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 public Public API
71 /** @defgroup Version Version Macros
74 /** Library major version */
75 #define MDB_VERSION_MAJOR 0
76 /** Library minor version */
77 #define MDB_VERSION_MINOR 9
78 /** Library patch version */
79 #define MDB_VERSION_PATCH 0
81 /** Combine args a,b,c into a single integer for easy version comparisons */
82 #define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
84 /** The full library version as a single integer */
85 #define MDB_VERSION_FULL \
86 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
88 /** The release date of this library version */
89 #define MDB_VERSION_DATE "September 1, 2011"
91 /** A stringifier for the version info */
92 #define MDB_VERSTR(a,b,c,d) "MDB " #a "." #b "." #c ": (" #d ")"
94 /** A helper for the stringifier macro */
95 #define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d)
97 /** The full library version as a C string */
98 #define MDB_VERSION_STRING \
99 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
102 /** Opaque structure for a database environment. A DB environment supports multiple
103 * databases, all residing in the same shared-memory map.
105 typedef struct MDB_env MDB_env;
107 /** Opaque structure for a transaction handle. All database operations require
108 * a transaction handle. Transactions may be read-only or read-write.
110 typedef struct MDB_txn MDB_txn;
112 /** A handle for an individual database in the DB environment. */
113 typedef unsigned int MDB_dbi;
115 /** Opaque structure for navigating through a database */
116 typedef struct MDB_cursor MDB_cursor;
118 /** Generic structure used for passing keys and data in and out of the database. */
119 typedef struct MDB_val {
120 size_t mv_size; /**< size of the data item */
121 void *mv_data; /**< address of the data item */
124 /** A callback function used to compare two keys in a database */
125 typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
127 /** A callback function used to relocate a position-dependent data item
128 * in a fixed-address database. The \b newptr gives the item's desired address in
129 * the memory map, and \b oldptr gives its previous address. The item's actual
130 * data resides at the address in \b item. This callback is expected to walk
131 * through the fields of the record in \b item and modify any
132 * values based at the \b oldptr address to be relative to the \b newptr address.
133 * @param[in,out] item The item that is to be relocated.
134 * @param[in] oldptr The previous address.
135 * @param[in] newptr The new address to relocate to.
136 * @param[in] relctx An application-provided context, set by #mdb_set_relctx().
137 * @todo This feature is currently unimplemented.
139 typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
141 /** @defgroup mdb_env Environment Flags
144 /** mmap at a fixed address */
145 #define MDB_FIXEDMAP 0x01
146 /** don't fsync after commit */
147 #define MDB_NOSYNC 0x10000
149 #define MDB_RDONLY 0x20000
152 /** @defgroup mdb_open Database Flags
155 /** use reverse string keys */
156 #define MDB_REVERSEKEY 0x02
157 /** use sorted duplicates */
158 #define MDB_DUPSORT 0x04
159 /** numeric keys in native byte order.
160 * The keys must all be of the same size. */
161 #define MDB_INTEGERKEY 0x08
162 /** with #MDB_DUPSORT, sorted dup items have fixed size */
163 #define MDB_DUPFIXED 0x10
164 /** with #MDB_DUPSORT, dups are numeric in native byte order */
165 #define MDB_INTEGERDUP 0x20
166 /** with #MDB_DUPSORT, use reverse string dups */
167 #define MDB_REVERSEDUP 0x40
168 /** create DB if not already existing */
169 #define MDB_CREATE 0x40000
172 /** @defgroup mdb_put Write Flags
175 /** For put: Don't write if the key already exists. */
176 #define MDB_NOOVERWRITE 0x10
177 /** Only for #MDB_DUPSORT<br>
178 * For put: don't write if the key and data pair already exist.<br>
179 * For mdb_cursor_del: remove all duplicate data items.
181 #define MDB_NODUPDATA 0x20
182 /** For mdb_cursor_put: overwrite the current key/data pair */
183 #define MDB_CURRENT 0x40
186 /** Cursor Get operations
187 * This is the set of all operations for retrieving data
190 typedef enum MDB_cursor_op {
191 MDB_FIRST, /**< Position at first key/data item */
192 MDB_FIRST_DUP, /**< Position at first data item of current key.
193 Only for #MDB_DUPSORT */
194 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
195 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
196 MDB_GET_MULTIPLE, /**< Return all the duplicate data items at the current
197 cursor position. Only for #MDB_DUPFIXED */
198 MDB_LAST, /**< Position at last key/data item */
199 MDB_LAST_DUP, /**< Position at last data item of current key.
200 Only for #MDB_DUPSORT */
201 MDB_NEXT, /**< Position at next data item */
202 MDB_NEXT_DUP, /**< Position at next data item of current key.
203 Only for #MDB_DUPSORT */
204 MDB_NEXT_MULTIPLE, /**< Return all duplicate data items at the next
205 cursor position. Only for #MDB_DUPFIXED */
206 MDB_NEXT_NODUP, /**< Position at first data item of next key.
207 Only for #MDB_DUPSORT */
208 MDB_PREV, /**< Position at previous data item */
209 MDB_PREV_DUP, /**< Position at previous data item of current key.
210 Only for #MDB_DUPSORT */
211 MDB_PREV_NODUP, /**< Position at last data item of previous key.
212 Only for #MDB_DUPSORT */
213 MDB_SET, /**< Position at specified key */
214 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
217 /** @defgroup errors Return Codes
219 * BerkeleyDB uses -30800 to -30999, we'll go under them
222 /** Successful result */
223 #define MDB_SUCCESS 0
224 /** key/data pair already exists */
225 #define MDB_KEYEXIST (-30799)
226 /** key/data pair not found (EOF) */
227 #define MDB_NOTFOUND (-30798)
228 /** Requested page not found - this usually indicates corruption */
229 #define MDB_PAGE_NOTFOUND (-30797)
230 /** Located page was wrong type */
231 #define MDB_CORRUPTED (-30796)
232 /** Update of meta page failed, probably I/O error */
233 #define MDB_PANIC (-30795)
234 /** Environment version mismatch */
235 #define MDB_VERSION_MISMATCH (-30794)
238 /** Statistics for a database in the environment */
239 typedef struct MDB_stat {
240 unsigned int ms_psize; /**< Size of a database page.
241 This is currently the same for all databases. */
242 unsigned int ms_depth; /**< Depth (height) of the B-tree */
243 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
244 size_t ms_leaf_pages; /**< Number of leaf pages */
245 size_t ms_overflow_pages; /**< Number of overflow pages */
246 size_t ms_entries; /**< Number of data items */
249 /** Return the mdb library version information.
250 * @param[out] major if non-NULL, the library major version number is copied here
251 * @param[out] minor if non-NULL, the library minor version number is copied here
252 * @param[out] patch if non-NULL, the library patch version number is copied here
253 * @retval "version string" The library version as a string
255 char *mdb_version(int *major, int *minor, int *patch);
257 /** Return a string describing a given error code.
258 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
259 * function. If the error code is greater than or equal to 0, then the string
260 * returned by the system function strerror(3) is returned. If the error code
261 * is less than 0, an error string corresponding to the MDB library error is
262 * returned. See @ref errors for a list of MDB-specific error codes.
263 * @param[in] err The error code
264 * @retval "error message" The description of the error
266 char *mdb_strerror(int err);
268 /** Create an MDB environment handle.
269 * This function allocates memory for a #MDB_env structure. To release
270 * the allocated memory and discard the handle, call #mdb_env_close().
271 * Before the handle may be used, it must be opened using #mdb_env_open().
272 * Various other options may also need to be set before opening the handle,
273 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
274 * depending on usage requirements.
275 * @param[out] env The address where the new handle will be stored
276 * @return A non-zero error value on failure and 0 on success.
278 int mdb_env_create(MDB_env **env);
280 /** Open an environment handle.
281 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
282 * @param[in] env An environment handle returned by #mdb_env_create()
283 * @param[in] path The directory in which the database files reside. This
284 * directory must already exist and be writable.
285 * @param[in] flags Special options for this environment. This parameter
286 * must be set to 0 or by bitwise OR'ing together one or more of the
287 * values described here.
290 * use a fixed address for the mmap region. This flag must be specified
291 * when creating the environment, and is stored persistently in the environment.
292 * If successful, the memory map will always reside at the same virtual address
293 * and pointers used to reference data items in the database will be constant
294 * across multiple invocations. This option may not always work, depending on
295 * how the operating system has allocated memory to shared libraries and other uses.
296 * The feature is highly experimental.
298 * Don't perform a synchronous flush after committing a transaction. This means
299 * transactions will exhibit the ACI (atomicity, consistency, and isolation)
300 * properties, but not D (durability); that is database integrity will be
301 * maintained but it is possible some number of the most recently committed
302 * transactions may be undone after a system crash. The number of transactions
303 * at risk is governed by how often the system flushes dirty buffers to disk
304 * and how often #mdb_env_sync() is called. This flag may be changed
305 * at any time using #mdb_env_set_flags().
307 * Open the environment in read-only mode. No write operations will be allowed.
309 * @param[in] mode The UNIX permissions to set on created files. This parameter
310 * is ignored on Windows.
311 * @return A non-zero error value on failure and 0 on success. Some possible
314 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
315 * version that created the database environment.
316 * <li>EINVAL - the environment file headers are corrupted.
317 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
318 * <li>EACCES - the user didn't have permission to access the environment files.
319 * <li>EAGAIN - the environment was locked by another process.
322 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mode_t mode);
324 /** Return statistics about the MDB environment.
325 * @param[in] env An environment handle returned by #mdb_env_create()
326 * @param[out] stat The address of an #MDB_stat structure
327 * where the statistics will be copied
329 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
331 /** Flush the data buffers to disk.
332 * Data is always written to disk when #mdb_txn_commit() is called,
333 * but the operating system may keep it buffered. MDB always flushes
334 * the OS buffers upon commit as well, unless the environment was
335 * opened with #MDB_NOSYNC.
336 * @param[in] env An environment handle returned by #mdb_env_create()
337 * @param[in] force If non-zero, force the flush to occur. Otherwise
338 * if the environment has the #MDB_NOSYNC flag set the flushes
340 * @return A non-zero error value on failure and 0 on success. Some possible
343 * <li>EINVAL - an invalid parameter was specified.
344 * <li>EIO - an error occurred during synchronization.
347 int mdb_env_sync(MDB_env *env, int force);
349 /** Close the environment and release the memory map.
350 * Only a single thread may call this function. All transactions, databases,
351 * and cursors must already be closed before calling this function. Attempts to
352 * use any such handles after calling this function will cause a SIGSEGV.
353 * The environment handle will be freed and must not be used again after this call.
354 * @param[in] env An environment handle returned by #mdb_env_create()
356 void mdb_env_close(MDB_env *env);
358 /** Set environment flags.
359 * This may be used to set some flags that weren't already set during
360 * #mdb_env_open(), or to unset these flags. Currently only the
361 * #MDB_NOSYNC flag setting may be changed with this function.
362 * @param[in] env An environment handle returned by #mdb_env_create()
363 * @param[in] flags The flags to change, bitwise OR'ed together
364 * @param[in] onoff A non-zero value sets the flags, zero clears them.
365 * @return A non-zero error value on failure and 0 on success. Some possible
368 * <li>EINVAL - an invalid parameter was specified.
371 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
373 /** Get environment flags.
374 * @param[in] env An environment handle returned by #mdb_env_create()
375 * @param[out] flags The address of an integer to store the flags
376 * @return A non-zero error value on failure and 0 on success. Some possible
379 * <li>EINVAL - an invalid parameter was specified.
382 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
384 /** Return the path that was used in #mdb_env_open().
385 * @param[in] env An environment handle returned by #mdb_env_create()
386 * @param[out] path Address of a string pointer to contain the path. This
387 * is the actual string in the environment, not a copy. It should not be
388 * altered in any way.
389 * @return A non-zero error value on failure and 0 on success. Some possible
392 * <li>EINVAL - an invalid parameter was specified.
395 int mdb_env_get_path(MDB_env *env, const char **path);
397 /** Set the size of the memory map to use for this environment.
398 * The size should be a multiple of the OS page size. The default is
399 * 10485760 bytes. The size of the memory map is also the maximum size
400 * of the database. The value should be chosen as large as possible,
401 * to accomodate future growth of the database.
402 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
403 * @param[in] env An environment handle returned by #mdb_env_create()
404 * @param[in] size The size in bytes
405 * @return A non-zero error value on failure and 0 on success. Some possible
408 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
411 int mdb_env_set_mapsize(MDB_env *env, size_t size);
413 /** Set the maximum number of threads for the environment.
414 * This defines the number of slots in the lock table that is used to track readers in the
415 * the environment. The default is 126.
416 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
417 * @param[in] env An environment handle returned by #mdb_env_create()
418 * @param[in] readers The maximum number of threads
419 * @return A non-zero error value on failure and 0 on success. Some possible
422 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
425 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
427 /** Get the maximum number of threads for the environment.
428 * @param[in] env An environment handle returned by #mdb_env_create()
429 * @param[out] readers Address of an integer to store the number of readers
430 * @return A non-zero error value on failure and 0 on success. Some possible
433 * <li>EINVAL - an invalid parameter was specified.
436 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
438 /** Set the maximum number of databases for the environment.
439 * This function is only needed if multiple databases will be used in the
440 * environment. Simpler applications that only use a single database can ignore
442 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
443 * @param[in] env An environment handle returned by #mdb_env_create()
444 * @param[in] dbs The maximum number of databases
445 * @return A non-zero error value on failure and 0 on success. Some possible
448 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
451 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
453 /** Create a transaction for use with the environment.
454 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
455 * @note Transactions may not span threads, a transaction must only be used by a
457 * @note Cursors may not span transactions; each cursor must be opened and closed
458 * within a single transaction.
459 * @param[in] env An environment handle returned by #mdb_env_create()
460 * @param[in] flags Special options for this transaction. This parameter
461 * must be set to 0 or by bitwise OR'ing together one or more of the
462 * values described here.
465 * This transaction will not perform any write operations.
467 * @param[out] txn Address where the new #MDB_txn handle will be stored
468 * @return A non-zero error value on failure and 0 on success. Some possible
471 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
473 * <li>ENOMEM - out of memory, or a read-only transaction was requested and
474 * the reader lock table is full. See #mdb_env_set_maxreaders().
477 int mdb_txn_begin(MDB_env *env, unsigned int flags, MDB_txn **txn);
479 /** Commit all the operations of a transaction into the database.
480 * All cursors opened within the transaction must be closed before the transaction
482 * The transaction handle will be freed and must not be used again after this call.
483 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
484 * @return A non-zero error value on failure and 0 on success. Some possible
487 * <li>EINVAL - an invalid parameter was specified.
488 * <li>ENOSPC - no more disk space.
489 * <li>EIO - a low-level I/O error occurred while writing.
492 int mdb_txn_commit(MDB_txn *txn);
494 /** Abandon all the operations of the transaction instead of saving them.
495 * All cursors opened within the transaction must be closed before the transaction
497 * The transaction handle will be freed and must not be used again after this call.
498 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
500 void mdb_txn_abort(MDB_txn *txn);
502 /** Reset a read-only transaction.
503 * This releases the current reader lock but doesn't free the
504 * transaction handle, allowing it to be used again later by #mdb_txn_renew().
505 * It otherwise has the same effect as #mdb_txn_abort() but saves some memory
506 * allocation/deallocation overhead if a thread is going to start a new
507 * read-only transaction again soon.
508 * All cursors opened within the transaction must be closed before the transaction
510 * Reader locks generally don't interfere with writers, but they keep old
511 * versions of database pages allocated. Thus they prevent the old pages
512 * from being reused when writers commit new data, and so under heavy load
513 * the database size may grow much more rapidly than otherwise.
514 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
516 void mdb_txn_reset(MDB_txn *txn);
518 /** Renew a read-only transaction.
519 * This acquires a new reader lock for a transaction handle that had been
520 * released by #mdb_txn_reset(). It must be called before a reset transaction
522 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
523 * @return A non-zero error value on failure and 0 on success. Some possible
526 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
528 * <li>EINVAL - an invalid parameter was specified.
531 int mdb_txn_renew(MDB_txn *txn);
533 /** Open a database in the environment.
534 * The database handle may be discarded by calling #mdb_close().
535 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
536 * @param[in] name The name of the database to open. If only a single
537 * database is needed in the enviroment, this value may be NULL.
538 * @param[in] flags Special options for this database. This parameter
539 * must be set to 0 or by bitwise OR'ing together one or more of the
540 * values described here.
542 * <li>#MDB_REVERSEKEY
543 * Keys are strings to be compared in reverse order, from the end
544 * of the strings to the beginning. By default, Keys are treated as strings and
545 * compared from beginning to end.
547 * Duplicate keys may be used in the database. (Or, from another perspective,
548 * keys may have multiple data items, stored in sorted order.) By default
549 * keys must be unique and may have only a single data item.
550 * <li>#MDB_INTEGERKEY
551 * Keys are binary integers in native byte order. Setting this option
552 * requires all keys to be the same size, typically sizeof(int)
555 * This flag may only be used in combination with #MDB_DUPSORT. This option
556 * tells the library that the data items for this database are all the same
557 * size, which allows further optimizations in storage and retrieval. When
558 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
559 * cursor operations may be used to retrieve multiple items at once.
560 * <li>#MDB_INTEGERDUP
561 * This option specifies that duplicate data items are also integers, and
562 * should be sorted as such.
563 * <li>#MDB_REVERSEDUP
564 * This option specifies that duplicate data items should be compared as
565 * strings in reverse order.
567 * Create the named database if it doesn't exist. This option is not
568 * allowed in a read-only transaction or a read-only environment.
570 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
571 * @return A non-zero error value on failure and 0 on success. Some possible
574 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
575 * and #MDB_CREATE was not specified.
576 * <li>ENFILE - too many databases have been opened. See #mdb_env_set_maxdbs().
579 int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
581 /** Retrieve statistics for a database.
582 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
583 * @param[in] dbi A database handle returned by #mdb_open()
584 * @param[out] stat The address of an #MDB_stat structure
585 * where the statistics will be copied
586 * @return A non-zero error value on failure and 0 on success. Some possible
589 * <li>EINVAL - an invalid parameter was specified.
592 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
594 /** Close a database handle.
595 * This call is not mutex protected. Handles should only be closed by
596 * a single thread, and only if no other threads are going to reference
597 * the database handle any further.
598 * @param[in] env An environment handle returned by #mdb_env_create()
599 * @param[in] dbi A database handle returned by #mdb_open()
601 void mdb_close(MDB_env *env, MDB_dbi dbi);
603 /** Delete a database and free all its pages.
604 * This function acquires its own write transaction to perform its
605 * work, so it must not be called if there is already an open write
606 * transaction in the environment. The database handle will also be
607 * closed as part of this operation.
608 * @param[in] env An environment handle returned by #mdb_env_create()
609 * @param[in] dbi A database handle returned by #mdb_open()
610 * @return A non-zero error value on failure and 0 on success. Some possible
613 * <li>EINVAL - an invalid parameter was specified.
614 * <li>EBUSY - there is already a write transaction.
617 int mdb_drop(MDB_env *env, MDB_dbi dbi);
619 /** Set a custom key comparison function for a database.
620 * The comparison function is called whenever it is necessary to compare a
621 * key specified by the application with a key currently stored in the database.
622 * If no comparison function is specified, and no speAGAINcial key flags were specified
623 * with #mdb_open(), the keys are compared lexically, with shorter keys collating
624 * before longer keys.
625 * @warning This function must be called before any data access functions are used,
626 * otherwise data corruption may occur. The same comparison function must be used by every
627 * program accessing the database, every time the database is used.
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] cmp A #MDB_cmp_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_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
639 /** Set a custom data comparison function for a #MDB_DUPSORT database.
640 * This comparison function is called whenever it is necessary to compare a data
641 * item specified by the application with a data item currently stored in the database.
642 * This function only takes effect if the database was opened with the #MDB_DUPSORT
644 * If no comparison function is specified, and no special key flags were specified
645 * with #mdb_open(), the data items are compared lexically, with shorter items collating
646 * before longer items.
647 * @warning This function must be called before any data access functions are used,
648 * otherwise data corruption may occur. The same comparison function must be used by every
649 * program accessing the database, every time the database is used.
650 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
651 * @param[in] dbi A database handle returned by #mdb_open()
652 * @param[in] cmp A #MDB_cmp_func function
653 * @return A non-zero error value on failure and 0 on success. Some possible
656 * <li>EINVAL - an invalid parameter was specified.
659 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
661 /** Set a relocation function for a #MDB_FIXEDMAP database.
662 * @todo The relocation function is called whenever it is necessary to move the data
663 * of an item to a different position in the database (e.g. through tree
664 * balancing operations, shifts as a result of adds or deletes, etc.). It is
665 * intended to allow address/position-dependent data items to be stored in
666 * a database in an environment opened with the #MDB_FIXEDMAP option.
667 * Currently the relocation feature is unimplemented and setting
668 * this function has no effect.
669 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
670 * @param[in] dbi A database handle returned by #mdb_open()
671 * @param[in] rel A #MDB_rel_func function
672 * @return A non-zero error value on failure and 0 on success. Some possible
675 * <li>EINVAL - an invalid parameter was specified.
678 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
680 /** Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
681 * See #mdb_set_relfunc and #MDB_rel_func for more details.
682 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
683 * @param[in] dbi A database handle returned by #mdb_open()
684 * @param[in] ctx An arbitrary pointer for whatever the application needs.
685 * It will be passed to the callback function set by #mdb_set_relfunc
686 * as its \b relctx parameter whenever the callback is invoked.
687 * @return A non-zero error value on failure and 0 on success. Some possible
690 * <li>EINVAL - an invalid parameter was specified.
693 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
695 /** Get items from a database.
696 * This function retrieves key/data pairs from the database. The address
697 * and length of the data associated with the specified \b key are returned
698 * in the structure to which \b data refers.
699 * If the database supports duplicate keys (#MDB_DUPSORT) then the
700 * first data item for the key will be returned. Retrieval of other
701 * items requires the use of #mdb_cursor_get().
703 * @note The memory pointed to by the returned values is owned by the
704 * database. The caller need not dispose of the memory, and may not
705 * modify it in any way. For values returned in a read-only transaction
706 * any modification attempts will cause a SIGSEGV.
707 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
708 * @param[in] dbi A database handle returned by #mdb_open()
709 * @param[in] key The key to search for in the database
710 * @param[out] data The data corresponding to the key
711 * @return A non-zero error value on failure and 0 on success. Some possible
714 * <li>#MDB_NOTFOUND - the key was not in the database.
715 * <li>EINVAL - an invalid parameter was specified.
718 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
720 /** Store items into a database.
721 * This function stores key/data pairs in the database. The default behavior
722 * is to enter the new key/data pair, replacing any previously existing key
723 * if duplicates are disallowed, or adding a duplicate data item if
724 * duplicates are allowed (#MDB_DUPSORT).
725 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
726 * @param[in] dbi A database handle returned by #mdb_open()
727 * @param[in] key The key to store in the database
728 * @param[in,out] data The data to store
729 * @param[in] flags Special options for this operation. This parameter
730 * must be set to 0 or by bitwise OR'ing together one or more of the
731 * values described here.
733 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
734 * already appear in the database. This flag may only be specified
735 * if the database was opened with #MDB_DUPSORT. The function will
736 * return #MDB_KEYEXIST if the key/data pair already appears in the
738 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
739 * does not already appear in the database. The function will return
740 * #MDB_KEYEXIST if the key already appears in the database, even if
741 * the database supports duplicates (#MDB_DUPSORT). The \b data
742 * parameter will be set to point to the existing item.
744 * @return A non-zero error value on failure and 0 on success. Some possible
747 * <li>EACCESS - an attempt was made to write in a read-only transaction.
748 * <li>EINVAL - an invalid parameter was specified.
749 * <li>ENOMEM - the database is full, see #mdb_env_set_mapsize().
752 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
755 /** Delete items from a database.
756 * This function removes key/data pairs from the database.
757 * If the database does not support sorted duplicate data items
758 * (#MDB_DUPSORT) the data parameter is ignored.
759 * If the database supports sorted duplicates and the data parameter
760 * is NULL, all of the duplicate data items for the key will be
761 * deleted. Otherwise, if the data parameter is non-NULL
762 * only the matching data item will be deleted.
763 * This function will return #MDB_NOTFOUND if the specified key/data
764 * pair is not in the database.
765 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
766 * @param[in] dbi A database handle returned by #mdb_open()
767 * @param[in] key The key to delete from the database
768 * @param[in] data The data to delete
769 * @return A non-zero error value on failure and 0 on success. Some possible
772 * <li>EACCESS - an attempt was made to write in a read-only transaction.
773 * <li>EINVAL - an invalid parameter was specified.
776 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
778 /** Create a cursor handle.
779 * Cursors are associated with a specific transaction and database and
780 * may not span threads.
781 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
782 * @param[in] dbi A database handle returned by #mdb_open()
783 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
784 * @return A non-zero error value on failure and 0 on success. Some possible
787 * <li>EINVAL - an invalid parameter was specified.
790 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
792 /** Close a cursor handle.
793 * The cursor handle will be freed and must not be used again after this call.
794 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
796 void mdb_cursor_close(MDB_cursor *cursor);
798 /** Retrieve by cursor.
799 * This function retrieves key/data pairs from the database. The address and length
800 * of the key are returned in the object to which \b key refers (except for the
801 * case of the #MDB_SET option, in which the \b key object is unchanged), and
802 * the address and length of the data are returned in the object to which \b data
804 * @bug Cursors are not coordinated with write operations. If a cursor in a
805 * write transaction is performing a sequential scan while records are being
806 * inserted or deleted in the same transaction, the cursor will be corrupted.
807 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
808 * @param[in,out] key The key for a retrieved item
809 * @param[in,out] data The data of a retrieved item
810 * @param[in] op A cursor operation #MDB_cursor_op
811 * @return A non-zero error value on failure and 0 on success. Some possible
814 * <li>#MDB_NOTFOUND - no matching key found.
815 * <li>EINVAL - an invalid parameter was specified.
818 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
822 * This function stores key/data pairs into the database.
823 * If the function fails for any reason, the state of the cursor will be
824 * unchanged. If the function succeeds and an item is inserted into the
825 * database, the cursor is always positioned to refer to the newly inserted item.
826 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
827 * @param[in] key The key operated on.
828 * @param[in] data The data operated on.
829 * @param[in] flags Options for this operation. This parameter
830 * must be set to 0 or one of the values described here.
832 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which
833 * the cursor refers with the specified data item. The \b key
834 * parameter is ignored.
835 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
836 * already appear in the database. This flag may only be specified
837 * if the database was opened with #MDB_DUPSORT. The function will
838 * return #MDB_KEYEXIST if the key/data pair already appears in the
840 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
841 * does not already appear in the database. The function will return
842 * #MDB_KEYEXIST if the key already appears in the database, even if
843 * the database supports duplicates (#MDB_DUPSORT).
845 * @return A non-zero error value on failure and 0 on success. Some possible
848 * <li>EACCES - an attempt was made to modify a read-only database.
849 * <li>EINVAL - an invalid parameter was specified.
852 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
855 /** Delete current key/data pair
856 * This function deletes the key/data pair to which the cursor refers.
857 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
858 * @param[in] flags Options for this operation. This parameter
859 * must be set to 0 or one of the values described here.
861 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
862 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
864 * @return A non-zero error value on failure and 0 on success. Some possible
867 * <li>EACCES - an attempt was made to modify a read-only database.
868 * <li>EINVAL - an invalid parameter was specified.
871 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
873 /** Return count of duplicates for current key.
874 * This call is only valid on databases that support sorted duplicate
875 * data items #MDB_DUPSORT.
876 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
877 * @param[out] countp Address where the count will be stored
878 * @return A non-zero error value on failure and 0 on success. Some possible
881 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
884 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
886 /** Compare two data items according to a particular database.
887 * This returns a comparison as if the two data items were keys in the
888 * specified database.
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[in] a The first item to compare
892 * @param[in] b The second item to compare
893 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
895 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
897 /** Compare two data items according to a particular database.
898 * This returns a comparison as if the two items were data items of
899 * a sorted duplicates #MDB_DUPSORT database.
900 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
901 * @param[in] dbi A database handle returned by #mdb_open()
902 * @param[in] a The first item to compare
903 * @param[in] b The second item to compare
904 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
906 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);