NULL, the library major version number is copied here
304 * @param[out] minor if non-NULL, the library minor version number is copied here
305 * @param[out] patch if non-NULL, the library patch version number is copied here
306 * @retval "version string" The library version as a string
308 char *mdb_version(int *major, int *minor, int *patch);
310 /** @brief Return a string describing a given error code.
312 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
313 * function. If the error code is greater than or equal to 0, then the string
314 * returned by the system function strerror(3) is returned. If the error code
315 * is less than 0, an error string corresponding to the MDB library error is
316 * returned. See @ref errors for a list of MDB-specific error codes.
317 * @param[in] err The error code
318 * @retval "error message" The description of the error
320 char *mdb_strerror(int err);
322 /** @brief Create an MDB environment handle.
324 * This function allocates memory for a #MDB_env structure. To release
325 * the allocated memory and discard the handle, call #mdb_env_close().
326 * Before the handle may be used, it must be opened using #mdb_env_open().
327 * Various other options may also need to be set before opening the handle,
328 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
329 * depending on usage requirements.
330 * @param[out] env The address where the new handle will be stored
331 * @return A non-zero error value on failure and 0 on success.
333 int mdb_env_create(MDB_env **env);
335 /** @brief Open an environment handle.
337 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
338 * @param[in] env An environment handle returned by #mdb_env_create()
339 * @param[in] path The directory in which the database files reside. This
340 * directory must already exist and be writable.
341 * @param[in] flags Special options for this environment. This parameter
342 * must be set to 0 or by bitwise OR'ing together one or more of the
343 * values described here.
346 * use a fixed address for the mmap region. This flag must be specified
347 * when creating the environment, and is stored persistently in the environment.
348 * If successful, the memory map will always reside at the same virtual address
349 * and pointers used to reference data items in the database will be constant
350 * across multiple invocations. This option may not always work, depending on
351 * how the operating system has allocated memory to shared libraries and other uses.
352 * The feature is highly experimental.
354 * By default, MDB creates its environment in a directory whose
355 * pathname is given in \b path, and creates its data and lock files
356 * under that directory. With this option, \b path is used as-is for
357 * the database main data file. The database lock file is the \b path
358 * with "-lock" appended.
360 * Don't perform a synchronous flush after committing a transaction. This means
361 * transactions will exhibit the ACI (atomicity, consistency, and isolation)
362 * properties, but not D (durability); that is database integrity will be
363 * maintained but it is possible some number of the most recently committed
364 * transactions may be undone after a system crash. The number of transactions
365 * at risk is governed by how often the system flushes dirty buffers to disk
366 * and how often #mdb_env_sync() is called. This flag may be changed
367 * at any time using #mdb_env_set_flags().
368 * <li>#MDB_NOMETASYNC
369 * Don't perform a synchronous flush of the meta page after committing
370 * a transaction. This is similar to the #MDB_NOSYNC case, but safer
371 * because the transaction data is still flushed. The meta page for any
372 * transaction N will be flushed by the data flush of transaction N+1.
373 * In case of a system crash, the last committed transaction may be
374 * lost. This flag may be changed at any time using #mdb_env_set_flags().
376 * Open the environment in read-only mode. No write operations will be allowed.
378 * @param[in] mode The UNIX permissions to set on created files. This parameter
379 * is ignored on Windows.
380 * @return A non-zero error value on failure and 0 on success. Some possible
383 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
384 * version that created the database environment.
385 * <li>EINVAL - the environment file headers are corrupted.
386 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
387 * <li>EACCES - the user didn't have permission to access the environment files.
388 * <li>EAGAIN - the environment was locked by another process.
391 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mode_t mode);
393 /** @brief Return statistics about the MDB environment.
395 * @param[in] env An environment handle returned by #mdb_env_create()
396 * @param[out] stat The address of an #MDB_stat structure
397 * where the statistics will be copied
399 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
401 /** @brief Flush the data buffers to disk.
403 * Data is always written to disk when #mdb_txn_commit() is called,
404 * but the operating system may keep it buffered. MDB always flushes
405 * the OS buffers upon commit as well, unless the environment was
406 * opened with #MDB_NOSYNC.
407 * @param[in] env An environment handle returned by #mdb_env_create()
408 * @param[in] force If non-zero, force the flush to occur. Otherwise
409 * if the environment has the #MDB_NOSYNC flag set the flushes
411 * @return A non-zero error value on failure and 0 on success. Some possible
414 * <li>EINVAL - an invalid parameter was specified.
415 * <li>EIO - an error occurred during synchronization.
418 int mdb_env_sync(MDB_env *env, int force);
420 /** @brief Close the environment and release the memory map.
422 * Only a single thread may call this function. All transactions, databases,
423 * and cursors must already be closed before calling this function. Attempts to
424 * use any such handles after calling this function will cause a SIGSEGV.
425 * The environment handle will be freed and must not be used again after this call.
426 * @param[in] env An environment handle returned by #mdb_env_create()
428 void mdb_env_close(MDB_env *env);
430 /** @brief Set environment flags.
432 * This may be used to set some flags that weren't already set during
433 * #mdb_env_open(), or to unset these flags.
434 * @param[in] env An environment handle returned by #mdb_env_create()
435 * @param[in] flags The flags to change, bitwise OR'ed together
436 * @param[in] onoff A non-zero value sets the flags, zero clears them.
437 * @return A non-zero error value on failure and 0 on success. Some possible
440 * <li>EINVAL - an invalid parameter was specified.
443 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
445 /** @brief Get environment flags.
447 * @param[in] env An environment handle returned by #mdb_env_create()
448 * @param[out] flags The address of an integer to store the flags
449 * @return A non-zero error value on failure and 0 on success. Some possible
452 * <li>EINVAL - an invalid parameter was specified.
455 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
457 /** @brief Return the path that was used in #mdb_env_open().
459 * @param[in] env An environment handle returned by #mdb_env_create()
460 * @param[out] path Address of a string pointer to contain the path. This
461 * is the actual string in the environment, not a copy. It should not be
462 * altered in any way.
463 * @return A non-zero error value on failure and 0 on success. Some possible
466 * <li>EINVAL - an invalid parameter was specified.
469 int mdb_env_get_path(MDB_env *env, const char **path);
471 /** @brief Set the size of the memory map to use for this environment.
473 * The size should be a multiple of the OS page size. The default is
474 * 10485760 bytes. The size of the memory map is also the maximum size
475 * of the database. The value should be chosen as large as possible,
476 * to accommodate future growth of the database.
477 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
478 * @param[in] env An environment handle returned by #mdb_env_create()
479 * @param[in] size The size in bytes
480 * @return A non-zero error value on failure and 0 on success. Some possible
483 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
486 int mdb_env_set_mapsize(MDB_env *env, size_t size);
488 /** @brief Set the maximum number of threads for the environment.
490 * This defines the number of slots in the lock table that is used to track readers in the
491 * the environment. The default is 126.
492 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
493 * @param[in] env An environment handle returned by #mdb_env_create()
494 * @param[in] readers The maximum number of threads
495 * @return A non-zero error value on failure and 0 on success. Some possible
498 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
501 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
503 /** @brief Get the maximum number of threads for the environment.
505 * @param[in] env An environment handle returned by #mdb_env_create()
506 * @param[out] readers Address of an integer to store the number of readers
507 * @return A non-zero error value on failure and 0 on success. Some possible
510 * <li>EINVAL - an invalid parameter was specified.
513 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
515 /** @brief Set the maximum number of databases for the environment.
517 * This function is only needed if multiple databases will be used in the
518 * environment. Simpler applications that only use a single database can ignore
520 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
521 * @param[in] env An environment handle returned by #mdb_env_create()
522 * @param[in] dbs The maximum number of databases
523 * @return A non-zero error value on failure and 0 on success. Some possible
526 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
529 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
531 /** @brief Create a transaction for use with the environment.
533 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
534 * @note Transactions may not span threads; a transaction must only be used by a
535 * single thread. Also, a thread may only have a single transaction.
536 * @note Cursors may not span transactions; each cursor must be opened and closed
537 * within a single transaction.
538 * @param[in] env An environment handle returned by #mdb_env_create()
539 * @param[in] parent If this parameter is non-NULL, the new transaction
540 * will be a nested transaction, with the transaction indicated by \b parent
541 * as its parent. Transactions may be nested to any level. A parent
542 * transaction may not issue any other operations besides mdb_txn_begin,
543 * mdb_txn_abort, or mdb_txn_commit while it has active child transactions.
544 * @param[in] flags Special options for this transaction. This parameter
545 * must be set to 0 or by bitwise OR'ing together one or more of the
546 * values described here.
549 * This transaction will not perform any write operations.
551 * @param[out] txn Address where the new #MDB_txn handle will be stored
552 * @return A non-zero error value on failure and 0 on success. Some possible
555 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
557 * <li>ENOMEM - out of memory, or a read-only transaction was requested and
558 * the reader lock table is full. See #mdb_env_set_maxreaders().
561 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
563 /** @brief Commit all the operations of a transaction into the database.
565 * All cursors opened within the transaction will be closed by this call. The cursors
566 * and transaction handle will be freed and must not be used again after this call.
567 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
568 * @return A non-zero error value on failure and 0 on success. Some possible
571 * <li>EINVAL - an invalid parameter was specified.
572 * <li>ENOSPC - no more disk space.
573 * <li>EIO - a low-level I/O error occurred while writing.
574 * <li>ENOMEM - the transaction is nested and could not be merged into its parent.
577 int mdb_txn_commit(MDB_txn *txn);
579 /** @brief Abandon all the operations of the transaction instead of saving them.
581 * All cursors opened within the transaction will be closed by this call. The cursors
582 * and transaction handle will be freed and must not be used again after this call.
583 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
585 void mdb_txn_abort(MDB_txn *txn);
587 /** @brief Reset a read-only transaction.
589 * This releases the current reader lock but doesn't free the
590 * transaction handle, allowing it to be used again later by #mdb_txn_renew().
591 * It otherwise has the same effect as #mdb_txn_abort() but saves some memory
592 * allocation/deallocation overhead if a thread is going to start a new
593 * read-only transaction again soon.
594 * All cursors opened within the transaction must be closed before the transaction
596 * Reader locks generally don't interfere with writers, but they keep old
597 * versions of database pages allocated. Thus they prevent the old pages
598 * from being reused when writers commit new data, and so under heavy load
599 * the database size may grow much more rapidly than otherwise.
600 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
602 void mdb_txn_reset(MDB_txn *txn);
604 /** @brief Renew a read-only transaction.
606 * This acquires a new reader lock for a transaction handle that had been
607 * released by #mdb_txn_reset(). It must be called before a reset transaction
609 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
610 * @return A non-zero error value on failure and 0 on success. Some possible
613 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
615 * <li>EINVAL - an invalid parameter was specified.
618 int mdb_txn_renew(MDB_txn *txn);
620 /** @brief Open a database in the environment.
622 * The database handle may be discarded by calling #mdb_close(). The
623 * database handle resides in the shared environment, it is not owned
624 * by the given transaction. Only one thread should call this function;
625 * it is not mutex-protected in a read-only transaction.
626 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
627 * @param[in] name The name of the database to open. If only a single
628 * database is needed in the environment, this value may be NULL.
629 * @param[in] flags Special options for this database. This parameter
630 * must be set to 0 or by bitwise OR'ing together one or more of the
631 * values described here.
633 * <li>#MDB_REVERSEKEY
634 * Keys are strings to be compared in reverse order, from the end
635 * of the strings to the beginning. By default, Keys are treated as strings and
636 * compared from beginning to end.
638 * Duplicate keys may be used in the database. (Or, from another perspective,
639 * keys may have multiple data items, stored in sorted order.) By default
640 * keys must be unique and may have only a single data item.
641 * <li>#MDB_INTEGERKEY
642 * Keys are binary integers in native byte order. Setting this option
643 * requires all keys to be the same size, typically sizeof(int)
646 * This flag may only be used in combination with #MDB_DUPSORT. This option
647 * tells the library that the data items for this database are all the same
648 * size, which allows further optimizations in storage and retrieval. When
649 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
650 * cursor operations may be used to retrieve multiple items at once.
651 * <li>#MDB_INTEGERDUP
652 * This option specifies that duplicate data items are also integers, and
653 * should be sorted as such.
654 * <li>#MDB_REVERSEDUP
655 * This option specifies that duplicate data items should be compared as
656 * strings in reverse order.
658 * Create the named database if it doesn't exist. This option is not
659 * allowed in a read-only transaction or a read-only environment.
661 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
662 * @return A non-zero error value on failure and 0 on success. Some possible
665 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
666 * and #MDB_CREATE was not specified.
667 * <li>ENFILE - too many databases have been opened. See #mdb_env_set_maxdbs().
670 int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
672 /** @brief Retrieve statistics for a database.
674 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
675 * @param[in] dbi A database handle returned by #mdb_open()
676 * @param[out] stat The address of an #MDB_stat structure
677 * where the statistics will be copied
678 * @return A non-zero error value on failure and 0 on success. Some possible
681 * <li>EINVAL - an invalid parameter was specified.
684 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
686 /** @brief Close a database handle.
688 * This call is not mutex protected. Handles should only be closed by
689 * a single thread, and only if no other threads are going to reference
690 * the database handle any further.
691 * @param[in] env An environment handle returned by #mdb_env_create()
692 * @param[in] dbi A database handle returned by #mdb_open()
694 void mdb_close(MDB_env *env, MDB_dbi dbi);
696 /** @brief Delete a database and/or free all its pages.
698 * If the \b del parameter is non-zero the DB handle will be closed
699 * and the DB will be deleted.
700 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
701 * @param[in] dbi A database handle returned by #mdb_open()
702 * @param[in] del non-zero to delete the DB from the environment,
703 * otherwise just free its pages.
704 * @return A non-zero error value on failure and 0 on success.
706 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
708 /** @brief Set a custom key comparison function for a database.
710 * The comparison function is called whenever it is necessary to compare a
711 * key specified by the application with a key currently stored in the database.
712 * If no comparison function is specified, and no special key flags were specified
713 * with #mdb_open(), the keys are compared lexically, with shorter keys collating
714 * before longer keys.
715 * @warning This function must be called before any data access functions are used,
716 * otherwise data corruption may occur. The same comparison function must be used by every
717 * program accessing the database, every time the database is used.
718 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
719 * @param[in] dbi A database handle returned by #mdb_open()
720 * @param[in] cmp A #MDB_cmp_func function
721 * @return A non-zero error value on failure and 0 on success. Some possible
724 * <li>EINVAL - an invalid parameter was specified.
727 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
729 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
731 * This comparison function is called whenever it is necessary to compare a data
732 * item specified by the application with a data item currently stored in the database.
733 * This function only takes effect if the database was opened with the #MDB_DUPSORT
735 * If no comparison function is specified, and no special key flags were specified
736 * with #mdb_open(), the data items are compared lexically, with shorter items collating
737 * before longer items.
738 * @warning This function must be called before any data access functions are used,
739 * otherwise data corruption may occur. The same comparison function must be used by every
740 * program accessing the database, every time the database is used.
741 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
742 * @param[in] dbi A database handle returned by #mdb_open()
743 * @param[in] cmp A #MDB_cmp_func function
744 * @return A non-zero error value on failure and 0 on success. Some possible
747 * <li>EINVAL - an invalid parameter was specified.
750 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
752 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
754 * @todo The relocation function is called whenever it is necessary to move the data
755 * of an item to a different position in the database (e.g. through tree
756 * balancing operations, shifts as a result of adds or deletes, etc.). It is
757 * intended to allow address/position-dependent data items to be stored in
758 * a database in an environment opened with the #MDB_FIXEDMAP option.
759 * Currently the relocation feature is unimplemented and setting
760 * this function has no effect.
761 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
762 * @param[in] dbi A database handle returned by #mdb_open()
763 * @param[in] rel A #MDB_rel_func function
764 * @return A non-zero error value on failure and 0 on success. Some possible
767 * <li>EINVAL - an invalid parameter was specified.
770 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
772 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
774 * See #mdb_set_relfunc and #MDB_rel_func for more details.
775 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
776 * @param[in] dbi A database handle returned by #mdb_open()
777 * @param[in] ctx An arbitrary pointer for whatever the application needs.
778 * It will be passed to the callback function set by #mdb_set_relfunc
779 * as its \b relctx parameter whenever the callback is invoked.
780 * @return A non-zero error value on failure and 0 on success. Some possible
783 * <li>EINVAL - an invalid parameter was specified.
786 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
788 /** @brief Get items from a database.
790 * This function retrieves key/data pairs from the database. The address
791 * and length of the data associated with the specified \b key are returned
792 * in the structure to which \b data refers.
793 * If the database supports duplicate keys (#MDB_DUPSORT) then the
794 * first data item for the key will be returned. Retrieval of other
795 * items requires the use of #mdb_cursor_get().
797 * @note The memory pointed to by the returned values is owned by the
798 * database. The caller need not dispose of the memory, and may not
799 * modify it in any way. For values returned in a read-only transaction
800 * any modification attempts will cause a SIGSEGV.
801 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
802 * @param[in] dbi A database handle returned by #mdb_open()
803 * @param[in] key The key to search for in the database
804 * @param[out] data The data corresponding to the key
805 * @return A non-zero error value on failure and 0 on success. Some possible
808 * <li>#MDB_NOTFOUND - the key was not in the database.
809 * <li>EINVAL - an invalid parameter was specified.
812 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
814 /** @brief Store items into a database.
816 * This function stores key/data pairs in the database. The default behavior
817 * is to enter the new key/data pair, replacing any previously existing key
818 * if duplicates are disallowed, or adding a duplicate data item if
819 * duplicates are allowed (#MDB_DUPSORT).
820 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
821 * @param[in] dbi A database handle returned by #mdb_open()
822 * @param[in] key The key to store in the database
823 * @param[in,out] data The data to store
824 * @param[in] flags Special options for this operation. This parameter
825 * must be set to 0 or by bitwise OR'ing together one or more of the
826 * values described here.
828 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
829 * already appear in the database. This flag may only be specified
830 * if the database was opened with #MDB_DUPSORT. The function will
831 * return #MDB_KEYEXIST if the key/data pair already appears in the
833 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
834 * does not already appear in the database. The function will return
835 * #MDB_KEYEXIST if the key already appears in the database, even if
836 * the database supports duplicates (#MDB_DUPSORT). The \b data
837 * parameter will be set to point to the existing item.
838 * <li>#MDB_RESERVE - reserve space for data of the given size, but
839 * don't copy the given data. Instead, return a pointer to the
840 * reserved space, which the caller can fill in later. This saves
841 * an extra memcpy if the data is being generated later.
842 * <li>#MDB_APPEND - append the given key/data pair to the end of the
843 * database. No key comparisons are performed. This option allows
844 * fast bulk loading when keys are already known to be in the
845 * correct order. Loading unsorted keys with this flag will cause
847 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
849 * @return A non-zero error value on failure and 0 on success. Some possible
852 * <li>EACCES - an attempt was made to write in a read-only transaction.
853 * <li>EINVAL - an invalid parameter was specified.
854 * <li>ENOMEM - the database is full, see #mdb_env_set_mapsize().
857 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
860 /** @brief Delete items from a database.
862 * This function removes key/data pairs from the database.
863 * If the database does not support sorted duplicate data items
864 * (#MDB_DUPSORT) the data parameter is ignored.
865 * If the database supports sorted duplicates and the data parameter
866 * is NULL, all of the duplicate data items for the key will be
867 * deleted. Otherwise, if the data parameter is non-NULL
868 * only the matching data item will be deleted.
869 * This function will return #MDB_NOTFOUND if the specified key/data
870 * pair is not in the database.
871 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
872 * @param[in] dbi A database handle returned by #mdb_open()
873 * @param[in] key The key to delete from the database
874 * @param[in] data The data to delete
875 * @return A non-zero error value on failure and 0 on success. Some possible
878 * <li>EACCES - an attempt was made to write in a read-only transaction.
879 * <li>EINVAL - an invalid parameter was specified.
882 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
884 /** @brief Create a cursor handle.
886 * Cursors are associated with a specific transaction and database and
887 * may not span threads.
888 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
889 * @param[in] dbi A database handle returned by #mdb_open()
890 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
891 * @return A non-zero error value on failure and 0 on success. Some possible
894 * <li>EINVAL - an invalid parameter was specified.
897 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
899 /** @brief Close a cursor handle.
901 * The cursor handle will be freed and must not be used again after this call.
902 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
904 void mdb_cursor_close(MDB_cursor *cursor);
906 /** @brief Return the cursor's transaction handle.
908 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
910 MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
912 /** @brief Return the cursor's database handle.
914 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
916 MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor);
918 /** @brief Retrieve by cursor.
920 * This function retrieves key/data pairs from the database. The address and length
921 * of the key are returned in the object to which \b key refers (except for the
922 * case of the #MDB_SET option, in which the \b key object is unchanged), and
923 * the address and length of the data are returned in the object to which \b data
925 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
926 * @param[in,out] key The key for a retrieved item
927 * @param[in,out] data The data of a retrieved item
928 * @param[in] op A cursor operation #MDB_cursor_op
929 * @return A non-zero error value on failure and 0 on success. Some possible
932 * <li>#MDB_NOTFOUND - no matching key found.
933 * <li>EINVAL - an invalid parameter was specified.
936 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
939 /** @brief Store by cursor.
941 * This function stores key/data pairs into the database.
942 * If the function fails for any reason, the state of the cursor will be
943 * unchanged. If the function succeeds and an item is inserted into the
944 * database, the cursor is always positioned to refer to the newly inserted item.
945 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
946 * @param[in] key The key operated on.
947 * @param[in] data The data operated on.
948 * @param[in] flags Options for this operation. This parameter
949 * must be set to 0 or one of the values described here.
951 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which
952 * the cursor refers with the specified data item. The \b key
953 * parameter is ignored.
954 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
955 * already appear in the database. This flag may only be specified
956 * if the database was opened with #MDB_DUPSORT. The function will
957 * return #MDB_KEYEXIST if the key/data pair already appears in the
959 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
960 * does not already appear in the database. The function will return
961 * #MDB_KEYEXIST if the key already appears in the database, even if
962 * the database supports duplicates (#MDB_DUPSORT).
963 * <li>#MDB_RESERVE - reserve space for data of the given size, but
964 * don't copy the given data. Instead, return a pointer to the
965 * reserved space, which the caller can fill in later. This saves
966 * an extra memcpy if the data is being generated later.
967 * <li>#MDB_APPEND - append the given key/data pair to the end of the
968 * database. No key comparisons are performed. This option allows
969 * fast bulk loading when keys are already known to be in the
970 * correct order. Loading unsorted keys with this flag will cause
972 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
974 * @return A non-zero error value on failure and 0 on success. Some possible
977 * <li>EACCES - an attempt was made to modify a read-only database.
978 * <li>EINVAL - an invalid parameter was specified.
981 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
984 /** @brief Delete current key/data pair
986 * This function deletes the key/data pair to which the cursor refers.
987 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
988 * @param[in] flags Options for this operation. This parameter
989 * must be set to 0 or one of the values described here.
991 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
992 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
994 * @return A non-zero error value on failure and 0 on success. Some possible
997 * <li>EACCES - an attempt was made to modify a read-only database.
998 * <li>EINVAL - an invalid parameter was specified.
1001 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
1003 /** @brief Return count of duplicates for current key.
1005 * This call is only valid on databases that support sorted duplicate
1006 * data items #MDB_DUPSORT.
1007 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1008 * @param[out] countp Address where the count will be stored
1009 * @return A non-zero error value on failure and 0 on success. Some possible
1012 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
1015 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
1017 /** @brief Compare two data items according to a particular database.
1019 * This returns a comparison as if the two data items were keys in the
1020 * specified database.
1021 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1022 * @param[in] dbi A database handle returned by #mdb_open()
1023 * @param[in] a The first item to compare
1024 * @param[in] b The second item to compare
1025 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1027 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1029 /** @brief Compare two data items according to a particular database.
1031 * This returns a comparison as if the two items were data items of
1032 * a sorted duplicates #MDB_DUPSORT database.
1033 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1034 * @param[in] dbi A database handle returned by #mdb_open()
1035 * @param[in] a The first item to compare
1036 * @param[in] b The second item to compare
1037 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1039 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1045 #endif /* _MDB_H_ */