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 /** @brief Opaque structure for a database environment.
104 * A DB environment supports multiple databases, all residing in the same
107 typedef struct MDB_env MDB_env;
109 /** @brief Opaque structure for a transaction handle.
111 * All database operations require a transaction handle. Transactions may be
112 * read-only or read-write.
114 typedef struct MDB_txn MDB_txn;
116 /** @brief A handle for an individual database in the DB environment. */
117 typedef unsigned int MDB_dbi;
119 /** @brief Opaque structure for navigating through a database */
120 typedef struct MDB_cursor MDB_cursor;
122 /** @brief Generic structure used for passing keys and data in and out of the database. */
123 typedef struct MDB_val {
124 size_t mv_size; /**< size of the data item */
125 void *mv_data; /**< address of the data item */
128 /** @brief A callback function used to compare two keys in a database */
129 typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
131 /** @brief A callback function used to relocate a position-dependent data item
132 * in a fixed-address database.
134 * The \b newptr gives the item's desired address in
135 * the memory map, and \b oldptr gives its previous address. The item's actual
136 * data resides at the address in \b item. This callback is expected to walk
137 * through the fields of the record in \b item and modify any
138 * values based at the \b oldptr address to be relative to the \b newptr address.
139 * @param[in,out] item The item that is to be relocated.
140 * @param[in] oldptr The previous address.
141 * @param[in] newptr The new address to relocate to.
142 * @param[in] relctx An application-provided context, set by #mdb_set_relctx().
143 * @todo This feature is currently unimplemented.
145 typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
147 /** @defgroup mdb_env Environment Flags
150 /** mmap at a fixed address */
151 #define MDB_FIXEDMAP 0x01
152 /** no environment directory */
153 #define MDB_NOSUBDIR 0x02
154 /** don't fsync after commit */
155 #define MDB_NOSYNC 0x10000
157 #define MDB_RDONLY 0x20000
160 /** @defgroup mdb_open Database Flags
163 /** use reverse string keys */
164 #define MDB_REVERSEKEY 0x02
165 /** use sorted duplicates */
166 #define MDB_DUPSORT 0x04
167 /** numeric keys in native byte order.
168 * The keys must all be of the same size. */
169 #define MDB_INTEGERKEY 0x08
170 /** with #MDB_DUPSORT, sorted dup items have fixed size */
171 #define MDB_DUPFIXED 0x10
172 /** with #MDB_DUPSORT, dups are numeric in native byte order */
173 #define MDB_INTEGERDUP 0x20
174 /** with #MDB_DUPSORT, use reverse string dups */
175 #define MDB_REVERSEDUP 0x40
176 /** create DB if not already existing */
177 #define MDB_CREATE 0x40000
180 /** @defgroup mdb_put Write Flags
183 /** For put: Don't write if the key already exists. */
184 #define MDB_NOOVERWRITE 0x10
185 /** Only for #MDB_DUPSORT<br>
186 * For put: don't write if the key and data pair already exist.<br>
187 * For mdb_cursor_del: remove all duplicate data items.
189 #define MDB_NODUPDATA 0x20
190 /** For mdb_cursor_put: overwrite the current key/data pair */
191 #define MDB_CURRENT 0x40
194 /** @brief Cursor Get operations.
196 * This is the set of all operations for retrieving data
199 typedef enum MDB_cursor_op {
200 MDB_FIRST, /**< Position at first key/data item */
201 MDB_FIRST_DUP, /**< Position at first data item of current key.
202 Only for #MDB_DUPSORT */
203 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
204 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
205 MDB_GET_MULTIPLE, /**< Return all the duplicate data items at the current
206 cursor position. Only for #MDB_DUPFIXED */
207 MDB_LAST, /**< Position at last key/data item */
208 MDB_LAST_DUP, /**< Position at last data item of current key.
209 Only for #MDB_DUPSORT */
210 MDB_NEXT, /**< Position at next data item */
211 MDB_NEXT_DUP, /**< Position at next data item of current key.
212 Only for #MDB_DUPSORT */
213 MDB_NEXT_MULTIPLE, /**< Return all duplicate data items at the next
214 cursor position. Only for #MDB_DUPFIXED */
215 MDB_NEXT_NODUP, /**< Position at first data item of next key.
216 Only for #MDB_DUPSORT */
217 MDB_PREV, /**< Position at previous data item */
218 MDB_PREV_DUP, /**< Position at previous data item of current key.
219 Only for #MDB_DUPSORT */
220 MDB_PREV_NODUP, /**< Position at last data item of previous key.
221 Only for #MDB_DUPSORT */
222 MDB_SET, /**< Position at specified key */
223 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
226 /** @defgroup errors Return Codes
228 * BerkeleyDB uses -30800 to -30999, we'll go under them
231 /** Successful result */
232 #define MDB_SUCCESS 0
233 /** key/data pair already exists */
234 #define MDB_KEYEXIST (-30799)
235 /** key/data pair not found (EOF) */
236 #define MDB_NOTFOUND (-30798)
237 /** Requested page not found - this usually indicates corruption */
238 #define MDB_PAGE_NOTFOUND (-30797)
239 /** Located page was wrong type */
240 #define MDB_CORRUPTED (-30796)
241 /** Update of meta page failed, probably I/O error */
242 #define MDB_PANIC (-30795)
243 /** Environment version mismatch */
244 #define MDB_VERSION_MISMATCH (-30794)
247 /** @brief Statistics for a database in the environment */
248 typedef struct MDB_stat {
249 unsigned int ms_psize; /**< Size of a database page.
250 This is currently the same for all databases. */
251 unsigned int ms_depth; /**< Depth (height) of the B-tree */
252 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
253 size_t ms_leaf_pages; /**< Number of leaf pages */
254 size_t ms_overflow_pages; /**< Number of overflow pages */
255 size_t ms_entries; /**< Number of data items */
258 /** @brief Return the mdb library version information.
260 * @param[out] major if non-NULL, the library major version number is copied here
261 * @param[out] minor if non-NULL, the library minor version number is copied here
262 * @param[out] patch if non-NULL, the library patch version number is copied here
263 * @retval "version string" The library version as a string
265 char *mdb_version(int *major, int *minor, int *patch);
267 /** @brief Return a string describing a given error code.
269 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
270 * function. If the error code is greater than or equal to 0, then the string
271 * returned by the system function strerror(3) is returned. If the error code
272 * is less than 0, an error string corresponding to the MDB library error is
273 * returned. See @ref errors for a list of MDB-specific error codes.
274 * @param[in] err The error code
275 * @retval "error message" The description of the error
277 char *mdb_strerror(int err);
279 /** @brief Create an MDB environment handle.
281 * This function allocates memory for a #MDB_env structure. To release
282 * the allocated memory and discard the handle, call #mdb_env_close().
283 * Before the handle may be used, it must be opened using #mdb_env_open().
284 * Various other options may also need to be set before opening the handle,
285 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
286 * depending on usage requirements.
287 * @param[out] env The address where the new handle will be stored
288 * @return A non-zero error value on failure and 0 on success.
290 int mdb_env_create(MDB_env **env);
292 /** @brief Open an environment handle.
294 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
295 * @param[in] env An environment handle returned by #mdb_env_create()
296 * @param[in] path The directory in which the database files reside. This
297 * directory must already exist and be writable.
298 * @param[in] flags Special options for this environment. This parameter
299 * must be set to 0 or by bitwise OR'ing together one or more of the
300 * values described here.
303 * use a fixed address for the mmap region. This flag must be specified
304 * when creating the environment, and is stored persistently in the environment.
305 * If successful, the memory map will always reside at the same virtual address
306 * and pointers used to reference data items in the database will be constant
307 * across multiple invocations. This option may not always work, depending on
308 * how the operating system has allocated memory to shared libraries and other uses.
309 * The feature is highly experimental.
311 * By default, MDB creates its environment in a directory whose
312 * pathname is given in \b path, and creates its data and lock files
313 * under that directory. With this option, \b path is used as-is for
314 * the database main data file. The database lock file is the \b path
315 * with "-lock" appended.
317 * Don't perform a synchronous flush after committing a transaction. This means
318 * transactions will exhibit the ACI (atomicity, consistency, and isolation)
319 * properties, but not D (durability); that is database integrity will be
320 * maintained but it is possible some number of the most recently committed
321 * transactions may be undone after a system crash. The number of transactions
322 * at risk is governed by how often the system flushes dirty buffers to disk
323 * and how often #mdb_env_sync() is called. This flag may be changed
324 * at any time using #mdb_env_set_flags().
326 * Open the environment in read-only mode. No write operations will be allowed.
328 * @param[in] mode The UNIX permissions to set on created files. This parameter
329 * is ignored on Windows.
330 * @return A non-zero error value on failure and 0 on success. Some possible
333 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
334 * version that created the database environment.
335 * <li>EINVAL - the environment file headers are corrupted.
336 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
337 * <li>EACCES - the user didn't have permission to access the environment files.
338 * <li>EAGAIN - the environment was locked by another process.
341 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mode_t mode);
343 /** @brief Return statistics about the MDB environment.
345 * @param[in] env An environment handle returned by #mdb_env_create()
346 * @param[out] stat The address of an #MDB_stat structure
347 * where the statistics will be copied
349 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
351 /** @brief Flush the data buffers to disk.
353 * Data is always written to disk when #mdb_txn_commit() is called,
354 * but the operating system may keep it buffered. MDB always flushes
355 * the OS buffers upon commit as well, unless the environment was
356 * opened with #MDB_NOSYNC.
357 * @param[in] env An environment handle returned by #mdb_env_create()
358 * @param[in] force If non-zero, force the flush to occur. Otherwise
359 * if the environment has the #MDB_NOSYNC flag set the flushes
361 * @return A non-zero error value on failure and 0 on success. Some possible
364 * <li>EINVAL - an invalid parameter was specified.
365 * <li>EIO - an error occurred during synchronization.
368 int mdb_env_sync(MDB_env *env, int force);
370 /** @brief Close the environment and release the memory map.
372 * Only a single thread may call this function. All transactions, databases,
373 * and cursors must already be closed before calling this function. Attempts to
374 * use any such handles after calling this function will cause a SIGSEGV.
375 * The environment handle will be freed and must not be used again after this call.
376 * @param[in] env An environment handle returned by #mdb_env_create()
378 void mdb_env_close(MDB_env *env);
380 /** @brief Set environment flags.
382 * This may be used to set some flags that weren't already set during
383 * #mdb_env_open(), or to unset these flags. Currently only the
384 * #MDB_NOSYNC flag setting may be changed with this function.
385 * @param[in] env An environment handle returned by #mdb_env_create()
386 * @param[in] flags The flags to change, bitwise OR'ed together
387 * @param[in] onoff A non-zero value sets the flags, zero clears them.
388 * @return A non-zero error value on failure and 0 on success. Some possible
391 * <li>EINVAL - an invalid parameter was specified.
394 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
396 /** @brief Get environment flags.
398 * @param[in] env An environment handle returned by #mdb_env_create()
399 * @param[out] flags The address of an integer to store the flags
400 * @return A non-zero error value on failure and 0 on success. Some possible
403 * <li>EINVAL - an invalid parameter was specified.
406 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
408 /** @brief Return the path that was used in #mdb_env_open().
410 * @param[in] env An environment handle returned by #mdb_env_create()
411 * @param[out] path Address of a string pointer to contain the path. This
412 * is the actual string in the environment, not a copy. It should not be
413 * altered in any way.
414 * @return A non-zero error value on failure and 0 on success. Some possible
417 * <li>EINVAL - an invalid parameter was specified.
420 int mdb_env_get_path(MDB_env *env, const char **path);
422 /** @brief Set the size of the memory map to use for this environment.
424 * The size should be a multiple of the OS page size. The default is
425 * 10485760 bytes. The size of the memory map is also the maximum size
426 * of the database. The value should be chosen as large as possible,
427 * to accomodate future growth of the database.
428 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
429 * @param[in] env An environment handle returned by #mdb_env_create()
430 * @param[in] size The size in bytes
431 * @return A non-zero error value on failure and 0 on success. Some possible
434 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
437 int mdb_env_set_mapsize(MDB_env *env, size_t size);
439 /** @brief Set the maximum number of threads for the environment.
441 * This defines the number of slots in the lock table that is used to track readers in the
442 * the environment. The default is 126.
443 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
444 * @param[in] env An environment handle returned by #mdb_env_create()
445 * @param[in] readers The maximum number of threads
446 * @return A non-zero error value on failure and 0 on success. Some possible
449 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
452 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
454 /** @brief Get the maximum number of threads for the environment.
456 * @param[in] env An environment handle returned by #mdb_env_create()
457 * @param[out] readers Address of an integer to store the number of readers
458 * @return A non-zero error value on failure and 0 on success. Some possible
461 * <li>EINVAL - an invalid parameter was specified.
464 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
466 /** @brief Set the maximum number of databases for the environment.
468 * This function is only needed if multiple databases will be used in the
469 * environment. Simpler applications that only use a single database can ignore
471 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
472 * @param[in] env An environment handle returned by #mdb_env_create()
473 * @param[in] dbs The maximum number of databases
474 * @return A non-zero error value on failure and 0 on success. Some possible
477 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
480 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
482 /** @brief Create a transaction for use with the environment.
484 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
485 * @note Transactions may not span threads, a transaction must only be used by a
487 * @note Cursors may not span transactions; each cursor must be opened and closed
488 * within a single transaction.
489 * @param[in] env An environment handle returned by #mdb_env_create()
490 * @param[in] parent If this parameter is non-NULL, the new transaction
491 * will be a nested transaction, with the transaction indicated by \b parent
492 * as its parent. Transactions may be nested to any level. A parent
493 * transaction may not issue any other operations besides mdb_txn_begin,
494 * mdb_txn_abort, or mdb_txn_commit while it has active child transactions.
495 * @param[in] flags Special options for this transaction. This parameter
496 * must be set to 0 or by bitwise OR'ing together one or more of the
497 * values described here.
500 * This transaction will not perform any write operations.
502 * @param[out] txn Address where the new #MDB_txn handle will be stored
503 * @return A non-zero error value on failure and 0 on success. Some possible
506 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
508 * <li>ENOMEM - out of memory, or a read-only transaction was requested and
509 * the reader lock table is full. See #mdb_env_set_maxreaders().
512 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
514 /** @brief Commit all the operations of a transaction into the database.
516 * All cursors opened within the transaction will be closed by this call. The cursors
517 * and transaction handle will be freed and must not be used again after this call.
518 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
519 * @return A non-zero error value on failure and 0 on success. Some possible
522 * <li>EINVAL - an invalid parameter was specified.
523 * <li>ENOSPC - no more disk space.
524 * <li>EIO - a low-level I/O error occurred while writing.
527 int mdb_txn_commit(MDB_txn *txn);
529 /** @brief Abandon all the operations of the transaction instead of saving them.
531 * All cursors opened within the transaction will be closed by this call. The cursors
532 * and transaction handle will be freed and must not be used again after this call.
533 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
535 void mdb_txn_abort(MDB_txn *txn);
537 /** @brief Reset a read-only transaction.
539 * This releases the current reader lock but doesn't free the
540 * transaction handle, allowing it to be used again later by #mdb_txn_renew().
541 * It otherwise has the same effect as #mdb_txn_abort() but saves some memory
542 * allocation/deallocation overhead if a thread is going to start a new
543 * read-only transaction again soon.
544 * All cursors opened within the transaction must be closed before the transaction
546 * Reader locks generally don't interfere with writers, but they keep old
547 * versions of database pages allocated. Thus they prevent the old pages
548 * from being reused when writers commit new data, and so under heavy load
549 * the database size may grow much more rapidly than otherwise.
550 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
552 void mdb_txn_reset(MDB_txn *txn);
554 /** @brief Renew a read-only transaction.
556 * This acquires a new reader lock for a transaction handle that had been
557 * released by #mdb_txn_reset(). It must be called before a reset transaction
559 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
560 * @return A non-zero error value on failure and 0 on success. Some possible
563 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
565 * <li>EINVAL - an invalid parameter was specified.
568 int mdb_txn_renew(MDB_txn *txn);
570 /** @brief Open a database in the environment.
572 * The database handle may be discarded by calling #mdb_close(). Only
573 * one thread should call this function; it is not mutex-protected in
574 * a read-only transaction.
575 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
576 * @param[in] name The name of the database to open. If only a single
577 * database is needed in the enviroment, this value may be NULL.
578 * @param[in] flags Special options for this database. This parameter
579 * must be set to 0 or by bitwise OR'ing together one or more of the
580 * values described here.
582 * <li>#MDB_REVERSEKEY
583 * Keys are strings to be compared in reverse order, from the end
584 * of the strings to the beginning. By default, Keys are treated as strings and
585 * compared from beginning to end.
587 * Duplicate keys may be used in the database. (Or, from another perspective,
588 * keys may have multiple data items, stored in sorted order.) By default
589 * keys must be unique and may have only a single data item.
590 * <li>#MDB_INTEGERKEY
591 * Keys are binary integers in native byte order. Setting this option
592 * requires all keys to be the same size, typically sizeof(int)
595 * This flag may only be used in combination with #MDB_DUPSORT. This option
596 * tells the library that the data items for this database are all the same
597 * size, which allows further optimizations in storage and retrieval. When
598 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
599 * cursor operations may be used to retrieve multiple items at once.
600 * <li>#MDB_INTEGERDUP
601 * This option specifies that duplicate data items are also integers, and
602 * should be sorted as such.
603 * <li>#MDB_REVERSEDUP
604 * This option specifies that duplicate data items should be compared as
605 * strings in reverse order.
607 * Create the named database if it doesn't exist. This option is not
608 * allowed in a read-only transaction or a read-only environment.
610 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
611 * @return A non-zero error value on failure and 0 on success. Some possible
614 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
615 * and #MDB_CREATE was not specified.
616 * <li>ENFILE - too many databases have been opened. See #mdb_env_set_maxdbs().
619 int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
621 /** @brief Retrieve statistics for a database.
623 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
624 * @param[in] dbi A database handle returned by #mdb_open()
625 * @param[out] stat The address of an #MDB_stat structure
626 * where the statistics will be copied
627 * @return A non-zero error value on failure and 0 on success. Some possible
630 * <li>EINVAL - an invalid parameter was specified.
633 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
635 /** @brief Close a database handle.
637 * This call is not mutex protected. Handles should only be closed by
638 * a single thread, and only if no other threads are going to reference
639 * the database handle any further.
640 * @param[in] env An environment handle returned by #mdb_env_create()
641 * @param[in] dbi A database handle returned by #mdb_open()
643 void mdb_close(MDB_env *env, MDB_dbi dbi);
645 /** @brief Delete a database and/or free all its pages.
647 * If the \b del parameter is non-zero the DB handle will be closed
648 * and the DB will be deleted.
649 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
650 * @param[in] dbi A database handle returned by #mdb_open()
651 * @param[in] del non-zero to delete the DB from the environment,
652 * otherwise just free its pages.
653 * @return A non-zero error value on failure and 0 on success.
655 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
657 /** @brief Set a custom key comparison function for a database.
659 * The comparison function is called whenever it is necessary to compare a
660 * key specified by the application with a key currently stored in the database.
661 * If no comparison function is specified, and no speAGAINcial key flags were specified
662 * with #mdb_open(), the keys are compared lexically, with shorter keys collating
663 * before longer keys.
664 * @warning This function must be called before any data access functions are used,
665 * otherwise data corruption may occur. The same comparison function must be used by every
666 * program accessing the database, every time the database is used.
667 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
668 * @param[in] dbi A database handle returned by #mdb_open()
669 * @param[in] cmp A #MDB_cmp_func function
670 * @return A non-zero error value on failure and 0 on success. Some possible
673 * <li>EINVAL - an invalid parameter was specified.
676 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
678 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
680 * This comparison function is called whenever it is necessary to compare a data
681 * item specified by the application with a data item currently stored in the database.
682 * This function only takes effect if the database was opened with the #MDB_DUPSORT
684 * If no comparison function is specified, and no special key flags were specified
685 * with #mdb_open(), the data items are compared lexically, with shorter items collating
686 * before longer items.
687 * @warning This function must be called before any data access functions are used,
688 * otherwise data corruption may occur. The same comparison function must be used by every
689 * program accessing the database, every time the database is used.
690 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
691 * @param[in] dbi A database handle returned by #mdb_open()
692 * @param[in] cmp A #MDB_cmp_func function
693 * @return A non-zero error value on failure and 0 on success. Some possible
696 * <li>EINVAL - an invalid parameter was specified.
699 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
701 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
703 * @todo The relocation function is called whenever it is necessary to move the data
704 * of an item to a different position in the database (e.g. through tree
705 * balancing operations, shifts as a result of adds or deletes, etc.). It is
706 * intended to allow address/position-dependent data items to be stored in
707 * a database in an environment opened with the #MDB_FIXEDMAP option.
708 * Currently the relocation feature is unimplemented and setting
709 * this function has no effect.
710 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
711 * @param[in] dbi A database handle returned by #mdb_open()
712 * @param[in] rel A #MDB_rel_func function
713 * @return A non-zero error value on failure and 0 on success. Some possible
716 * <li>EINVAL - an invalid parameter was specified.
719 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
721 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
723 * See #mdb_set_relfunc and #MDB_rel_func for more details.
724 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
725 * @param[in] dbi A database handle returned by #mdb_open()
726 * @param[in] ctx An arbitrary pointer for whatever the application needs.
727 * It will be passed to the callback function set by #mdb_set_relfunc
728 * as its \b relctx parameter whenever the callback is invoked.
729 * @return A non-zero error value on failure and 0 on success. Some possible
732 * <li>EINVAL - an invalid parameter was specified.
735 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
737 /** @brief Get items from a database.
739 * This function retrieves key/data pairs from the database. The address
740 * and length of the data associated with the specified \b key are returned
741 * in the structure to which \b data refers.
742 * If the database supports duplicate keys (#MDB_DUPSORT) then the
743 * first data item for the key will be returned. Retrieval of other
744 * items requires the use of #mdb_cursor_get().
746 * @note The memory pointed to by the returned values is owned by the
747 * database. The caller need not dispose of the memory, and may not
748 * modify it in any way. For values returned in a read-only transaction
749 * any modification attempts will cause a SIGSEGV.
750 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
751 * @param[in] dbi A database handle returned by #mdb_open()
752 * @param[in] key The key to search for in the database
753 * @param[out] data The data corresponding to the key
754 * @return A non-zero error value on failure and 0 on success. Some possible
757 * <li>#MDB_NOTFOUND - the key was not in the database.
758 * <li>EINVAL - an invalid parameter was specified.
761 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
763 /** @brief Store items into a database.
765 * This function stores key/data pairs in the database. The default behavior
766 * is to enter the new key/data pair, replacing any previously existing key
767 * if duplicates are disallowed, or adding a duplicate data item if
768 * duplicates are allowed (#MDB_DUPSORT).
769 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
770 * @param[in] dbi A database handle returned by #mdb_open()
771 * @param[in] key The key to store in the database
772 * @param[in,out] data The data to store
773 * @param[in] flags Special options for this operation. This parameter
774 * must be set to 0 or by bitwise OR'ing together one or more of the
775 * values described here.
777 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
778 * already appear in the database. This flag may only be specified
779 * if the database was opened with #MDB_DUPSORT. The function will
780 * return #MDB_KEYEXIST if the key/data pair already appears in the
782 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
783 * does not already appear in the database. The function will return
784 * #MDB_KEYEXIST if the key already appears in the database, even if
785 * the database supports duplicates (#MDB_DUPSORT). The \b data
786 * parameter will be set to point to the existing item.
788 * @return A non-zero error value on failure and 0 on success. Some possible
791 * <li>EACCESS - an attempt was made to write in a read-only transaction.
792 * <li>EINVAL - an invalid parameter was specified.
793 * <li>ENOMEM - the database is full, see #mdb_env_set_mapsize().
796 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
799 /** @brief Delete items from a database.
801 * This function removes key/data pairs from the database.
802 * If the database does not support sorted duplicate data items
803 * (#MDB_DUPSORT) the data parameter is ignored.
804 * If the database supports sorted duplicates and the data parameter
805 * is NULL, all of the duplicate data items for the key will be
806 * deleted. Otherwise, if the data parameter is non-NULL
807 * only the matching data item will be deleted.
808 * This function will return #MDB_NOTFOUND if the specified key/data
809 * pair is not in the database.
810 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
811 * @param[in] dbi A database handle returned by #mdb_open()
812 * @param[in] key The key to delete from the database
813 * @param[in] data The data to delete
814 * @return A non-zero error value on failure and 0 on success. Some possible
817 * <li>EACCESS - an attempt was made to write in a read-only transaction.
818 * <li>EINVAL - an invalid parameter was specified.
821 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
823 /** @brief Create a cursor handle.
825 * Cursors are associated with a specific transaction and database and
826 * may not span threads.
827 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
828 * @param[in] dbi A database handle returned by #mdb_open()
829 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
830 * @return A non-zero error value on failure and 0 on success. Some possible
833 * <li>EINVAL - an invalid parameter was specified.
836 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
838 /** @brief Close a cursor handle.
840 * The cursor handle will be freed and must not be used again after this call.
841 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
843 void mdb_cursor_close(MDB_cursor *cursor);
845 /** @brief Retrieve by cursor.
847 * This function retrieves key/data pairs from the database. The address and length
848 * of the key are returned in the object to which \b key refers (except for the
849 * case of the #MDB_SET option, in which the \b key object is unchanged), and
850 * the address and length of the data are returned in the object to which \b data
852 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
853 * @param[in,out] key The key for a retrieved item
854 * @param[in,out] data The data of a retrieved item
855 * @param[in] op A cursor operation #MDB_cursor_op
856 * @return A non-zero error value on failure and 0 on success. Some possible
859 * <li>#MDB_NOTFOUND - no matching key found.
860 * <li>EINVAL - an invalid parameter was specified.
863 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
866 /** @brief Store by cursor.
868 * This function stores key/data pairs into the database.
869 * If the function fails for any reason, the state of the cursor will be
870 * unchanged. If the function succeeds and an item is inserted into the
871 * database, the cursor is always positioned to refer to the newly inserted item.
872 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
873 * @param[in] key The key operated on.
874 * @param[in] data The data operated on.
875 * @param[in] flags Options for this operation. This parameter
876 * must be set to 0 or one of the values described here.
878 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which
879 * the cursor refers with the specified data item. The \b key
880 * parameter is ignored.
881 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
882 * already appear in the database. This flag may only be specified
883 * if the database was opened with #MDB_DUPSORT. The function will
884 * return #MDB_KEYEXIST if the key/data pair already appears in the
886 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
887 * does not already appear in the database. The function will return
888 * #MDB_KEYEXIST if the key already appears in the database, even if
889 * the database supports duplicates (#MDB_DUPSORT).
891 * @return A non-zero error value on failure and 0 on success. Some possible
894 * <li>EACCES - an attempt was made to modify a read-only database.
895 * <li>EINVAL - an invalid parameter was specified.
898 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
901 /** @brief Delete current key/data pair
903 * This function deletes the key/data pair to which the cursor refers.
904 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
905 * @param[in] flags Options for this operation. This parameter
906 * must be set to 0 or one of the values described here.
908 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
909 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
911 * @return A non-zero error value on failure and 0 on success. Some possible
914 * <li>EACCES - an attempt was made to modify a read-only database.
915 * <li>EINVAL - an invalid parameter was specified.
918 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
920 /** @brief Return count of duplicates for current key.
922 * This call is only valid on databases that support sorted duplicate
923 * data items #MDB_DUPSORT.
924 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
925 * @param[out] countp Address where the count will be stored
926 * @return A non-zero error value on failure and 0 on success. Some possible
929 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
932 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
934 /** @brief Compare two data items according to a particular database.
936 * This returns a comparison as if the two data items were keys in the
937 * specified database.
938 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
939 * @param[in] dbi A database handle returned by #mdb_open()
940 * @param[in] a The first item to compare
941 * @param[in] b The second item to compare
942 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
944 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
946 /** @brief Compare two data items according to a particular database.
948 * This returns a comparison as if the two items were data items of
949 * a sorted duplicates #MDB_DUPSORT database.
950 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
951 * @param[in] dbi A database handle returned by #mdb_open()
952 * @param[in] a The first item to compare
953 * @param[in] b The second item to compare
954 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
956 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);