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 2011-2012 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>
72 /** @defgroup public Public API
75 /** @defgroup Version Version Macros
78 /** Library major version */
79 #define MDB_VERSION_MAJOR 0
80 /** Library minor version */
81 #define MDB_VERSION_MINOR 9
82 /** Library patch version */
83 #define MDB_VERSION_PATCH 2
85 /** Combine args a,b,c into a single integer for easy version comparisons */
86 #define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
88 /** The full library version as a single integer */
89 #define MDB_VERSION_FULL \
90 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
92 /** The release date of this library version */
93 #define MDB_VERSION_DATE "August 2, 2012"
95 /** A stringifier for the version info */
96 #define MDB_VERSTR(a,b,c,d) "MDB " #a "." #b "." #c ": (" d ")"
98 /** A helper for the stringifier macro */
99 #define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d)
101 /** The full library version as a C string */
102 #define MDB_VERSION_STRING \
103 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
106 /** @brief Opaque structure for a database environment.
108 * A DB environment supports multiple databases, all residing in the same
111 typedef struct MDB_env MDB_env;
113 /** @brief Opaque structure for a transaction handle.
115 * All database operations require a transaction handle. Transactions may be
116 * read-only or read-write.
118 typedef struct MDB_txn MDB_txn;
120 /** @brief A handle for an individual database in the DB environment. */
121 typedef unsigned int MDB_dbi;
123 /** @brief Opaque structure for navigating through a database */
124 typedef struct MDB_cursor MDB_cursor;
126 /** @brief Generic structure used for passing keys and data in and out of the database. */
127 typedef struct MDB_val {
128 size_t mv_size; /**< size of the data item */
129 void *mv_data; /**< address of the data item */
132 /** @brief A callback function used to compare two keys in a database */
133 typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
135 /** @brief A callback function used to relocate a position-dependent data item
136 * in a fixed-address database.
138 * The \b newptr gives the item's desired address in
139 * the memory map, and \b oldptr gives its previous address. The item's actual
140 * data resides at the address in \b item. This callback is expected to walk
141 * through the fields of the record in \b item and modify any
142 * values based at the \b oldptr address to be relative to the \b newptr address.
143 * @param[in,out] item The item that is to be relocated.
144 * @param[in] oldptr The previous address.
145 * @param[in] newptr The new address to relocate to.
146 * @param[in] relctx An application-provided context, set by #mdb_set_relctx().
147 * @todo This feature is currently unimplemented.
149 typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
151 /** @defgroup mdb_env Environment Flags
154 /** mmap at a fixed address */
155 #define MDB_FIXEDMAP 0x01
156 /** no environment directory */
157 #define MDB_NOSUBDIR 0x02
158 /** don't fsync after commit */
159 #define MDB_NOSYNC 0x10000
161 #define MDB_RDONLY 0x20000
162 /** don't fsync metapage after commit */
163 #define MDB_NOMETASYNC 0x40000
164 /** use writable mmap */
165 #define MDB_WRITEMAP 0x80000
166 /** use asynchronous msync */
167 #define MDB_MAPASYNC 0x100000
170 /** @defgroup mdb_open Database Flags
173 /** use reverse string keys */
174 #define MDB_REVERSEKEY 0x02
175 /** use sorted duplicates */
176 #define MDB_DUPSORT 0x04
177 /** numeric keys in native byte order.
178 * The keys must all be of the same size. */
179 #define MDB_INTEGERKEY 0x08
180 /** with #MDB_DUPSORT, sorted dup items have fixed size */
181 #define MDB_DUPFIXED 0x10
182 /** with #MDB_DUPSORT, dups are numeric in native byte order */
183 #define MDB_INTEGERDUP 0x20
184 /** with #MDB_DUPSORT, use reverse string dups */
185 #define MDB_REVERSEDUP 0x40
186 /** create DB if not already existing */
187 #define MDB_CREATE 0x40000
190 /** @defgroup mdb_put Write Flags
193 /** For put: Don't write if the key already exists. */
194 #define MDB_NOOVERWRITE 0x10
195 /** Only for #MDB_DUPSORT<br>
196 * For put: don't write if the key and data pair already exist.<br>
197 * For mdb_cursor_del: remove all duplicate data items.
199 #define MDB_NODUPDATA 0x20
200 /** For mdb_cursor_put: overwrite the current key/data pair */
201 #define MDB_CURRENT 0x40
202 /** For put: Just reserve space for data, don't copy it. Return a
203 * pointer to the reserved space.
205 #define MDB_RESERVE 0x10000
206 /** Data is being appended, don't split full pages. */
207 #define MDB_APPEND 0x20000
208 /** Duplicate data is being appended, don't split full pages. */
209 #define MDB_APPENDDUP 0x40000
210 /** Store multiple data items in one call. */
211 #define MDB_MULTIPLE 0x80000
214 /** @brief Cursor Get operations.
216 * This is the set of all operations for retrieving data
219 typedef enum MDB_cursor_op {
220 MDB_FIRST, /**< Position at first key/data item */
221 MDB_FIRST_DUP, /**< Position at first data item of current key.
222 Only for #MDB_DUPSORT */
223 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
224 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
225 MDB_GET_MULTIPLE, /**< Return all the duplicate data items at the current
226 cursor position. Only for #MDB_DUPFIXED */
227 MDB_LAST, /**< Position at last key/data item */
228 MDB_LAST_DUP, /**< Position at last data item of current key.
229 Only for #MDB_DUPSORT */
230 MDB_NEXT, /**< Position at next data item */
231 MDB_NEXT_DUP, /**< Position at next data item of current key.
232 Only for #MDB_DUPSORT */
233 MDB_NEXT_MULTIPLE, /**< Return all duplicate data items at the next
234 cursor position. Only for #MDB_DUPFIXED */
235 MDB_NEXT_NODUP, /**< Position at first data item of next key.
236 Only for #MDB_DUPSORT */
237 MDB_PREV, /**< Position at previous data item */
238 MDB_PREV_DUP, /**< Position at previous data item of current key.
239 Only for #MDB_DUPSORT */
240 MDB_PREV_NODUP, /**< Position at last data item of previous key.
241 Only for #MDB_DUPSORT */
242 MDB_SET, /**< Position at specified key */
243 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
246 /** @defgroup errors Return Codes
248 * BerkeleyDB uses -30800 to -30999, we'll go under them
251 /** Successful result */
252 #define MDB_SUCCESS 0
253 /** key/data pair already exists */
254 #define MDB_KEYEXIST (-30799)
255 /** key/data pair not found (EOF) */
256 #define MDB_NOTFOUND (-30798)
257 /** Requested page not found - this usually indicates corruption */
258 #define MDB_PAGE_NOTFOUND (-30797)
259 /** Located page was wrong type */
260 #define MDB_CORRUPTED (-30796)
261 /** Update of meta page failed, probably I/O error */
262 #define MDB_PANIC (-30795)
263 /** Environment version mismatch */
264 #define MDB_VERSION_MISMATCH (-30794)
267 /** @brief Statistics for a database in the environment */
268 typedef struct MDB_stat {
269 unsigned int ms_psize; /**< Size of a database page.
270 This is currently the same for all databases. */
271 unsigned int ms_depth; /**< Depth (height) of the B-tree */
272 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
273 size_t ms_leaf_pages; /**< Number of leaf pages */
274 size_t ms_overflow_pages; /**< Number of overflow pages */
275 size_t ms_entries; /**< Number of data items */
278 /** @brief Return the mdb library version information.
280 * @param[out] major if non-NULL, the library major version number is copied here
281 * @param[out] minor if non-NULL, the library minor version number is copied here
282 * @param[out] patch if non-NULL, the library patch version number is copied here
283 * @retval "version string" The library version as a string
285 char *mdb_version(int *major, int *minor, int *patch);
287 /** @brief Return a string describing a given error code.
289 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
290 * function. If the error code is greater than or equal to 0, then the string
291 * returned by the system function strerror(3) is returned. If the error code
292 * is less than 0, an error string corresponding to the MDB library error is
293 * returned. See @ref errors for a list of MDB-specific error codes.
294 * @param[in] err The error code
295 * @retval "error message" The description of the error
297 char *mdb_strerror(int err);
299 /** @brief Create an MDB environment handle.
301 * This function allocates memory for a #MDB_env structure. To release
302 * the allocated memory and discard the handle, call #mdb_env_close().
303 * Before the handle may be used, it must be opened using #mdb_env_open().
304 * Various other options may also need to be set before opening the handle,
305 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
306 * depending on usage requirements.
307 * @param[out] env The address where the new handle will be stored
308 * @return A non-zero error value on failure and 0 on success.
310 int mdb_env_create(MDB_env **env);
312 /** @brief Open an environment handle.
314 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
315 * @param[in] env An environment handle returned by #mdb_env_create()
316 * @param[in] path The directory in which the database files reside. This
317 * directory must already exist and be writable.
318 * @param[in] flags Special options for this environment. This parameter
319 * must be set to 0 or by bitwise OR'ing together one or more of the
320 * values described here.
323 * use a fixed address for the mmap region. This flag must be specified
324 * when creating the environment, and is stored persistently in the environment.
325 * If successful, the memory map will always reside at the same virtual address
326 * and pointers used to reference data items in the database will be constant
327 * across multiple invocations. This option may not always work, depending on
328 * how the operating system has allocated memory to shared libraries and other uses.
329 * The feature is highly experimental.
331 * By default, MDB creates its environment in a directory whose
332 * pathname is given in \b path, and creates its data and lock files
333 * under that directory. With this option, \b path is used as-is for
334 * the database main data file. The database lock file is the \b path
335 * with "-lock" appended.
337 * Don't perform a synchronous flush after committing a transaction. This means
338 * transactions will exhibit the ACI (atomicity, consistency, and isolation)
339 * properties, but not D (durability); that is database integrity will be
340 * maintained but it is possible some number of the most recently committed
341 * transactions may be undone after a system crash. The number of transactions
342 * at risk is governed by how often the system flushes dirty buffers to disk
343 * and how often #mdb_env_sync() is called. This flag may be changed
344 * at any time using #mdb_env_set_flags().
345 * <li>#MDB_NOMETASYNC
346 * Don't perform a synchronous flush of the meta page after committing
347 * a transaction. This is similar to the #MDB_NOSYNC case, but safer
348 * because the transaction data is still flushed. The meta page for any
349 * transaction N will be flushed by the data flush of transaction N+1.
350 * In case of a system crash, the last committed transaction may be
351 * lost. This flag may be changed at any time using #mdb_env_set_flags().
353 * Open the environment in read-only mode. No write operations will be allowed.
355 * @param[in] mode The UNIX permissions to set on created files. This parameter
356 * is ignored on Windows.
357 * @return A non-zero error value on failure and 0 on success. Some possible
360 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the
361 * version that created the database environment.
362 * <li>EINVAL - the environment file headers are corrupted.
363 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
364 * <li>EACCES - the user didn't have permission to access the environment files.
365 * <li>EAGAIN - the environment was locked by another process.
368 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mode_t mode);
370 /** @brief Return statistics about the MDB environment.
372 * @param[in] env An environment handle returned by #mdb_env_create()
373 * @param[out] stat The address of an #MDB_stat structure
374 * where the statistics will be copied
376 int mdb_env_stat(MDB_env *env, MDB_stat *stat);
378 /** @brief Flush the data buffers to disk.
380 * Data is always written to disk when #mdb_txn_commit() is called,
381 * but the operating system may keep it buffered. MDB always flushes
382 * the OS buffers upon commit as well, unless the environment was
383 * opened with #MDB_NOSYNC.
384 * @param[in] env An environment handle returned by #mdb_env_create()
385 * @param[in] force If non-zero, force the flush to occur. Otherwise
386 * if the environment has the #MDB_NOSYNC flag set the flushes
388 * @return A non-zero error value on failure and 0 on success. Some possible
391 * <li>EINVAL - an invalid parameter was specified.
392 * <li>EIO - an error occurred during synchronization.
395 int mdb_env_sync(MDB_env *env, int force);
397 /** @brief Close the environment and release the memory map.
399 * Only a single thread may call this function. All transactions, databases,
400 * and cursors must already be closed before calling this function. Attempts to
401 * use any such handles after calling this function will cause a SIGSEGV.
402 * The environment handle will be freed and must not be used again after this call.
403 * @param[in] env An environment handle returned by #mdb_env_create()
405 void mdb_env_close(MDB_env *env);
407 /** @brief Set environment flags.
409 * This may be used to set some flags that weren't already set during
410 * #mdb_env_open(), or to unset these flags.
411 * @param[in] env An environment handle returned by #mdb_env_create()
412 * @param[in] flags The flags to change, bitwise OR'ed together
413 * @param[in] onoff A non-zero value sets the flags, zero clears them.
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_set_flags(MDB_env *env, unsigned int flags, int onoff);
422 /** @brief Get environment flags.
424 * @param[in] env An environment handle returned by #mdb_env_create()
425 * @param[out] flags The address of an integer to store the flags
426 * @return A non-zero error value on failure and 0 on success. Some possible
429 * <li>EINVAL - an invalid parameter was specified.
432 int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
434 /** @brief Return the path that was used in #mdb_env_open().
436 * @param[in] env An environment handle returned by #mdb_env_create()
437 * @param[out] path Address of a string pointer to contain the path. This
438 * is the actual string in the environment, not a copy. It should not be
439 * altered in any way.
440 * @return A non-zero error value on failure and 0 on success. Some possible
443 * <li>EINVAL - an invalid parameter was specified.
446 int mdb_env_get_path(MDB_env *env, const char **path);
448 /** @brief Set the size of the memory map to use for this environment.
450 * The size should be a multiple of the OS page size. The default is
451 * 10485760 bytes. The size of the memory map is also the maximum size
452 * of the database. The value should be chosen as large as possible,
453 * to accommodate future growth of the database.
454 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
455 * @param[in] env An environment handle returned by #mdb_env_create()
456 * @param[in] size The size in bytes
457 * @return A non-zero error value on failure and 0 on success. Some possible
460 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
463 int mdb_env_set_mapsize(MDB_env *env, size_t size);
465 /** @brief Set the maximum number of threads for the environment.
467 * This defines the number of slots in the lock table that is used to track readers in the
468 * the environment. The default is 126.
469 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
470 * @param[in] env An environment handle returned by #mdb_env_create()
471 * @param[in] readers The maximum number of threads
472 * @return A non-zero error value on failure and 0 on success. Some possible
475 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
478 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
480 /** @brief Get the maximum number of threads for the environment.
482 * @param[in] env An environment handle returned by #mdb_env_create()
483 * @param[out] readers Address of an integer to store the number of readers
484 * @return A non-zero error value on failure and 0 on success. Some possible
487 * <li>EINVAL - an invalid parameter was specified.
490 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
492 /** @brief Set the maximum number of databases for the environment.
494 * This function is only needed if multiple databases will be used in the
495 * environment. Simpler applications that only use a single database can ignore
497 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
498 * @param[in] env An environment handle returned by #mdb_env_create()
499 * @param[in] dbs The maximum number of databases
500 * @return A non-zero error value on failure and 0 on success. Some possible
503 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
506 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
508 /** @brief Create a transaction for use with the environment.
510 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
511 * @note Transactions may not span threads; a transaction must only be used by a
512 * single thread. Also, a thread may only have a single transaction.
513 * @note Cursors may not span transactions; each cursor must be opened and closed
514 * within a single transaction.
515 * @param[in] env An environment handle returned by #mdb_env_create()
516 * @param[in] parent If this parameter is non-NULL, the new transaction
517 * will be a nested transaction, with the transaction indicated by \b parent
518 * as its parent. Transactions may be nested to any level. A parent
519 * transaction may not issue any other operations besides mdb_txn_begin,
520 * mdb_txn_abort, or mdb_txn_commit while it has active child transactions.
521 * @param[in] flags Special options for this transaction. This parameter
522 * must be set to 0 or by bitwise OR'ing together one or more of the
523 * values described here.
526 * This transaction will not perform any write operations.
528 * @param[out] txn Address where the new #MDB_txn handle will be stored
529 * @return A non-zero error value on failure and 0 on success. Some possible
532 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
534 * <li>ENOMEM - out of memory, or a read-only transaction was requested and
535 * the reader lock table is full. See #mdb_env_set_maxreaders().
538 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
540 /** @brief Commit all the operations of a transaction into the database.
542 * All cursors opened within the transaction will be closed by this call. The cursors
543 * and transaction handle will be freed and must not be used again after this call.
544 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
545 * @return A non-zero error value on failure and 0 on success. Some possible
548 * <li>EINVAL - an invalid parameter was specified.
549 * <li>ENOSPC - no more disk space.
550 * <li>EIO - a low-level I/O error occurred while writing.
551 * <li>ENOMEM - the transaction is nested and could not be merged into its parent.
554 int mdb_txn_commit(MDB_txn *txn);
556 /** @brief Abandon all the operations of the transaction instead of saving them.
558 * All cursors opened within the transaction will be closed by this call. The cursors
559 * and transaction handle will be freed and must not be used again after this call.
560 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
562 void mdb_txn_abort(MDB_txn *txn);
564 /** @brief Reset a read-only transaction.
566 * This releases the current reader lock but doesn't free the
567 * transaction handle, allowing it to be used again later by #mdb_txn_renew().
568 * It otherwise has the same effect as #mdb_txn_abort() but saves some memory
569 * allocation/deallocation overhead if a thread is going to start a new
570 * read-only transaction again soon.
571 * All cursors opened within the transaction must be closed before the transaction
573 * Reader locks generally don't interfere with writers, but they keep old
574 * versions of database pages allocated. Thus they prevent the old pages
575 * from being reused when writers commit new data, and so under heavy load
576 * the database size may grow much more rapidly than otherwise.
577 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
579 void mdb_txn_reset(MDB_txn *txn);
581 /** @brief Renew a read-only transaction.
583 * This acquires a new reader lock for a transaction handle that had been
584 * released by #mdb_txn_reset(). It must be called before a reset transaction
586 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
587 * @return A non-zero error value on failure and 0 on success. Some possible
590 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
592 * <li>EINVAL - an invalid parameter was specified.
595 int mdb_txn_renew(MDB_txn *txn);
597 /** @brief Open a database in the environment.
599 * The database handle may be discarded by calling #mdb_close(). The
600 * database handle resides in the shared environment, it is not owned
601 * by the given transaction. Only one thread should call this function;
602 * it is not mutex-protected in a read-only transaction.
603 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
604 * @param[in] name The name of the database to open. If only a single
605 * database is needed in the environment, this value may be NULL.
606 * @param[in] flags Special options for this database. This parameter
607 * must be set to 0 or by bitwise OR'ing together one or more of the
608 * values described here.
610 * <li>#MDB_REVERSEKEY
611 * Keys are strings to be compared in reverse order, from the end
612 * of the strings to the beginning. By default, Keys are treated as strings and
613 * compared from beginning to end.
615 * Duplicate keys may be used in the database. (Or, from another perspective,
616 * keys may have multiple data items, stored in sorted order.) By default
617 * keys must be unique and may have only a single data item.
618 * <li>#MDB_INTEGERKEY
619 * Keys are binary integers in native byte order. Setting this option
620 * requires all keys to be the same size, typically sizeof(int)
623 * This flag may only be used in combination with #MDB_DUPSORT. This option
624 * tells the library that the data items for this database are all the same
625 * size, which allows further optimizations in storage and retrieval. When
626 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
627 * cursor operations may be used to retrieve multiple items at once.
628 * <li>#MDB_INTEGERDUP
629 * This option specifies that duplicate data items are also integers, and
630 * should be sorted as such.
631 * <li>#MDB_REVERSEDUP
632 * This option specifies that duplicate data items should be compared as
633 * strings in reverse order.
635 * Create the named database if it doesn't exist. This option is not
636 * allowed in a read-only transaction or a read-only environment.
638 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
639 * @return A non-zero error value on failure and 0 on success. Some possible
642 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
643 * and #MDB_CREATE was not specified.
644 * <li>ENFILE - too many databases have been opened. See #mdb_env_set_maxdbs().
647 int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
649 /** @brief Retrieve statistics for a database.
651 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
652 * @param[in] dbi A database handle returned by #mdb_open()
653 * @param[out] stat The address of an #MDB_stat structure
654 * where the statistics will be copied
655 * @return A non-zero error value on failure and 0 on success. Some possible
658 * <li>EINVAL - an invalid parameter was specified.
661 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
663 /** @brief Close a database handle.
665 * This call is not mutex protected. Handles should only be closed by
666 * a single thread, and only if no other threads are going to reference
667 * the database handle any further.
668 * @param[in] env An environment handle returned by #mdb_env_create()
669 * @param[in] dbi A database handle returned by #mdb_open()
671 void mdb_close(MDB_env *env, MDB_dbi dbi);
673 /** @brief Delete a database and/or free all its pages.
675 * If the \b del parameter is non-zero the DB handle will be closed
676 * and the DB will be deleted.
677 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
678 * @param[in] dbi A database handle returned by #mdb_open()
679 * @param[in] del non-zero to delete the DB from the environment,
680 * otherwise just free its pages.
681 * @return A non-zero error value on failure and 0 on success.
683 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
685 /** @brief Set a custom key comparison function for a database.
687 * The comparison function is called whenever it is necessary to compare a
688 * key specified by the application with a key currently stored in the database.
689 * If no comparison function is specified, and no special key flags were specified
690 * with #mdb_open(), the keys are compared lexically, with shorter keys collating
691 * before longer keys.
692 * @warning This function must be called before any data access functions are used,
693 * otherwise data corruption may occur. The same comparison function must be used by every
694 * program accessing the database, every time the database is used.
695 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
696 * @param[in] dbi A database handle returned by #mdb_open()
697 * @param[in] cmp A #MDB_cmp_func function
698 * @return A non-zero error value on failure and 0 on success. Some possible
701 * <li>EINVAL - an invalid parameter was specified.
704 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
706 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
708 * This comparison function is called whenever it is necessary to compare a data
709 * item specified by the application with a data item currently stored in the database.
710 * This function only takes effect if the database was opened with the #MDB_DUPSORT
712 * If no comparison function is specified, and no special key flags were specified
713 * with #mdb_open(), the data items are compared lexically, with shorter items collating
714 * before longer items.
715 * @warning This function must be called before any data access functions are used,
716 * otherwise data corruption may occur. The same comparison function must be used by every
717 * program accessing the database, every time the database is used.
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] cmp A #MDB_cmp_func function
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_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
729 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
731 * @todo The relocation function is called whenever it is necessary to move the data
732 * of an item to a different position in the database (e.g. through tree
733 * balancing operations, shifts as a result of adds or deletes, etc.). It is
734 * intended to allow address/position-dependent data items to be stored in
735 * a database in an environment opened with the #MDB_FIXEDMAP option.
736 * Currently the relocation feature is unimplemented and setting
737 * this function has no effect.
738 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
739 * @param[in] dbi A database handle returned by #mdb_open()
740 * @param[in] rel A #MDB_rel_func function
741 * @return A non-zero error value on failure and 0 on success. Some possible
744 * <li>EINVAL - an invalid parameter was specified.
747 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
749 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
751 * See #mdb_set_relfunc and #MDB_rel_func for more details.
752 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
753 * @param[in] dbi A database handle returned by #mdb_open()
754 * @param[in] ctx An arbitrary pointer for whatever the application needs.
755 * It will be passed to the callback function set by #mdb_set_relfunc
756 * as its \b relctx parameter whenever the callback is invoked.
757 * @return A non-zero error value on failure and 0 on success. Some possible
760 * <li>EINVAL - an invalid parameter was specified.
763 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
765 /** @brief Get items from a database.
767 * This function retrieves key/data pairs from the database. The address
768 * and length of the data associated with the specified \b key are returned
769 * in the structure to which \b data refers.
770 * If the database supports duplicate keys (#MDB_DUPSORT) then the
771 * first data item for the key will be returned. Retrieval of other
772 * items requires the use of #mdb_cursor_get().
774 * @note The memory pointed to by the returned values is owned by the
775 * database. The caller need not dispose of the memory, and may not
776 * modify it in any way. For values returned in a read-only transaction
777 * any modification attempts will cause a SIGSEGV.
778 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
779 * @param[in] dbi A database handle returned by #mdb_open()
780 * @param[in] key The key to search for in the database
781 * @param[out] data The data corresponding to the key
782 * @return A non-zero error value on failure and 0 on success. Some possible
785 * <li>#MDB_NOTFOUND - the key was not in the database.
786 * <li>EINVAL - an invalid parameter was specified.
789 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
791 /** @brief Store items into a database.
793 * This function stores key/data pairs in the database. The default behavior
794 * is to enter the new key/data pair, replacing any previously existing key
795 * if duplicates are disallowed, or adding a duplicate data item if
796 * duplicates are allowed (#MDB_DUPSORT).
797 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
798 * @param[in] dbi A database handle returned by #mdb_open()
799 * @param[in] key The key to store in the database
800 * @param[in,out] data The data to store
801 * @param[in] flags Special options for this operation. This parameter
802 * must be set to 0 or by bitwise OR'ing together one or more of the
803 * values described here.
805 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
806 * already appear in the database. This flag may only be specified
807 * if the database was opened with #MDB_DUPSORT. The function will
808 * return #MDB_KEYEXIST if the key/data pair already appears in the
810 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
811 * does not already appear in the database. The function will return
812 * #MDB_KEYEXIST if the key already appears in the database, even if
813 * the database supports duplicates (#MDB_DUPSORT). The \b data
814 * parameter will be set to point to the existing item.
815 * <li>#MDB_RESERVE - reserve space for data of the given size, but
816 * don't copy the given data. Instead, return a pointer to the
817 * reserved space, which the caller can fill in later. This saves
818 * an extra memcpy if the data is being generated later.
819 * <li>#MDB_APPEND - append the given key/data pair to the end of the
820 * database. No key comparisons are performed. This option allows
821 * fast bulk loading when keys are already known to be in the
822 * correct order. Loading unsorted keys with this flag will cause
824 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
826 * @return A non-zero error value on failure and 0 on success. Some possible
829 * <li>EACCES - an attempt was made to write in a read-only transaction.
830 * <li>EINVAL - an invalid parameter was specified.
831 * <li>ENOMEM - the database is full, see #mdb_env_set_mapsize().
834 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
837 /** @brief Delete items from a database.
839 * This function removes key/data pairs from the database.
840 * If the database does not support sorted duplicate data items
841 * (#MDB_DUPSORT) the data parameter is ignored.
842 * If the database supports sorted duplicates and the data parameter
843 * is NULL, all of the duplicate data items for the key will be
844 * deleted. Otherwise, if the data parameter is non-NULL
845 * only the matching data item will be deleted.
846 * This function will return #MDB_NOTFOUND if the specified key/data
847 * pair is not in the database.
848 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
849 * @param[in] dbi A database handle returned by #mdb_open()
850 * @param[in] key The key to delete from the database
851 * @param[in] data The data to delete
852 * @return A non-zero error value on failure and 0 on success. Some possible
855 * <li>EACCES - an attempt was made to write in a read-only transaction.
856 * <li>EINVAL - an invalid parameter was specified.
859 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
861 /** @brief Create a cursor handle.
863 * Cursors are associated with a specific transaction and database and
864 * may not span threads.
865 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
866 * @param[in] dbi A database handle returned by #mdb_open()
867 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
868 * @return A non-zero error value on failure and 0 on success. Some possible
871 * <li>EINVAL - an invalid parameter was specified.
874 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
876 /** @brief Close a cursor handle.
878 * The cursor handle will be freed and must not be used again after this call.
879 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
881 void mdb_cursor_close(MDB_cursor *cursor);
883 /** @brief Return the cursor's transaction handle.
885 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
887 MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
889 /** @brief Return the cursor's database handle.
891 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
893 MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor);
895 /** @brief Retrieve by cursor.
897 * This function retrieves key/data pairs from the database. The address and length
898 * of the key are returned in the object to which \b key refers (except for the
899 * case of the #MDB_SET option, in which the \b key object is unchanged), and
900 * the address and length of the data are returned in the object to which \b data
902 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
903 * @param[in,out] key The key for a retrieved item
904 * @param[in,out] data The data of a retrieved item
905 * @param[in] op A cursor operation #MDB_cursor_op
906 * @return A non-zero error value on failure and 0 on success. Some possible
909 * <li>#MDB_NOTFOUND - no matching key found.
910 * <li>EINVAL - an invalid parameter was specified.
913 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
916 /** @brief Store by cursor.
918 * This function stores key/data pairs into the database.
919 * If the function fails for any reason, the state of the cursor will be
920 * unchanged. If the function succeeds and an item is inserted into the
921 * database, the cursor is always positioned to refer to the newly inserted item.
922 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
923 * @param[in] key The key operated on.
924 * @param[in] data The data operated on.
925 * @param[in] flags Options for this operation. This parameter
926 * must be set to 0 or one of the values described here.
928 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which
929 * the cursor refers with the specified data item. The \b key
930 * parameter is ignored.
931 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
932 * already appear in the database. This flag may only be specified
933 * if the database was opened with #MDB_DUPSORT. The function will
934 * return #MDB_KEYEXIST if the key/data pair already appears in the
936 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
937 * does not already appear in the database. The function will return
938 * #MDB_KEYEXIST if the key already appears in the database, even if
939 * the database supports duplicates (#MDB_DUPSORT).
940 * <li>#MDB_RESERVE - reserve space for data of the given size, but
941 * don't copy the given data. Instead, return a pointer to the
942 * reserved space, which the caller can fill in later. This saves
943 * an extra memcpy if the data is being generated later.
944 * <li>#MDB_APPEND - append the given key/data pair to the end of the
945 * database. No key comparisons are performed. This option allows
946 * fast bulk loading when keys are already known to be in the
947 * correct order. Loading unsorted keys with this flag will cause
949 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
951 * @return A non-zero error value on failure and 0 on success. Some possible
954 * <li>EACCES - an attempt was made to modify a read-only database.
955 * <li>EINVAL - an invalid parameter was specified.
958 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
961 /** @brief Delete current key/data pair
963 * This function deletes the key/data pair to which the cursor refers.
964 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
965 * @param[in] flags Options for this operation. This parameter
966 * must be set to 0 or one of the values described here.
968 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
969 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
971 * @return A non-zero error value on failure and 0 on success. Some possible
974 * <li>EACCES - an attempt was made to modify a read-only database.
975 * <li>EINVAL - an invalid parameter was specified.
978 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
980 /** @brief Return count of duplicates for current key.
982 * This call is only valid on databases that support sorted duplicate
983 * data items #MDB_DUPSORT.
984 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
985 * @param[out] countp Address where the count will be stored
986 * @return A non-zero error value on failure and 0 on success. Some possible
989 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
992 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
994 /** @brief Compare two data items according to a particular database.
996 * This returns a comparison as if the two data items were keys in the
997 * specified database.
998 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
999 * @param[in] dbi A database handle returned by #mdb_open()
1000 * @param[in] a The first item to compare
1001 * @param[in] b The second item to compare
1002 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1004 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1006 /** @brief Compare two data items according to a particular database.
1008 * This returns a comparison as if the two items were data items of
1009 * a sorted duplicates #MDB_DUPSORT database.
1010 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1011 * @param[in] dbi A database handle returned by #mdb_open()
1012 * @param[in] a The first item to compare
1013 * @param[in] b The second item to compare
1014 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1016 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1022 #endif /* _MDB_H_ */