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 /** don't fsync after commit */
153 #define MDB_NOSYNC 0x10000
155 #define MDB_RDONLY 0x20000
158 /** @defgroup mdb_open Database Flags
161 /** use reverse string keys */
162 #define MDB_REVERSEKEY 0x02
163 /** use sorted duplicates */
164 #define MDB_DUPSORT 0x04
165 /** numeric keys in native byte order.
166 * The keys must all be of the same size. */
167 #define MDB_INTEGERKEY 0x08
168 /** with #MDB_DUPSORT, sorted dup items have fixed size */
169 #define MDB_DUPFIXED 0x10
170 /** with #MDB_DUPSORT, dups are numeric in native byte order */
171 #define MDB_INTEGERDUP 0x20
172 /** with #MDB_DUPSORT, use reverse string dups */
173 #define MDB_REVERSEDUP 0x40
174 /** create DB if not already existing */
175 #define MDB_CREATE 0x40000
178 /** @defgroup mdb_put Write Flags
181 /** For put: Don't write if the key already exists. */
182 #define MDB_NOOVERWRITE 0x10
183 /** Only for #MDB_DUPSORT<br>
184 * For put: don't write if the key and data pair already exist.<br>
185 * For mdb_cursor_del: remove all duplicate data items.
187 #define MDB_NODUPDATA 0x20
188 /** For mdb_cursor_put: overwrite the current key/data pair */
189 #define MDB_CURRENT 0x40
192 /** @brief Cursor Get operations.
194 * This is the set of all operations for retrieving data
197 typedef enum MDB_cursor_op {
198 MDB_FIRST, /**< Position at first key/data item */
199 MDB_FIRST_DUP, /**< Position at first data item of current key.
200 Only for #MDB_DUPSORT */
201 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
202 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
203 MDB_GET_MULTIPLE, /**< Return all the duplicate data items at the current
204 cursor position. Only for #MDB_DUPFIXED */
205 MDB_LAST, /**< Position at last key/data item */
206 MDB_LAST_DUP, /**< Position at last data item of current key.
207 Only for #MDB_DUPSORT */
208 MDB_NEXT, /**< Position at next data item */
209 MDB_NEXT_DUP, /**< Position at next data item of current key.
210 Only for #MDB_DUPSORT */
211 MDB_NEXT_MULTIPLE, /**< Return all duplicate data items at the next
212 cursor position. Only for #MDB_DUPFIXED */
213 MDB_NEXT_NODUP, /**< Position at first data item of next key.
214 Only for #MDB_DUPSORT */
215 MDB_PREV, /**< Position at previous data item */
216 MDB_PREV_DUP, /**< Position at previous data item of current key.
217 Only for #MDB_DUPSORT */
218 MDB_PREV_NODUP, /**< Position at last data item of previous key.
219 Only for #MDB_DUPSORT */
220 MDB_SET, /**< Position at specified key */
221 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
224 /** @defgroup errors Return Codes
226 * BerkeleyDB uses -30800 to -30999, we'll go under them
229 /** Successful result */
230 #define MDB_SUCCESS 0
231 /** key/data pair already exists */
232 #define MDB_KEYEXIST (-30799)
233 /** key/data pair not found (EOF) */
234 #define MDB_NOTFOUND (-30798)
235 /** Requested page not found - this usually indicates corruption */
236 #define MDB_PAGE_NOTFOUND (-30797)
237 /** Located page was wrong type */
238 #define MDB_CORRUPTED (-30796)
239 /** Update of meta page failed, probably I/O error */
240 #define MDB_PANIC (-30795)
241 /** Environment version mismatch */
242 #define MDB_VERSION_MISMATCH (-30794)
245 /** @brief Statistics for a database in the environment */
246 typedef struct MDB_stat {
247 unsigned int ms_psize; /**< Size of a database page.
248 This is currently the same for all databases. */
249 unsigned int ms_depth; /**< Depth (height) of the B-tree */
250 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
251 size_t ms_leaf_pages; /**< Number of leaf pages */
252 size_t ms_overflow_pages; /**< Number of overflow pages */
253 size_t ms_entries; /**< Number of data items */
256 /** @brief Return the mdb library version information.
258 * @param[out] major if non-NULL, the library major version number is copied here
259 * @param[out] minor if non-NULL, the library minor version number is copied here
260 * @param[out] patch if non-NULL, the library patch version number is copied here
261 * @retval "version string" The library version as a string
263 char *mdb_version(int *major, int *minor, int *patch);
265 /** @brief Return a string describing a given error code.
267 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
268 * function. If the error code is greater than or equal to 0, then the string
269 * returned by the system function strerror(3) is returned. If the error code
270 * is less than 0, an error string corresponding to the MDB library error is
271 * returned. See @ref errors for a list of MDB-specific error codes.
272 * @param[in] err The error code
273 * @retval "error message" The description of the error
275 char *mdb_strerror(int err);
277 /** @brief Create an MDB environment handle.
279 * This function allocates memory for a #MDB_env structure. To release
280 * the allocated memory and discard the handle, call #mdb_env_close().
281 * Before the handle may be used, it must be opened using #mdb_env_open().
282 * Various other options may also need to be set before opening the handle,
283 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
284 * depending on usage requirements.
285 * @param[out] env The address where the new handle will be stored
286 * @return A non-zero error value on failure and 0 on success.
288 int mdb_env_create(MDB_env **env);
290 /** @brief Open an environment handle.
292 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
293 * @param[in] env An environment handle returned by #mdb_env_create()
294 * @param[in] path The directory in which the database files reside. This
295 * directory must already exist and be writable.
296 * @param[in] flags Special options for this environment. This parameter
297 * must be set to 0 or by bitwise OR'ing together one or more of the
298 * values described here.
301 * use a fixed address for the mmap region. This flag must be specified
302 * when creating the environment, and is stored persistently in the environment.
303 * If successful, the memory map will always reside at the same virtual address
304 * and pointers used to reference data items in the database will be constant
305 * across multiple invocations. This option may not always work, depending on
306 * how the operating system has allocated memory to shared libraries and other uses.
307 * The feature is highly experimental.
309 * Don't perform a synchronous flush after committing a transaction. This means
310 * transactions will exhibit the ACI (atomicity, consistency, and isolation)
311 * properties, but not D (durability); that is database integrity will be
312 * maintained but it is possible some number of the most recently committed
313 * transactions may be undone after a system crash. The number of transactions
314 * at risk is governed by how often the system flushes dirty buffers to disk
315 * and how often #mdb_env_sync() is called. This flag may be changed
316 * at any time using #mdb_env_set_flags().
318 * Open the environment in read-only mode. No write operations will be allowed.
320 * @param[in] mode The UNIX permissions to set on created files. This parameter
321 * is ignored on Windows.
322 * @return A non-zero error value on failure and 0 on success. Some possible
325 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
326 * version that created the database environment.
327 * <li>EINVAL - the environment file headers are corrupted.
328 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
329 * <li>EACCES - the user didn't have permission to access the environment files.
330 * <li>EAGAIN - the environment was locked by another process.
333 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mode_t mode);
335 /** @brief Return statistics about the MDB environment.
337 * @param[in] env An environment handle returned by #mdb_env_create()
338 * @param[out] stat The address of an #MDB_stat structure
339 * where the statistics will be copied
341 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
343 /** @brief Flush the data buffers to disk.
345 * Data is always written to disk when #mdb_txn_commit() is called,
346 * but the operating system may keep it buffered. MDB always flushes
347 * the OS buffers upon commit as well, unless the environment was
348 * opened with #MDB_NOSYNC.
349 * @param[in] env An environment handle returned by #mdb_env_create()
350 * @param[in] force If non-zero, force the flush to occur. Otherwise
351 * if the environment has the #MDB_NOSYNC flag set the flushes
353 * @return A non-zero error value on failure and 0 on success. Some possible
356 * <li>EINVAL - an invalid parameter was specified.
357 * <li>EIO - an error occurred during synchronization.
360 int mdb_env_sync(MDB_env *env, int force);
362 /** @brief Close the environment and release the memory map.
364 * Only a single thread may call this function. All transactions, databases,
365 * and cursors must already be closed before calling this function. Attempts to
366 * use any such handles after calling this function will cause a SIGSEGV.
367 * The environment handle will be freed and must not be used again after this call.
368 * @param[in] env An environment handle returned by #mdb_env_create()
370 void mdb_env_close(MDB_env *env);
372 /** @brief Set environment flags.
374 * This may be used to set some flags that weren't already set during
375 * #mdb_env_open(), or to unset these flags. Currently only the
376 * #MDB_NOSYNC flag setting may be changed with this function.
377 * @param[in] env An environment handle returned by #mdb_env_create()
378 * @param[in] flags The flags to change, bitwise OR'ed together
379 * @param[in] onoff A non-zero value sets the flags, zero clears them.
380 * @return A non-zero error value on failure and 0 on success. Some possible
383 * <li>EINVAL - an invalid parameter was specified.
386 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
388 /** @brief Get environment flags.
390 * @param[in] env An environment handle returned by #mdb_env_create()
391 * @param[out] flags The address of an integer to store the flags
392 * @return A non-zero error value on failure and 0 on success. Some possible
395 * <li>EINVAL - an invalid parameter was specified.
398 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
400 /** @brief Return the path that was used in #mdb_env_open().
402 * @param[in] env An environment handle returned by #mdb_env_create()
403 * @param[out] path Address of a string pointer to contain the path. This
404 * is the actual string in the environment, not a copy. It should not be
405 * altered in any way.
406 * @return A non-zero error value on failure and 0 on success. Some possible
409 * <li>EINVAL - an invalid parameter was specified.
412 int mdb_env_get_path(MDB_env *env, const char **path);
414 /** @brief Set the size of the memory map to use for this environment.
416 * The size should be a multiple of the OS page size. The default is
417 * 10485760 bytes. The size of the memory map is also the maximum size
418 * of the database. The value should be chosen as large as possible,
419 * to accomodate future growth of the database.
420 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
421 * @param[in] env An environment handle returned by #mdb_env_create()
422 * @param[in] size The size in bytes
423 * @return A non-zero error value on failure and 0 on success. Some possible
426 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
429 int mdb_env_set_mapsize(MDB_env *env, size_t size);
431 /** @brief Set the maximum number of threads for the environment.
433 * This defines the number of slots in the lock table that is used to track readers in the
434 * the environment. The default is 126.
435 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
436 * @param[in] env An environment handle returned by #mdb_env_create()
437 * @param[in] readers The maximum number of threads
438 * @return A non-zero error value on failure and 0 on success. Some possible
441 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
444 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
446 /** @brief Get the maximum number of threads for the environment.
448 * @param[in] env An environment handle returned by #mdb_env_create()
449 * @param[out] readers Address of an integer to store the number of readers
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_maxreaders(MDB_env *env, unsigned int *readers);
458 /** @brief Set the maximum number of databases for the environment.
460 * This function is only needed if multiple databases will be used in the
461 * environment. Simpler applications that only use a single database can ignore
463 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
464 * @param[in] env An environment handle returned by #mdb_env_create()
465 * @param[in] dbs The maximum number of databases
466 * @return A non-zero error value on failure and 0 on success. Some possible
469 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
472 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
474 /** @brief Create a transaction for use with the environment.
476 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
477 * @note Transactions may not span threads, a transaction must only be used by a
479 * @note Cursors may not span transactions; each cursor must be opened and closed
480 * within a single transaction.
481 * @param[in] env An environment handle returned by #mdb_env_create()
482 * @param[in] parent If this parameter is non-NULL, the new transaction
483 * will be a nested transaction, with the transaction indicated by \b parent
484 * as its parent. Transactions may be nested to any level. A parent
485 * transaction may not issue any other operations besides mdb_txn_begin,
486 * mdb_txn_abort, or mdb_txn_commit while it has active child transactions.
487 * @param[in] flags Special options for this transaction. This parameter
488 * must be set to 0 or by bitwise OR'ing together one or more of the
489 * values described here.
492 * This transaction will not perform any write operations.
494 * @param[out] txn Address where the new #MDB_txn handle will be stored
495 * @return A non-zero error value on failure and 0 on success. Some possible
498 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
500 * <li>ENOMEM - out of memory, or a read-only transaction was requested and
501 * the reader lock table is full. See #mdb_env_set_maxreaders().
504 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
506 /** @brief Commit all the operations of a transaction into the database.
508 * All cursors opened within the transaction will be closed by this call. The cursors
509 * and transaction handle will be freed and must not be used again after this call.
510 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
511 * @return A non-zero error value on failure and 0 on success. Some possible
514 * <li>EINVAL - an invalid parameter was specified.
515 * <li>ENOSPC - no more disk space.
516 * <li>EIO - a low-level I/O error occurred while writing.
519 int mdb_txn_commit(MDB_txn *txn);
521 /** @brief Abandon all the operations of the transaction instead of saving them.
523 * All cursors opened within the transaction will be closed by this call. The cursors
524 * and transaction handle will be freed and must not be used again after this call.
525 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
527 void mdb_txn_abort(MDB_txn *txn);
529 /** @brief Reset a read-only transaction.
531 * This releases the current reader lock but doesn't free the
532 * transaction handle, allowing it to be used again later by #mdb_txn_renew().
533 * It otherwise has the same effect as #mdb_txn_abort() but saves some memory
534 * allocation/deallocation overhead if a thread is going to start a new
535 * read-only transaction again soon.
536 * All cursors opened within the transaction must be closed before the transaction
538 * Reader locks generally don't interfere with writers, but they keep old
539 * versions of database pages allocated. Thus they prevent the old pages
540 * from being reused when writers commit new data, and so under heavy load
541 * the database size may grow much more rapidly than otherwise.
542 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
544 void mdb_txn_reset(MDB_txn *txn);
546 /** @brief Renew a read-only transaction.
548 * This acquires a new reader lock for a transaction handle that had been
549 * released by #mdb_txn_reset(). It must be called before a reset transaction
551 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
552 * @return A non-zero error value on failure and 0 on success. Some possible
555 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
557 * <li>EINVAL - an invalid parameter was specified.
560 int mdb_txn_renew(MDB_txn *txn);
562 /** @brief Open a database in the environment.
564 * The database handle may be discarded by calling #mdb_close(). Only
565 * one thread should call this function; it is not mutex-protected in
566 * a read-only transaction.
567 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
568 * @param[in] name The name of the database to open. If only a single
569 * database is needed in the enviroment, this value may be NULL.
570 * @param[in] flags Special options for this database. This parameter
571 * must be set to 0 or by bitwise OR'ing together one or more of the
572 * values described here.
574 * <li>#MDB_REVERSEKEY
575 * Keys are strings to be compared in reverse order, from the end
576 * of the strings to the beginning. By default, Keys are treated as strings and
577 * compared from beginning to end.
579 * Duplicate keys may be used in the database. (Or, from another perspective,
580 * keys may have multiple data items, stored in sorted order.) By default
581 * keys must be unique and may have only a single data item.
582 * <li>#MDB_INTEGERKEY
583 * Keys are binary integers in native byte order. Setting this option
584 * requires all keys to be the same size, typically sizeof(int)
587 * This flag may only be used in combination with #MDB_DUPSORT. This option
588 * tells the library that the data items for this database are all the same
589 * size, which allows further optimizations in storage and retrieval. When
590 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
591 * cursor operations may be used to retrieve multiple items at once.
592 * <li>#MDB_INTEGERDUP
593 * This option specifies that duplicate data items are also integers, and
594 * should be sorted as such.
595 * <li>#MDB_REVERSEDUP
596 * This option specifies that duplicate data items should be compared as
597 * strings in reverse order.
599 * Create the named database if it doesn't exist. This option is not
600 * allowed in a read-only transaction or a read-only environment.
602 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
603 * @return A non-zero error value on failure and 0 on success. Some possible
606 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
607 * and #MDB_CREATE was not specified.
608 * <li>ENFILE - too many databases have been opened. See #mdb_env_set_maxdbs().
611 int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
613 /** @brief Retrieve statistics for a database.
615 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
616 * @param[in] dbi A database handle returned by #mdb_open()
617 * @param[out] stat The address of an #MDB_stat structure
618 * where the statistics will be copied
619 * @return A non-zero error value on failure and 0 on success. Some possible
622 * <li>EINVAL - an invalid parameter was specified.
625 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
627 /** @brief Close a database handle.
629 * This call is not mutex protected. Handles should only be closed by
630 * a single thread, and only if no other threads are going to reference
631 * the database handle any further.
632 * @param[in] env An environment handle returned by #mdb_env_create()
633 * @param[in] dbi A database handle returned by #mdb_open()
635 void mdb_close(MDB_env *env, MDB_dbi dbi);
637 /** @brief Delete a database and/or free all its pages.
639 * If the \b del parameter is non-zero the DB handle will be closed
640 * and the DB will be deleted.
641 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
642 * @param[in] dbi A database handle returned by #mdb_open()
643 * @param[in] del non-zero to delete the DB from the environment,
644 * otherwise just free its pages.
645 * @return A non-zero error value on failure and 0 on success.
647 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
649 /** @brief Set a custom key comparison function for a database.
651 * The comparison function is called whenever it is necessary to compare a
652 * key specified by the application with a key currently stored in the database.
653 * If no comparison function is specified, and no speAGAINcial key flags were specified
654 * with #mdb_open(), the keys are compared lexically, with shorter keys collating
655 * before longer keys.
656 * @warning This function must be called before any data access functions are used,
657 * otherwise data corruption may occur. The same comparison function must be used by every
658 * program accessing the database, every time the database is used.
659 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
660 * @param[in] dbi A database handle returned by #mdb_open()
661 * @param[in] cmp A #MDB_cmp_func function
662 * @return A non-zero error value on failure and 0 on success. Some possible
665 * <li>EINVAL - an invalid parameter was specified.
668 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
670 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
672 * This comparison function is called whenever it is necessary to compare a data
673 * item specified by the application with a data item currently stored in the database.
674 * This function only takes effect if the database was opened with the #MDB_DUPSORT
676 * If no comparison function is specified, and no special key flags were specified
677 * with #mdb_open(), the data items are compared lexically, with shorter items collating
678 * before longer items.
679 * @warning This function must be called before any data access functions are used,
680 * otherwise data corruption may occur. The same comparison function must be used by every
681 * program accessing the database, every time the database is used.
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] cmp A #MDB_cmp_func function
685 * @return A non-zero error value on failure and 0 on success. Some possible
688 * <li>EINVAL - an invalid parameter was specified.
691 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
693 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
695 * @todo The relocation function is called whenever it is necessary to move the data
696 * of an item to a different position in the database (e.g. through tree
697 * balancing operations, shifts as a result of adds or deletes, etc.). It is
698 * intended to allow address/position-dependent data items to be stored in
699 * a database in an environment opened with the #MDB_FIXEDMAP option.
700 * Currently the relocation feature is unimplemented and setting
701 * this function has no effect.
702 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
703 * @param[in] dbi A database handle returned by #mdb_open()
704 * @param[in] rel A #MDB_rel_func function
705 * @return A non-zero error value on failure and 0 on success. Some possible
708 * <li>EINVAL - an invalid parameter was specified.
711 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
713 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
715 * See #mdb_set_relfunc and #MDB_rel_func for more details.
716 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
717 * @param[in] dbi A database handle returned by #mdb_open()
718 * @param[in] ctx An arbitrary pointer for whatever the application needs.
719 * It will be passed to the callback function set by #mdb_set_relfunc
720 * as its \b relctx parameter whenever the callback is invoked.
721 * @return A non-zero error value on failure and 0 on success. Some possible
724 * <li>EINVAL - an invalid parameter was specified.
727 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
729 /** @brief Get items from a database.
731 * This function retrieves key/data pairs from the database. The address
732 * and length of the data associated with the specified \b key are returned
733 * in the structure to which \b data refers.
734 * If the database supports duplicate keys (#MDB_DUPSORT) then the
735 * first data item for the key will be returned. Retrieval of other
736 * items requires the use of #mdb_cursor_get().
738 * @note The memory pointed to by the returned values is owned by the
739 * database. The caller need not dispose of the memory, and may not
740 * modify it in any way. For values returned in a read-only transaction
741 * any modification attempts will cause a SIGSEGV.
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] key The key to search for in the database
745 * @param[out] data The data corresponding to the key
746 * @return A non-zero error value on failure and 0 on success. Some possible
749 * <li>#MDB_NOTFOUND - the key was not in the database.
750 * <li>EINVAL - an invalid parameter was specified.
753 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
755 /** @brief Store items into a database.
757 * This function stores key/data pairs in the database. The default behavior
758 * is to enter the new key/data pair, replacing any previously existing key
759 * if duplicates are disallowed, or adding a duplicate data item if
760 * duplicates are allowed (#MDB_DUPSORT).
761 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
762 * @param[in] dbi A database handle returned by #mdb_open()
763 * @param[in] key The key to store in the database
764 * @param[in,out] data The data to store
765 * @param[in] flags Special options for this operation. This parameter
766 * must be set to 0 or by bitwise OR'ing together one or more of the
767 * values described here.
769 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
770 * already appear in the database. This flag may only be specified
771 * if the database was opened with #MDB_DUPSORT. The function will
772 * return #MDB_KEYEXIST if the key/data pair already appears in the
774 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
775 * does not already appear in the database. The function will return
776 * #MDB_KEYEXIST if the key already appears in the database, even if
777 * the database supports duplicates (#MDB_DUPSORT). The \b data
778 * parameter will be set to point to the existing item.
780 * @return A non-zero error value on failure and 0 on success. Some possible
783 * <li>EACCESS - an attempt was made to write in a read-only transaction.
784 * <li>EINVAL - an invalid parameter was specified.
785 * <li>ENOMEM - the database is full, see #mdb_env_set_mapsize().
788 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
791 /** @brief Delete items from a database.
793 * This function removes key/data pairs from the database.
794 * If the database does not support sorted duplicate data items
795 * (#MDB_DUPSORT) the data parameter is ignored.
796 * If the database supports sorted duplicates and the data parameter
797 * is NULL, all of the duplicate data items for the key will be
798 * deleted. Otherwise, if the data parameter is non-NULL
799 * only the matching data item will be deleted.
800 * This function will return #MDB_NOTFOUND if the specified key/data
801 * pair is not in the database.
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 delete from the database
805 * @param[in] data The data to delete
806 * @return A non-zero error value on failure and 0 on success. Some possible
809 * <li>EACCESS - an attempt was made to write in a read-only transaction.
810 * <li>EINVAL - an invalid parameter was specified.
813 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
815 /** @brief Create a cursor handle.
817 * Cursors are associated with a specific transaction and database and
818 * may not span threads.
819 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
820 * @param[in] dbi A database handle returned by #mdb_open()
821 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
822 * @return A non-zero error value on failure and 0 on success. Some possible
825 * <li>EINVAL - an invalid parameter was specified.
828 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
830 /** @brief Close a cursor handle.
832 * The cursor handle will be freed and must not be used again after this call.
833 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
835 void mdb_cursor_close(MDB_cursor *cursor);
837 /** @brief Retrieve by cursor.
839 * This function retrieves key/data pairs from the database. The address and length
840 * of the key are returned in the object to which \b key refers (except for the
841 * case of the #MDB_SET option, in which the \b key object is unchanged), and
842 * the address and length of the data are returned in the object to which \b data
844 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
845 * @param[in,out] key The key for a retrieved item
846 * @param[in,out] data The data of a retrieved item
847 * @param[in] op A cursor operation #MDB_cursor_op
848 * @return A non-zero error value on failure and 0 on success. Some possible
851 * <li>#MDB_NOTFOUND - no matching key found.
852 * <li>EINVAL - an invalid parameter was specified.
855 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
858 /** @brief Store by cursor.
860 * This function stores key/data pairs into the database.
861 * If the function fails for any reason, the state of the cursor will be
862 * unchanged. If the function succeeds and an item is inserted into the
863 * database, the cursor is always positioned to refer to the newly inserted item.
864 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
865 * @param[in] key The key operated on.
866 * @param[in] data The data operated on.
867 * @param[in] flags Options for this operation. This parameter
868 * must be set to 0 or one of the values described here.
870 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which
871 * the cursor refers with the specified data item. The \b key
872 * parameter is ignored.
873 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
874 * already appear in the database. This flag may only be specified
875 * if the database was opened with #MDB_DUPSORT. The function will
876 * return #MDB_KEYEXIST if the key/data pair already appears in the
878 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
879 * does not already appear in the database. The function will return
880 * #MDB_KEYEXIST if the key already appears in the database, even if
881 * the database supports duplicates (#MDB_DUPSORT).
883 * @return A non-zero error value on failure and 0 on success. Some possible
886 * <li>EACCES - an attempt was made to modify a read-only database.
887 * <li>EINVAL - an invalid parameter was specified.
890 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
893 /** @brief Delete current key/data pair
895 * This function deletes the key/data pair to which the cursor refers.
896 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
897 * @param[in] flags Options for this operation. This parameter
898 * must be set to 0 or one of the values described here.
900 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
901 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
903 * @return A non-zero error value on failure and 0 on success. Some possible
906 * <li>EACCES - an attempt was made to modify a read-only database.
907 * <li>EINVAL - an invalid parameter was specified.
910 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
912 /** @brief Return count of duplicates for current key.
914 * This call is only valid on databases that support sorted duplicate
915 * data items #MDB_DUPSORT.
916 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
917 * @param[out] countp Address where the count will be stored
918 * @return A non-zero error value on failure and 0 on success. Some possible
921 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
924 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
926 /** @brief Compare two data items according to a particular database.
928 * This returns a comparison as if the two data items were keys in the
929 * specified database.
930 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
931 * @param[in] dbi A database handle returned by #mdb_open()
932 * @param[in] a The first item to compare
933 * @param[in] b The second item to compare
934 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
936 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
938 /** @brief Compare two data items according to a particular database.
940 * This returns a comparison as if the two items were data items of
941 * a sorted duplicates #MDB_DUPSORT database.
942 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
943 * @param[in] dbi A database handle returned by #mdb_open()
944 * @param[in] a The first item to compare
945 * @param[in] b The second item to compare
946 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
948 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);