lmdb.h 69.8 KB
Newer Older
Howard Chu's avatar
Howard Chu committed
1
2
/** @file lmdb.h
 *	@brief Lightning memory-mapped database library
3
 *
Howard Chu's avatar
Howard Chu committed
4
 *	@mainpage	Lightning Memory-Mapped Database Manager (LMDB)
Howard Chu's avatar
Howard Chu committed
5
6
 *
 *	@section intro_sec Introduction
Howard Chu's avatar
Howard Chu committed
7
 *	LMDB is a Btree-based database management library modeled loosely on the
8
 *	BerkeleyDB API, but much simplified. The entire database is exposed
Howard Chu's avatar
Howard Chu committed
9
 *	in a memory map, and all data fetches return data directly
10
11
12
13
 *	from the mapped memory, so no malloc's or memcpy's occur during
 *	data fetches. As such, the library is extremely simple because it
 *	requires no page caching layer of its own, and it is extremely high
 *	performance and memory-efficient. It is also fully transactional with
Howard Chu's avatar
Howard Chu committed
14
 *	full ACID semantics, and when the memory map is read-only, the
15
16
17
18
19
20
21
22
23
24
25
26
27
28
 *	database integrity cannot be corrupted by stray pointer writes from
 *	application code.
 *
 *	The library is fully thread-aware and supports concurrent read/write
 *	access from multiple processes and threads. Data pages use a copy-on-
 *	write strategy so no active data pages are ever overwritten, which
 *	also provides resistance to corruption and eliminates the need of any
 *	special recovery procedures after a system crash. Writes are fully
 *	serialized; only one write transaction may be active at a time, which
 *	guarantees that writers can never deadlock. The database structure is
 *	multi-versioned so readers run with no locks; writers cannot block
 *	readers, and readers don't block writers.
 *
 *	Unlike other well-known database mechanisms which use either write-ahead
Howard Chu's avatar
Howard Chu committed
29
 *	transaction logs or append-only data writes, LMDB requires no maintenance
30
31
 *	during operation. Both write-ahead loggers and append-only databases
 *	require periodic checkpointing and/or compaction of their log or database
Howard Chu's avatar
Howard Chu committed
32
 *	files otherwise they grow without bound. LMDB tracks free pages within
33
34
35
 *	the database and re-uses them for new write operations, so the database
 *	size does not grow without bound in normal use.
 *
Howard Chu's avatar
Howard Chu committed
36
37
38
39
40
41
42
 *	The memory map can be used as a read-only or read-write map. It is
 *	read-only by default as this provides total immunity to corruption.
 *	Using read-write mode offers much higher write performance, but adds
 *	the possibility for stray application writes thru pointers to silently
 *	corrupt the database. Of course if your application code is known to
 *	be bug-free (...) then this is not an issue.
 *
Howard Chu's avatar
Howard Chu committed
43
 *	@section caveats_sec Caveats
44
45
46
47
48
49
50
 *	Troubleshooting the lock file, plus semaphores on BSD systems:
 *
 *	- A broken lockfile can cause sync issues.
 *	  Stale reader transactions left behind by an aborted program
 *	  cause further writes to grow the database quickly, and
 *	  stale locks can block further operation.
 *
51
 *	  Fix: Check for stale readers periodically, using the
Howard Chu's avatar
Howard Chu committed
52
 *	  #mdb_reader_check function or the \ref mdb_stat_1 "mdb_stat" tool. Or just
53
54
 *	  make all programs using the database close it; the lockfile
 *	  is always reset on first open of the environment.
55
56
57
58
59
60
61
62
63
64
65
66
67
68
 *
 *	- On BSD systems or others configured with MDB_USE_POSIX_SEM,
 *	  startup can fail due to semaphores owned by another userid.
 *
 *	  Fix: Open and close the database as the user which owns the
 *	  semaphores (likely last user) or as root, while no other
 *	  process is using the database.
 *
 *	Restrictions/caveats (in addition to those listed for some functions):
 *
 *	- Only the database owner should normally use the database on
 *	  BSD systems or when otherwise configured with MDB_USE_POSIX_SEM.
 *	  Multiple users can cause startup to fail later, as noted above.
 *
69
70
71
72
 *	- There is normally no pure read-only mode, since readers need write
 *	  access to locks and lock file. Exceptions: On read-only filesystems
 *	  or with the #MDB_NOLOCK flag described under #mdb_env_open().
 *
Howard Chu's avatar
Howard Chu committed
73
74
 *	- By default, in versions before 0.9.10, unused portions of the data
 *	  file might receive garbage data from memory freed by other code.
Howard Chu's avatar
Howard Chu committed
75
 *	  (This does not happen when using the #MDB_WRITEMAP flag.) As of
Howard Chu's avatar
Howard Chu committed
76
77
78
79
 *	  0.9.10 the default behavior is to initialize such memory before
 *	  writing to the data file. Since there may be a slight performance
 *	  cost due to this initialization, applications may disable it using
 *	  the #MDB_NOMEMINIT flag. Applications handling sensitive data
Howard Chu's avatar
Howard Chu committed
80
81
 *	  which must not be written should not use this flag. This flag is
 *	  irrelevant when using #MDB_WRITEMAP.
Hallvard Furuseth's avatar
Hallvard Furuseth committed
82
 *
83
84
 *	- A thread can only use one transaction at a time, plus any child
 *	  transactions.  Each transaction belongs to one thread.  See below.
Howard Chu's avatar
Howard Chu committed
85
 *	  The #MDB_NOTLS flag changes this for read-only transactions.
86
87
88
 *
 *	- Use an MDB_env* in the process which opened it, without fork()ing.
 *
Howard Chu's avatar
Howard Chu committed
89
 *	- Do not have open an LMDB database twice in the same process at
90
91
92
93
94
95
96
97
98
 *	  the same time.  Not even from a plain open() call - close()ing it
 *	  breaks flock() advisory locking.
 *
 *	- Avoid long-lived transactions.  Read transactions prevent
 *	  reuse of pages freed by newer write transactions, thus the
 *	  database can grow quickly.  Write transactions prevent
 *	  other write transactions, since writes are serialized.
 *
 *	- Avoid suspending a process with active transactions.  These
99
100
101
102
 *	  would then be "long-lived" as above.  Also read transactions
 *	  suspended when writers commit could sometimes see wrong data.
 *
 *	...when several processes can use a database concurrently:
103
104
 *
 *	- Avoid aborting a process with an active transaction.
105
106
107
 *	  The transaction becomes "long-lived" as above until a check
 *	  for stale readers is performed or the lockfile is reset,
 *	  since the process may not remove it from the lockfile.
108
 *
109
110
 *	- If you do that anyway, do a periodic check for stale readers. Or
 *	  close the environment once in a while, so the lockfile can get reset.
111
 *
Howard Chu's avatar
Howard Chu committed
112
 *	- Do not use LMDB databases on remote filesystems, even between
Hallvard Furuseth's avatar
Hallvard Furuseth committed
113
114
115
 *	  processes on the same host.  This breaks flock() on some OSes,
 *	  possibly memory map sync, and certainly sync between programs
 *	  on different hosts.
116
117
118
119
 *
 *	- Opening a database can fail if another process is opening or
 *	  closing it at exactly the same time.
 *
120
121
 *	@author	Howard Chu, Symas Corporation.
 *
Quanah Gibson-Mount's avatar
Quanah Gibson-Mount committed
122
 *	@copyright Copyright 2011-2015 Howard Chu, Symas Corp. All rights reserved.
Howard Chu's avatar
Howard Chu committed
123
124
125
126
127
128
129
130
131
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted only as authorized by the OpenLDAP
 * Public License.
 *
 * A copy of this license is available in the file LICENSE in the
 * top-level directory of the distribution or, alternatively, at
 * <http://www.OpenLDAP.org/license.html>.
 *
Howard Chu's avatar
Howard Chu committed
132
 *	@par Derived From:
Howard Chu's avatar
Howard Chu committed
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
 * This code is derived from btree.c written by Martin Hedenfalk.
 *
 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
Howard Chu's avatar
Howard Chu committed
149
150
#ifndef _LMDB_H_
#define _LMDB_H_
Howard Chu's avatar
Howard Chu committed
151
152
153

#include <sys/types.h>

154
155
156
157
#ifdef __cplusplus
extern "C" {
#endif

158
/** Unix permissions for creating files, or dummy definition for Windows */
Howard Chu's avatar
Howard Chu committed
159
#ifdef _MSC_VER
160
161
162
typedef	int	mdb_mode_t;
#else
typedef	mode_t	mdb_mode_t;
Howard Chu's avatar
Howard Chu committed
163
164
#endif

165
166
167
168
169
170
171
172
/** An abstraction for a file handle.
 *	On POSIX systems file handles are small integers. On Windows
 *	they're opaque pointers.
 */
#ifdef _WIN32
typedef	void *mdb_filehandle_t;
#else
typedef int mdb_filehandle_t;
Howard Chu's avatar
Howard Chu committed
173
174
#endif

Howard Chu's avatar
Howard Chu committed
175
/** @defgroup mdb LMDB API
176
 *	@{
Howard Chu's avatar
Howard Chu committed
177
 *	@brief OpenLDAP Lightning Memory-Mapped Database Manager
178
 */
179
180
181
182
/** @defgroup Version Version Macros
 *	@{
 */
/** Library major version */
183
#define MDB_VERSION_MAJOR	0
184
/** Library minor version */
Howard Chu's avatar
Howard Chu committed
185
#define MDB_VERSION_MINOR	9
186
/** Library patch version */
Howard Chu's avatar
Howard Chu committed
187
#define MDB_VERSION_PATCH	15
188
189

/** Combine args a,b,c into a single integer for easy version comparisons */
190
#define MDB_VERINT(a,b,c)	(((a) << 24) | ((b) << 16) | (c))
191
192

/** The full library version as a single integer */
Howard Chu's avatar
Howard Chu committed
193
194
#define MDB_VERSION_FULL	\
	MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
195
196

/** The release date of this library version */
Howard Chu's avatar
Howard Chu committed
197
#define MDB_VERSION_DATE	"June 19, 2015"
198
199

/** A stringifier for the version info */
Howard Chu's avatar
Howard Chu committed
200
#define MDB_VERSTR(a,b,c,d)	"LMDB " #a "." #b "." #c ": (" d ")"
201
202

/** A helper for the stringifier macro */
Howard Chu's avatar
Howard Chu committed
203
#define MDB_VERFOO(a,b,c,d)	MDB_VERSTR(a,b,c,d)
204
205

/** The full library version as a C string */
Howard Chu's avatar
Howard Chu committed
206
207
#define	MDB_VERSION_STRING	\
	MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
208
/**	@} */
209

210
211
212
213
/** @brief Opaque structure for a database environment.
 *
 * A DB environment supports multiple databases, all residing in the same
 * shared-memory map.
Howard Chu's avatar
Howard Chu committed
214
215
 */
typedef struct MDB_env MDB_env;
216

217
218
219
220
/** @brief Opaque structure for a transaction handle.
 *
 * All database operations require a transaction handle. Transactions may be
 * read-only or read-write.
221
 */
Howard Chu's avatar
Howard Chu committed
222
typedef struct MDB_txn MDB_txn;
223

224
/** @brief A handle for an individual database in the DB environment. */
Howard Chu's avatar
Howard Chu committed
225
226
typedef unsigned int	MDB_dbi;

227
/** @brief Opaque structure for navigating through a database */
Howard Chu's avatar
Howard Chu committed
228
229
typedef struct MDB_cursor MDB_cursor;

230
231
232
/** @brief Generic structure used for passing keys and data in and out
 * of the database.
 *
233
 * Values returned from the database are valid only until a subsequent
234
235
236
237
238
239
 * update operation, or the end of the transaction. Do not modify or
 * free them, they commonly point into the database itself.
 *
 * Key sizes must be between 1 and #mdb_env_get_maxkeysize() inclusive.
 * The same applies to data sizes in databases with the #MDB_DUPSORT flag.
 * Other data items can in theory be from 0 to 0xffffffff bytes long.
240
 */
Howard Chu's avatar
Howard Chu committed
241
typedef struct MDB_val {
242
243
	size_t		 mv_size;	/**< size of the data item */
	void		*mv_data;	/**< address of the data item */
Howard Chu's avatar
Howard Chu committed
244
245
} MDB_val;

246
/** @brief A callback function used to compare two keys in a database */
Howard Chu's avatar
Howard Chu committed
247
typedef int  (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
248

249
250
251
252
/** @brief A callback function used to relocate a position-dependent data item
 * in a fixed-address database.
 *
 * The \b newptr gives the item's desired address in
253
254
255
 * the memory map, and \b oldptr gives its previous address. The item's actual
 * data resides at the address in \b item.  This callback is expected to walk
 * through the fields of the record in \b item and modify any
Howard Chu's avatar
Howard Chu committed
256
 * values based at the \b oldptr address to be relative to the \b newptr address.
257
258
259
260
 * @param[in,out] item The item that is to be relocated.
 * @param[in] oldptr The previous address.
 * @param[in] newptr The new address to relocate to.
 * @param[in] relctx An application-provided context, set by #mdb_set_relctx().
Howard Chu's avatar
Howard Chu committed
261
 * @todo This feature is currently unimplemented.
262
 */
263
typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
Howard Chu's avatar
Howard Chu committed
264

265
/** @defgroup	mdb_env	Environment Flags
Howard Chu's avatar
Howard Chu committed
266
267
 *	@{
 */
268
	/** mmap at a fixed address (experimental) */
Howard Chu's avatar
Howard Chu committed
269
#define MDB_FIXEDMAP	0x01
Howard Chu's avatar
Howard Chu committed
270
	/** no environment directory */
271
#define MDB_NOSUBDIR	0x4000
Howard Chu's avatar
Howard Chu committed
272
273
274
275
	/** don't fsync after commit */
#define MDB_NOSYNC		0x10000
	/** read only */
#define MDB_RDONLY		0x20000
Howard Chu's avatar
Howard Chu committed
276
277
	/** don't fsync metapage after commit */
#define MDB_NOMETASYNC		0x40000
278
279
	/** use writable mmap */
#define MDB_WRITEMAP		0x80000
Howard Chu's avatar
Howard Chu committed
280
	/** use asynchronous msync when #MDB_WRITEMAP is used */
281
#define MDB_MAPASYNC		0x100000
Howard Chu's avatar
Howard Chu committed
282
283
	/** tie reader locktable slots to #MDB_txn objects instead of to threads */
#define MDB_NOTLS		0x200000
Howard Chu's avatar
Howard Chu committed
284
285
	/** don't do any locking, caller must manage their own locks */
#define MDB_NOLOCK		0x400000
286
287
	/** don't do readahead (no effect on Windows) */
#define MDB_NORDAHEAD	0x800000
Howard Chu's avatar
Howard Chu committed
288
289
	/** don't initialize malloc'd memory before writing to datafile */
#define MDB_NOMEMINIT	0x1000000
Howard Chu's avatar
Howard Chu committed
290
291
/** @} */

292
/**	@defgroup	mdb_dbi_open	Database Flags
Howard Chu's avatar
Howard Chu committed
293
294
295
296
297
298
 *	@{
 */
	/** use reverse string keys */
#define MDB_REVERSEKEY	0x02
	/** use sorted duplicates */
#define MDB_DUPSORT		0x04
299
	/** numeric keys in native byte order: either unsigned int or size_t.
300
	 *  The keys must all be of the same size. */
Howard Chu's avatar
Howard Chu committed
301
302
303
#define MDB_INTEGERKEY	0x08
	/** with #MDB_DUPSORT, sorted dup items have fixed size */
#define MDB_DUPFIXED	0x10
304
	/** with #MDB_DUPSORT, dups are #MDB_INTEGERKEY-style integers */
Howard Chu's avatar
Howard Chu committed
305
#define MDB_INTEGERDUP	0x20
Howard Chu's avatar
Howard Chu committed
306
307
	/** with #MDB_DUPSORT, use reverse string dups */
#define MDB_REVERSEDUP	0x40
Howard Chu's avatar
Howard Chu committed
308
309
310
	/** create DB if not already existing */
#define MDB_CREATE		0x40000
/** @} */
Howard Chu's avatar
Howard Chu committed
311

312
/**	@defgroup mdb_put	Write Flags
313
314
 *	@{
 */
315
/** For put: Don't write if the key already exists. */
Howard Chu's avatar
Howard Chu committed
316
#define MDB_NOOVERWRITE	0x10
317
318
319
/** Only for #MDB_DUPSORT<br>
 * For put: don't write if the key and data pair already exist.<br>
 * For mdb_cursor_del: remove all duplicate data items.
320
 */
Howard Chu's avatar
Howard Chu committed
321
#define MDB_NODUPDATA	0x20
322
323
/** For mdb_cursor_put: overwrite the current key/data pair */
#define MDB_CURRENT	0x40
Howard Chu's avatar
Howard Chu committed
324
325
326
327
/** For put: Just reserve space for data, don't copy it. Return a
 * pointer to the reserved space.
 */
#define MDB_RESERVE	0x10000
328
329
/** Data is being appended, don't split full pages. */
#define MDB_APPEND	0x20000
Howard Chu's avatar
Howard Chu committed
330
331
/** Duplicate data is being appended, don't split full pages. */
#define MDB_APPENDDUP	0x40000
Howard Chu's avatar
Howard Chu committed
332
/** Store multiple data items in one call. Only for #MDB_DUPFIXED. */
Howard Chu's avatar
Howard Chu committed
333
#define MDB_MULTIPLE	0x80000
334
335
/*	@} */

Howard Chu's avatar
Howard Chu committed
336
337
338
339
340
341
342
343
344
/**	@defgroup mdb_copy	Copy Flags
 *	@{
 */
/** Compacting copy: Omit free space from copy, and renumber all
 * pages sequentially.
 */
#define MDB_CP_COMPACT	0x01
/*	@} */

345
346
/** @brief Cursor Get operations.
 *
347
348
349
 *	This is the set of all operations for retrieving data
 *	using a cursor.
 */
350
351
typedef enum MDB_cursor_op {
	MDB_FIRST,				/**< Position at first key/data item */
352
353
	MDB_FIRST_DUP,			/**< Position at first data item of current key.
								Only for #MDB_DUPSORT */
354
355
	MDB_GET_BOTH,			/**< Position at key/data pair. Only for #MDB_DUPSORT */
	MDB_GET_BOTH_RANGE,		/**< position at key, nearest data. Only for #MDB_DUPSORT */
Howard Chu's avatar
Howard Chu committed
356
	MDB_GET_CURRENT,		/**< Return key/data at current cursor position */
357
358
359
	MDB_GET_MULTIPLE,		/**< Return key and up to a page of duplicate data items
								from current cursor position. Move cursor to prepare
								for #MDB_NEXT_MULTIPLE. Only for #MDB_DUPFIXED */
360
	MDB_LAST,				/**< Position at last key/data item */
361
362
	MDB_LAST_DUP,			/**< Position at last data item of current key.
								Only for #MDB_DUPSORT */
363
364
365
	MDB_NEXT,				/**< Position at next data item */
	MDB_NEXT_DUP,			/**< Position at next data item of current key.
								Only for #MDB_DUPSORT */
366
367
368
	MDB_NEXT_MULTIPLE,		/**< Return key and up to a page of duplicate data items
								from next cursor position. Move cursor to prepare
								for #MDB_NEXT_MULTIPLE. Only for #MDB_DUPFIXED */
369
	MDB_NEXT_NODUP,			/**< Position at first data item of next key */
370
371
372
	MDB_PREV,				/**< Position at previous data item */
	MDB_PREV_DUP,			/**< Position at previous data item of current key.
								Only for #MDB_DUPSORT */
373
	MDB_PREV_NODUP,			/**< Position at last data item of previous key */
374
	MDB_SET,				/**< Position at specified key */
Howard Chu's avatar
Howard Chu committed
375
	MDB_SET_KEY,			/**< Position at specified key, return key + data */
376
	MDB_SET_RANGE			/**< Position at first key greater than or equal to specified key. */
Howard Chu's avatar
Howard Chu committed
377
378
} MDB_cursor_op;

379
380
381
382
383
384
/** @defgroup  errors	Return Codes
 *
 *	BerkeleyDB uses -30800 to -30999, we'll go under them
 *	@{
 */
	/**	Successful result */
Howard Chu's avatar
Howard Chu committed
385
#define MDB_SUCCESS	 0
386
387
388
389
390
391
392
393
	/** key/data pair already exists */
#define MDB_KEYEXIST	(-30799)
	/** key/data pair not found (EOF) */
#define MDB_NOTFOUND	(-30798)
	/** Requested page not found - this usually indicates corruption */
#define MDB_PAGE_NOTFOUND	(-30797)
	/** Located page was wrong type */
#define MDB_CORRUPTED	(-30796)
394
	/** Update of meta page failed, probably I/O error */
395
396
397
#define MDB_PANIC		(-30795)
	/** Environment version mismatch */
#define MDB_VERSION_MISMATCH	(-30794)
Howard Chu's avatar
Howard Chu committed
398
	/** File is not a valid LMDB file */
399
400
401
402
403
404
405
406
407
#define MDB_INVALID	(-30793)
	/** Environment mapsize reached */
#define MDB_MAP_FULL	(-30792)
	/** Environment maxdbs reached */
#define MDB_DBS_FULL	(-30791)
	/** Environment maxreaders reached */
#define MDB_READERS_FULL	(-30790)
	/** Too many TLS keys in use - Windows only */
#define MDB_TLS_FULL	(-30789)
408
	/** Txn has too many dirty pages */
409
410
411
412
413
#define MDB_TXN_FULL	(-30788)
	/** Cursor stack too deep - internal error */
#define MDB_CURSOR_FULL	(-30787)
	/** Page has not enough space - internal error */
#define MDB_PAGE_FULL	(-30786)
414
	/** Database contents grew beyond environment mapsize */
415
#define MDB_MAP_RESIZED	(-30785)
416
	/** MDB_INCOMPATIBLE: Operation and DB incompatible, or DB flags changed */
417
#define MDB_INCOMPATIBLE	(-30784)
418
419
	/** Invalid reuse of reader locktable slot */
#define MDB_BAD_RSLOT		(-30783)
420
421
	/** Transaction cannot recover - it must be aborted */
#define MDB_BAD_TXN			(-30782)
422
	/** Unsupported size of key/DB name/data, or wrong DUPFIXED size */
423
#define MDB_BAD_VALSIZE		(-30781)
424
425
426
427
	/** The specified DBI was changed unexpectedly */
#define MDB_BAD_DBI		(-30780)
	/** The last defined error code */
#define MDB_LAST_ERRCODE	MDB_BAD_DBI
428
429
/** @} */

430
/** @brief Statistics for a database in the environment */
Howard Chu's avatar
Howard Chu committed
431
typedef struct MDB_stat {
432
433
434
	unsigned int	ms_psize;			/**< Size of a database page.
											This is currently the same for all databases. */
	unsigned int	ms_depth;			/**< Depth (height) of the B-tree */
435
436
437
438
	size_t		ms_branch_pages;	/**< Number of internal (non-leaf) pages */
	size_t		ms_leaf_pages;		/**< Number of leaf pages */
	size_t		ms_overflow_pages;	/**< Number of overflow pages */
	size_t		ms_entries;			/**< Number of data items */
Howard Chu's avatar
Howard Chu committed
439
440
} MDB_stat;

441
442
/** @brief Information about the environment */
typedef struct MDB_envinfo {
Howard Chu's avatar
Howard Chu committed
443
	void	*me_mapaddr;			/**< Address of map, if fixed */
444
445
	size_t	me_mapsize;				/**< Size of the data memory map */
	size_t	me_last_pgno;			/**< ID of the last used page */
Howard Chu's avatar
Howard Chu committed
446
	size_t	me_last_txnid;			/**< ID of the last committed transaction */
Howard Chu's avatar
Howard Chu committed
447
448
	unsigned int me_maxreaders;		/**< max reader slots in the environment */
	unsigned int me_numreaders;		/**< max reader slots used in the environment */
449
450
} MDB_envinfo;

Howard Chu's avatar
Howard Chu committed
451
	/** @brief Return the LMDB library version information.
452
	 *
453
454
455
456
457
	 * @param[out] major if non-NULL, the library major version number is copied here
	 * @param[out] minor if non-NULL, the library minor version number is copied here
	 * @param[out] patch if non-NULL, the library patch version number is copied here
	 * @retval "version string" The library version as a string
	 */
Howard Chu's avatar
Howard Chu committed
458
char *mdb_version(int *major, int *minor, int *patch);
459

460
461
	/** @brief Return a string describing a given error code.
	 *
462
463
464
	 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
	 * function. If the error code is greater than or equal to 0, then the string
	 * returned by the system function strerror(3) is returned. If the error code
Howard Chu's avatar
Howard Chu committed
465
466
	 * is less than 0, an error string corresponding to the LMDB library error is
	 * returned. See @ref errors for a list of LMDB-specific error codes.
467
468
469
	 * @param[in] err The error code
	 * @retval "error message" The description of the error
	 */
470
char *mdb_strerror(int err);
471

Howard Chu's avatar
Howard Chu committed
472
	/** @brief Create an LMDB environment handle.
473
	 *
474
475
476
477
478
479
480
481
482
	 * This function allocates memory for a #MDB_env structure. To release
	 * the allocated memory and discard the handle, call #mdb_env_close().
	 * Before the handle may be used, it must be opened using #mdb_env_open().
	 * Various other options may also need to be set before opening the handle,
	 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
	 * depending on usage requirements.
	 * @param[out] env The address where the new handle will be stored
	 * @return A non-zero error value on failure and 0 on success.
	 */
Howard Chu's avatar
Howard Chu committed
483
int  mdb_env_create(MDB_env **env);
484

485
486
	/** @brief Open an environment handle.
	 *
487
488
	 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
	 * @param[in] env An environment handle returned by #mdb_env_create()
Howard Chu's avatar
Howard Chu committed
489
490
	 * @param[in] path The directory in which the database files reside. This
	 * directory must already exist and be writable.
491
492
493
	 * @param[in] flags Special options for this environment. This parameter
	 * must be set to 0 or by bitwise OR'ing together one or more of the
	 * values described here.
494
	 * Flags set by mdb_env_set_flags() are also used.
495
496
497
498
499
500
501
502
503
	 * <ul>
	 *	<li>#MDB_FIXEDMAP
	 *      use a fixed address for the mmap region. This flag must be specified
	 *      when creating the environment, and is stored persistently in the environment.
	 *		If successful, the memory map will always reside at the same virtual address
	 *		and pointers used to reference data items in the database will be constant
	 *		across multiple invocations. This option may not always work, depending on
	 *		how the operating system has allocated memory to shared libraries and other uses.
	 *		The feature is highly experimental.
504
	 *	<li>#MDB_NOSUBDIR
Howard Chu's avatar
Howard Chu committed
505
	 *		By default, LMDB creates its environment in a directory whose
506
507
508
509
	 *		pathname is given in \b path, and creates its data and lock files
	 *		under that directory. With this option, \b path is used as-is for
	 *		the database main data file. The database lock file is the \b path
	 *		with "-lock" appended.
510
	 *	<li>#MDB_RDONLY
511
	 *		Open the environment in read-only mode. No write operations will be
Howard Chu's avatar
Howard Chu committed
512
513
	 *		allowed. LMDB will still modify the lock file - except on read-only
	 *		filesystems, where LMDB does not use locks.
514
515
516
517
518
	 *	<li>#MDB_WRITEMAP
	 *		Use a writeable memory map unless MDB_RDONLY is set. This is faster
	 *		and uses fewer mallocs, but loses protection from application bugs
	 *		like wild pointer writes and other bad updates into the database.
	 *		Incompatible with nested transactions.
519
520
	 *		Do not mix processes with and without MDB_WRITEMAP on the same
	 *		environment.  This can defeat durability (#mdb_env_sync etc).
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
	 *	<li>#MDB_NOMETASYNC
	 *		Flush system buffers to disk only once per transaction, omit the
	 *		metadata flush. Defer that until the system flushes files to disk,
	 *		or next non-MDB_RDONLY commit or #mdb_env_sync(). This optimization
	 *		maintains database integrity, but a system crash may undo the last
	 *		committed transaction. I.e. it preserves the ACI (atomicity,
	 *		consistency, isolation) but not D (durability) database property.
	 *		This flag may be changed at any time using #mdb_env_set_flags().
	 *	<li>#MDB_NOSYNC
	 *		Don't flush system buffers to disk when committing a transaction.
	 *		This optimization means a system crash can corrupt the database or
	 *		lose the last transactions if buffers are not yet flushed to disk.
	 *		The risk is governed by how often the system flushes dirty buffers
	 *		to disk and how often #mdb_env_sync() is called.  However, if the
	 *		filesystem preserves write order and the #MDB_WRITEMAP flag is not
	 *		used, transactions exhibit ACI (atomicity, consistency, isolation)
	 *		properties and only lose D (durability).  I.e. database integrity
	 *		is maintained, but a system crash may undo the final transactions.
	 *		Note that (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no
	 *		hint for when to write transactions to disk, unless #mdb_env_sync()
	 *		is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable.
	 *		This flag may be changed at any time using #mdb_env_set_flags().
	 *	<li>#MDB_MAPASYNC
	 *		When using #MDB_WRITEMAP, use asynchronous flushes to disk.
	 *		As with #MDB_NOSYNC, a system crash can then corrupt the
	 *		database or lose the last transactions. Calling #mdb_env_sync()
	 *		ensures on-disk database integrity until next commit.
	 *		This flag may be changed at any time using #mdb_env_set_flags().
Howard Chu's avatar
Howard Chu committed
549
550
551
552
553
554
555
556
	 *	<li>#MDB_NOTLS
	 *		Don't use Thread-Local Storage. Tie reader locktable slots to
	 *		#MDB_txn objects instead of to threads. I.e. #mdb_txn_reset() keeps
	 *		the slot reseved for the #MDB_txn object. A thread may use parallel
	 *		read-only transactions. A read-only transaction may span threads if
	 *		the user synchronizes its use. Applications that multiplex many
	 *		user threads over individual OS threads need this option. Such an
	 *		application must also serialize the write transactions in an OS
Howard Chu's avatar
Howard Chu committed
557
	 *		thread, since LMDB's write locking is unaware of the user threads.
Howard Chu's avatar
Howard Chu committed
558
559
560
561
562
563
564
	 *	<li>#MDB_NOLOCK
	 *		Don't do any locking. If concurrent access is anticipated, the
	 *		caller must manage all concurrency itself. For proper operation
	 *		the caller must enforce single-writer semantics, and must ensure
	 *		that no readers are using old transactions while a writer is
	 *		active. The simplest approach is to use an exclusive lock so that
	 *		no readers may be active at all when a writer begins.
565
566
567
568
569
570
	 *	<li>#MDB_NORDAHEAD
	 *		Turn off readahead. Most operating systems perform readahead on
	 *		read requests by default. This option turns it off if the OS
	 *		supports it. Turning it off may help random read performance
	 *		when the DB is larger than RAM and system RAM is full.
	 *		The option is not implemented on Windows.
Howard Chu's avatar
Howard Chu committed
571
572
573
574
575
576
577
578
579
	 *	<li>#MDB_NOMEMINIT
	 *		Don't initialize malloc'd memory before writing to unused spaces
	 *		in the data file. By default, memory for pages written to the data
	 *		file is obtained using malloc. While these pages may be reused in
	 *		subsequent transactions, freshly malloc'd pages will be initialized
	 *		to zeroes before use. This avoids persisting leftover data from other
	 *		code (that used the heap and subsequently freed the memory) into the
	 *		data file. Note that many other system libraries may allocate
	 *		and free memory from the heap for arbitrary uses. E.g., stdio may
Howard Chu's avatar
Howard Chu committed
580
581
	 *		use the heap for file I/O buffers. This initialization step has a
	 *		modest performance cost so some applications may want to disable
Howard Chu's avatar
Howard Chu committed
582
583
584
585
	 *		it using this flag. This option can be a problem for applications
	 *		which handle sensitive data like passwords, and it makes memory
	 *		checkers like Valgrind noisy. This flag is not needed with #MDB_WRITEMAP,
	 *		which writes directly to the mmap instead of using malloc for pages. The
Hallvard Furuseth's avatar
Hallvard Furuseth committed
586
587
588
589
	 *		initialization is also skipped if #MDB_RESERVE is used; the
	 *		caller is expected to overwrite all of the memory that was
	 *		reserved in that case.
	 *		This flag may be changed at any time using #mdb_env_set_flags().
590
	 * </ul>
591
592
	 * @param[in] mode The UNIX permissions to set on created files and semaphores.
	 * This parameter is ignored on Windows.
593
594
595
	 * @return A non-zero error value on failure and 0 on success. Some possible
	 * errors are:
	 * <ul>
Howard Chu's avatar
Howard Chu committed
596
	 *	<li>#MDB_VERSION_MISMATCH - the version of the LMDB library doesn't match the
597
	 *	version that created the database environment.
Howard Chu's avatar
Howard Chu committed
598
	 *	<li>#MDB_INVALID - the environment file headers are corrupted.
599
600
601
602
603
	 *	<li>ENOENT - the directory specified by the path parameter doesn't exist.
	 *	<li>EACCES - the user didn't have permission to access the environment files.
	 *	<li>EAGAIN - the environment was locked by another process.
	 * </ul>
	 */
604
int  mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode);
605

Howard Chu's avatar
Howard Chu committed
606
	/** @brief Copy an LMDB environment to the specified path.
607
608
	 *
	 * This function may be used to make a backup of an existing environment.
609
610
611
612
	 * No lockfile is created, since it gets recreated at need.
	 * @note This call can trigger significant file size growth if run in
	 * parallel with write transactions, because it employs a read-only
	 * transaction. See long-lived transactions under @ref caveats_sec.
613
614
615
616
617
618
619
620
621
	 * @param[in] env An environment handle returned by #mdb_env_create(). It
	 * must have already been opened successfully.
	 * @param[in] path The directory in which the copy will reside. This
	 * directory must already exist and be writable but must otherwise be
	 * empty.
	 * @return A non-zero error value on failure and 0 on success.
	 */
int  mdb_env_copy(MDB_env *env, const char *path);

Howard Chu's avatar
Howard Chu committed
622
	/** @brief Copy an LMDB environment to the specified file descriptor.
Howard Chu's avatar
Howard Chu committed
623
624
	 *
	 * This function may be used to make a backup of an existing environment.
625
626
627
628
	 * No lockfile is created, since it gets recreated at need.
	 * @note This call can trigger significant file size growth if run in
	 * parallel with write transactions, because it employs a read-only
	 * transaction. See long-lived transactions under @ref caveats_sec.
Howard Chu's avatar
Howard Chu committed
629
630
631
632
633
634
	 * @param[in] env An environment handle returned by #mdb_env_create(). It
	 * must have already been opened successfully.
	 * @param[in] fd The filedescriptor to write the copy to. It must
	 * have already been opened for Write access.
	 * @return A non-zero error value on failure and 0 on success.
	 */
635
int  mdb_env_copyfd(MDB_env *env, mdb_filehandle_t fd);
Howard Chu's avatar
Howard Chu committed
636

Howard Chu's avatar
Howard Chu committed
637
	/** @brief Copy an LMDB environment to the specified path, with options.
Howard Chu's avatar
Howard Chu committed
638
639
	 *
	 * This function may be used to make a backup of an existing environment.
Howard Chu's avatar
Howard Chu committed
640
	 * No lockfile is created, since it gets recreated at need.
Howard Chu's avatar
Howard Chu committed
641
642
643
644
645
646
647
648
	 * @note This call can trigger significant file size growth if run in
	 * parallel with write transactions, because it employs a read-only
	 * transaction. See long-lived transactions under @ref caveats_sec.
	 * @param[in] env An environment handle returned by #mdb_env_create(). It
	 * must have already been opened successfully.
	 * @param[in] path The directory in which the copy will reside. This
	 * directory must already exist and be writable but must otherwise be
	 * empty.
Howard Chu's avatar
Howard Chu committed
649
650
651
652
653
654
655
656
	 * @param[in] flags Special options for this operation. This parameter
	 * must be set to 0 or by bitwise OR'ing together one or more of the
	 * values described here.
	 * <ul>
	 *	<li>#MDB_CP_COMPACT - Perform compaction while copying: omit free
	 *		pages and sequentially renumber all pages in output. This option
	 *		consumes more CPU and runs more slowly than the default.
	 * </ul>
Howard Chu's avatar
Howard Chu committed
657
658
	 * @return A non-zero error value on failure and 0 on success.
	 */
Howard Chu's avatar
Howard Chu committed
659
int  mdb_env_copy2(MDB_env *env, const char *path, unsigned int flags);
Howard Chu's avatar
Howard Chu committed
660
661

	/** @brief Copy an LMDB environment to the specified file descriptor,
Howard Chu's avatar
Howard Chu committed
662
	 *	with options.
Howard Chu's avatar
Howard Chu committed
663
664
665
666
667
668
669
670
671
672
673
	 *
	 * This function may be used to make a backup of an existing environment.
	 * No lockfile is created, since it gets recreated at need. See
	 * #mdb_env_copy2() for further details.
	 * @note This call can trigger significant file size growth if run in
	 * parallel with write transactions, because it employs a read-only
	 * transaction. See long-lived transactions under @ref caveats_sec.
	 * @param[in] env An environment handle returned by #mdb_env_create(). It
	 * must have already been opened successfully.
	 * @param[in] fd The filedescriptor to write the copy to. It must
	 * have already been opened for Write access.
Howard Chu's avatar
Howard Chu committed
674
675
	 * @param[in] flags Special options for this operation.
	 * See #mdb_env_copy2() for options.
Howard Chu's avatar
Howard Chu committed
676
677
	 * @return A non-zero error value on failure and 0 on success.
	 */
Howard Chu's avatar
Howard Chu committed
678
int  mdb_env_copyfd2(MDB_env *env, mdb_filehandle_t fd, unsigned int flags);
Howard Chu's avatar
Howard Chu committed
679

Howard Chu's avatar
Howard Chu committed
680
	/** @brief Return statistics about the LMDB environment.
681
	 *
682
683
684
685
	 * @param[in] env An environment handle returned by #mdb_env_create()
	 * @param[out] stat The address of an #MDB_stat structure
	 * 	where the statistics will be copied
	 */
Howard Chu's avatar
Howard Chu committed
686
int  mdb_env_stat(MDB_env *env, MDB_stat *stat);
687

Howard Chu's avatar
Howard Chu committed
688
	/** @brief Return information about the LMDB environment.
689
690
691
692
693
694
695
	 *
	 * @param[in] env An environment handle returned by #mdb_env_create()
	 * @param[out] stat The address of an #MDB_envinfo structure
	 * 	where the information will be copied
	 */
int  mdb_env_info(MDB_env *env, MDB_envinfo *stat);

696
697
	/** @brief Flush the data buffers to disk.
	 *
698
	 * Data is always written to disk when #mdb_txn_commit() is called,
Howard Chu's avatar
Howard Chu committed
699
	 * but the operating system may keep it buffered. LMDB always flushes
700
	 * the OS buffers upon commit as well, unless the environment was
701
702
	 * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC. This call is
	 * not valid if the environment was opened with #MDB_RDONLY.
703
	 * @param[in] env An environment handle returned by #mdb_env_create()
704
	 * @param[in] force If non-zero, force a synchronous flush.  Otherwise
705
	 *  if the environment has the #MDB_NOSYNC flag set the flushes
706
	 *	will be omitted, and with #MDB_MAPASYNC they will be asynchronous.
707
708
709
	 * @return A non-zero error value on failure and 0 on success. Some possible
	 * errors are:
	 * <ul>
710
	 *	<li>EACCES - the environment is read-only.
711
712
713
714
	 *	<li>EINVAL - an invalid parameter was specified.
	 *	<li>EIO - an error occurred during synchronization.
	 * </ul>
	 */
Howard Chu's avatar
Howard Chu committed
715
int  mdb_env_sync(MDB_env *env, int force);
716

717
718
	/** @brief Close the environment and release the memory map.
	 *
719
720
721
722
723
724
	 * Only a single thread may call this function. All transactions, databases,
	 * and cursors must already be closed before calling this function. Attempts to
	 * use any such handles after calling this function will cause a SIGSEGV.
	 * The environment handle will be freed and must not be used again after this call.
	 * @param[in] env An environment handle returned by #mdb_env_create()
	 */
Howard Chu's avatar
Howard Chu committed
725
void mdb_env_close(MDB_env *env);
726

727
728
	/** @brief Set environment flags.
	 *
729
	 * This may be used to set some flags in addition to those from
730
731
	 * #mdb_env_open(), or to unset these flags.  If several threads
	 * change the flags at the same time, the result is undefined.
732
733
734
735
736
737
738
739
740
	 * @param[in] env An environment handle returned by #mdb_env_create()
	 * @param[in] flags The flags to change, bitwise OR'ed together
	 * @param[in] onoff A non-zero value sets the flags, zero clears them.
	 * @return A non-zero error value on failure and 0 on success. Some possible
	 * errors are:
	 * <ul>
	 *	<li>EINVAL - an invalid parameter was specified.
	 * </ul>
	 */
741
int  mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
742

743
744
	/** @brief Get environment flags.
	 *
745
746
747
748
749
750
751
752
	 * @param[in] env An environment handle returned by #mdb_env_create()
	 * @param[out] flags The address of an integer to store the flags
	 * @return A non-zero error value on failure and 0 on success. Some possible
	 * errors are:
	 * <ul>
	 *	<li>EINVAL - an invalid parameter was specified.
	 * </ul>
	 */
Howard Chu's avatar
Howard Chu committed
753
int  mdb_env_get_flags(MDB_env *env, unsigned int *flags);
754

755
756
	/** @brief Return the path that was used in #mdb_env_open().
	 *
757
758
759
760
761
762
763
764
765
766
	 * @param[in] env An environment handle returned by #mdb_env_create()
	 * @param[out] path Address of a string pointer to contain the path. This
	 * is the actual string in the environment, not a copy. It should not be
	 * altered in any way.
	 * @return A non-zero error value on failure and 0 on success. Some possible
	 * errors are:
	 * <ul>
	 *	<li>EINVAL - an invalid parameter was specified.
	 * </ul>
	 */
Howard Chu's avatar
Howard Chu committed
767
int  mdb_env_get_path(MDB_env *env, const char **path);
768

Howard Chu's avatar
Howard Chu committed
769
770
771
772
773
774
775
776
777
778
779
780
	/** @brief Return the filedescriptor for the given environment.
	 *
	 * @param[in] env An environment handle returned by #mdb_env_create()
	 * @param[out] fd Address of a mdb_filehandle_t to contain the descriptor.
	 * @return A non-zero error value on failure and 0 on success. Some possible
	 * errors are:
	 * <ul>
	 *	<li>EINVAL - an invalid parameter was specified.
	 * </ul>
	 */
int  mdb_env_get_fd(MDB_env *env, mdb_filehandle_t *fd);

781
782
	/** @brief Set the size of the memory map to use for this environment.
	 *
783
	 * The size should be a multiple of the OS page size. The default is
Howard Chu's avatar
Howard Chu committed
784
785
	 * 10485760 bytes. The size of the memory map is also the maximum size
	 * of the database. The value should be chosen as large as possible,
Hallvard Furuseth's avatar
Hallvard Furuseth committed
786
	 * to accommodate future growth of the database.
787
788
789
	 * This function should be called after #mdb_env_create() and before #mdb_env_open().
	 * It may be called at later times if no transactions are active in
	 * this process. Note that the library does not check for this condition,
790
	 * the caller must ensure it explicitly.
791
	 *
Howard Chu's avatar
Howard Chu committed
792
793
794
795
796
797
798
	 * The new size takes effect immediately for the current process but
	 * will not be persisted to any others until a write transaction has been
	 * committed by the current process. Also, only mapsize increases are
	 * persisted into the environment.
	 *
	 * If the mapsize is increased by another process, and data has grown
	 * beyond the range of the current mapsize, #mdb_txn_begin() will
799
800
801
	 * return #MDB_MAP_RESIZED. This function may be called with a size
	 * of zero to adopt the new size.
	 *
802
803
	 * Any attempt to set a size smaller than the space already consumed
	 * by the environment will be silently changed to the current size of the used space.
804
805
806
807
808
	 * @param[in] env An environment handle returned by #mdb_env_create()
	 * @param[in] size The size in bytes
	 * @return A non-zero error value on failure and 0 on success. Some possible
	 * errors are:
	 * <ul>
809
810
	 *	<li>EINVAL - an invalid parameter was specified, or the environment has
	 *   	an active write transaction.
811
812
	 * </ul>
	 */
Howard Chu's avatar
Howard Chu committed
813
int  mdb_env_set_mapsize(MDB_env *env, size_t size);
814

Howard Chu's avatar
Howard Chu committed
815
	/** @brief Set the maximum number of threads/reader slots for the environment.
816
	 *
817
818
	 * This defines the number of slots in the lock table that is used to track readers in the
	 * the environment. The default is 126.
Howard Chu's avatar
Howard Chu committed
819
820
821
822
	 * Starting a read-only transaction normally ties a lock table slot to the
	 * current thread until the environment closes or the thread exits. If
	 * MDB_NOTLS is in use, #mdb_txn_begin() instead ties the slot to the
	 * MDB_txn object until it or the #MDB_env object is destroyed.
823
824
	 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
	 * @param[in] env An environment handle returned by #mdb_env_create()
Howard Chu's avatar
Howard Chu committed
825
	 * @param[in] readers The maximum number of reader lock table slots
826
827
828
829
830
831
	 * @return A non-zero error value on failure and 0 on success. Some possible
	 * errors are:
	 * <ul>
	 *	<li>EINVAL - an invalid parameter was specified, or the environment is already open.
	 * </ul>
	 */
832
int  mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
833

Howard Chu's avatar
Howard Chu committed
834
	/** @brief Get the maximum number of threads/reader slots for the environment.
835
	 *
836
837
838
839
840
841
842
843
	 * @param[in] env An environment handle returned by #mdb_env_create()
	 * @param[out] readers Address of an integer to store the number of readers
	 * @return A non-zero error value on failure and 0 on success. Some possible
	 * errors are:
	 * <ul>
	 *	<li>EINVAL - an invalid parameter was specified.
	 * </ul>
	 */
844
int  mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
845

846
	/** @brief Set the maximum number of named databases for the environment.
847
	 *
848
	 * This function is only needed if multiple databases will be used in the
849
850
	 * environment. Simpler applications that use the environment as a single
	 * unnamed database can ignore this option.
851
	 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
852
853
854
855
	 *
	 * Currently a moderate number of slots are cheap but a huge number gets
	 * expensive: 7-120 words per transaction, and every #mdb_dbi_open()
	 * does a linear search of the opened slots.
856
857
858
859
860
861
862
863
	 * @param[in] env An environment handle returned by #mdb_env_create()
	 * @param[in] dbs The maximum number of databases
	 * @return A non-zero error value on failure and 0 on success. Some possible
	 * errors are:
	 * <ul>
	 *	<li>EINVAL - an invalid parameter was specified, or the environment is already open.
	 * </ul>
	 */
864
int  mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
Howard Chu's avatar
Howard Chu committed
865

866
	/** @brief Get the maximum size of keys and #MDB_DUPSORT data we can write.
Howard Chu's avatar
Howard Chu committed
867
	 *
868
	 * Depends on the compile-time constant #MDB_MAXKEYSIZE. Default 511.
869
	 * See @ref MDB_val.
Howard Chu's avatar
Howard Chu committed
870
	 * @param[in] env An environment handle returned by #mdb_env_create()
871
	 * @return The maximum size of a key we can write
Howard Chu's avatar
Howard Chu committed
872
873
874
	 */
int  mdb_env_get_maxkeysize(MDB_env *env);

875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
	/** @brief Set application information associated with the #MDB_env.
	 *
	 * @param[in] env An environment handle returned by #mdb_env_create()
	 * @param[in] ctx An arbitrary pointer for whatever the application needs.
	 * @return A non-zero error value on failure and 0 on success.
	 */
int  mdb_env_set_userctx(MDB_env *env, void *ctx);

	/** @brief Get the application information associated with the #MDB_env.
	 *
	 * @param[in] env An environment handle returned by #mdb_env_create()
	 * @return The pointer set by #mdb_env_set_userctx().
	 */
void *mdb_env_get_userctx(MDB_env *env);

Howard Chu's avatar
Howard Chu committed
890
	/** @brief A callback function for most LMDB assert() failures,
891
892
893
894
895
896
897
898
899
900
901
	 * called before printing the message and aborting.
	 *
	 * @param[in] env An environment handle returned by #mdb_env_create().
	 * @param[in] msg The assertion message, not including newline.
	 */
typedef void MDB_assert_func(MDB_env *env, const char *msg);

	/** Set or reset the assert() callback of the environment.
	 * Disabled if liblmdb is buillt with NDEBUG.
	 * @note This hack should become obsolete as lmdb's error handling matures.
	 * @param[in] env An environment handle returned by #mdb_env_create().
Hallvard Furuseth's avatar
Hallvard Furuseth committed
902
	 * @param[in] func An #MDB_assert_func function, or 0.
903
904
905
906
	 * @return A non-zero error value on failure and 0 on success.
	 */
int  mdb_env_set_assert(MDB_env *env, MDB_assert_func *func);

907
908
	/** @brief Create a transaction for use with the environment.
	 *
909
	 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
Howard Chu's avatar
Howard Chu committed
910
911
912
	 * @note A transaction and its cursors must only be used by a single
	 * thread, and a thread may only have a single transaction at a time.
	 * If #MDB_NOTLS is in use, this does not apply to read-only transactions.
913
	 * @note Cursors may not span transactions.
914
	 * @param[in] env An environment handle returned by #mdb_env_create()
915
916
917
	 * @param[in] parent If this parameter is non-NULL, the new transaction
	 * will be a nested transaction, with the transaction indicated by \b parent
	 * as its parent. Transactions may be nested to any level. A parent
918
919
	 * transaction and its cursors may not issue any other operations than
	 * mdb_txn_commit and mdb_txn_abort while it has active child transactions.
920
921
922
923
924
925
926
927
928
929
930
931
	 * @param[in] flags Special options for this transaction. This parameter
	 * must be set to 0 or by bitwise OR'ing together one or more of the
	 * values described here.
	 * <ul>
	 *	<li>#MDB_RDONLY
	 *		This transaction will not perform any write operations.
	 * </ul>
	 * @param[out] txn Address where the new #MDB_txn handle will be stored
	 * @return A non-zero error value on failure and 0 on success. Some possible
	 * errors are:
	 * <ul>
	 *	<li>#MDB_PANIC - a fatal error occurred earlier and the environment
932
	 *		must be shut down.
933
	 *	<li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's
934
935
	 *		mapsize and this environment's map must be resized as well.
	 *		See #mdb_env_set_mapsize().
Howard Chu's avatar
Howard Chu committed
936
	 *	<li>#MDB_READERS_FULL - a read-only transaction was requested and
937
	 *		the reader lock table is full. See #mdb_env_set_maxreaders().
Howard Chu's avatar
Howard Chu committed
938
	 *	<li>ENOMEM - out of memory.
939
940
	 * </ul>
	 */
941
int  mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
942

943
944
945
946
947
948
	/** @brief Returns the transaction's #MDB_env
	 *
	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
	 */
MDB_env *mdb_txn_env(MDB_txn *txn);

949
950
	/** @brief Commit all the operations of a transaction into the database.
	 *
951
952
953
954
	 * The transaction handle is freed. It and its cursors must not be used
	 * again after this call, except with #mdb_cursor_renew().
	 * @note Earlier documentation incorrectly said all cursors would be freed.
	 * Only write-transactions free cursors.
955
956
957
958
959
960
961
	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
	 * @return A non-zero error value on failure and 0 on success. Some possible
	 * errors are:
	 * <ul>
	 *	<li>EINVAL - an invalid parameter was specified.
	 *	<li>ENOSPC - no more disk space.
	 *	<li>EIO - a low-level I/O error occurred while writing.
Howard Chu's avatar
Howard Chu committed
962
	 *	<li>ENOMEM - out of memory.
963
964
	 * </ul>
	 */
Howard Chu's avatar
Howard Chu committed
965
int  mdb_txn_commit(MDB_txn *txn);
966

967
968
	/** @brief Abandon all the operations of the transaction instead of saving them.
	 *
969
970
971
972
	 * The transaction handle is freed. It and its cursors must not be used
	 * again after this call, except with #mdb_cursor_renew().
	 * @note Earlier documentation incorrectly said all cursors would be freed.
	 * Only write-transactions free cursors.
973
974
	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
	 */
Howard Chu's avatar
Howard Chu committed
975
976
void mdb_txn_abort(MDB_txn *txn);

977
978
	/** @brief Reset a read-only transaction.
	 *
Howard Chu's avatar
Howard Chu committed
979
980
981
982
983
984
985
	 * Abort the transaction like #mdb_txn_abort(), but keep the transaction
	 * handle. #mdb_txn_renew() may reuse the handle. This saves allocation
	 * overhead if the process will start a new read-only transaction soon,
	 * and also locking overhead if #MDB_NOTLS is in use. The reader table
	 * lock is released, but the table slot stays tied to its thread or
	 * #MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free
	 * its lock table slot if MDB_NOTLS is in use.
986
987
	 * Cursors opened within the transaction must not be used
	 * again after this call, except with #mdb_cursor_renew().
988
989
990
991
992
993
994
995
	 * Reader locks generally don't interfere with writers, but they keep old
	 * versions of database pages allocated. Thus they prevent the old pages
	 * from being reused when writers commit new data, and so under heavy load
	 * the database size may grow much more rapidly than otherwise.
	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
	 */
void mdb_txn_reset(MDB_txn *txn);

996
997
	/** @brief Renew a read-only transaction.
	 *
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
	 * This acquires a new reader lock for a transaction handle that had been
	 * released by #mdb_txn_reset(). It must be called before a reset transaction
	 * may be used again.
	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
	 * @return A non-zero error value on failure and 0 on success. Some possible
	 * errors are:
	 * <ul>
	 *	<li>#MDB_PANIC - a fatal error occurred earlier and the environment
	 *		must be shut down.
	 *	<li>EINVAL - an invalid parameter was specified.
	 * </ul>
	 */
int  mdb_txn_renew(MDB_txn *txn);

1012
1013
1014
1015
1016
/** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
#define mdb_open(txn,name,flags,dbi)	mdb_dbi_open(txn,name,flags,dbi)
/** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
#define mdb_close(env,dbi)				mdb_dbi_close(env,dbi)

1017
1018
	/** @brief Open a database in the environment.
	 *
1019
1020
	 * A database handle denotes the name and parameters of a database,
	 * independently of whether such a database exists.
1021
	 * The database handle may be discarded by calling #mdb_dbi_close().
1022
	 * The old database handle is returned if the database was already open.
1023
	 * The handle may only be closed once.
1024
	 *
1025
1026
1027
	 * The database handle will be private to the current transaction until
	 * the transaction is successfully committed. If the transaction is
	 * aborted the handle will be closed automatically.
1028
1029
1030
1031
1032
1033
	 * After a successful commit the handle will reside in the shared
	 * environment, and may be used by other transactions.
	 *
	 * This function must not be called from multiple concurrent
	 * transactions in the same process. A transaction that uses
	 * this function must finish (either commit or abort) before
Howard Chu's avatar
Howard Chu committed
1034
	 * any other transaction in the process may use this function.
1035
	 *
1036
	 * To use named databases (with name != NULL), #mdb_env_set_maxdbs()
1037
1038
	 * must be called before opening the environment.  Database names
	 * are kept as keys in the unnamed database.
1039
1040
	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
	 * @param[in] name The name of the database to open. If only a single
Hallvard Furuseth's avatar
Hallvard Furuseth committed
1041
	 * 	database is needed in the environment, this value may be NULL.
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
	 * @param[in] flags Special options for this database. This parameter
	 * must be set to 0 or by bitwise OR'ing together one or more of the
	 * values described here.
	 * <ul>
	 *	<li>#MDB_REVERSEKEY
	 *		Keys are strings to be compared in reverse order, from the end
	 *		of the strings to the beginning. By default, Keys are treated as strings and
	 *		compared from beginning to end.
	 *	<li>#MDB_DUPSORT
	 *		Duplicate keys may be used in the database. (Or, from another perspective,
	 *		keys may have multiple data items, stored in sorted order.) By default
	 *		keys must be unique and may have only a single data item.
	 *	<li>#MDB_INTEGERKEY
1055
1056
1057
	 *		Keys are binary integers in native byte order, either unsigned int
	 *		or size_t, and will be sorted as such.
	 *		The keys must all be of the same size.
1058
1059
1060
1061
1062
1063
1064
	 *	<li>#MDB_DUPFIXED
	 *		This flag may only be used in combination with #MDB_DUPSORT. This option
	 *		tells the library that the data items for this database are all the same
	 *		size, which allows further optimizations in storage and retrieval. When
	 *		all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE
	 *		cursor operations may be used to retrieve multiple items at once.
	 *	<li>#MDB_INTEGERDUP
1065
1066
	 *		This option specifies that duplicate data items are binary integers,
	 *		similar to #MDB_INTEGERKEY keys.
1067
1068
1069
	 *	<li>#MDB_REVERSEDUP
	 *		This option specifies that duplicate data items should be compared as
	 *		strings in reverse order.
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
	 *	<li>#MDB_CREATE
	 *		Create the named database if it doesn't exist. This option is not
	 *		allowed in a read-only transaction or a read-only environment.
	 * </ul>
	 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
	 * @return A non-zero error value on failure and 0 on success. Some possible
	 * errors are:
	 * <ul>
	 *	<li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
	 *		and #MDB_CREATE was not specified.
Howard Chu's avatar
Howard Chu committed
1080
	 *	<li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs().
1081
1082
	 * </ul>
	 */
1083
int  mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
1084

1085
1086
	/** @brief Retrieve statistics for a database.
	 *
1087
	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1088
	 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1089
1090
1091
1092
1093
1094
1095
1096
	 * @param[out] stat The address of an #MDB_stat structure
	 * 	where the statistics will be copied
	 * @return A non-zero error value on failure and 0 on success. Some possible
	 * errors are:
	 * <ul>
	 *	<li>EINVAL - an invalid parameter was specified.
	 * </ul>
	 */
Howard Chu's avatar
Howard Chu committed
1097
int  mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
1098

Howard Chu's avatar
Howard Chu committed
1099
1100
	/** @brief Retrieve the DB flags for a database handle.
	 *
Howard Chu's avatar
Howard Chu committed
1101
	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
Howard Chu's avatar
Howard Chu committed
1102
1103
1104
1105
	 * @param[in] dbi A database handle returned by #mdb_dbi_open()
	 * @param[out] flags Address where the flags will be returned.
	 * @return A non-zero error value on failure and 0 on success.
	 */
Howard Chu's avatar
Howard Chu committed
1106
int mdb_dbi_flags(MDB_txn *txn, MDB_dbi dbi, unsigned int *flags);
Howard Chu's avatar
Howard Chu committed
1107

1108
	/** @brief Close a database handle. Normally unnecessary. Use with care:
1109
	 *
Howard Chu's avatar
Howard Chu committed
1110
1111
	 * This call is not mutex protected. Handles should only be closed by
	 * a single thread, and only if no other threads are going to reference
1112
1113
	 * the database handle or one of its cursors any further. Do not close
	 * a handle if an existing transaction has modified its database.
1114
1115
1116
1117
1118
1119
1120
	 * Doing so can cause misbehavior from database corruption to errors
	 * like MDB_BAD_VALSIZE (since the DB name is gone).
	 *
	 * Closing a database handle is not necessary, but lets #mdb_dbi_open()
	 * reuse the handle value.  Usually it's better to set a bigger
	 * #mdb_env_set_maxdbs(), unless that value would be large.
	 *
Howard Chu's avatar
Howard Chu committed
1121
	 * @param[in] env An environment handle returned by #mdb_env_create()
1122
	 * @param[in] dbi A database handle returned by #mdb_dbi_open()
Howard Chu's avatar
Howard Chu committed
1123
	 */
1124
void mdb_dbi_close(MDB_env *env, MDB_dbi dbi);
Howard Chu's avatar
Howard Chu committed
1125

1126
	/** @brief Empty or delete+close a database.
1127
	 *
1128
	 * See #mdb_dbi_close() for restrictions about closing the DB handle.
Howard Chu's avatar
Howard Chu committed
1129
	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1130
	 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1131
1132
	 * @param[in] del 0 to empty the DB, 1 to delete it from the
	 * environment and close the DB handle.
Howard Chu's avatar
Howard Chu committed
1133
	 * @return A non-zero error value on failure and 0 on success.
1134