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 * Don't perform a synchronous flush after committing a transaction. This means
312 * transactions will exhibit the ACI (atomicity, consistency, and isolation)
313 * properties, but not D (durability); that is database integrity will be
314 * maintained but it is possible some number of the most recently committed
315 * transactions may be undone after a system crash. The number of transactions
316 * at risk is governed by how often the system flushes dirty buffers to disk
317 * and how often #mdb_env_sync() is called. This flag may be changed
318 * at any time using #mdb_env_set_flags().
320 * Open the environment in read-only mode. No write operations will be allowed.
322 * @param[in] mode The UNIX permissions to set on created files. This parameter
323 * is ignored on Windows.
324 * @return A non-zero error value on failure and 0 on success. Some possible
327 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
328 * version that created the database environment.
329 * <li>EINVAL - the environment file headers are corrupted.
330 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
331 * <li>EACCES - the user didn't have permission to access the environment files.
332 * <li>EAGAIN - the environment was locked by another process.
335 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mode_t mode);
337 /** @brief Return statistics about the MDB environment.
339 * @param[in] env An environment handle returned by #mdb_env_create()
340 * @param[out] stat The address of an #MDB_stat structure
341 * where the statistics will be copied
343 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
345 /** @brief Flush the data buffers to disk.
347 * Data is always written to disk when #mdb_txn_commit() is called,
348 * but the operating system may keep it buffered. MDB always flushes
349 * the OS buffers upon commit as well, unless the environment was
350 * opened with #MDB_NOSYNC.
351 * @param[in] env An environment handle returned by #mdb_env_create()
352 * @param[in] force If non-zero, force the flush to occur. Otherwise
353 * if the environment has the #MDB_NOSYNC flag set the flushes
355 * @return A non-zero error value on failure and 0 on success. Some possible
358 * <li>EINVAL - an invalid parameter was specified.
359 * <li>EIO - an error occurred during synchronization.
362 int mdb_env_sync(MDB_env *env, int force);
364 /** @brief Close the environment and release the memory map.
366 * Only a single thread may call this function. All transactions, databases,
367 * and cursors must already be closed before calling this function. Attempts to
368 * use any such handles after calling this function will cause a SIGSEGV.
369 * The environment handle will be freed and must not be used again after this call.
370 * @param[in] env An environment handle returned by #mdb_env_create()
372 void mdb_env_close(MDB_env *env);
374 /** @brief Set environment flags.
376 * This may be used to set some flags that weren't already set during
377 * #mdb_env_open(), or to unset these flags. Currently only the
378 * #MDB_NOSYNC flag setting may be changed with this function.
379 * @param[in] env An environment handle returned by #mdb_env_create()
380 * @param[in] flags The flags to change, bitwise OR'ed together
381 * @param[in] onoff A non-zero value sets the flags, zero clears them.
382 * @return A non-zero error value on failure and 0 on success. Some possible
385 * <li>EINVAL - an invalid parameter was specified.
388 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
390 /** @brief Get environment flags.
392 * @param[in] env An environment handle returned by #mdb_env_create()
393 * @param[out] flags The address of an integer to store the flags
394 * @return A non-zero error value on failure and 0 on success. Some possible
397 * <li>EINVAL - an invalid parameter was specified.
400 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
402 /** @brief Return the path that was used in #mdb_env_open().
404 * @param[in] env An environment handle returned by #mdb_env_create()
405 * @param[out] path Address of a string pointer to contain the path. This
406 * is the actual string in the environment, not a copy. It should not be
407 * altered in any way.
408 * @return A non-zero error value on failure and 0 on success. Some possible
411 * <li>EINVAL - an invalid parameter was specified.
414 int mdb_env_get_path(MDB_env *env, const char **path);
416 /** @brief Set the size of the memory map to use for this environment.
418 * The size should be a multiple of the OS page size. The default is
419 * 10485760 bytes. The size of the memory map is also the maximum size
420 * of the database. The value should be chosen as large as possible,
421 * to accomodate future growth of the database.
422 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
423 * @param[in] env An environment handle returned by #mdb_env_create()
424 * @param[in] size The size in bytes
425 * @return A non-zero error value on failure and 0 on success. Some possible
428 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
431 int mdb_env_set_mapsize(MDB_env *env, size_t size);
433 /** @brief Set the maximum number of threads for the environment.
435 * This defines the number of slots in the lock table that is used to track readers in the
436 * the environment. The default is 126.
437 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
438 * @param[in] env An environment handle returned by #mdb_env_create()
439 * @param[in] readers The maximum number of threads
440 * @return A non-zero error value on failure and 0 on success. Some possible
443 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
446 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
448 /** @brief Get the maximum number of threads for the environment.
450 * @param[in] env An environment handle returned by #mdb_env_create()
451 * @param[out] readers Address of an integer to store the number of readers
452 * @return A non-zero error value on failure and 0 on success. Some possible
455 * <li>EINVAL - an invalid parameter was specified.
458 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
460 /** @brief Set the maximum number of databases for the environment.
462 * This function is only needed if multiple databases will be used in the
463 * environment. Simpler applications that only use a single database can ignore
465 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
466 * @param[in] env An environment handle returned by #mdb_env_create()
467 * @param[in] dbs The maximum number of databases
468 * @return A non-zero error value on failure and 0 on success. Some possible
471 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
474 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
476 /** @brief Create a transaction for use with the environment.
478 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
479 * @note Transactions may not span threads, a transaction must only be used by a
481 * @note Cursors may not span transactions; each cursor must be opened and closed
482 * within a single transaction.
483 * @param[in] env An environment handle returned by #mdb_env_create()
484 * @param[in] parent If this parameter is non-NULL, the new transaction
485 * will be a nested transaction, with the transaction indicated by \b parent
486 * as its parent. Transactions may be nested to any level. A parent
487 * transaction may not issue any other operations besides mdb_txn_begin,
488 * mdb_txn_abort, or mdb_txn_commit while it has active child transactions.
489 * @param[in] flags Special options for this transaction. This parameter
490 * must be set to 0 or by bitwise OR'ing together one or more of the
491 * values described here.
494 * This transaction will not perform any write operations.
496 * @param[out] txn Address where the new #MDB_txn handle will be stored
497 * @return A non-zero error value on failure and 0 on success. Some possible
500 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
502 * <li>ENOMEM - out of memory, or a read-only transaction was requested and
503 * the reader lock table is full. See #mdb_env_set_maxreaders().
506 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
508 /** @brief Commit all the operations of a transaction into the database.
510 * All cursors opened within the transaction will be closed by this call. The cursors
511 * and transaction handle will be freed and must not be used again after this call.
512 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
513 * @return A non-zero error value on failure and 0 on success. Some possible
516 * <li>EINVAL - an invalid parameter was specified.
517 * <li>ENOSPC - no more disk space.
518 * <li>EIO - a low-level I/O error occurred while writing.
521 int mdb_txn_commit(MDB_txn *txn);
523 /** @brief Abandon all the operations of the transaction instead of saving them.
525 * All cursors opened within the transaction will be closed by this call. The cursors
526 * and transaction handle will be freed and must not be used again after this call.
527 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
529 void mdb_txn_abort(MDB_txn *txn);
531 /** @brief Reset a read-only transaction.
533 * This releases the current reader lock but doesn't free the
534 * transaction handle, allowing it to be used again later by #mdb_txn_renew().
535 * It otherwise has the same effect as #mdb_txn_abort() but saves some memory
536 * allocation/deallocation overhead if a thread is going to start a new
537 * read-only transaction again soon.
538 * All cursors opened within the transaction must be closed before the transaction
540 * Reader locks generally don't interfere with writers, but they keep old
541 * versions of database pages allocated. Thus they prevent the old pages
542 * from being reused when writers commit new data, and so under heavy load
543 * the database size may grow much more rapidly than otherwise.
544 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
546 void mdb_txn_reset(MDB_txn *txn);
548 /** @brief Renew a read-only transaction.
550 * This acquires a new reader lock for a transaction handle that had been
551 * released by #mdb_txn_reset(). It must be called before a reset transaction
553 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
554 * @return A non-zero error value on failure and 0 on success. Some possible
557 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
559 * <li>EINVAL - an invalid parameter was specified.
562 int mdb_txn_renew(MDB_txn *txn);
564 /** @brief Open a database in the environment.
566 * The database handle may be discarded by calling #mdb_close(). Only
567 * one thread should call this function; it is not mutex-protected in
568 * a read-only transaction.
569 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
570 * @param[in] name The name of the database to open. If only a single
571 * database is needed in the enviroment, this value may be NULL.
572 * @param[in] flags Special options for this database. This parameter
573 * must be set to 0 or by bitwise OR'ing together one or more of the
574 * values described here.
576 * <li>#MDB_REVERSEKEY
577 * Keys are strings to be compared in reverse order, from the end
578 * of the strings to the beginning. By default, Keys are treated as strings and
579 * compared from beginning to end.
581 * Duplicate keys may be used in the database. (Or, from another perspective,
582 * keys may have multiple data items, stored in sorted order.) By default
583 * keys must be unique and may have only a single data item.
584 * <li>#MDB_INTEGERKEY
585 * Keys are binary integers in native byte order. Setting this option
586 * requires all keys to be the same size, typically sizeof(int)
589 * This flag may only be used in combination with #MDB_DUPSORT. This option
590 * tells the library that the data items for this database are all the same
591 * size, which allows further optimizations in storage and retrieval. When
592 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
593 * cursor operations may be used to retrieve multiple items at once.
594 * <li>#MDB_INTEGERDUP
595 * This option specifies that duplicate data items are also integers, and
596 * should be sorted as such.
597 * <li>#MDB_REVERSEDUP
598 * This option specifies that duplicate data items should be compared as
599 * strings in reverse order.
601 * Create the named database if it doesn't exist. This option is not
602 * allowed in a read-only transaction or a read-only environment.
604 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
605 * @return A non-zero error value on failure and 0 on success. Some possible
608 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
609 * and #MDB_CREATE was not specified.
610 * <li>ENFILE - too many databases have been opened. See #mdb_env_set_maxdbs().
613 int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
615 /** @brief Retrieve statistics for a database.
617 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
618 * @param[in] dbi A database handle returned by #mdb_open()
619 * @param[out] stat The address of an #MDB_stat structure
620 * where the statistics will be copied
621 * @return A non-zero error value on failure and 0 on success. Some possible
624 * <li>EINVAL - an invalid parameter was specified.
627 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
629 /** @brief Close a database handle.
631 * This call is not mutex protected. Handles should only be closed by
632 * a single thread, and only if no other threads are going to reference
633 * the database handle any further.
634 * @param[in] env An environment handle returned by #mdb_env_create()
635 * @param[in] dbi A database handle returned by #mdb_open()
637 void mdb_close(MDB_env *env, MDB_dbi dbi);
639 /** @brief Delete a database and/or free all its pages.
641 * If the \b del parameter is non-zero the DB handle will be closed
642 * and the DB will be deleted.
643 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
644 * @param[in] dbi A database handle returned by #mdb_open()
645 * @param[in] del non-zero to delete the DB from the environment,
646 * otherwise just free its pages.
647 * @return A non-zero error value on failure and 0 on success.
649 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
651 /** @brief Set a custom key comparison function for a database.
653 * The comparison function is called whenever it is necessary to compare a
654 * key specified by the application with a key currently stored in the database.
655 * If no comparison function is specified, and no speAGAINcial key flags were specified
656 * with #mdb_open(), the keys are compared lexically, with shorter keys collating
657 * before longer keys.
658 * @warning This function must be called before any data access functions are used,
659 * otherwise data corruption may occur. The same comparison function must be used by every
660 * program accessing the database, every time the database is used.
661 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
662 * @param[in] dbi A database handle returned by #mdb_open()
663 * @param[in] cmp A #MDB_cmp_func function
664 * @return A non-zero error value on failure and 0 on success. Some possible
667 * <li>EINVAL - an invalid parameter was specified.
670 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
672 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
674 * This comparison function is called whenever it is necessary to compare a data
675 * item specified by the application with a data item currently stored in the database.
676 * This function only takes effect if the database was opened with the #MDB_DUPSORT
678 * If no comparison function is specified, and no special key flags were specified
679 * with #mdb_open(), the data items are compared lexically, with shorter items collating
680 * before longer items.
681 * @warning This function must be called before any data access functions are used,
682 * otherwise data corruption may occur. The same comparison function must be used by every
683 * program accessing the database, every time the database is used.
684 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
685 * @param[in] dbi A database handle returned by #mdb_open()
686 * @param[in] cmp A #MDB_cmp_func function
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_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
695 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
697 * @todo The relocation function is called whenever it is necessary to move the data
698 * of an item to a different position in the database (e.g. through tree
699 * balancing operations, shifts as a result of adds or deletes, etc.). It is
700 * intended to allow address/position-dependent data items to be stored in
701 * a database in an environment opened with the #MDB_FIXEDMAP option.
702 * Currently the relocation feature is unimplemented and setting
703 * this function has no effect.
704 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
705 * @param[in] dbi A database handle returned by #mdb_open()
706 * @param[in] rel A #MDB_rel_func function
707 * @return A non-zero error value on failure and 0 on success. Some possible
710 * <li>EINVAL - an invalid parameter was specified.
713 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
715 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
717 * See #mdb_set_relfunc and #MDB_rel_func for more details.
718 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
719 * @param[in] dbi A database handle returned by #mdb_open()
720 * @param[in] ctx An arbitrary pointer for whatever the application needs.
721 * It will be passed to the callback function set by #mdb_set_relfunc
722 * as its \b relctx parameter whenever the callback is invoked.
723 * @return A non-zero error value on failure and 0 on success. Some possible
726 * <li>EINVAL - an invalid parameter was specified.
729 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
731 /** @brief Get items from a database.
733 * This function retrieves key/data pairs from the database. The address
734 * and length of the data associated with the specified \b key are returned
735 * in the structure to which \b data refers.
736 * If the database supports duplicate keys (#MDB_DUPSORT) then the
737 * first data item for the key will be returned. Retrieval of other
738 * items requires the use of #mdb_cursor_get().
740 * @note The memory pointed to by the returned values is owned by the
741 * database. The caller need not dispose of the memory, and may not
742 * modify it in any way. For values returned in a read-only transaction
743 * any modification attempts will cause a SIGSEGV.
744 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
745 * @param[in] dbi A database handle returned by #mdb_open()
746 * @param[in] key The key to search for in the database
747 * @param[out] data The data corresponding to the key
748 * @return A non-zero error value on failure and 0 on success. Some possible
751 * <li>#MDB_NOTFOUND - the key was not in the database.
752 * <li>EINVAL - an invalid parameter was specified.
755 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
757 /** @brief Store items into a database.
759 * This function stores key/data pairs in the database. The default behavior
760 * is to enter the new key/data pair, replacing any previously existing key
761 * if duplicates are disallowed, or adding a duplicate data item if
762 * duplicates are allowed (#MDB_DUPSORT).
763 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
764 * @param[in] dbi A database handle returned by #mdb_open()
765 * @param[in] key The key to store in the database
766 * @param[in,out] data The data to store
767 * @param[in] flags Special options for this operation. This parameter
768 * must be set to 0 or by bitwise OR'ing together one or more of the
769 * values described here.
771 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
772 * already appear in the database. This flag may only be specified
773 * if the database was opened with #MDB_DUPSORT. The function will
774 * return #MDB_KEYEXIST if the key/data pair already appears in the
776 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
777 * does not already appear in the database. The function will return
778 * #MDB_KEYEXIST if the key already appears in the database, even if
779 * the database supports duplicates (#MDB_DUPSORT). The \b data
780 * parameter will be set to point to the existing item.
782 * @return A non-zero error value on failure and 0 on success. Some possible
785 * <li>EACCESS - an attempt was made to write in a read-only transaction.
786 * <li>EINVAL - an invalid parameter was specified.
787 * <li>ENOMEM - the database is full, see #mdb_env_set_mapsize().
790 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
793 /** @brief Delete items from a database.
795 * This function removes key/data pairs from the database.
796 * If the database does not support sorted duplicate data items
797 * (#MDB_DUPSORT) the data parameter is ignored.
798 * If the database supports sorted duplicates and the data parameter
799 * is NULL, all of the duplicate data items for the key will be
800 * deleted. Otherwise, if the data parameter is non-NULL
801 * only the matching data item will be deleted.
802 * This function will return #MDB_NOTFOUND if the specified key/data
803 * pair is not in the database.
804 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
805 * @param[in] dbi A database handle returned by #mdb_open()
806 * @param[in] key The key to delete from the database
807 * @param[in] data The data to delete
808 * @return A non-zero error value on failure and 0 on success. Some possible
811 * <li>EACCESS - an attempt was made to write in a read-only transaction.
812 * <li>EINVAL - an invalid parameter was specified.
815 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
817 /** @brief Create a cursor handle.
819 * Cursors are associated with a specific transaction and database and
820 * may not span threads.
821 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
822 * @param[in] dbi A database handle returned by #mdb_open()
823 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
824 * @return A non-zero error value on failure and 0 on success. Some possible
827 * <li>EINVAL - an invalid parameter was specified.
830 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
832 /** @brief Close a cursor handle.
834 * The cursor handle will be freed and must not be used again after this call.
835 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
837 void mdb_cursor_close(MDB_cursor *cursor);
839 /** @brief Retrieve by cursor.
841 * This function retrieves key/data pairs from the database. The address and length
842 * of the key are returned in the object to which \b key refers (except for the
843 * case of the #MDB_SET option, in which the \b key object is unchanged), and
844 * the address and length of the data are returned in the object to which \b data
846 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
847 * @param[in,out] key The key for a retrieved item
848 * @param[in,out] data The data of a retrieved item
849 * @param[in] op A cursor operation #MDB_cursor_op
850 * @return A non-zero error value on failure and 0 on success. Some possible
853 * <li>#MDB_NOTFOUND - no matching key found.
854 * <li>EINVAL - an invalid parameter was specified.
857 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
860 /** @brief Store by cursor.
862 * This function stores key/data pairs into the database.
863 * If the function fails for any reason, the state of the cursor will be
864 * unchanged. If the function succeeds and an item is inserted into the
865 * database, the cursor is always positioned to refer to the newly inserted item.
866 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
867 * @param[in] key The key operated on.
868 * @param[in] data The data operated on.
869 * @param[in] flags Options for this operation. This parameter
870 * must be set to 0 or one of the values described here.
872 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which
873 * the cursor refers with the specified data item. The \b key
874 * parameter is ignored.
875 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
876 * already appear in the database. This flag may only be specified
877 * if the database was opened with #MDB_DUPSORT. The function will
878 * return #MDB_KEYEXIST if the key/data pair already appears in the
880 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
881 * does not already appear in the database. The function will return
882 * #MDB_KEYEXIST if the key already appears in the database, even if
883 * the database supports duplicates (#MDB_DUPSORT).
885 * @return A non-zero error value on failure and 0 on success. Some possible
888 * <li>EACCES - an attempt was made to modify a read-only database.
889 * <li>EINVAL - an invalid parameter was specified.
892 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
895 /** @brief Delete current key/data pair
897 * This function deletes the key/data pair to which the cursor refers.
898 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
899 * @param[in] flags Options for this operation. This parameter
900 * must be set to 0 or one of the values described here.
902 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
903 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
905 * @return A non-zero error value on failure and 0 on success. Some possible
908 * <li>EACCES - an attempt was made to modify a read-only database.
909 * <li>EINVAL - an invalid parameter was specified.
912 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
914 /** @brief Return count of duplicates for current key.
916 * This call is only valid on databases that support sorted duplicate
917 * data items #MDB_DUPSORT.
918 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
919 * @param[out] countp Address where the count will be stored
920 * @return A non-zero error value on failure and 0 on success. Some possible
923 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
926 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
928 /** @brief Compare two data items according to a particular database.
930 * This returns a comparison as if the two data items were keys in the
931 * specified database.
932 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
933 * @param[in] dbi A database handle returned by #mdb_open()
934 * @param[in] a The first item to compare
935 * @param[in] b The second item to compare
936 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
938 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
940 /** @brief Compare two data items according to a particular database.
942 * This returns a comparison as if the two items were data items of
943 * a sorted duplicates #MDB_DUPSORT database.
944 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
945 * @param[in] dbi A database handle returned by #mdb_open()
946 * @param[in] a The first item to compare
947 * @param[in] b The second item to compare
948 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
950 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);