1/** @file lmdb.h
2 * @brief Lightning memory-mapped database library
3 *
4 * @mainpage Lightning Memory-Mapped Database Manager (LMDB)
5 *
6 * @section intro_sec Introduction
7 * LMDB is a Btree-based database management library modeled loosely on the
8 * BerkeleyDB API, but much simplified. The entire database is exposed
9 * in a memory map, and all data fetches return data directly
10 * from the mapped memory, so no malloc's or memcpy's occur during
11 * data fetches. As such, the library is extremely simple because it
12 * requires no page caching layer of its own, and it is extremely high
13 * performance and memory-efficient. It is also fully transactional with
14 * full ACID semantics, and when the memory map is read-only, the
15 * database integrity cannot be corrupted by stray pointer writes from
16 * application code.
17 *
18 * The library is fully thread-aware and supports concurrent read/write
19 * access from multiple processes and threads. Data pages use a copy-on-
20 * write strategy so no active data pages are ever overwritten, which
21 * also provides resistance to corruption and eliminates the need of any
22 * special recovery procedures after a system crash. Writes are fully
23 * serialized; only one write transaction may be active at a time, which
24 * guarantees that writers can never deadlock. The database structure is
25 * multi-versioned so readers run with no locks; writers cannot block
26 * readers, and readers don't block writers.
27 *
28 * Unlike other well-known database mechanisms which use either write-ahead
29 * transaction logs or append-only data writes, LMDB requires no maintenance
30 * during operation. Both write-ahead loggers and append-only databases
31 * require periodic checkpointing and/or compaction of their log or database
32 * files otherwise they grow without bound. LMDB tracks free pages within
33 * the database and re-uses them for new write operations, so the database
34 * size does not grow without bound in normal use.
35 *
36 * The memory map can be used as a read-only or read-write map. It is
37 * read-only by default as this provides total immunity to corruption.
38 * Using read-write mode offers much higher write performance, but adds
39 * the possibility for stray application writes thru pointers to silently
40 * corrupt the database. Of course if your application code is known to
41 * be bug-free (...) then this is not an issue.
42 *
43 * If this is your first time using a transactional embedded key/value
44 * store, you may find the \ref starting page to be helpful.
45 *
46 * @section caveats_sec Caveats
47 * Troubleshooting the lock file, plus semaphores on BSD systems:
48 *
49 * - A broken lockfile can cause sync issues.
50 * Stale reader transactions left behind by an aborted program
51 * cause further writes to grow the database quickly, and
52 * stale locks can block further operation.
53 *
54 * Fix: Check for stale readers periodically, using the
55 * #mdb_reader_check function or the \ref mdb_stat_1 "mdb_stat" tool.
56 * Stale writers will be cleared automatically on some systems:
57 * - Windows - automatic
58 * - Linux, systems using POSIX mutexes with Robust option - automatic
59 * - not on BSD, systems using POSIX semaphores.
60 * Otherwise just make all programs using the database close it;
61 * the lockfile is always reset on first open of the environment.
62 *
63 * - On BSD systems or others configured with MDB_USE_POSIX_SEM,
64 * startup can fail due to semaphores owned by another userid.
65 *
66 * Fix: Open and close the database as the user which owns the
67 * semaphores (likely last user) or as root, while no other
68 * process is using the database.
69 *
70 * Restrictions/caveats (in addition to those listed for some functions):
71 *
72 * - Only the database owner should normally use the database on
73 * BSD systems or when otherwise configured with MDB_USE_POSIX_SEM.
74 * Multiple users can cause startup to fail later, as noted above.
75 *
76 * - There is normally no pure read-only mode, since readers need write
77 * access to locks and lock file. Exceptions: On read-only filesystems
78 * or with the #MDB_NOLOCK flag described under #mdb_env_open().
79 *
80 * - An LMDB configuration will often reserve considerable \b unused
81 * memory address space and maybe file size for future growth.
82 * This does not use actual memory or disk space, but users may need
83 * to understand the difference so they won't be scared off.
84 *
85 * - By default, in versions before 0.9.10, unused portions of the data
86 * file might receive garbage data from memory freed by other code.
87 * (This does not happen when using the #MDB_WRITEMAP flag.) As of
88 * 0.9.10 the default behavior is to initialize such memory before
89 * writing to the data file. Since there may be a slight performance
90 * cost due to this initialization, applications may disable it using
91 * the #MDB_NOMEMINIT flag. Applications handling sensitive data
92 * which must not be written should not use this flag. This flag is
93 * irrelevant when using #MDB_WRITEMAP.
94 *
95 * - A thread can only use one transaction at a time, plus any child
96 * transactions. Each transaction belongs to one thread. See below.
97 * The #MDB_NOTLS flag changes this for read-only transactions.
98 *
99 * - Use an MDB_env* in the process which opened it, not after fork().
100 *
101 * - Do not have open an LMDB database twice in the same process at
102 * the same time. Not even from a plain open() call - close()ing it
103 * breaks fcntl() advisory locking. (It is OK to reopen it after
104 * fork() - exec*(), since the lockfile has FD_CLOEXEC set.)
105 *
106 * - Avoid long-lived transactions. Read transactions prevent
107 * reuse of pages freed by newer write transactions, thus the
108 * database can grow quickly. Write transactions prevent
109 * other write transactions, since writes are serialized.
110 *
111 * - Avoid suspending a process with active transactions. These
112 * would then be "long-lived" as above. Also read transactions
113 * suspended when writers commit could sometimes see wrong data.
114 *
115 * ...when several processes can use a database concurrently:
116 *
117 * - Avoid aborting a process with an active transaction.
118 * The transaction becomes "long-lived" as above until a check
119 * for stale readers is performed or the lockfile is reset,
120 * since the process may not remove it from the lockfile.
121 *
122 * This does not apply to write transactions if the system clears
123 * stale writers, see above.
124 *
125 * - If you do that anyway, do a periodic check for stale readers. Or
126 * close the environment once in a while, so the lockfile can get reset.
127 *
128 * - Do not use LMDB databases on remote filesystems, even between
129 * processes on the same host. This breaks flock() on some OSes,
130 * possibly memory map sync, and certainly sync between programs
131 * on different hosts.
132 *
133 * - Opening a database can fail if another process is opening or
134 * closing it at exactly the same time.
135 *
136 * @author Howard Chu, Symas Corporation.
137 *
138 * @copyright Copyright 2011-2018 Howard Chu, Symas Corp. All rights reserved.
139 *
140 * Redistribution and use in source and binary forms, with or without
141 * modification, are permitted only as authorized by the OpenLDAP
142 * Public License.
143 *
144 * A copy of this license is available in the file LICENSE in the
145 * top-level directory of the distribution or, alternatively, at
146 * <http://www.OpenLDAP.org/license.html>.
147 *
148 * @par Derived From:
149 * This code is derived from btree.c written by Martin Hedenfalk.
150 *
151 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
152 *
153 * Permission to use, copy, modify, and distribute this software for any
154 * purpose with or without fee is hereby granted, provided that the above
155 * copyright notice and this permission notice appear in all copies.
156 *
157 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
158 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
159 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
160 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
161 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
162 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
163 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
164 */
165#ifndef _LMDB_H_
166#define _LMDB_H_
167
168#include <sys/types.h>
169
170#ifdef __cplusplus
171extern "C" {
172#endif
173
174/** Unix permissions for creating files, or dummy definition for Windows */
175#ifdef _MSC_VER
176typedef int mdb_mode_t;
177#else
178typedef mode_t mdb_mode_t;
179#endif
180
181/** An abstraction for a file handle.
182 * On POSIX systems file handles are small integers. On Windows
183 * they're opaque pointers.
184 */
185#ifdef _WIN32
186typedef void *mdb_filehandle_t;
187#else
188typedef int mdb_filehandle_t;
189#endif
190
191/** @defgroup mdb LMDB API
192 * @{
193 * @brief OpenLDAP Lightning Memory-Mapped Database Manager
194 */
195/** @defgroup Version Version Macros
196 * @{
197 */
198/** Library major version */
199#define MDB_VERSION_MAJOR 0
200/** Library minor version */
201#define MDB_VERSION_MINOR 9
202/** Library patch version */
203#define MDB_VERSION_PATCH 23
204
205/** Combine args a,b,c into a single integer for easy version comparisons */
206#define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
207
208/** The full library version as a single integer */
209#define MDB_VERSION_FULL \
210 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
211
212/** The release date of this library version */
213#define MDB_VERSION_DATE "December 19, 2018"
214
215/** A stringifier for the version info */
216#define MDB_VERSTR(a,b,c,d) "LMDB " #a "." #b "." #c ": (" d ")"
217
218/** A helper for the stringifier macro */
219#define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d)
220
221/** The full library version as a C string */
222#define MDB_VERSION_STRING \
223 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
224/** @} */
225
226/** @brief Opaque structure for a database environment.
227 *
228 * A DB environment supports multiple databases, all residing in the same
229 * shared-memory map.
230 */
231typedef struct MDB_env MDB_env;
232
233/** @brief Opaque structure for a transaction handle.
234 *
235 * All database operations require a transaction handle. Transactions may be
236 * read-only or read-write.
237 */
238typedef struct MDB_txn MDB_txn;
239
240/** @brief A handle for an individual database in the DB environment. */
241typedef unsigned int MDB_dbi;
242
243/** @brief Opaque structure for navigating through a database */
244typedef struct MDB_cursor MDB_cursor;
245
246/** @brief Generic structure used for passing keys and data in and out
247 * of the database.
248 *
249 * Values returned from the database are valid only until a subsequent
250 * update operation, or the end of the transaction. Do not modify or
251 * free them, they commonly point into the database itself.
252 *
253 * Key sizes must be between 1 and #mdb_env_get_maxkeysize() inclusive.
254 * The same applies to data sizes in databases with the #MDB_DUPSORT flag.
255 * Other data items can in theory be from 0 to 0xffffffff bytes long.
256 */
257typedef struct MDB_val {
258 size_t mv_size; /**< size of the data item */
259 void *mv_data; /**< address of the data item */
260} MDB_val;
261
262/** @brief A callback function used to compare two keys in a database */
263typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
264
265/** @brief A callback function used to relocate a position-dependent data item
266 * in a fixed-address database.
267 *
268 * The \b newptr gives the item's desired address in
269 * the memory map, and \b oldptr gives its previous address. The item's actual
270 * data resides at the address in \b item. This callback is expected to walk
271 * through the fields of the record in \b item and modify any
272 * values based at the \b oldptr address to be relative to the \b newptr address.
273 * @param[in,out] item The item that is to be relocated.
274 * @param[in] oldptr The previous address.
275 * @param[in] newptr The new address to relocate to.
276 * @param[in] relctx An application-provided context, set by #mdb_set_relctx().
277 * @todo This feature is currently unimplemented.
278 */
279typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
280
281/** @defgroup mdb_env Environment Flags
282 * @{
283 */
284 /** mmap at a fixed address (experimental) */
285#define MDB_FIXEDMAP 0x01
286 /** no environment directory */
287#define MDB_NOSUBDIR 0x4000
288 /** don't fsync after commit */
289#define MDB_NOSYNC 0x10000
290 /** read only */
291#define MDB_RDONLY 0x20000
292 /** don't fsync metapage after commit */
293#define MDB_NOMETASYNC 0x40000
294 /** use writable mmap */
295#define MDB_WRITEMAP 0x80000
296 /** use asynchronous msync when #MDB_WRITEMAP is used */
297#define MDB_MAPASYNC 0x100000
298 /** tie reader locktable slots to #MDB_txn objects instead of to threads */
299#define MDB_NOTLS 0x200000
300 /** don't do any locking, caller must manage their own locks */
301#define MDB_NOLOCK 0x400000
302 /** don't do readahead (no effect on Windows) */
303#define MDB_NORDAHEAD 0x800000
304 /** don't initialize malloc'd memory before writing to datafile */
305#define MDB_NOMEMINIT 0x1000000
306/** @} */
307
308/** @defgroup mdb_dbi_open Database Flags
309 * @{
310 */
311 /** use reverse string keys */
312#define MDB_REVERSEKEY 0x02
313 /** use sorted duplicates */
314#define MDB_DUPSORT 0x04
315 /** numeric keys in native byte order: either unsigned int or size_t.
316 * The keys must all be of the same size. */
317#define MDB_INTEGERKEY 0x08
318 /** with #MDB_DUPSORT, sorted dup items have fixed size */
319#define MDB_DUPFIXED 0x10
320 /** with #MDB_DUPSORT, dups are #MDB_INTEGERKEY-style integers */
321#define MDB_INTEGERDUP 0x20
322 /** with #MDB_DUPSORT, use reverse string dups */
323#define MDB_REVERSEDUP 0x40
324 /** create DB if not already existing */
325#define MDB_CREATE 0x40000
326/** @} */
327
328/** @defgroup mdb_put Write Flags
329 * @{
330 */
331/** For put: Don't write if the key already exists. */
332#define MDB_NOOVERWRITE 0x10
333/** Only for #MDB_DUPSORT<br>
334 * For put: don't write if the key and data pair already exist.<br>
335 * For mdb_cursor_del: remove all duplicate data items.
336 */
337#define MDB_NODUPDATA 0x20
338/** For mdb_cursor_put: overwrite the current key/data pair */
339#define MDB_CURRENT 0x40
340/** For put: Just reserve space for data, don't copy it. Return a
341 * pointer to the reserved space.
342 */
343#define MDB_RESERVE 0x10000
344/** Data is being appended, don't split full pages. */
345#define MDB_APPEND 0x20000
346/** Duplicate data is being appended, don't split full pages. */
347#define MDB_APPENDDUP 0x40000
348/** Store multiple data items in one call. Only for #MDB_DUPFIXED. */
349#define MDB_MULTIPLE 0x80000
350/* @} */
351
352/** @defgroup mdb_copy Copy Flags
353 * @{
354 */
355/** Compacting copy: Omit free space from copy, and renumber all
356 * pages sequentially.
357 */
358#define MDB_CP_COMPACT 0x01
359/* @} */
360
361/** @brief Cursor Get operations.
362 *
363 * This is the set of all operations for retrieving data
364 * using a cursor.
365 */
366typedef enum MDB_cursor_op {
367 MDB_FIRST, /**< Position at first key/data item */
368 MDB_FIRST_DUP, /**< Position at first data item of current key.
369 Only for #MDB_DUPSORT */
370 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
371 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
372 MDB_GET_CURRENT, /**< Return key/data at current cursor position */
373 MDB_GET_MULTIPLE, /**< Return up to a page of duplicate data items
374 from current cursor position. Move cursor to prepare
375 for #MDB_NEXT_MULTIPLE. Only for #MDB_DUPFIXED */
376 MDB_LAST, /**< Position at last key/data item */
377 MDB_LAST_DUP, /**< Position at last data item of current key.
378 Only for #MDB_DUPSORT */
379 MDB_NEXT, /**< Position at next data item */
380 MDB_NEXT_DUP, /**< Position at next data item of current key.
381 Only for #MDB_DUPSORT */
382 MDB_NEXT_MULTIPLE, /**< Return up to a page of duplicate data items
383 from next cursor position. Move cursor to prepare
384 for #MDB_NEXT_MULTIPLE. Only for #MDB_DUPFIXED */
385 MDB_NEXT_NODUP, /**< Position at first data item of next key */
386 MDB_PREV, /**< Position at previous data item */
387 MDB_PREV_DUP, /**< Position at previous data item of current key.
388 Only for #MDB_DUPSORT */
389 MDB_PREV_NODUP, /**< Position at last data item of previous key */
390 MDB_SET, /**< Position at specified key */
391 MDB_SET_KEY, /**< Position at specified key, return key + data */
392 MDB_SET_RANGE, /**< Position at first key greater than or equal to specified key. */
393 MDB_PREV_MULTIPLE /**< Position at previous page and return up to
394 a page of duplicate data items. Only for #MDB_DUPFIXED */
395} MDB_cursor_op;
396
397/** @defgroup errors Return Codes
398 *
399 * BerkeleyDB uses -30800 to -30999, we'll go under them
400 * @{
401 */
402 /** Successful result */
403#define MDB_SUCCESS 0
404 /** key/data pair already exists */
405#define MDB_KEYEXIST (-30799)
406 /** key/data pair not found (EOF) */
407#define MDB_NOTFOUND (-30798)
408 /** Requested page not found - this usually indicates corruption */
409#define MDB_PAGE_NOTFOUND (-30797)
410 /** Located page was wrong type */
411#define MDB_CORRUPTED (-30796)
412 /** Update of meta page failed or environment had fatal error */
413#define MDB_PANIC (-30795)
414 /** Environment version mismatch */
415#define MDB_VERSION_MISMATCH (-30794)
416 /** File is not a valid LMDB file */
417#define MDB_INVALID (-30793)
418 /** Environment mapsize reached */
419#define MDB_MAP_FULL (-30792)
420 /** Environment maxdbs reached */
421#define MDB_DBS_FULL (-30791)
422 /** Environment maxreaders reached */
423#define MDB_READERS_FULL (-30790)
424 /** Too many TLS keys in use - Windows only */
425#define MDB_TLS_FULL (-30789)
426 /** Txn has too many dirty pages */
427#define MDB_TXN_FULL (-30788)
428 /** Cursor stack too deep - internal error */
429#define MDB_CURSOR_FULL (-30787)
430 /** Page has not enough space - internal error */
431#define MDB_PAGE_FULL (-30786)
432 /** Database contents grew beyond environment mapsize */
433#define MDB_MAP_RESIZED (-30785)
434 /** Operation and DB incompatible, or DB type changed. This can mean:
435 * <ul>
436 * <li>The operation expects an #MDB_DUPSORT / #MDB_DUPFIXED database.
437 * <li>Opening a named DB when the unnamed DB has #MDB_DUPSORT / #MDB_INTEGERKEY.
438 * <li>Accessing a data record as a database, or vice versa.
439 * <li>The database was dropped and recreated with different flags.
440 * </ul>
441 */
442#define MDB_INCOMPATIBLE (-30784)
443 /** Invalid reuse of reader locktable slot */
444#define MDB_BAD_RSLOT (-30783)
445 /** Transaction must abort, has a child, or is invalid */
446#define MDB_BAD_TXN (-30782)
447 /** Unsupported size of key/DB name/data, or wrong DUPFIXED size */
448#define MDB_BAD_VALSIZE (-30781)
449 /** The specified DBI was changed unexpectedly */
450#define MDB_BAD_DBI (-30780)
451 /** The last defined error code */
452#define MDB_LAST_ERRCODE MDB_BAD_DBI
453/** @} */
454
455/** @brief Statistics for a database in the environment */
456typedef struct MDB_stat {
457 unsigned int ms_psize; /**< Size of a database page.
458 This is currently the same for all databases. */
459 unsigned int ms_depth; /**< Depth (height) of the B-tree */
460 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
461 size_t ms_leaf_pages; /**< Number of leaf pages */
462 size_t ms_overflow_pages; /**< Number of overflow pages */
463 size_t ms_entries; /**< Number of data items */
464} MDB_stat;
465
466/** @brief Information about the environment */
467typedef struct MDB_envinfo {
468 void *me_mapaddr; /**< Address of map, if fixed */
469 size_t me_mapsize; /**< Size of the data memory map */
470 size_t me_last_pgno; /**< ID of the last used page */
471 size_t me_last_txnid; /**< ID of the last committed transaction */
472 unsigned int me_maxreaders; /**< max reader slots in the environment */
473 unsigned int me_numreaders; /**< max reader slots used in the environment */
474} MDB_envinfo;
475
476 /** @brief Return the LMDB library version information.
477 *
478 * @param[out] major if non-NULL, the library major version number is copied here
479 * @param[out] minor if non-NULL, the library minor version number is copied here
480 * @param[out] patch if non-NULL, the library patch version number is copied here
481 * @retval "version string" The library version as a string
482 */
483char *mdb_version(int *major, int *minor, int *patch);
484
485 /** @brief Return a string describing a given error code.
486 *
487 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
488 * function. If the error code is greater than or equal to 0, then the string
489 * returned by the system function strerror(3) is returned. If the error code
490 * is less than 0, an error string corresponding to the LMDB library error is
491 * returned. See @ref errors for a list of LMDB-specific error codes.
492 * @param[in] err The error code
493 * @retval "error message" The description of the error
494 */
495char *mdb_strerror(int err);
496
497 /** @brief Create an LMDB environment handle.
498 *
499 * This function allocates memory for a #MDB_env structure. To release
500 * the allocated memory and discard the handle, call #mdb_env_close().
501 * Before the handle may be used, it must be opened using #mdb_env_open().
502 * Various other options may also need to be set before opening the handle,
503 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
504 * depending on usage requirements.
505 * @param[out] env The address where the new handle will be stored
506 * @return A non-zero error value on failure and 0 on success.
507 */
508int mdb_env_create(MDB_env **env);
509
510 /** @brief Open an environment handle.
511 *
512 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
513 * @param[in] env An environment handle returned by #mdb_env_create()
514 * @param[in] path The directory in which the database files reside. This
515 * directory must already exist and be writable.
516 * @param[in] flags Special options for this environment. This parameter
517 * must be set to 0 or by bitwise OR'ing together one or more of the
518 * values described here.
519 * Flags set by mdb_env_set_flags() are also used.
520 * <ul>
521 * <li>#MDB_FIXEDMAP
522 * use a fixed address for the mmap region. This flag must be specified
523 * when creating the environment, and is stored persistently in the environment.
524 * If successful, the memory map will always reside at the same virtual address
525 * and pointers used to reference data items in the database will be constant
526 * across multiple invocations. This option may not always work, depending on
527 * how the operating system has allocated memory to shared libraries and other uses.
528 * The feature is highly experimental.
529 * <li>#MDB_NOSUBDIR
530 * By default, LMDB creates its environment in a directory whose
531 * pathname is given in \b path, and creates its data and lock files
532 * under that directory. With this option, \b path is used as-is for
533 * the database main data file. The database lock file is the \b path
534 * with "-lock" appended.
535 * <li>#MDB_RDONLY
536 * Open the environment in read-only mode. No write operations will be
537 * allowed. LMDB will still modify the lock file - except on read-only
538 * filesystems, where LMDB does not use locks.
539 * <li>#MDB_WRITEMAP
540 * Use a writeable memory map unless MDB_RDONLY is set. This uses
541 * fewer mallocs but loses protection from application bugs
542 * like wild pointer writes and other bad updates into the database.
543 * This may be slightly faster for DBs that fit entirely in RAM, but
544 * is slower for DBs larger than RAM.
545 * Incompatible with nested transactions.
546 * Do not mix processes with and without MDB_WRITEMAP on the same
547 * environment. This can defeat durability (#mdb_env_sync etc).
548 * <li>#MDB_NOMETASYNC
549 * Flush system buffers to disk only once per transaction, omit the
550 * metadata flush. Defer that until the system flushes files to disk,
551 * or next non-MDB_RDONLY commit or #mdb_env_sync(). This optimization
552 * maintains database integrity, but a system crash may undo the last
553 * committed transaction. I.e. it preserves the ACI (atomicity,
554 * consistency, isolation) but not D (durability) database property.
555 * This flag may be changed at any time using #mdb_env_set_flags().
556 * <li>#MDB_NOSYNC
557 * Don't flush system buffers to disk when committing a transaction.
558 * This optimization means a system crash can corrupt the database or
559 * lose the last transactions if buffers are not yet flushed to disk.
560 * The risk is governed by how often the system flushes dirty buffers
561 * to disk and how often #mdb_env_sync() is called. However, if the
562 * filesystem preserves write order and the #MDB_WRITEMAP flag is not
563 * used, transactions exhibit ACI (atomicity, consistency, isolation)
564 * properties and only lose D (durability). I.e. database integrity
565 * is maintained, but a system crash may undo the final transactions.
566 * Note that (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no
567 * hint for when to write transactions to disk, unless #mdb_env_sync()
568 * is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable.
569 * This flag may be changed at any time using #mdb_env_set_flags().
570 * <li>#MDB_MAPASYNC
571 * When using #MDB_WRITEMAP, use asynchronous flushes to disk.
572 * As with #MDB_NOSYNC, a system crash can then corrupt the
573 * database or lose the last transactions. Calling #mdb_env_sync()
574 * ensures on-disk database integrity until next commit.
575 * This flag may be changed at any time using #mdb_env_set_flags().
576 * <li>#MDB_NOTLS
577 * Don't use Thread-Local Storage. Tie reader locktable slots to
578 * #MDB_txn objects instead of to threads. I.e. #mdb_txn_reset() keeps
579 * the slot reseved for the #MDB_txn object. A thread may use parallel
580 * read-only transactions. A read-only transaction may span threads if
581 * the user synchronizes its use. Applications that multiplex many
582 * user threads over individual OS threads need this option. Such an
583 * application must also serialize the write transactions in an OS
584 * thread, since LMDB's write locking is unaware of the user threads.
585 * <li>#MDB_NOLOCK
586 * Don't do any locking. If concurrent access is anticipated, the
587 * caller must manage all concurrency itself. For proper operation
588 * the caller must enforce single-writer semantics, and must ensure
589 * that no readers are using old transactions while a writer is
590 * active. The simplest approach is to use an exclusive lock so that
591 * no readers may be active at all when a writer begins.
592 * <li>#MDB_NORDAHEAD
593 * Turn off readahead. Most operating systems perform readahead on
594 * read requests by default. This option turns it off if the OS
595 * supports it. Turning it off may help random read performance
596 * when the DB is larger than RAM and system RAM is full.
597 * The option is not implemented on Windows.
598 * <li>#MDB_NOMEMINIT
599 * Don't initialize malloc'd memory before writing to unused spaces
600 * in the data file. By default, memory for pages written to the data
601 * file is obtained using malloc. While these pages may be reused in
602 * subsequent transactions, freshly malloc'd pages will be initialized
603 * to zeroes before use. This avoids persisting leftover data from other
604 * code (that used the heap and subsequently freed the memory) into the
605 * data file. Note that many other system libraries may allocate
606 * and free memory from the heap for arbitrary uses. E.g., stdio may
607 * use the heap for file I/O buffers. This initialization step has a
608 * modest performance cost so some applications may want to disable
609 * it using this flag. This option can be a problem for applications
610 * which handle sensitive data like passwords, and it makes memory
611 * checkers like Valgrind noisy. This flag is not needed with #MDB_WRITEMAP,
612 * which writes directly to the mmap instead of using malloc for pages. The
613 * initialization is also skipped if #MDB_RESERVE is used; the
614 * caller is expected to overwrite all of the memory that was
615 * reserved in that case.
616 * This flag may be changed at any time using #mdb_env_set_flags().
617 * </ul>
618 * @param[in] mode The UNIX permissions to set on created files and semaphores.
619 * This parameter is ignored on Windows.
620 * @return A non-zero error value on failure and 0 on success. Some possible
621 * errors are:
622 * <ul>
623 * <li>#MDB_VERSION_MISMATCH - the version of the LMDB library doesn't match the
624 * version that created the database environment.
625 * <li>#MDB_INVALID - the environment file headers are corrupted.
626 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
627 * <li>EACCES - the user didn't have permission to access the environment files.
628 * <li>EAGAIN - the environment was locked by another process.
629 * </ul>
630 */
631int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode);
632
633 /** @brief Copy an LMDB environment to the specified path.
634 *
635 * This function may be used to make a backup of an existing environment.
636 * No lockfile is created, since it gets recreated at need.
637 * @note This call can trigger significant file size growth if run in
638 * parallel with write transactions, because it employs a read-only
639 * transaction. See long-lived transactions under @ref caveats_sec.
640 * @param[in] env An environment handle returned by #mdb_env_create(). It
641 * must have already been opened successfully.
642 * @param[in] path The directory in which the copy will reside. This
643 * directory must already exist and be writable but must otherwise be
644 * empty.
645 * @return A non-zero error value on failure and 0 on success.
646 */
647int mdb_env_copy(MDB_env *env, const char *path);
648
649 /** @brief Copy an LMDB environment to the specified file descriptor.
650 *
651 * This function may be used to make a backup of an existing environment.
652 * No lockfile is created, since it gets recreated at need.
653 * @note This call can trigger significant file size growth if run in
654 * parallel with write transactions, because it employs a read-only
655 * transaction. See long-lived transactions under @ref caveats_sec.
656 * @param[in] env An environment handle returned by #mdb_env_create(). It
657 * must have already been opened successfully.
658 * @param[in] fd The filedescriptor to write the copy to. It must
659 * have already been opened for Write access.
660 * @return A non-zero error value on failure and 0 on success.
661 */
662int mdb_env_copyfd(MDB_env *env, mdb_filehandle_t fd);
663
664 /** @brief Copy an LMDB environment to the specified path, with options.
665 *
666 * This function may be used to make a backup of an existing environment.
667 * No lockfile is created, since it gets recreated at need.
668 * @note This call can trigger significant file size growth if run in
669 * parallel with write transactions, because it employs a read-only
670 * transaction. See long-lived transactions under @ref caveats_sec.
671 * @param[in] env An environment handle returned by #mdb_env_create(). It
672 * must have already been opened successfully.
673 * @param[in] path The directory in which the copy will reside. This
674 * directory must already exist and be writable but must otherwise be
675 * empty.
676 * @param[in] flags Special options for this operation. This parameter
677 * must be set to 0 or by bitwise OR'ing together one or more of the
678 * values described here.
679 * <ul>
680 * <li>#MDB_CP_COMPACT - Perform compaction while copying: omit free
681 * pages and sequentially renumber all pages in output. This option
682 * consumes more CPU and runs more slowly than the default.
683 * Currently it fails if the environment has suffered a page leak.
684 * </ul>
685 * @return A non-zero error value on failure and 0 on success.
686 */
687int mdb_env_copy2(MDB_env *env, const char *path, unsigned int flags);
688
689 /** @brief Copy an LMDB environment to the specified file descriptor,
690 * with options.
691 *
692 * This function may be used to make a backup of an existing environment.
693 * No lockfile is created, since it gets recreated at need. See
694 * #mdb_env_copy2() for further details.
695 * @note This call can trigger significant file size growth if run in
696 * parallel with write transactions, because it employs a read-only
697 * transaction. See long-lived transactions under @ref caveats_sec.
698 * @param[in] env An environment handle returned by #mdb_env_create(). It
699 * must have already been opened successfully.
700 * @param[in] fd The filedescriptor to write the copy to. It must
701 * have already been opened for Write access.
702 * @param[in] flags Special options for this operation.
703 * See #mdb_env_copy2() for options.
704 * @return A non-zero error value on failure and 0 on success.
705 */
706int mdb_env_copyfd2(MDB_env *env, mdb_filehandle_t fd, unsigned int flags);
707
708 /** @brief Return statistics about the LMDB environment.
709 *
710 * @param[in] env An environment handle returned by #mdb_env_create()
711 * @param[out] stat The address of an #MDB_stat structure
712 * where the statistics will be copied
713 */
714int mdb_env_stat(MDB_env *env, MDB_stat *stat);
715
716 /** @brief Return information about the LMDB environment.
717 *
718 * @param[in] env An environment handle returned by #mdb_env_create()
719 * @param[out] stat The address of an #MDB_envinfo structure
720 * where the information will be copied
721 */
722int mdb_env_info(MDB_env *env, MDB_envinfo *stat);
723
724 /** @brief Flush the data buffers to disk.
725 *
726 * Data is always written to disk when #mdb_txn_commit() is called,
727 * but the operating system may keep it buffered. LMDB always flushes
728 * the OS buffers upon commit as well, unless the environment was
729 * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC. This call is
730 * not valid if the environment was opened with #MDB_RDONLY.
731 * @param[in] env An environment handle returned by #mdb_env_create()
732 * @param[in] force If non-zero, force a synchronous flush. Otherwise
733 * if the environment has the #MDB_NOSYNC flag set the flushes
734 * will be omitted, and with #MDB_MAPASYNC they will be asynchronous.
735 * @return A non-zero error value on failure and 0 on success. Some possible
736 * errors are:
737 * <ul>
738 * <li>EACCES - the environment is read-only.
739 * <li>EINVAL - an invalid parameter was specified.
740 * <li>EIO - an error occurred during synchronization.
741 * </ul>
742 */
743int mdb_env_sync(MDB_env *env, int force);
744
745 /** @brief Close the environment and release the memory map.
746 *
747 * Only a single thread may call this function. All transactions, databases,
748 * and cursors must already be closed before calling this function. Attempts to
749 * use any such handles after calling this function will cause a SIGSEGV.
750 * The environment handle will be freed and must not be used again after this call.
751 * @param[in] env An environment handle returned by #mdb_env_create()
752 */
753void mdb_env_close(MDB_env *env);
754
755 /** @brief Set environment flags.
756 *
757 * This may be used to set some flags in addition to those from
758 * #mdb_env_open(), or to unset these flags. If several threads
759 * change the flags at the same time, the result is undefined.
760 * @param[in] env An environment handle returned by #mdb_env_create()
761 * @param[in] flags The flags to change, bitwise OR'ed together
762 * @param[in] onoff A non-zero value sets the flags, zero clears them.
763 * @return A non-zero error value on failure and 0 on success. Some possible
764 * errors are:
765 * <ul>
766 * <li>EINVAL - an invalid parameter was specified.
767 * </ul>
768 */
769int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
770
771 /** @brief Get environment flags.
772 *
773 * @param[in] env An environment handle returned by #mdb_env_create()
774 * @param[out] flags The address of an integer to store the flags
775 * @return A non-zero error value on failure and 0 on success. Some possible
776 * errors are:
777 * <ul>
778 * <li>EINVAL - an invalid parameter was specified.
779 * </ul>
780 */
781int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
782
783 /** @brief Return the path that was used in #mdb_env_open().
784 *
785 * @param[in] env An environment handle returned by #mdb_env_create()
786 * @param[out] path Address of a string pointer to contain the path. This
787 * is the actual string in the environment, not a copy. It should not be
788 * altered in any way.
789 * @return A non-zero error value on failure and 0 on success. Some possible
790 * errors are:
791 * <ul>
792 * <li>EINVAL - an invalid parameter was specified.
793 * </ul>
794 */
795int mdb_env_get_path(MDB_env *env, const char **path);
796
797 /** @brief Return the filedescriptor for the given environment.
798 *
799 * This function may be called after fork(), so the descriptor can be
800 * closed before exec*(). Other LMDB file descriptors have FD_CLOEXEC.
801 * (Until LMDB 0.9.18, only the lockfile had that.)
802 *
803 * @param[in] env An environment handle returned by #mdb_env_create()
804 * @param[out] fd Address of a mdb_filehandle_t to contain the descriptor.
805 * @return A non-zero error value on failure and 0 on success. Some possible
806 * errors are:
807 * <ul>
808 * <li>EINVAL - an invalid parameter was specified.
809 * </ul>
810 */
811int mdb_env_get_fd(MDB_env *env, mdb_filehandle_t *fd);
812
813 /** @brief Set the size of the memory map to use for this environment.
814 *
815 * The size should be a multiple of the OS page size. The default is
816 * 10485760 bytes. The size of the memory map is also the maximum size
817 * of the database. The value should be chosen as large as possible,
818 * to accommodate future growth of the database.
819 * This function should be called after #mdb_env_create() and before #mdb_env_open().
820 * It may be called at later times if no transactions are active in
821 * this process. Note that the library does not check for this condition,
822 * the caller must ensure it explicitly.
823 *
824 * The new size takes effect immediately for the current process but
825 * will not be persisted to any others until a write transaction has been
826 * committed by the current process. Also, only mapsize increases are
827 * persisted into the environment.
828 *
829 * If the mapsize is increased by another process, and data has grown
830 * beyond the range of the current mapsize, #mdb_txn_begin() will
831 * return #MDB_MAP_RESIZED. This function may be called with a size
832 * of zero to adopt the new size.
833 *
834 * Any attempt to set a size smaller than the space already consumed
835 * by the environment will be silently changed to the current size of the used space.
836 * @param[in] env An environment handle returned by #mdb_env_create()
837 * @param[in] size The size in bytes
838 * @return A non-zero error value on failure and 0 on success. Some possible
839 * errors are:
840 * <ul>
841 * <li>EINVAL - an invalid parameter was specified, or the environment has
842 * an active write transaction.
843 * </ul>
844 */
845int mdb_env_set_mapsize(MDB_env *env, size_t size);
846
847 /** @brief Set the maximum number of threads/reader slots for the environment.
848 *
849 * This defines the number of slots in the lock table that is used to track readers in the
850 * the environment. The default is 126.
851 * Starting a read-only transaction normally ties a lock table slot to the
852 * current thread until the environment closes or the thread exits. If
853 * MDB_NOTLS is in use, #mdb_txn_begin() instead ties the slot to the
854 * MDB_txn object until it or the #MDB_env object is destroyed.
855 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
856 * @param[in] env An environment handle returned by #mdb_env_create()
857 * @param[in] readers The maximum number of reader lock table slots
858 * @return A non-zero error value on failure and 0 on success. Some possible
859 * errors are:
860 * <ul>
861 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
862 * </ul>
863 */
864int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
865
866 /** @brief Get the maximum number of threads/reader slots for the environment.
867 *
868 * @param[in] env An environment handle returned by #mdb_env_create()
869 * @param[out] readers Address of an integer to store the number of readers
870 * @return A non-zero error value on failure and 0 on success. Some possible
871 * errors are:
872 * <ul>
873 * <li>EINVAL - an invalid parameter was specified.
874 * </ul>
875 */
876int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
877
878 /** @brief Set the maximum number of named databases for the environment.
879 *
880 * This function is only needed if multiple databases will be used in the
881 * environment. Simpler applications that use the environment as a single
882 * unnamed database can ignore this option.
883 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
884 *
885 * Currently a moderate number of slots are cheap but a huge number gets
886 * expensive: 7-120 words per transaction, and every #mdb_dbi_open()
887 * does a linear search of the opened slots.
888 * @param[in] env An environment handle returned by #mdb_env_create()
889 * @param[in] dbs The maximum number of databases
890 * @return A non-zero error value on failure and 0 on success. Some possible
891 * errors are:
892 * <ul>
893 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
894 * </ul>
895 */
896int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
897
898 /** @brief Get the maximum size of keys and #MDB_DUPSORT data we can write.
899 *
900 * Depends on the compile-time constant #MDB_MAXKEYSIZE. Default 511.
901 * See @ref MDB_val.
902 * @param[in] env An environment handle returned by #mdb_env_create()
903 * @return The maximum size of a key we can write
904 */
905int mdb_env_get_maxkeysize(MDB_env *env);
906
907 /** @brief Set application information associated with the #MDB_env.
908 *
909 * @param[in] env An environment handle returned by #mdb_env_create()
910 * @param[in] ctx An arbitrary pointer for whatever the application needs.
911 * @return A non-zero error value on failure and 0 on success.
912 */
913int mdb_env_set_userctx(MDB_env *env, void *ctx);
914
915 /** @brief Get the application information associated with the #MDB_env.
916 *
917 * @param[in] env An environment handle returned by #mdb_env_create()
918 * @return The pointer set by #mdb_env_set_userctx().
919 */
920void *mdb_env_get_userctx(MDB_env *env);
921
922 /** @brief A callback function for most LMDB assert() failures,
923 * called before printing the message and aborting.
924 *
925 * @param[in] env An environment handle returned by #mdb_env_create().
926 * @param[in] msg The assertion message, not including newline.
927 */
928typedef void MDB_assert_func(MDB_env *env, const char *msg);
929
930 /** Set or reset the assert() callback of the environment.
931 * Disabled if liblmdb is buillt with NDEBUG.
932 * @note This hack should become obsolete as lmdb's error handling matures.
933 * @param[in] env An environment handle returned by #mdb_env_create().
934 * @param[in] func An #MDB_assert_func function, or 0.
935 * @return A non-zero error value on failure and 0 on success.
936 */
937int mdb_env_set_assert(MDB_env *env, MDB_assert_func *func);
938
939 /** @brief Create a transaction for use with the environment.
940 *
941 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
942 * @note A transaction and its cursors must only be used by a single
943 * thread, and a thread may only have a single transaction at a time.
944 * If #MDB_NOTLS is in use, this does not apply to read-only transactions.
945 * @note Cursors may not span transactions.
946 * @param[in] env An environment handle returned by #mdb_env_create()
947 * @param[in] parent If this parameter is non-NULL, the new transaction
948 * will be a nested transaction, with the transaction indicated by \b parent
949 * as its parent. Transactions may be nested to any level. A parent
950 * transaction and its cursors may not issue any other operations than
951 * mdb_txn_commit and mdb_txn_abort while it has active child transactions.
952 * @param[in] flags Special options for this transaction. This parameter
953 * must be set to 0 or by bitwise OR'ing together one or more of the
954 * values described here.
955 * <ul>
956 * <li>#MDB_RDONLY
957 * This transaction will not perform any write operations.
958 * </ul>
959 * @param[out] txn Address where the new #MDB_txn handle will be stored
960 * @return A non-zero error value on failure and 0 on success. Some possible
961 * errors are:
962 * <ul>
963 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
964 * must be shut down.
965 * <li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's
966 * mapsize and this environment's map must be resized as well.
967 * See #mdb_env_set_mapsize().
968 * <li>#MDB_READERS_FULL - a read-only transaction was requested and
969 * the reader lock table is full. See #mdb_env_set_maxreaders().
970 * <li>ENOMEM - out of memory.
971 * </ul>
972 */
973int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
974
975 /** @brief Returns the transaction's #MDB_env
976 *
977 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
978 */
979MDB_env *mdb_txn_env(MDB_txn *txn);
980
981 /** @brief Return the transaction's ID.
982 *
983 * This returns the identifier associated with this transaction. For a
984 * read-only transaction, this corresponds to the snapshot being read;
985 * concurrent readers will frequently have the same transaction ID.
986 *
987 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
988 * @return A transaction ID, valid if input is an active transaction.
989 */
990size_t mdb_txn_id(MDB_txn *txn);
991
992 /** @brief Commit all the operations of a transaction into the database.
993 *
994 * The transaction handle is freed. It and its cursors must not be used
995 * again after this call, except with #mdb_cursor_renew().
996 * @note Earlier documentation incorrectly said all cursors would be freed.
997 * Only write-transactions free cursors.
998 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
999 * @return A non-zero error value on failure and 0 on success. Some possible
1000 * errors are:
1001 * <ul>
1002 * <li>EINVAL - an invalid parameter was specified.
1003 * <li>ENOSPC - no more disk space.
1004 * <li>EIO - a low-level I/O error occurred while writing.
1005 * <li>ENOMEM - out of memory.
1006 * </ul>
1007 */
1008int mdb_txn_commit(MDB_txn *txn);
1009
1010 /** @brief Abandon all the operations of the transaction instead of saving them.
1011 *
1012 * The transaction handle is freed. It and its cursors must not be used
1013 * again after this call, except with #mdb_cursor_renew().
1014 * @note Earlier documentation incorrectly said all cursors would be freed.
1015 * Only write-transactions free cursors.
1016 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1017 */
1018void mdb_txn_abort(MDB_txn *txn);
1019
1020 /** @brief Reset a read-only transaction.
1021 *
1022 * Abort the transaction like #mdb_txn_abort(), but keep the transaction
1023 * handle. #mdb_txn_renew() may reuse the handle. This saves allocation
1024 * overhead if the process will start a new read-only transaction soon,
1025 * and also locking overhead if #MDB_NOTLS is in use. The reader table
1026 * lock is released, but the table slot stays tied to its thread or
1027 * #MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free
1028 * its lock table slot if MDB_NOTLS is in use.
1029 * Cursors opened within the transaction must not be used
1030 * again after this call, except with #mdb_cursor_renew().
1031 * Reader locks generally don't interfere with writers, but they keep old
1032 * versions of database pages allocated. Thus they prevent the old pages
1033 * from being reused when writers commit new data, and so under heavy load
1034 * the database size may grow much more rapidly than otherwise.
1035 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1036 */
1037void mdb_txn_reset(MDB_txn *txn);
1038
1039 /** @brief Renew a read-only transaction.
1040 *
1041 * This acquires a new reader lock for a transaction handle that had been
1042 * released by #mdb_txn_reset(). It must be called before a reset transaction
1043 * may be used again.
1044 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1045 * @return A non-zero error value on failure and 0 on success. Some possible
1046 * errors are:
1047 * <ul>
1048 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
1049 * must be shut down.
1050 * <li>EINVAL - an invalid parameter was specified.
1051 * </ul>
1052 */
1053int mdb_txn_renew(MDB_txn *txn);
1054
1055/** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
1056#define mdb_open(txn,name,flags,dbi) mdb_dbi_open(txn,name,flags,dbi)
1057/** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
1058#define mdb_close(env,dbi) mdb_dbi_close(env,dbi)
1059
1060 /** @brief Open a database in the environment.
1061 *
1062 * A database handle denotes the name and parameters of a database,
1063 * independently of whether such a database exists.
1064 * The database handle may be discarded by calling #mdb_dbi_close().
1065 * The old database handle is returned if the database was already open.
1066 * The handle may only be closed once.
1067 *
1068 * The database handle will be private to the current transaction until
1069 * the transaction is successfully committed. If the transaction is
1070 * aborted the handle will be closed automatically.
1071 * After a successful commit the handle will reside in the shared
1072 * environment, and may be used by other transactions.
1073 *
1074 * This function must not be called from multiple concurrent
1075 * transactions in the same process. A transaction that uses
1076 * this function must finish (either commit or abort) before
1077 * any other transaction in the process may use this function.
1078 *
1079 * To use named databases (with name != NULL), #mdb_env_set_maxdbs()
1080 * must be called before opening the environment. Database names are
1081 * keys in the unnamed database, and may be read but not written.
1082 *
1083 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1084 * @param[in] name The name of the database to open. If only a single
1085 * database is needed in the environment, this value may be NULL.
1086 * @param[in] flags Special options for this database. This parameter
1087 * must be set to 0 or by bitwise OR'ing together one or more of the
1088 * values described here.
1089 * <ul>
1090 * <li>#MDB_REVERSEKEY
1091 * Keys are strings to be compared in reverse order, from the end
1092 * of the strings to the beginning. By default, Keys are treated as strings and
1093 * compared from beginning to end.
1094 * <li>#MDB_DUPSORT
1095 * Duplicate keys may be used in the database. (Or, from another perspective,
1096 * keys may have multiple data items, stored in sorted order.) By default
1097 * keys must be unique and may have only a single data item.
1098 * <li>#MDB_INTEGERKEY
1099 * Keys are binary integers in native byte order, either unsigned int
1100 * or size_t, and will be sorted as such.
1101 * The keys must all be of the same size.
1102 * <li>#MDB_DUPFIXED
1103 * This flag may only be used in combination with #MDB_DUPSORT. This option
1104 * tells the library that the data items for this database are all the same
1105 * size, which allows further optimizations in storage and retrieval. When
1106 * all data items are the same size, the #MDB_GET_MULTIPLE, #MDB_NEXT_MULTIPLE
1107 * and #MDB_PREV_MULTIPLE cursor operations may be used to retrieve multiple
1108 * items at once.
1109 * <li>#MDB_INTEGERDUP
1110 * This option specifies that duplicate data items are binary integers,
1111 * similar to #MDB_INTEGERKEY keys.
1112 * <li>#MDB_REVERSEDUP
1113 * This option specifies that duplicate data items should be compared as
1114 * strings in reverse order.
1115 * <li>#MDB_CREATE
1116 * Create the named database if it doesn't exist. This option is not
1117 * allowed in a read-only transaction or a read-only environment.
1118 * </ul>
1119 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
1120 * @return A non-zero error value on failure and 0 on success. Some possible
1121 * errors are:
1122 * <ul>
1123 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
1124 * and #MDB_CREATE was not specified.
1125 * <li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs().
1126 * </ul>
1127 */
1128int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
1129
1130 /** @brief Retrieve statistics for a database.
1131 *
1132 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1133 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1134 * @param[out] stat The address of an #MDB_stat structure
1135 * where the statistics will be copied
1136 * @return A non-zero error value on failure and 0 on success. Some possible
1137 * errors are:
1138 * <ul>
1139 * <li>EINVAL - an invalid parameter was specified.
1140 * </ul>
1141 */
1142int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
1143
1144 /** @brief Retrieve the DB flags for a database handle.
1145 *
1146 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1147 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1148 * @param[out] flags Address where the flags will be returned.
1149 * @return A non-zero error value on failure and 0 on success.
1150 */
1151int mdb_dbi_flags(MDB_txn *txn, MDB_dbi dbi, unsigned int *flags);
1152
1153 /** @brief Close a database handle. Normally unnecessary. Use with care:
1154 *
1155 * This call is not mutex protected. Handles should only be closed by
1156 * a single thread, and only if no other threads are going to reference
1157 * the database handle or one of its cursors any further. Do not close
1158 * a handle if an existing transaction has modified its database.
1159 * Doing so can cause misbehavior from database corruption to errors
1160 * like MDB_BAD_VALSIZE (since the DB name is gone).
1161 *
1162 * Closing a database handle is not necessary, but lets #mdb_dbi_open()
1163 * reuse the handle value. Usually it's better to set a bigger
1164 * #mdb_env_set_maxdbs(), unless that value would be large.
1165 *
1166 * @param[in] env An environment handle returned by #mdb_env_create()
1167 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1168 */
1169void mdb_dbi_close(MDB_env *env, MDB_dbi dbi);
1170
1171 /** @brief Empty or delete+close a database.
1172 *
1173 * See #mdb_dbi_close() for restrictions about closing the DB handle.
1174 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1175 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1176 * @param[in] del 0 to empty the DB, 1 to delete it from the
1177 * environment and close the DB handle.
1178 * @return A non-zero error value on failure and 0 on success.
1179 */
1180int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
1181
1182 /** @brief Set a custom key comparison function for a database.
1183 *
1184 * The comparison function is called whenever it is necessary to compare a
1185 * key specified by the application with a key currently stored in the database.
1186 * If no comparison function is specified, and no special key flags were specified
1187 * with #mdb_dbi_open(), the keys are compared lexically, with shorter keys collating
1188 * before longer keys.
1189 * @warning This function must be called before any data access functions are used,
1190 * otherwise data corruption may occur. The same comparison function must be used by every
1191 * program accessing the database, every time the database is used.
1192 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1193 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1194 * @param[in] cmp A #MDB_cmp_func function
1195 * @return A non-zero error value on failure and 0 on success. Some possible
1196 * errors are:
1197 * <ul>
1198 * <li>EINVAL - an invalid parameter was specified.
1199 * </ul>
1200 */
1201int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
1202
1203 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
1204 *
1205 * This comparison function is called whenever it is necessary to compare a data
1206 * item specified by the application with a data item currently stored in the database.
1207 * This function only takes effect if the database was opened with the #MDB_DUPSORT
1208 * flag.
1209 * If no comparison function is specified, and no special key flags were specified
1210 * with #mdb_dbi_open(), the data items are compared lexically, with shorter items collating
1211 * before longer items.
1212 * @warning This function must be called before any data access functions are used,
1213 * otherwise data corruption may occur. The same comparison function must be used by every
1214 * program accessing the database, every time the database is used.
1215 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1216 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1217 * @param[in] cmp A #MDB_cmp_func function
1218 * @return A non-zero error value on failure and 0 on success. Some possible
1219 * errors are:
1220 * <ul>
1221 * <li>EINVAL - an invalid parameter was specified.
1222 * </ul>
1223 */
1224int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
1225
1226 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
1227 *
1228 * @todo The relocation function is called whenever it is necessary to move the data
1229 * of an item to a different position in the database (e.g. through tree
1230 * balancing operations, shifts as a result of adds or deletes, etc.). It is
1231 * intended to allow address/position-dependent data items to be stored in
1232 * a database in an environment opened with the #MDB_FIXEDMAP option.
1233 * Currently the relocation feature is unimplemented and setting
1234 * this function has no effect.
1235 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1236 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1237 * @param[in] rel A #MDB_rel_func function
1238 * @return A non-zero error value on failure and 0 on success. Some possible
1239 * errors are:
1240 * <ul>
1241 * <li>EINVAL - an invalid parameter was specified.
1242 * </ul>
1243 */
1244int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
1245
1246 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
1247 *
1248 * See #mdb_set_relfunc and #MDB_rel_func for more details.
1249 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1250 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1251 * @param[in] ctx An arbitrary pointer for whatever the application needs.
1252 * It will be passed to the callback function set by #mdb_set_relfunc
1253 * as its \b relctx parameter whenever the callback is invoked.
1254 * @return A non-zero error value on failure and 0 on success. Some possible
1255 * errors are:
1256 * <ul>
1257 * <li>EINVAL - an invalid parameter was specified.
1258 * </ul>
1259 */
1260int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
1261
1262 /** @brief Get items from a database.
1263 *
1264 * This function retrieves key/data pairs from the database. The address
1265 * and length of the data associated with the specified \b key are returned
1266 * in the structure to which \b data refers.
1267 * If the database supports duplicate keys (#MDB_DUPSORT) then the
1268 * first data item for the key will be returned. Retrieval of other
1269 * items requires the use of #mdb_cursor_get().
1270 *
1271 * @note The memory pointed to by the returned values is owned by the
1272 * database. The caller need not dispose of the memory, and may not
1273 * modify it in any way. For values returned in a read-only transaction
1274 * any modification attempts will cause a SIGSEGV.
1275 * @note Values returned from the database are valid only until a
1276 * subsequent update operation, or the end of the transaction.
1277 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1278 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1279 * @param[in] key The key to search for in the database
1280 * @param[out] data The data corresponding to the key
1281 * @return A non-zero error value on failure and 0 on success. Some possible
1282 * errors are:
1283 * <ul>
1284 * <li>#MDB_NOTFOUND - the key was not in the database.
1285 * <li>EINVAL - an invalid parameter was specified.
1286 * </ul>
1287 */
1288int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1289
1290 /** @brief Store items into a database.
1291 *
1292 * This function stores key/data pairs in the database. The default behavior
1293 * is to enter the new key/data pair, replacing any previously existing key
1294 * if duplicates are disallowed, or adding a duplicate data item if
1295 * duplicates are allowed (#MDB_DUPSORT).
1296 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1297 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1298 * @param[in] key The key to store in the database
1299 * @param[in,out] data The data to store
1300 * @param[in] flags Special options for this operation. This parameter
1301 * must be set to 0 or by bitwise OR'ing together one or more of the
1302 * values described here.
1303 * <ul>
1304 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1305 * already appear in the database. This flag may only be specified
1306 * if the database was opened with #MDB_DUPSORT. The function will
1307 * return #MDB_KEYEXIST if the key/data pair already appears in the
1308 * database.
1309 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1310 * does not already appear in the database. The function will return
1311 * #MDB_KEYEXIST if the key already appears in the database, even if
1312 * the database supports duplicates (#MDB_DUPSORT). The \b data
1313 * parameter will be set to point to the existing item.
1314 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1315 * don't copy the given data. Instead, return a pointer to the
1316 * reserved space, which the caller can fill in later - before
1317 * the next update operation or the transaction ends. This saves
1318 * an extra memcpy if the data is being generated later.
1319 * LMDB does nothing else with this memory, the caller is expected
1320 * to modify all of the space requested. This flag must not be
1321 * specified if the database was opened with #MDB_DUPSORT.
1322 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1323 * database. This option allows fast bulk loading when keys are
1324 * already known to be in the correct order. Loading unsorted keys
1325 * with this flag will cause a #MDB_KEYEXIST error.
1326 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1327 * </ul>
1328 * @return A non-zero error value on failure and 0 on success. Some possible
1329 * errors are:
1330 * <ul>
1331 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1332 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1333 * <li>EACCES - an attempt was made to write in a read-only transaction.
1334 * <li>EINVAL - an invalid parameter was specified.
1335 * </ul>
1336 */
1337int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
1338 unsigned int flags);
1339
1340 /** @brief Delete items from a database.
1341 *
1342 * This function removes key/data pairs from the database.
1343 * If the database does not support sorted duplicate data items
1344 * (#MDB_DUPSORT) the data parameter is ignored.
1345 * If the database supports sorted duplicates and the data parameter
1346 * is NULL, all of the duplicate data items for the key will be
1347 * deleted. Otherwise, if the data parameter is non-NULL
1348 * only the matching data item will be deleted.
1349 * This function will return #MDB_NOTFOUND if the specified key/data
1350 * pair is not in the database.
1351 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1352 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1353 * @param[in] key The key to delete from the database
1354 * @param[in] data The data to delete
1355 * @return A non-zero error value on failure and 0 on success. Some possible
1356 * errors are:
1357 * <ul>
1358 * <li>EACCES - an attempt was made to write in a read-only transaction.
1359 * <li>EINVAL - an invalid parameter was specified.
1360 * </ul>
1361 */
1362int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1363
1364 /** @brief Create a cursor handle.
1365 *
1366 * A cursor is associated with a specific transaction and database.
1367 * A cursor cannot be used when its database handle is closed. Nor
1368 * when its transaction has ended, except with #mdb_cursor_renew().
1369 * It can be discarded with #mdb_cursor_close().
1370 * A cursor in a write-transaction can be closed before its transaction
1371 * ends, and will otherwise be closed when its transaction ends.
1372 * A cursor in a read-only transaction must be closed explicitly, before
1373 * or after its transaction ends. It can be reused with
1374 * #mdb_cursor_renew() before finally closing it.
1375 * @note Earlier documentation said that cursors in every transaction
1376 * were closed when the transaction committed or aborted.
1377 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1378 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1379 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
1380 * @return A non-zero error value on failure and 0 on success. Some possible
1381 * errors are:
1382 * <ul>
1383 * <li>EINVAL - an invalid parameter was specified.
1384 * </ul>
1385 */
1386int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
1387
1388 /** @brief Close a cursor handle.
1389 *
1390 * The cursor handle will be freed and must not be used again after this call.
1391 * Its transaction must still be live if it is a write-transaction.
1392 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1393 */
1394void mdb_cursor_close(MDB_cursor *cursor);
1395
1396 /** @brief Renew a cursor handle.
1397 *
1398 * A cursor is associated with a specific transaction and database.
1399 * Cursors that are only used in read-only
1400 * transactions may be re-used, to avoid unnecessary malloc/free overhead.
1401 * The cursor may be associated with a new read-only transaction, and
1402 * referencing the same database handle as it was created with.
1403 * This may be done whether the previous transaction is live or dead.
1404 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1405 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1406 * @return A non-zero error value on failure and 0 on success. Some possible
1407 * errors are:
1408 * <ul>
1409 * <li>EINVAL - an invalid parameter was specified.
1410 * </ul>
1411 */
1412int mdb_cursor_renew(MDB_txn *txn, MDB_cursor *cursor);
1413
1414 /** @brief Return the cursor's transaction handle.
1415 *
1416 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1417 */
1418MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
1419
1420 /** @brief Return the cursor's database handle.
1421 *
1422 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1423 */
1424MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor);
1425
1426 /** @brief Retrieve by cursor.
1427 *
1428 * This function retrieves key/data pairs from the database. The address and length
1429 * of the key are returned in the object to which \b key refers (except for the
1430 * case of the #MDB_SET option, in which the \b key object is unchanged), and
1431 * the address and length of the data are returned in the object to which \b data
1432 * refers.
1433 * See #mdb_get() for restrictions on using the output values.
1434 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1435 * @param[in,out] key The key for a retrieved item
1436 * @param[in,out] data The data of a retrieved item
1437 * @param[in] op A cursor operation #MDB_cursor_op
1438 * @return A non-zero error value on failure and 0 on success. Some possible
1439 * errors are:
1440 * <ul>
1441 * <li>#MDB_NOTFOUND - no matching key found.
1442 * <li>EINVAL - an invalid parameter was specified.
1443 * </ul>
1444 */
1445int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1446 MDB_cursor_op op);
1447
1448 /** @brief Store by cursor.
1449 *
1450 * This function stores key/data pairs into the database.
1451 * The cursor is positioned at the new item, or on failure usually near it.
1452 * @note Earlier documentation incorrectly said errors would leave the
1453 * state of the cursor unchanged.
1454 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1455 * @param[in] key The key operated on.
1456 * @param[in] data The data operated on.
1457 * @param[in] flags Options for this operation. This parameter
1458 * must be set to 0 or one of the values described here.
1459 * <ul>
1460 * <li>#MDB_CURRENT - replace the item at the current cursor position.
1461 * The \b key parameter must still be provided, and must match it.
1462 * If using sorted duplicates (#MDB_DUPSORT) the data item must still
1463 * sort into the same place. This is intended to be used when the
1464 * new data is the same size as the old. Otherwise it will simply
1465 * perform a delete of the old record followed by an insert.
1466 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1467 * already appear in the database. This flag may only be specified
1468 * if the database was opened with #MDB_DUPSORT. The function will
1469 * return #MDB_KEYEXIST if the key/data pair already appears in the
1470 * database.
1471 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1472 * does not already appear in the database. The function will return
1473 * #MDB_KEYEXIST if the key already appears in the database, even if
1474 * the database supports duplicates (#MDB_DUPSORT).
1475 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1476 * don't copy the given data. Instead, return a pointer to the
1477 * reserved space, which the caller can fill in later - before
1478 * the next update operation or the transaction ends. This saves
1479 * an extra memcpy if the data is being generated later. This flag
1480 * must not be specified if the database was opened with #MDB_DUPSORT.
1481 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1482 * database. No key comparisons are performed. This option allows
1483 * fast bulk loading when keys are already known to be in the
1484 * correct order. Loading unsorted keys with this flag will cause
1485 * a #MDB_KEYEXIST error.
1486 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1487 * <li>#MDB_MULTIPLE - store multiple contiguous data elements in a
1488 * single request. This flag may only be specified if the database
1489 * was opened with #MDB_DUPFIXED. The \b data argument must be an
1490 * array of two MDB_vals. The mv_size of the first MDB_val must be
1491 * the size of a single data element. The mv_data of the first MDB_val
1492 * must point to the beginning of the array of contiguous data elements.
1493 * The mv_size of the second MDB_val must be the count of the number
1494 * of data elements to store. On return this field will be set to
1495 * the count of the number of elements actually written. The mv_data
1496 * of the second MDB_val is unused.
1497 * </ul>
1498 * @return A non-zero error value on failure and 0 on success. Some possible
1499 * errors are:
1500 * <ul>
1501 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1502 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1503 * <li>EACCES - an attempt was made to write in a read-only transaction.
1504 * <li>EINVAL - an invalid parameter was specified.
1505 * </ul>
1506 */
1507int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1508 unsigned int flags);
1509
1510 /** @brief Delete current key/data pair
1511 *
1512 * This function deletes the key/data pair to which the cursor refers.
1513 * This does not invalidate the cursor, so operations such as MDB_NEXT
1514 * can still be used on it.
1515 * Both MDB_NEXT and MDB_GET_CURRENT will return the same record after
1516 * this operation.
1517 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1518 * @param[in] flags Options for this operation. This parameter
1519 * must be set to 0 or one of the values described here.
1520 * <ul>
1521 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
1522 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
1523 * </ul>
1524 * @return A non-zero error value on failure and 0 on success. Some possible
1525 * errors are:
1526 * <ul>
1527 * <li>EACCES - an attempt was made to write in a read-only transaction.
1528 * <li>EINVAL - an invalid parameter was specified.
1529 * </ul>
1530 */
1531int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
1532
1533 /** @brief Return count of duplicates for current key.
1534 *
1535 * This call is only valid on databases that support sorted duplicate
1536 * data items #MDB_DUPSORT.
1537 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1538 * @param[out] countp Address where the count will be stored
1539 * @return A non-zero error value on failure and 0 on success. Some possible
1540 * errors are:
1541 * <ul>
1542 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
1543 * </ul>
1544 */
1545int mdb_cursor_count(MDB_cursor *cursor, size_t *countp);
1546
1547 /** @brief Compare two data items according to a particular database.
1548 *
1549 * This returns a comparison as if the two data items were keys in the
1550 * specified database.
1551 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1552 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1553 * @param[in] a The first item to compare
1554 * @param[in] b The second item to compare
1555 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1556 */
1557int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1558
1559 /** @brief Compare two data items according to a particular database.
1560 *
1561 * This returns a comparison as if the two items were data items of
1562 * the specified database. The database must have the #MDB_DUPSORT flag.
1563 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1564 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1565 * @param[in] a The first item to compare
1566 * @param[in] b The second item to compare
1567 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1568 */
1569int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1570
1571 /** @brief A callback function used to print a message from the library.
1572 *
1573 * @param[in] msg The string to be printed.
1574 * @param[in] ctx An arbitrary context pointer for the callback.
1575 * @return < 0 on failure, >= 0 on success.
1576 */
1577typedef int (MDB_msg_func)(const char *msg, void *ctx);
1578
1579 /** @brief Dump the entries in the reader lock table.
1580 *
1581 * @param[in] env An environment handle returned by #mdb_env_create()
1582 * @param[in] func A #MDB_msg_func function
1583 * @param[in] ctx Anything the message function needs
1584 * @return < 0 on failure, >= 0 on success.
1585 */
1586int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx);
1587
1588 /** @brief Check for stale entries in the reader lock table.
1589 *
1590 * @param[in] env An environment handle returned by #mdb_env_create()
1591 * @param[out] dead Number of stale slots that were cleared
1592 * @return 0 on success, non-zero on failure.
1593 */
1594int mdb_reader_check(MDB_env *env, int *dead);
1595/** @} */
1596
1597#ifdef __cplusplus
1598}
1599#endif
1600/** @page tools LMDB Command Line Tools
1601 The following describes the command line tools that are available for LMDB.
1602 \li \ref mdb_copy_1
1603 \li \ref mdb_dump_1
1604 \li \ref mdb_load_1
1605 \li \ref mdb_stat_1
1606*/
1607
1608#endif /* _LMDB_H_ */
1609