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_KEY, /**< Position at specified key, return key + data */
251 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
254 /** @defgroup errors Return Codes
256 * BerkeleyDB uses -30800 to -30999, we'll go under them
259 /** Successful result */
260 #define MDB_SUCCESS 0
261 /** key/data pair already exists */
262 #define MDB_KEYEXIST (-30799)
263 /** key/data pair not found (EOF) */
264 #define MDB_NOTFOUND (-30798)
265 /** Requested page not found - this usually indicates corruption */
266 #define MDB_PAGE_NOTFOUND (-30797)
267 /** Located page was wrong type */
268 #define MDB_CORRUPTED (-30796)
269 /** Update of meta page failed, probably I/O error */
270 #define MDB_PANIC (-30795)
271 /** Environment version mismatch */
272 #define MDB_VERSION_MISMATCH (-30794)
273 /** File is not a valid MDB file */
274 #define MDB_INVALID (-30793)
275 /** Environment mapsize reached */
276 #define MDB_MAP_FULL (-30792)
277 /** Environment maxdbs reached */
278 #define MDB_DBS_FULL (-30791)
279 /** Environment maxreaders reached */
280 #define MDB_READERS_FULL (-30790)
281 /** Too many TLS keys in use - Windows only */
282 #define MDB_TLS_FULL (-30789)
283 /** Nested txn has too many dirty pages */
284 #define MDB_TXN_FULL (-30788)
285 /** Cursor stack too deep - internal error */
286 #define MDB_CURSOR_FULL (-30787)
287 /** Page has not enough space - internal error */
288 #define MDB_PAGE_FULL (-30786)
291 /** @brief Statistics for a database in the environment */
292 typedef struct MDB_stat {
293 unsigned int ms_psize; /**< Size of a database page.
294 This is currently the same for all databases. */
295 unsigned int ms_depth; /**< Depth (height) of the B-tree */
296 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
297 size_t ms_leaf_pages; /**< Number of leaf pages */
298 size_t ms_overflow_pages; /**< Number of overflow pages */
299 size_t ms_entries; /**< Number of data items */
302 /** @brief Return the mdb library version information.
304 * @param[out] major if non-NULL, the library major version number is copied here
305 * @param[out] minor if non-NULL, the library minor version number is copied here
306 * @param[out] patch if non-NULL, the library patch version number is copied here
307 * @retval "version string" The library version as a string
309 char *mdb_version(int *major, int *minor, int *patch);
311 /** @brief Return a string describing a given error code.
313 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
314 * function. If the error code is greater than or equal to 0, then the string
315 * returned by the system function strerror(3) is returned. If the error code
316 * is less than 0, an error string corresponding to the MDB library error is
317 * returned. See @ref errors for a list of MDB-specific error codes.
318 * @param[in] err The error code
319 * @retval "error message" The description of the error
321 char *mdb_strerror(int err);
323 /** @brief Create an MDB environment handle.
325 * This function allocates memory for a #MDB_env structure. To release
326 * the allocated memory and discard the handle, call #mdb_env_close().
327 * Before the handle may be used, it must be opened using #mdb_env_open().
328 * Various other options may also need to be set before opening the handle,
329 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
330 * depending on usage requirements.
331 * @param[out] env The address where the new handle will be stored
332 * @return A non-zero error value on failure and 0 on success.
334 int mdb_env_create(MDB_env **env);
336 /** @brief Open an environment handle.
338 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
339 * @param[in] env An environment handle returned by #mdb_env_create()
340 * @param[in] path The directory in which the database files reside. This
341 * directory must already exist and be writable.
342 * @param[in] flags Special options for this environment. This parameter
343 * must be set to 0 or by bitwise OR'ing together one or more of the
344 * values described here.
347 * use a fixed address for the mmap region. This flag must be specified
348 * when creating the environment, and is stored persistently in the environment.
349 * If successful, the memory map will always reside at the same virtual address
350 * and pointers used to reference data items in the database will be constant
351 * across multiple invocations. This option may not always work, depending on
352 * how the operating system has allocated memory to shared libraries and other uses.
353 * The feature is highly experimental.
355 * By default, MDB creates its environment in a directory whose
356 * pathname is given in \b path, and creates its data and lock files
357 * under that directory. With this option, \b path is used as-is for
358 * the database main data file. The database lock file is the \b path
359 * with "-lock" appended.
361 * Don't perform a synchronous flush after committing a transaction. This means
362 * transactions will exhibit the ACI (atomicity, consistency, and isolation)
363 * properties, but not D (durability); that is database integrity will be
364 * maintained but it is possible some number of the most recently committed
365 * transactions may be undone after a system crash. The number of transactions
366 * at risk is governed by how often the system flushes dirty buffers to disk
367 * and how often #mdb_env_sync() is called. This flag may be changed
368 * at any time using #mdb_env_set_flags().
369 * <li>#MDB_NOMETASYNC
370 * Don't perform a synchronous flush of the meta page after committing
371 * a transaction. This is similar to the #MDB_NOSYNC case, but safer
372 * because the transaction data is still flushed. The meta page for any
373 * transaction N will be flushed by the data flush of transaction N+1.
374 * In case of a system crash, the last committed transaction may be
375 * lost. This flag may be changed at any time using #mdb_env_set_flags().
377 * Open the environment in read-only mode. No write operations will be allowed.
379 * @param[in] mode The UNIX permissions to set on created files. This parameter
380 * is ignored on Windows.
381 * @return A non-zero error value on failure and 0 on success. Some possible
384 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
385 * version that created the database environment.
386 * <li>EINVAL - the environment file headers are corrupted.
387 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
388 * <li>EACCES - the user didn't have permission to access the environment files.
389 * <li>EAGAIN - the environment was locked by another process.
392 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mode_t mode);
394 /** @brief Return statistics about the MDB environment.
396 * @param[in] env An environment handle returned by #mdb_env_create()
397 * @param[out] stat The address of an #MDB_stat structure
398 * where the statistics will be copied
400 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
402 /** @brief Flush the data buffers to disk.
404 * Data is always written to disk when #mdb_txn_commit() is called,
405 * but the operating system may keep it buffered. MDB always flushes
406 * the OS buffers upon commit as well, unless the environment was
407 * opened with #MDB_NOSYNC.
408 * @param[in] env An environment handle returned by #mdb_env_create()
409 * @param[in] force If non-zero, force the flush to occur. Otherwise
410 * if the environment has the #MDB_NOSYNC flag set the flushes
412 * @return A non-zero error value on failure and 0 on success. Some possible
415 * <li>EINVAL - an invalid parameter was specified.
416 * <li>EIO - an error occurred during synchronization.
419 int mdb_env_sync(MDB_env *env, int force);
421 /** @brief Close the environment and release the memory map.
423 * Only a single thread may call this function. All transactions, databases,
424 * and cursors must already be closed before calling this function. Attempts to
425 * use any such handles after calling this function will cause a SIGSEGV.
426 * The environment handle will be freed and must not be used again after this call.
427 * @param[in] env An environment handle returned by #mdb_env_create()
429 void mdb_env_close(MDB_env *env);
431 /** @brief Set environment flags.
433 * This may be used to set some flags that weren't already set during
434 * #mdb_env_open(), or to unset these flags.
435 * @param[in] env An environment handle returned by #mdb_env_create()
436 * @param[in] flags The flags to change, bitwise OR'ed together
437 * @param[in] onoff A non-zero value sets the flags, zero clears them.
438 * @return A non-zero error value on failure and 0 on success. Some possible
441 * <li>EINVAL - an invalid parameter was specified.
444 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
446 /** @brief Get environment flags.
448 * @param[in] env An environment handle returned by #mdb_env_create()
449 * @param[out] flags The address of an integer to store the flags
450 * @return A non-zero error value on failure and 0 on success. Some possible
453 * <li>EINVAL - an invalid parameter was specified.
456 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
458 /** @brief Return the path that was used in #mdb_env_open().
460 * @param[in] env An environment handle returned by #mdb_env_create()
461 * @param[out] path Address of a string pointer to contain the path. This
462 * is the actual string in the environment, not a copy. It should not be
463 * altered in any way.
464 * @return A non-zero error value on failure and 0 on success. Some possible
467 * <li>EINVAL - an invalid parameter was specified.
470 int mdb_env_get_path(MDB_env *env, const char **path);
472 /** @brief Set the size of the memory map to use for this environment.
474 * The size should be a multiple of the OS page size. The default is
475 * 10485760 bytes. The size of the memory map is also the maximum size
476 * of the database. The value should be chosen as large as possible,
477 * to accommodate future growth of the database.
478 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
479 * @param[in] env An environment handle returned by #mdb_env_create()
480 * @param[in] size The size in bytes
481 * @return A non-zero error value on failure and 0 on success. Some possible
484 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
487 int mdb_env_set_mapsize(MDB_env *env, size_t size);
489 /** @brief Set the maximum number of threads for the environment.
491 * This defines the number of slots in the lock table that is used to track readers in the
492 * the environment. The default is 126.
493 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
494 * @param[in] env An environment handle returned by #mdb_env_create()
495 * @param[in] readers The maximum number of threads
496 * @return A non-zero error value on failure and 0 on success. Some possible
499 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
502 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
504 /** @brief Get the maximum number of threads for the environment.
506 * @param[in] env An environment handle returned by #mdb_env_create()
507 * @param[out] readers Address of an integer to store the number of readers
508 * @return A non-zero error value on failure and 0 on success. Some possible
511 * <li>EINVAL - an invalid parameter was specified.
514 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
516 /** @brief Set the maximum number of databases for the environment.
518 * This function is only needed if multiple databases will be used in the
519 * environment. Simpler applications that only use a single database can ignore
521 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
522 * @param[in] env An environment handle returned by #mdb_env_create()
523 * @param[in] dbs The maximum number of databases
524 * @return A non-zero error value on failure and 0 on success. Some possible
527 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
530 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
532 /** @brief Create a transaction for use with the environment.
534 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
535 * @note Transactions may not span threads; a transaction must only be used by a
536 * single thread. Also, a thread may only have a single transaction.
537 * @note Cursors may not span transactions; each cursor must be opened and closed
538 * within a single transaction.
539 * @param[in] env An environment handle returned by #mdb_env_create()
540 * @param[in] parent If this parameter is non-NULL, the new transaction
541 * will be a nested transaction, with the transaction indicated by \b parent
542 * as its parent. Transactions may be nested to any level. A parent
543 * transaction may not issue any other operations besides mdb_txn_begin,
544 * mdb_txn_abort, or mdb_txn_commit while it has active child transactions.
545 * @param[in] flags Special options for this transaction. This parameter
546 * must be set to 0 or by bitwise OR'ing together one or more of the
547 * values described here.
550 * This transaction will not perform any write operations.
552 * @param[out] txn Address where the new #MDB_txn handle will be stored
553 * @return A non-zero error value on failure and 0 on success. Some possible
556 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
558 * <li>ENOMEM - out of memory, or a read-only transaction was requested and
559 * the reader lock table is full. See #mdb_env_set_maxreaders().
562 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
564 /** @brief Commit all the operations of a transaction into the database.
566 * All cursors opened within the transaction will be closed by this call. The cursors
567 * and transaction handle will be freed and must not be used again after this call.
568 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
569 * @return A non-zero error value on failure and 0 on success. Some possible
572 * <li>EINVAL - an invalid parameter was specified.
573 * <li>ENOSPC - no more disk space.
574 * <li>EIO - a low-level I/O error occurred while writing.
575 * <li>ENOMEM - the transaction is nested and could not be merged into its parent.
578 int mdb_txn_commit(MDB_txn *txn);
580 /** @brief Abandon all the operations of the transaction instead of saving them.
582 * All cursors opened within the transaction will be closed by this call. The cursors
583 * and transaction handle will be freed and must not be used again after this call.
584 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
586 void mdb_txn_abort(MDB_txn *txn);
588 /** @brief Reset a read-only transaction.
590 * This releases the current reader lock but doesn't free the
591 * transaction handle, allowing it to be used again later by #mdb_txn_renew().
592 * It otherwise has the same effect as #mdb_txn_abort() but saves some memory
593 * allocation/deallocation overhead if a thread is going to start a new
594 * read-only transaction again soon.
595 * All cursors opened within the transaction must be closed before the transaction
597 * Reader locks generally don't interfere with writers, but they keep old
598 * versions of database pages allocated. Thus they prevent the old pages
599 * from being reused when writers commit new data, and so under heavy load
600 * the database size may grow much more rapidly than otherwise.
601 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
603 void mdb_txn_reset(MDB_txn *txn);
605 /** @brief Renew a read-only transaction.
607 * This acquires a new reader lock for a transaction handle that had been
608 * released by #mdb_txn_reset(). It must be called before a reset transaction
610 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
611 * @return A non-zero error value on failure and 0 on success. Some possible
614 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
616 * <li>EINVAL - an invalid parameter was specified.
619 int mdb_txn_renew(MDB_txn *txn);
621 /** @brief Open a database in the environment.
623 * The database handle may be discarded by calling #mdb_close(). The
624 * database handle resides in the shared environment, it is not owned
625 * by the given transaction. Only one thread should call this function;
626 * it is not mutex-protected in a read-only transaction.
627 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
628 * @param[in] name The name of the database to open. If only a single
629 * database is needed in the environment, this value may be NULL.
630 * @param[in] flags Special options for this database. This parameter
631 * must be set to 0 or by bitwise OR'ing together one or more of the
632 * values described here.
634 * <li>#MDB_REVERSEKEY
635 * Keys are strings to be compared in reverse order, from the end
636 * of the strings to the beginning. By default, Keys are treated as strings and
637 * compared from beginning to end.
639 * Duplicate keys may be used in the database. (Or, from another perspective,
640 * keys may have multiple data items, stored in sorted order.) By default
641 * keys must be unique and may have only a single data item.
642 * <li>#MDB_INTEGERKEY
643 * Keys are binary integers in native byte order. Setting this option
644 * requires all keys to be the same size, typically sizeof(int)
647 * This flag may only be used in combination with #MDB_DUPSORT. This option
648 * tells the library that the data items for this database are all the same
649 * size, which allows further optimizations in storage and retrieval. When
650 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
651 * cursor operations may be used to retrieve multiple items at once.
652 * <li>#MDB_INTEGERDUP
653 * This option specifies that duplicate data items are also integers, and
654 * should be sorted as such.
655 * <li>#MDB_REVERSEDUP
656 * This option specifies that duplicate data items should be compared as
657 * strings in reverse order.
659 * Create the named database if it doesn't exist. This option is not
660 * allowed in a read-only transaction or a read-only environment.
662 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
663 * @return A non-zero error value on failure and 0 on success. Some possible
666 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
667 * and #MDB_CREATE was not specified.
668 * <li>ENFILE - too many databases have been opened. See #mdb_env_set_maxdbs().
671 int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
673 /** @brief Retrieve statistics for a database.
675 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
676 * @param[in] dbi A database handle returned by #mdb_open()
677 * @param[out] stat The address of an #MDB_stat structure
678 * where the statistics will be copied
679 * @return A non-zero error value on failure and 0 on success. Some possible
682 * <li>EINVAL - an invalid parameter was specified.
685 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
687 /** @brief Close a database handle.
689 * This call is not mutex protected. Handles should only be closed by
690 * a single thread, and only if no other threads are going to reference
691 * the database handle any further.
692 * @param[in] env An environment handle returned by #mdb_env_create()
693 * @param[in] dbi A database handle returned by #mdb_open()
695 void mdb_close(MDB_env *env, MDB_dbi dbi);
697 /** @brief Delete a database and/or free all its pages.
699 * If the \b del parameter is non-zero the DB handle will be closed
700 * and the DB will be deleted.
701 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
702 * @param[in] dbi A database handle returned by #mdb_open()
703 * @param[in] del non-zero to delete the DB from the environment,
704 * otherwise just free its pages.
705 * @return A non-zero error value on failure and 0 on success.
707 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
709 /** @brief Set a custom key comparison function for a database.
711 * The comparison function is called whenever it is necessary to compare a
712 * key specified by the application with a key currently stored in the database.
713 * If no comparison function is specified, and no special key flags were specified
714 * with #mdb_open(), the keys are compared lexically, with shorter keys collating
715 * before longer keys.
716 * @warning This function must be called before any data access functions are used,
717 * otherwise data corruption may occur. The same comparison function must be used by every
718 * program accessing the database, every time the database is used.
719 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
720 * @param[in] dbi A database handle returned by #mdb_open()
721 * @param[in] cmp A #MDB_cmp_func function
722 * @return A non-zero error value on failure and 0 on success. Some possible
725 * <li>EINVAL - an invalid parameter was specified.
728 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
730 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
732 * This comparison function is called whenever it is necessary to compare a data
733 * item specified by the application with a data item currently stored in the database.
734 * This function only takes effect if the database was opened with the #MDB_DUPSORT
736 * If no comparison function is specified, and no special key flags were specified
737 * with #mdb_open(), the data items are compared lexically, with shorter items collating
738 * before longer items.
739 * @warning This function must be called before any data access functions are used,
740 * otherwise data corruption may occur. The same comparison function must be used by every
741 * program accessing the database, every time the database is used.
742 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
743 * @param[in] dbi A database handle returned by #mdb_open()
744 * @param[in] cmp A #MDB_cmp_func function
745 * @return A non-zero error value on failure and 0 on success. Some possible
748 * <li>EINVAL - an invalid parameter was specified.
751 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
753 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
755 * @todo The relocation function is called whenever it is necessary to move the data
756 * of an item to a different position in the database (e.g. through tree
757 * balancing operations, shifts as a result of adds or deletes, etc.). It is
758 * intended to allow address/position-dependent data items to be stored in
759 * a database in an environment opened with the #MDB_FIXEDMAP option.
760 * Currently the relocation feature is unimplemented and setting
761 * this function has no effect.
762 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
763 * @param[in] dbi A database handle returned by #mdb_open()
764 * @param[in] rel A #MDB_rel_func function
765 * @return A non-zero error value on failure and 0 on success. Some possible
768 * <li>EINVAL - an invalid parameter was specified.
771 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
773 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
775 * See #mdb_set_relfunc and #MDB_rel_func for more details.
776 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
777 * @param[in] dbi A database handle returned by #mdb_open()
778 * @param[in] ctx An arbitrary pointer for whatever the application needs.
779 * It will be passed to the callback function set by #mdb_set_relfunc
780 * as its \b relctx parameter whenever the callback is invoked.
781 * @return A non-zero error value on failure and 0 on success. Some possible
784 * <li>EINVAL - an invalid parameter was specified.
787 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
789 /** @brief Get items from a database.
791 * This function retrieves key/data pairs from the database. The address
792 * and length of the data associated with the specified \b key are returned
793 * in the structure to which \b data refers.
794 * If the database supports duplicate keys (#MDB_DUPSORT) then the
795 * first data item for the key will be returned. Retrieval of other
796 * items requires the use of #mdb_cursor_get().
798 * @note The memory pointed to by the returned values is owned by the
799 * database. The caller need not dispose of the memory, and may not
800 * modify it in any way. For values returned in a read-only transaction
801 * any modification attempts will cause a SIGSEGV.
802 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
803 * @param[in] dbi A database handle returned by #mdb_open()
804 * @param[in] key The key to search for in the database
805 * @param[out] data The data corresponding to the key
806 * @return A non-zero error value on failure and 0 on success. Some possible
809 * <li>#MDB_NOTFOUND - the key was not in the database.
810 * <li>EINVAL - an invalid parameter was specified.
813 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
815 /** @brief Store items into a database.
817 * This function stores key/data pairs in the database. The default behavior
818 * is to enter the new key/data pair, replacing any previously existing key
819 * if duplicates are disallowed, or adding a duplicate data item if
820 * duplicates are allowed (#MDB_DUPSORT).
821 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
822 * @param[in] dbi A database handle returned by #mdb_open()
823 * @param[in] key The key to store in the database
824 * @param[in,out] data The data to store
825 * @param[in] flags Special options for this operation. This parameter
826 * must be set to 0 or by bitwise OR'ing together one or more of the
827 * values described here.
829 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
830 * already appear in the database. This flag may only be specified
831 * if the database was opened with #MDB_DUPSORT. The function will
832 * return #MDB_KEYEXIST if the key/data pair already appears in the
834 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
835 * does not already appear in the database. The function will return
836 * #MDB_KEYEXIST if the key already appears in the database, even if
837 * the database supports duplicates (#MDB_DUPSORT). The \b data
838 * parameter will be set to point to the existing item.
839 * <li>#MDB_RESERVE - reserve space for data of the given size, but
840 * don't copy the given data. Instead, return a pointer to the
841 * reserved space, which the caller can fill in later. This saves
842 * an extra memcpy if the data is being generated later.
843 * <li>#MDB_APPEND - append the given key/data pair to the end of the
844 * database. No key comparisons are performed. This option allows
845 * fast bulk loading when keys are already known to be in the
846 * correct order. Loading unsorted keys with this flag will cause
848 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
850 * @return A non-zero error value on failure and 0 on success. Some possible
853 * <li>EACCES - an attempt was made to write in a read-only transaction.
854 * <li>EINVAL - an invalid parameter was specified.
855 * <li>ENOMEM - the database is full, see #mdb_env_set_mapsize().
858 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
861 /** @brief Delete items from a database.
863 * This function removes key/data pairs from the database.
864 * If the database does not support sorted duplicate data items
865 * (#MDB_DUPSORT) the data parameter is ignored.
866 * If the database supports sorted duplicates and the data parameter
867 * is NULL, all of the duplicate data items for the key will be
868 * deleted. Otherwise, if the data parameter is non-NULL
869 * only the matching data item will be deleted.
870 * This function will return #MDB_NOTFOUND if the specified key/data
871 * pair is not in the database.
872 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
873 * @param[in] dbi A database handle returned by #mdb_open()
874 * @param[in] key The key to delete from the database
875 * @param[in] data The data to delete
876 * @return A non-zero error value on failure and 0 on success. Some possible
879 * <li>EACCES - an attempt was made to write in a read-only transaction.
880 * <li>EINVAL - an invalid parameter was specified.
883 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
885 /** @brief Create a cursor handle.
887 * Cursors are associated with a specific transaction and database and
888 * may not span threads.
889 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
890 * @param[in] dbi A database handle returned by #mdb_open()
891 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
892 * @return A non-zero error value on failure and 0 on success. Some possible
895 * <li>EINVAL - an invalid parameter was specified.
898 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
900 /** @brief Close a cursor handle.
902 * The cursor handle will be freed and must not be used again after this call.
903 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
905 void mdb_cursor_close(MDB_cursor *cursor);
907 /** @brief Return the cursor's transaction handle.
909 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
911 MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
913 /** @brief Return the cursor's database handle.
915 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
917 MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor);
919 /** @brief Retrieve by cursor.
921 * This function retrieves key/data pairs from the database. The address and length
922 * of the key are returned in the object to which \b key refers (except for the
923 * case of the #MDB_SET option, in which the \b key object is unchanged), and
924 * the address and length of the data are returned in the object to which \b data
926 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
927 * @param[in,out] key The key for a retrieved item
928 * @param[in,out] data The data of a retrieved item
929 * @param[in] op A cursor operation #MDB_cursor_op
930 * @return A non-zero error value on failure and 0 on success. Some possible
933 * <li>#MDB_NOTFOUND - no matching key found.
934 * <li>EINVAL - an invalid parameter was specified.
937 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
940 /** @brief Store by cursor.
942 * This function stores key/data pairs into the database.
943 * If the function fails for any reason, the state of the cursor will be
944 * unchanged. If the function succeeds and an item is inserted into the
945 * database, the cursor is always positioned to refer to the newly inserted item.
946 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
947 * @param[in] key The key operated on.
948 * @param[in] data The data operated on.
949 * @param[in] flags Options for this operation. This parameter
950 * must be set to 0 or one of the values described here.
952 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which
953 * the cursor refers with the specified data item. The \b key
954 * parameter is ignored.
955 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
956 * already appear in the database. This flag may only be specified
957 * if the database was opened with #MDB_DUPSORT. The function will
958 * return #MDB_KEYEXIST if the key/data pair already appears in the
960 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
961 * does not already appear in the database. The function will return
962 * #MDB_KEYEXIST if the key already appears in the database, even if
963 * the database supports duplicates (#MDB_DUPSORT).
964 * <li>#MDB_RESERVE - reserve space for data of the given size, but
965 * don't copy the given data. Instead, return a pointer to the
966 * reserved space, which the caller can fill in later. This saves
967 * an extra memcpy if the data is being generated later.
968 * <li>#MDB_APPEND - append the given key/data pair to the end of the
969 * database. No key comparisons are performed. This option allows
970 * fast bulk loading when keys are already known to be in the
971 * correct order. Loading unsorted keys with this flag will cause
973 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
975 * @return A non-zero error value on failure and 0 on success. Some possible
978 * <li>EACCES - an attempt was made to modify a read-only database.
979 * <li>EINVAL - an invalid parameter was specified.
982 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
985 /** @brief Delete current key/data pair
987 * This function deletes the key/data pair to which the cursor refers.
988 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
989 * @param[in] flags Options for this operation. This parameter
990 * must be set to 0 or one of the values described here.
992 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
993 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
995 * @return A non-zero error value on failure and 0 on success. Some possible
998 * <li>EACCES - an attempt was made to modify a read-only database.
999 * <li>EINVAL - an invalid parameter was specified.
1002 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
1004 /** @brief Return count of duplicates for current key.
1006 * This call is only valid on databases that support sorted duplicate
1007 * data items #MDB_DUPSORT.
1008 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1009 * @param[out] countp Address where the count will be stored
1010 * @return A non-zero error value on failure and 0 on success. Some possible
1013 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
1016 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
1018 /** @brief Compare two data items according to a particular database.
1020 * This returns a comparison as if the two data items were keys in the
1021 * specified database.
1022 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1023 * @param[in] dbi A database handle returned by #mdb_open()
1024 * @param[in] a The first item to compare
1025 * @param[in] b The second item to compare
1026 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1028 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1030 /** @brief Compare two data items according to a particular database.
1032 * This returns a comparison as if the two items were data items of
1033 * a sorted duplicates #MDB_DUPSORT database.
1034 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1035 * @param[in] dbi A database handle returned by #mdb_open()
1036 * @param[in] a The first item to compare
1037 * @param[in] b The second item to compare
1038 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1040 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1046 #endif /* _MDB_H_ */