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 most systems:
57 * - Windows - automatic
58 * - BSD, systems using SysV semaphores - automatic
59 * - Linux, systems using POSIX mutexes with Robust option - automatic
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_SYSV_SEM or
64 * MDB_USE_POSIX_SEM,
65 * startup can fail due to semaphores owned by another userid.
66 *
67 * Fix: Open and close the database as the user which owns the
68 * semaphores (likely last user) or as root, while no other
69 * process is using the database.
70 *
71 * Restrictions/caveats (in addition to those listed for some functions):
72 *
73 * - Only the database owner should normally use the database on
74 * BSD systems or when otherwise configured with MDB_USE_POSIX_SEM.
75 * Multiple users can cause startup to fail later, as noted above.
76 *
77 * - There is normally no pure read-only mode, since readers need write
78 * access to locks and lock file. Exceptions: On read-only filesystems
79 * or with the #MDB_NOLOCK flag described under #mdb_env_open().
80 *
81 * - An LMDB configuration will often reserve considerable \b unused
82 * memory address space and maybe file size for future growth.
83 * This does not use actual memory or disk space, but users may need
84 * to understand the difference so they won't be scared off.
85 *
86 * - By default, in versions before 0.9.10, unused portions of the data
87 * file might receive garbage data from memory freed by other code.
88 * (This does not happen when using the #MDB_WRITEMAP flag.) As of
89 * 0.9.10 the default behavior is to initialize such memory before
90 * writing to the data file. Since there may be a slight performance
91 * cost due to this initialization, applications may disable it using
92 * the #MDB_NOMEMINIT flag. Applications handling sensitive data
93 * which must not be written should not use this flag. This flag is
94 * irrelevant when using #MDB_WRITEMAP.
95 *
96 * - A thread can only use one transaction at a time, plus any child
97 * transactions. Each transaction belongs to one thread. See below.
98 * The #MDB_NOTLS flag changes this for read-only transactions.
99 *
100 * - Use an MDB_env* in the process which opened it, not after fork().
101 *
102 * - Do not have open an LMDB database twice in the same process at
103 * the same time. Not even from a plain open() call - close()ing it
104 * breaks fcntl() advisory locking. (It is OK to reopen it after
105 * fork() - exec*(), since the lockfile has FD_CLOEXEC set.)
106 *
107 * - Avoid long-lived transactions. Read transactions prevent
108 * reuse of pages freed by newer write transactions, thus the
109 * database can grow quickly. Write transactions prevent
110 * other write transactions, since writes are serialized.
111 *
112 * - Avoid suspending a process with active transactions. These
113 * would then be "long-lived" as above. Also read transactions
114 * suspended when writers commit could sometimes see wrong data.
115 *
116 * ...when several processes can use a database concurrently:
117 *
118 * - Avoid aborting a process with an active transaction.
119 * The transaction becomes "long-lived" as above until a check
120 * for stale readers is performed or the lockfile is reset,
121 * since the process may not remove it from the lockfile.
122 *
123 * This does not apply to write transactions if the system clears
124 * stale writers, see above.
125 *
126 * - If you do that anyway, do a periodic check for stale readers. Or
127 * close the environment once in a while, so the lockfile can get reset.
128 *
129 * - Do not use LMDB databases on remote filesystems, even between
130 * processes on the same host. This breaks flock() on some OSes,
131 * possibly memory map sync, and certainly sync between programs
132 * on different hosts.
133 *
134 * - Opening a database can fail if another process is opening or
135 * closing it at exactly the same time.
136 *
137 * @author Howard Chu, Symas Corporation.
138 *
139 * @copyright Copyright 2011-2019 Howard Chu, Symas Corp. All rights reserved.
140 *
141 * Redistribution and use in source and binary forms, with or without
142 * modification, are permitted only as authorized by the OpenLDAP
143 * Public License.
144 *
145 * A copy of this license is available in the file LICENSE in the
146 * top-level directory of the distribution or, alternatively, at
147 * <http://www.OpenLDAP.org/license.html>.
148 *
149 * @par Derived From:
150 * This code is derived from btree.c written by Martin Hedenfalk.
151 *
152 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
153 *
154 * Permission to use, copy, modify, and distribute this software for any
155 * purpose with or without fee is hereby granted, provided that the above
156 * copyright notice and this permission notice appear in all copies.
157 *
158 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
159 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
160 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
161 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
162 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
163 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
164 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
165 */
166#ifndef _LMDB_H_
167#define _LMDB_H_
168
169#include <sys/types.h>
170#include <inttypes.h>
171#include <limits.h>
172
173#ifdef __cplusplus
174extern "C" {
175#endif
176
177/** Unix permissions for creating files, or dummy definition for Windows */
178#ifdef _MSC_VER
179typedef int mdb_mode_t;
180#else
181typedef mode_t mdb_mode_t;
182#endif
183
184#ifdef _WIN32
185# define MDB_FMT_Z "I"
186#else
187# define MDB_FMT_Z "z" /**< printf/scanf format modifier for size_t */
188#endif
189
190#ifndef MDB_VL32
191/** Unsigned type used for mapsize, entry counts and page/transaction IDs.
192 *
193 * It is normally size_t, hence the name. Defining MDB_VL32 makes it
194 * uint64_t, but do not try this unless you know what you are doing.
195 */
196typedef size_t mdb_size_t;
197# define MDB_SIZE_MAX SIZE_MAX /**< max #mdb_size_t */
198/** #mdb_size_t printf formats, \b t = one of [diouxX] without quotes */
199# define MDB_PRIy(t) MDB_FMT_Z #t
200/** #mdb_size_t scanf formats, \b t = one of [dioux] without quotes */
201# define MDB_SCNy(t) MDB_FMT_Z #t
202#else
203typedef uint64_t mdb_size_t;
204# define MDB_SIZE_MAX UINT64_MAX
205# define MDB_PRIy(t) PRI##t##64
206# define MDB_SCNy(t) SCN##t##64
207# define mdb_env_create mdb_env_create_vl32 /**< Prevent mixing with non-VL32 builds */
208#endif
209
210/** An abstraction for a file handle.
211 * On POSIX systems file handles are small integers. On Windows
212 * they're opaque pointers.
213 */
214#ifdef _WIN32
215typedef void *mdb_filehandle_t;
216#else
217typedef int mdb_filehandle_t;
218#endif
219
220/** @defgroup mdb LMDB API
221 * @{
222 * @brief OpenLDAP Lightning Memory-Mapped Database Manager
223 */
224/** @defgroup Version Version Macros
225 * @{
226 */
227/** Library major version */
228#define MDB_VERSION_MAJOR 0
229/** Library minor version */
230#define MDB_VERSION_MINOR 9
231/** Library patch version */
232#define MDB_VERSION_PATCH 70
233
234/** Combine args a,b,c into a single integer for easy version comparisons */
235#define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
236
237/** The full library version as a single integer */
238#define MDB_VERSION_FULL \
239 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
240
241/** The release date of this library version */
242#define MDB_VERSION_DATE "December 19, 2015"
243
244/** A stringifier for the version info */
245#define MDB_VERSTR(a,b,c,d) "LMDB " #a "." #b "." #c ": (" d ")"
246
247/** A helper for the stringifier macro */
248#define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d)
249
250/** The full library version as a C string */
251#define MDB_VERSION_STRING \
252 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
253/** @} */
254
255/** @brief Opaque structure for a database environment.
256 *
257 * A DB environment supports multiple databases, all residing in the same
258 * shared-memory map.
259 */
260typedef struct MDB_env MDB_env;
261
262/** @brief Opaque structure for a transaction handle.
263 *
264 * All database operations require a transaction handle. Transactions may be
265 * read-only or read-write.
266 */
267typedef struct MDB_txn MDB_txn;
268
269/** @brief A handle for an individual database in the DB environment. */
270typedef unsigned int MDB_dbi;
271
272/** @brief Opaque structure for navigating through a database */
273typedef struct MDB_cursor MDB_cursor;
274
275/** @brief Generic structure used for passing keys and data in and out
276 * of the database.
277 *
278 * Values returned from the database are valid only until a subsequent
279 * update operation, or the end of the transaction. Do not modify or
280 * free them, they commonly point into the database itself.
281 *
282 * Key sizes must be between 1 and #mdb_env_get_maxkeysize() inclusive.
283 * The same applies to data sizes in databases with the #MDB_DUPSORT flag.
284 * Other data items can in theory be from 0 to 0xffffffff bytes long.
285 */
286typedef struct MDB_val {
287 size_t mv_size; /**< size of the data item */
288 void *mv_data; /**< address of the data item */
289} MDB_val;
290
291/** @brief A callback function used to compare two keys in a database */
292typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
293
294/** @brief A callback function used to relocate a position-dependent data item
295 * in a fixed-address database.
296 *
297 * The \b newptr gives the item's desired address in
298 * the memory map, and \b oldptr gives its previous address. The item's actual
299 * data resides at the address in \b item. This callback is expected to walk
300 * through the fields of the record in \b item and modify any
301 * values based at the \b oldptr address to be relative to the \b newptr address.
302 * @param[in,out] item The item that is to be relocated.
303 * @param[in] oldptr The previous address.
304 * @param[in] newptr The new address to relocate to.
305 * @param[in] relctx An application-provided context, set by #mdb_set_relctx().
306 * @todo This feature is currently unimplemented.
307 */
308typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
309
310/** @defgroup mdb_env Environment Flags
311 * @{
312 */
313 /** mmap at a fixed address (experimental) */
314#define MDB_FIXEDMAP 0x01
315 /** no environment directory */
316#define MDB_NOSUBDIR 0x4000
317 /** don't fsync after commit */
318#define MDB_NOSYNC 0x10000
319 /** read only */
320#define MDB_RDONLY 0x20000
321 /** don't fsync metapage after commit */
322#define MDB_NOMETASYNC 0x40000
323 /** use writable mmap */
324#define MDB_WRITEMAP 0x80000
325 /** use asynchronous msync when #MDB_WRITEMAP is used */
326#define MDB_MAPASYNC 0x100000
327 /** tie reader locktable slots to #MDB_txn objects instead of to threads */
328#define MDB_NOTLS 0x200000
329 /** don't do any locking, caller must manage their own locks */
330#define MDB_NOLOCK 0x400000
331 /** don't do readahead (no effect on Windows) */
332#define MDB_NORDAHEAD 0x800000
333 /** don't initialize malloc'd memory before writing to datafile */
334#define MDB_NOMEMINIT 0x1000000
335 /** use the previous snapshot rather than the latest one */
336#define MDB_PREVSNAPSHOT 0x2000000
337/** @} */
338
339/** @defgroup mdb_dbi_open Database Flags
340 * @{
341 */
342 /** use reverse string keys */
343#define MDB_REVERSEKEY 0x02
344 /** use sorted duplicates */
345#define MDB_DUPSORT 0x04
346 /** numeric keys in native byte order, either unsigned int or #mdb_size_t.
347 * (lmdb expects 32-bit int <= size_t <= 32/64-bit mdb_size_t.)
348 * The keys must all be of the same size. */
349#define MDB_INTEGERKEY 0x08
350 /** with #MDB_DUPSORT, sorted dup items have fixed size */
351#define MDB_DUPFIXED 0x10
352 /** with #MDB_DUPSORT, dups are #MDB_INTEGERKEY-style integers */
353#define MDB_INTEGERDUP 0x20
354 /** with #MDB_DUPSORT, use reverse string dups */
355#define MDB_REVERSEDUP 0x40
356 /** create DB if not already existing */
357#define MDB_CREATE 0x40000
358/** @} */
359
360/** @defgroup mdb_put Write Flags
361 * @{
362 */
363/** For put: Don't write if the key already exists. */
364#define MDB_NOOVERWRITE 0x10
365/** Only for #MDB_DUPSORT<br>
366 * For put: don't write if the key and data pair already exist.<br>
367 * For mdb_cursor_del: remove all duplicate data items.
368 */
369#define MDB_NODUPDATA 0x20
370/** For mdb_cursor_put: overwrite the current key/data pair */
371#define MDB_CURRENT 0x40
372/** For put: Just reserve space for data, don't copy it. Return a
373 * pointer to the reserved space.
374 */
375#define MDB_RESERVE 0x10000
376/** Data is being appended, don't split full pages. */
377#define MDB_APPEND 0x20000
378/** Duplicate data is being appended, don't split full pages. */
379#define MDB_APPENDDUP 0x40000
380/** Store multiple data items in one call. Only for #MDB_DUPFIXED. */
381#define MDB_MULTIPLE 0x80000
382/* @} */
383
384/** @defgroup mdb_copy Copy Flags
385 * @{
386 */
387/** Compacting copy: Omit free space from copy, and renumber all
388 * pages sequentially.
389 */
390#define MDB_CP_COMPACT 0x01
391/* @} */
392
393/** @brief Cursor Get operations.
394 *
395 * This is the set of all operations for retrieving data
396 * using a cursor.
397 */
398typedef enum MDB_cursor_op {
399 MDB_FIRST, /**< Position at first key/data item */
400 MDB_FIRST_DUP, /**< Position at first data item of current key.
401 Only for #MDB_DUPSORT */
402 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */
403 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */
404 MDB_GET_CURRENT, /**< Return key/data at current cursor position */
405 MDB_GET_MULTIPLE, /**< Return up to a page of duplicate data items
406 from current cursor position. Move cursor to prepare
407 for #MDB_NEXT_MULTIPLE. Only for #MDB_DUPFIXED */
408 MDB_LAST, /**< Position at last key/data item */
409 MDB_LAST_DUP, /**< Position at last data item of current key.
410 Only for #MDB_DUPSORT */
411 MDB_NEXT, /**< Position at next data item */
412 MDB_NEXT_DUP, /**< Position at next data item of current key.
413 Only for #MDB_DUPSORT */
414 MDB_NEXT_MULTIPLE, /**< Return up to a page of duplicate data items
415 from next cursor position. Move cursor to prepare
416 for #MDB_NEXT_MULTIPLE. Only for #MDB_DUPFIXED */
417 MDB_NEXT_NODUP, /**< Position at first data item of next key */
418 MDB_PREV, /**< Position at previous data item */
419 MDB_PREV_DUP, /**< Position at previous data item of current key.
420 Only for #MDB_DUPSORT */
421 MDB_PREV_NODUP, /**< Position at last data item of previous key */
422 MDB_SET, /**< Position at specified key */
423 MDB_SET_KEY, /**< Position at specified key, return key + data */
424 MDB_SET_RANGE, /**< Position at first key greater than or equal to specified key. */
425 MDB_PREV_MULTIPLE /**< Position at previous page and return up to
426 a page of duplicate data items. Only for #MDB_DUPFIXED */
427} MDB_cursor_op;
428
429/** @defgroup errors Return Codes
430 *
431 * BerkeleyDB uses -30800 to -30999, we'll go under them
432 * @{
433 */
434 /** Successful result */
435#define MDB_SUCCESS 0
436 /** key/data pair already exists */
437#define MDB_KEYEXIST (-30799)
438 /** key/data pair not found (EOF) */
439#define MDB_NOTFOUND (-30798)
440 /** Requested page not found - this usually indicates corruption */
441#define MDB_PAGE_NOTFOUND (-30797)
442 /** Located page was wrong type */
443#define MDB_CORRUPTED (-30796)
444 /** Update of meta page failed or environment had fatal error */
445#define MDB_PANIC (-30795)
446 /** Environment version mismatch */
447#define MDB_VERSION_MISMATCH (-30794)
448 /** File is not a valid LMDB file */
449#define MDB_INVALID (-30793)
450 /** Environment mapsize reached */
451#define MDB_MAP_FULL (-30792)
452 /** Environment maxdbs reached */
453#define MDB_DBS_FULL (-30791)
454 /** Environment maxreaders reached */
455#define MDB_READERS_FULL (-30790)
456 /** Too many TLS keys in use - Windows only */
457#define MDB_TLS_FULL (-30789)
458 /** Txn has too many dirty pages */
459#define MDB_TXN_FULL (-30788)
460 /** Cursor stack too deep - internal error */
461#define MDB_CURSOR_FULL (-30787)
462 /** Page has not enough space - internal error */
463#define MDB_PAGE_FULL (-30786)
464 /** Database contents grew beyond environment mapsize */
465#define MDB_MAP_RESIZED (-30785)
466 /** Operation and DB incompatible, or DB type changed. This can mean:
467 * <ul>
468 * <li>The operation expects an #MDB_DUPSORT / #MDB_DUPFIXED database.
469 * <li>Opening a named DB when the unnamed DB has #MDB_DUPSORT / #MDB_INTEGERKEY.
470 * <li>Accessing a data record as a database, or vice versa.
471 * <li>The database was dropped and recreated with different flags.
472 * </ul>
473 */
474#define MDB_INCOMPATIBLE (-30784)
475 /** Invalid reuse of reader locktable slot */
476#define MDB_BAD_RSLOT (-30783)
477 /** Transaction must abort, has a child, or is invalid */
478#define MDB_BAD_TXN (-30782)
479 /** Unsupported size of key/DB name/data, or wrong DUPFIXED size */
480#define MDB_BAD_VALSIZE (-30781)
481 /** The specified DBI was changed unexpectedly */
482#define MDB_BAD_DBI (-30780)
483 /** Unexpected problem - txn should abort */
484#define MDB_PROBLEM (-30779)
485 /** The last defined error code */
486#define MDB_LAST_ERRCODE MDB_PROBLEM
487/** @} */
488
489/** @brief Statistics for a database in the environment */
490typedef struct MDB_stat {
491 unsigned int ms_psize; /**< Size of a database page.
492 This is currently the same for all databases. */
493 unsigned int ms_depth; /**< Depth (height) of the B-tree */
494 mdb_size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */
495 mdb_size_t ms_leaf_pages; /**< Number of leaf pages */
496 mdb_size_t ms_overflow_pages; /**< Number of overflow pages */
497 mdb_size_t ms_entries; /**< Number of data items */
498} MDB_stat;
499
500/** @brief Information about the environment */
501typedef struct MDB_envinfo {
502 void *me_mapaddr; /**< Address of map, if fixed */
503 mdb_size_t me_mapsize; /**< Size of the data memory map */
504 mdb_size_t me_last_pgno; /**< ID of the last used page */
505 mdb_size_t me_last_txnid; /**< ID of the last committed transaction */
506 unsigned int me_maxreaders; /**< max reader slots in the environment */
507 unsigned int me_numreaders; /**< max reader slots used in the environment */
508} MDB_envinfo;
509
510 /** @brief Return the LMDB library version information.
511 *
512 * @param[out] major if non-NULL, the library major version number is copied here
513 * @param[out] minor if non-NULL, the library minor version number is copied here
514 * @param[out] patch if non-NULL, the library patch version number is copied here
515 * @retval "version string" The library version as a string
516 */
517char *mdb_version(int *major, int *minor, int *patch);
518
519 /** @brief Return a string describing a given error code.
520 *
521 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3)
522 * function. If the error code is greater than or equal to 0, then the string
523 * returned by the system function strerror(3) is returned. If the error code
524 * is less than 0, an error string corresponding to the LMDB library error is
525 * returned. See @ref errors for a list of LMDB-specific error codes.
526 * @param[in] err The error code
527 * @retval "error message" The description of the error
528 */
529char *mdb_strerror(int err);
530
531 /** @brief Create an LMDB environment handle.
532 *
533 * This function allocates memory for a #MDB_env structure. To release
534 * the allocated memory and discard the handle, call #mdb_env_close().
535 * Before the handle may be used, it must be opened using #mdb_env_open().
536 * Various other options may also need to be set before opening the handle,
537 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(),
538 * depending on usage requirements.
539 * @param[out] env The address where the new handle will be stored
540 * @return A non-zero error value on failure and 0 on success.
541 */
542int mdb_env_create(MDB_env **env);
543
544 /** @brief Open an environment handle.
545 *
546 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle.
547 * @param[in] env An environment handle returned by #mdb_env_create()
548 * @param[in] path The directory in which the database files reside. This
549 * directory must already exist and be writable.
550 * @param[in] flags Special options for this environment. This parameter
551 * must be set to 0 or by bitwise OR'ing together one or more of the
552 * values described here.
553 * Flags set by mdb_env_set_flags() are also used.
554 * <ul>
555 * <li>#MDB_FIXEDMAP
556 * use a fixed address for the mmap region. This flag must be specified
557 * when creating the environment, and is stored persistently in the environment.
558 * If successful, the memory map will always reside at the same virtual address
559 * and pointers used to reference data items in the database will be constant
560 * across multiple invocations. This option may not always work, depending on
561 * how the operating system has allocated memory to shared libraries and other uses.
562 * The feature is highly experimental.
563 * <li>#MDB_NOSUBDIR
564 * By default, LMDB creates its environment in a directory whose
565 * pathname is given in \b path, and creates its data and lock files
566 * under that directory. With this option, \b path is used as-is for
567 * the database main data file. The database lock file is the \b path
568 * with "-lock" appended.
569 * <li>#MDB_RDONLY
570 * Open the environment in read-only mode. No write operations will be
571 * allowed. LMDB will still modify the lock file - except on read-only
572 * filesystems, where LMDB does not use locks.
573 * <li>#MDB_WRITEMAP
574 * Use a writeable memory map unless MDB_RDONLY is set. This uses
575 * fewer mallocs but loses protection from application bugs
576 * like wild pointer writes and other bad updates into the database.
577 * This may be slightly faster for DBs that fit entirely in RAM, but
578 * is slower for DBs larger than RAM.
579 * Incompatible with nested transactions.
580 * Do not mix processes with and without MDB_WRITEMAP on the same
581 * environment. This can defeat durability (#mdb_env_sync etc).
582 * <li>#MDB_NOMETASYNC
583 * Flush system buffers to disk only once per transaction, omit the
584 * metadata flush. Defer that until the system flushes files to disk,
585 * or next non-MDB_RDONLY commit or #mdb_env_sync(). This optimization
586 * maintains database integrity, but a system crash may undo the last
587 * committed transaction. I.e. it preserves the ACI (atomicity,
588 * consistency, isolation) but not D (durability) database property.
589 * This flag may be changed at any time using #mdb_env_set_flags().
590 * <li>#MDB_NOSYNC
591 * Don't flush system buffers to disk when committing a transaction.
592 * This optimization means a system crash can corrupt the database or
593 * lose the last transactions if buffers are not yet flushed to disk.
594 * The risk is governed by how often the system flushes dirty buffers
595 * to disk and how often #mdb_env_sync() is called. However, if the
596 * filesystem preserves write order and the #MDB_WRITEMAP flag is not
597 * used, transactions exhibit ACI (atomicity, consistency, isolation)
598 * properties and only lose D (durability). I.e. database integrity
599 * is maintained, but a system crash may undo the final transactions.
600 * Note that (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no
601 * hint for when to write transactions to disk, unless #mdb_env_sync()
602 * is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable.
603 * This flag may be changed at any time using #mdb_env_set_flags().
604 * <li>#MDB_MAPASYNC
605 * When using #MDB_WRITEMAP, use asynchronous flushes to disk.
606 * As with #MDB_NOSYNC, a system crash can then corrupt the
607 * database or lose the last transactions. Calling #mdb_env_sync()
608 * ensures on-disk database integrity until next commit.
609 * This flag may be changed at any time using #mdb_env_set_flags().
610 * <li>#MDB_NOTLS
611 * Don't use Thread-Local Storage. Tie reader locktable slots to
612 * #MDB_txn objects instead of to threads. I.e. #mdb_txn_reset() keeps
613 * the slot reseved for the #MDB_txn object. A thread may use parallel
614 * read-only transactions. A read-only transaction may span threads if
615 * the user synchronizes its use. Applications that multiplex many
616 * user threads over individual OS threads need this option. Such an
617 * application must also serialize the write transactions in an OS
618 * thread, since LMDB's write locking is unaware of the user threads.
619 * <li>#MDB_NOLOCK
620 * Don't do any locking. If concurrent access is anticipated, the
621 * caller must manage all concurrency itself. For proper operation
622 * the caller must enforce single-writer semantics, and must ensure
623 * that no readers are using old transactions while a writer is
624 * active. The simplest approach is to use an exclusive lock so that
625 * no readers may be active at all when a writer begins.
626 * <li>#MDB_NORDAHEAD
627 * Turn off readahead. Most operating systems perform readahead on
628 * read requests by default. This option turns it off if the OS
629 * supports it. Turning it off may help random read performance
630 * when the DB is larger than RAM and system RAM is full.
631 * The option is not implemented on Windows.
632 * <li>#MDB_NOMEMINIT
633 * Don't initialize malloc'd memory before writing to unused spaces
634 * in the data file. By default, memory for pages written to the data
635 * file is obtained using malloc. While these pages may be reused in
636 * subsequent transactions, freshly malloc'd pages will be initialized
637 * to zeroes before use. This avoids persisting leftover data from other
638 * code (that used the heap and subsequently freed the memory) into the
639 * data file. Note that many other system libraries may allocate
640 * and free memory from the heap for arbitrary uses. E.g., stdio may
641 * use the heap for file I/O buffers. This initialization step has a
642 * modest performance cost so some applications may want to disable
643 * it using this flag. This option can be a problem for applications
644 * which handle sensitive data like passwords, and it makes memory
645 * checkers like Valgrind noisy. This flag is not needed with #MDB_WRITEMAP,
646 * which writes directly to the mmap instead of using malloc for pages. The
647 * initialization is also skipped if #MDB_RESERVE is used; the
648 * caller is expected to overwrite all of the memory that was
649 * reserved in that case.
650 * This flag may be changed at any time using #mdb_env_set_flags().
651 * <li>#MDB_PREVSNAPSHOT
652 * Open the environment with the previous snapshot rather than the latest
653 * one. This loses the latest transaction, but may help work around some
654 * types of corruption. If opened with write access, this must be the
655 * only process using the environment. This flag is automatically reset
656 * after a write transaction is successfully committed.
657 * </ul>
658 * @param[in] mode The UNIX permissions to set on created files and semaphores.
659 * This parameter is ignored on Windows.
660 * @return A non-zero error value on failure and 0 on success. Some possible
661 * errors are:
662 * <ul>
663 * <li>#MDB_VERSION_MISMATCH - the version of the LMDB library doesn't match the
664 * version that created the database environment.
665 * <li>#MDB_INVALID - the environment file headers are corrupted.
666 * <li>ENOENT - the directory specified by the path parameter doesn't exist.
667 * <li>EACCES - the user didn't have permission to access the environment files.
668 * <li>EAGAIN - the environment was locked by another process.
669 * </ul>
670 */
671int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode);
672
673 /** @brief Copy an LMDB environment to the specified path.
674 *
675 * This function may be used to make a backup of an existing environment.
676 * No lockfile is created, since it gets recreated at need.
677 * @note This call can trigger significant file size growth if run in
678 * parallel with write transactions, because it employs a read-only
679 * transaction. See long-lived transactions under @ref caveats_sec.
680 * @param[in] env An environment handle returned by #mdb_env_create(). It
681 * must have already been opened successfully.
682 * @param[in] path The directory in which the copy will reside. This
683 * directory must already exist and be writable but must otherwise be
684 * empty.
685 * @return A non-zero error value on failure and 0 on success.
686 */
687int mdb_env_copy(MDB_env *env, const char *path);
688
689 /** @brief Copy an LMDB environment to the specified file descriptor.
690 *
691 * This function may be used to make a backup of an existing environment.
692 * No lockfile is created, since it gets recreated at need.
693 * @note This call can trigger significant file size growth if run in
694 * parallel with write transactions, because it employs a read-only
695 * transaction. See long-lived transactions under @ref caveats_sec.
696 * @param[in] env An environment handle returned by #mdb_env_create(). It
697 * must have already been opened successfully.
698 * @param[in] fd The filedescriptor to write the copy to. It must
699 * have already been opened for Write access.
700 * @return A non-zero error value on failure and 0 on success.
701 */
702int mdb_env_copyfd(MDB_env *env, mdb_filehandle_t fd);
703
704 /** @brief Copy an LMDB environment to the specified path, with options.
705 *
706 * This function may be used to make a backup of an existing environment.
707 * No lockfile is created, since it gets recreated at need.
708 * @note This call can trigger significant file size growth if run in
709 * parallel with write transactions, because it employs a read-only
710 * transaction. See long-lived transactions under @ref caveats_sec.
711 * @param[in] env An environment handle returned by #mdb_env_create(). It
712 * must have already been opened successfully.
713 * @param[in] path The directory in which the copy will reside. This
714 * directory must already exist and be writable but must otherwise be
715 * empty.
716 * @param[in] flags Special options for this operation. This parameter
717 * must be set to 0 or by bitwise OR'ing together one or more of the
718 * values described here.
719 * <ul>
720 * <li>#MDB_CP_COMPACT - Perform compaction while copying: omit free
721 * pages and sequentially renumber all pages in output. This option
722 * consumes more CPU and runs more slowly than the default.
723 * Currently it fails if the environment has suffered a page leak.
724 * </ul>
725 * @return A non-zero error value on failure and 0 on success.
726 */
727int mdb_env_copy2(MDB_env *env, const char *path, unsigned int flags);
728
729 /** @brief Copy an LMDB environment to the specified file descriptor,
730 * with options.
731 *
732 * This function may be used to make a backup of an existing environment.
733 * No lockfile is created, since it gets recreated at need. See
734 * #mdb_env_copy2() for further details.
735 * @note This call can trigger significant file size growth if run in
736 * parallel with write transactions, because it employs a read-only
737 * transaction. See long-lived transactions under @ref caveats_sec.
738 * @param[in] env An environment handle returned by #mdb_env_create(). It
739 * must have already been opened successfully.
740 * @param[in] fd The filedescriptor to write the copy to. It must
741 * have already been opened for Write access.
742 * @param[in] flags Special options for this operation.
743 * See #mdb_env_copy2() for options.
744 * @return A non-zero error value on failure and 0 on success.
745 */
746int mdb_env_copyfd2(MDB_env *env, mdb_filehandle_t fd, unsigned int flags);
747
748 /** @brief Return statistics about the LMDB environment.
749 *
750 * @param[in] env An environment handle returned by #mdb_env_create()
751 * @param[out] stat The address of an #MDB_stat structure
752 * where the statistics will be copied
753 */
754int mdb_env_stat(MDB_env *env, MDB_stat *stat);
755
756 /** @brief Return information about the LMDB environment.
757 *
758 * @param[in] env An environment handle returned by #mdb_env_create()
759 * @param[out] stat The address of an #MDB_envinfo structure
760 * where the information will be copied
761 */
762int mdb_env_info(MDB_env *env, MDB_envinfo *stat);
763
764 /** @brief Flush the data buffers to disk.
765 *
766 * Data is always written to disk when #mdb_txn_commit() is called,
767 * but the operating system may keep it buffered. LMDB always flushes
768 * the OS buffers upon commit as well, unless the environment was
769 * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC. This call is
770 * not valid if the environment was opened with #MDB_RDONLY.
771 * @param[in] env An environment handle returned by #mdb_env_create()
772 * @param[in] force If non-zero, force a synchronous flush. Otherwise
773 * if the environment has the #MDB_NOSYNC flag set the flushes
774 * will be omitted, and with #MDB_MAPASYNC they will be asynchronous.
775 * @return A non-zero error value on failure and 0 on success. Some possible
776 * errors are:
777 * <ul>
778 * <li>EACCES - the environment is read-only.
779 * <li>EINVAL - an invalid parameter was specified.
780 * <li>EIO - an error occurred during synchronization.
781 * </ul>
782 */
783int mdb_env_sync(MDB_env *env, int force);
784
785 /** @brief Close the environment and release the memory map.
786 *
787 * Only a single thread may call this function. All transactions, databases,
788 * and cursors must already be closed before calling this function. Attempts to
789 * use any such handles after calling this function will cause a SIGSEGV.
790 * The environment handle will be freed and must not be used again after this call.
791 * @param[in] env An environment handle returned by #mdb_env_create()
792 */
793void mdb_env_close(MDB_env *env);
794
795 /** @brief Set environment flags.
796 *
797 * This may be used to set some flags in addition to those from
798 * #mdb_env_open(), or to unset these flags. If several threads
799 * change the flags at the same time, the result is undefined.
800 * @param[in] env An environment handle returned by #mdb_env_create()
801 * @param[in] flags The flags to change, bitwise OR'ed together
802 * @param[in] onoff A non-zero value sets the flags, zero clears them.
803 * @return A non-zero error value on failure and 0 on success. Some possible
804 * errors are:
805 * <ul>
806 * <li>EINVAL - an invalid parameter was specified.
807 * </ul>
808 */
809int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff);
810
811 /** @brief Get environment flags.
812 *
813 * @param[in] env An environment handle returned by #mdb_env_create()
814 * @param[out] flags The address of an integer to store the flags
815 * @return A non-zero error value on failure and 0 on success. Some possible
816 * errors are:
817 * <ul>
818 * <li>EINVAL - an invalid parameter was specified.
819 * </ul>
820 */
821int mdb_env_get_flags(MDB_env *env, unsigned int *flags);
822
823 /** @brief Return the path that was used in #mdb_env_open().
824 *
825 * @param[in] env An environment handle returned by #mdb_env_create()
826 * @param[out] path Address of a string pointer to contain the path. This
827 * is the actual string in the environment, not a copy. It should not be
828 * altered in any way.
829 * @return A non-zero error value on failure and 0 on success. Some possible
830 * errors are:
831 * <ul>
832 * <li>EINVAL - an invalid parameter was specified.
833 * </ul>
834 */
835int mdb_env_get_path(MDB_env *env, const char **path);
836
837 /** @brief Return the filedescriptor for the given environment.
838 *
839 * This function may be called after fork(), so the descriptor can be
840 * closed before exec*(). Other LMDB file descriptors have FD_CLOEXEC.
841 * (Until LMDB 0.9.18, only the lockfile had that.)
842 *
843 * @param[in] env An environment handle returned by #mdb_env_create()
844 * @param[out] fd Address of a mdb_filehandle_t to contain the descriptor.
845 * @return A non-zero error value on failure and 0 on success. Some possible
846 * errors are:
847 * <ul>
848 * <li>EINVAL - an invalid parameter was specified.
849 * </ul>
850 */
851int mdb_env_get_fd(MDB_env *env, mdb_filehandle_t *fd);
852
853 /** @brief Set the size of the memory map to use for this environment.
854 *
855 * The size should be a multiple of the OS page size. The default is
856 * 10485760 bytes. The size of the memory map is also the maximum size
857 * of the database. The value should be chosen as large as possible,
858 * to accommodate future growth of the database.
859 * This function should be called after #mdb_env_create() and before #mdb_env_open().
860 * It may be called at later times if no transactions are active in
861 * this process. Note that the library does not check for this condition,
862 * the caller must ensure it explicitly.
863 *
864 * The new size takes effect immediately for the current process but
865 * will not be persisted to any others until a write transaction has been
866 * committed by the current process. Also, only mapsize increases are
867 * persisted into the environment.
868 *
869 * If the mapsize is increased by another process, and data has grown
870 * beyond the range of the current mapsize, #mdb_txn_begin() will
871 * return #MDB_MAP_RESIZED. This function may be called with a size
872 * of zero to adopt the new size.
873 *
874 * Any attempt to set a size smaller than the space already consumed
875 * by the environment will be silently changed to the current size of the used space.
876 * @param[in] env An environment handle returned by #mdb_env_create()
877 * @param[in] size The size in bytes
878 * @return A non-zero error value on failure and 0 on success. Some possible
879 * errors are:
880 * <ul>
881 * <li>EINVAL - an invalid parameter was specified, or the environment has
882 * an active write transaction.
883 * </ul>
884 */
885int mdb_env_set_mapsize(MDB_env *env, mdb_size_t size);
886
887 /** @brief Set the maximum number of threads/reader slots for the environment.
888 *
889 * This defines the number of slots in the lock table that is used to track readers in the
890 * the environment. The default is 126.
891 * Starting a read-only transaction normally ties a lock table slot to the
892 * current thread until the environment closes or the thread exits. If
893 * MDB_NOTLS is in use, #mdb_txn_begin() instead ties the slot to the
894 * MDB_txn object until it or the #MDB_env object is destroyed.
895 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
896 * @param[in] env An environment handle returned by #mdb_env_create()
897 * @param[in] readers The maximum number of reader lock table slots
898 * @return A non-zero error value on failure and 0 on success. Some possible
899 * errors are:
900 * <ul>
901 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
902 * </ul>
903 */
904int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers);
905
906 /** @brief Get the maximum number of threads/reader slots for the environment.
907 *
908 * @param[in] env An environment handle returned by #mdb_env_create()
909 * @param[out] readers Address of an integer to store the number of readers
910 * @return A non-zero error value on failure and 0 on success. Some possible
911 * errors are:
912 * <ul>
913 * <li>EINVAL - an invalid parameter was specified.
914 * </ul>
915 */
916int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers);
917
918 /** @brief Set the maximum number of named databases for the environment.
919 *
920 * This function is only needed if multiple databases will be used in the
921 * environment. Simpler applications that use the environment as a single
922 * unnamed database can ignore this option.
923 * This function may only be called after #mdb_env_create() and before #mdb_env_open().
924 *
925 * Currently a moderate number of slots are cheap but a huge number gets
926 * expensive: 7-120 words per transaction, and every #mdb_dbi_open()
927 * does a linear search of the opened slots.
928 * @param[in] env An environment handle returned by #mdb_env_create()
929 * @param[in] dbs The maximum number of databases
930 * @return A non-zero error value on failure and 0 on success. Some possible
931 * errors are:
932 * <ul>
933 * <li>EINVAL - an invalid parameter was specified, or the environment is already open.
934 * </ul>
935 */
936int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
937
938 /** @brief Get the maximum size of keys and #MDB_DUPSORT data we can write.
939 *
940 * Depends on the compile-time constant #MDB_MAXKEYSIZE. Default 511.
941 * See @ref MDB_val.
942 * @param[in] env An environment handle returned by #mdb_env_create()
943 * @return The maximum size of a key we can write
944 */
945int mdb_env_get_maxkeysize(MDB_env *env);
946
947 /** @brief Set application information associated with the #MDB_env.
948 *
949 * @param[in] env An environment handle returned by #mdb_env_create()
950 * @param[in] ctx An arbitrary pointer for whatever the application needs.
951 * @return A non-zero error value on failure and 0 on success.
952 */
953int mdb_env_set_userctx(MDB_env *env, void *ctx);
954
955 /** @brief Get the application information associated with the #MDB_env.
956 *
957 * @param[in] env An environment handle returned by #mdb_env_create()
958 * @return The pointer set by #mdb_env_set_userctx().
959 */
960void *mdb_env_get_userctx(MDB_env *env);
961
962 /** @brief A callback function for most LMDB assert() failures,
963 * called before printing the message and aborting.
964 *
965 * @param[in] env An environment handle returned by #mdb_env_create().
966 * @param[in] msg The assertion message, not including newline.
967 */
968typedef void MDB_assert_func(MDB_env *env, const char *msg);
969
970 /** Set or reset the assert() callback of the environment.
971 * Disabled if liblmdb is buillt with NDEBUG.
972 * @note This hack should become obsolete as lmdb's error handling matures.
973 * @param[in] env An environment handle returned by #mdb_env_create().
974 * @param[in] func An #MDB_assert_func function, or 0.
975 * @return A non-zero error value on failure and 0 on success.
976 */
977int mdb_env_set_assert(MDB_env *env, MDB_assert_func *func);
978
979 /** @brief Create a transaction for use with the environment.
980 *
981 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit().
982 * @note A transaction and its cursors must only be used by a single
983 * thread, and a thread may only have a single transaction at a time.
984 * If #MDB_NOTLS is in use, this does not apply to read-only transactions.
985 * @note Cursors may not span transactions.
986 * @param[in] env An environment handle returned by #mdb_env_create()
987 * @param[in] parent If this parameter is non-NULL, the new transaction
988 * will be a nested transaction, with the transaction indicated by \b parent
989 * as its parent. Transactions may be nested to any level. A parent
990 * transaction and its cursors may not issue any other operations than
991 * mdb_txn_commit and mdb_txn_abort while it has active child transactions.
992 * @param[in] flags Special options for this transaction. This parameter
993 * must be set to 0 or by bitwise OR'ing together one or more of the
994 * values described here.
995 * <ul>
996 * <li>#MDB_RDONLY
997 * This transaction will not perform any write operations.
998 * <li>#MDB_NOSYNC
999 * Don't flush system buffers to disk when committing this transaction.
1000 * <li>#MDB_NOMETASYNC
1001 * Flush system buffers but omit metadata flush when committing this transaction.
1002 * </ul>
1003 * @param[out] txn Address where the new #MDB_txn handle will be stored
1004 * @return A non-zero error value on failure and 0 on success. Some possible
1005 * errors are:
1006 * <ul>
1007 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
1008 * must be shut down.
1009 * <li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's
1010 * mapsize and this environment's map must be resized as well.
1011 * See #mdb_env_set_mapsize().
1012 * <li>#MDB_READERS_FULL - a read-only transaction was requested and
1013 * the reader lock table is full. See #mdb_env_set_maxreaders().
1014 * <li>ENOMEM - out of memory.
1015 * </ul>
1016 */
1017int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
1018
1019 /** @brief Returns the transaction's #MDB_env
1020 *
1021 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1022 */
1023MDB_env *mdb_txn_env(MDB_txn *txn);
1024
1025 /** @brief Return the transaction's ID.
1026 *
1027 * This returns the identifier associated with this transaction. For a
1028 * read-only transaction, this corresponds to the snapshot being read;
1029 * concurrent readers will frequently have the same transaction ID.
1030 *
1031 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1032 * @return A transaction ID, valid if input is an active transaction.
1033 */
1034mdb_size_t mdb_txn_id(MDB_txn *txn);
1035
1036 /** @brief Commit all the operations of a transaction into the database.
1037 *
1038 * The transaction handle is freed. It and its cursors must not be used
1039 * again after this call, except with #mdb_cursor_renew().
1040 * @note Earlier documentation incorrectly said all cursors would be freed.
1041 * Only write-transactions free cursors.
1042 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1043 * @return A non-zero error value on failure and 0 on success. Some possible
1044 * errors are:
1045 * <ul>
1046 * <li>EINVAL - an invalid parameter was specified.
1047 * <li>ENOSPC - no more disk space.
1048 * <li>EIO - a low-level I/O error occurred while writing.
1049 * <li>ENOMEM - out of memory.
1050 * </ul>
1051 */
1052int mdb_txn_commit(MDB_txn *txn);
1053
1054 /** @brief Abandon all the operations of the transaction instead of saving them.
1055 *
1056 * The transaction handle is freed. It and its cursors must not be used
1057 * again after this call, except with #mdb_cursor_renew().
1058 * @note Earlier documentation incorrectly said all cursors would be freed.
1059 * Only write-transactions free cursors.
1060 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1061 */
1062void mdb_txn_abort(MDB_txn *txn);
1063
1064 /** @brief Reset a read-only transaction.
1065 *
1066 * Abort the transaction like #mdb_txn_abort(), but keep the transaction
1067 * handle. #mdb_txn_renew() may reuse the handle. This saves allocation
1068 * overhead if the process will start a new read-only transaction soon,
1069 * and also locking overhead if #MDB_NOTLS is in use. The reader table
1070 * lock is released, but the table slot stays tied to its thread or
1071 * #MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free
1072 * its lock table slot if MDB_NOTLS is in use.
1073 * Cursors opened within the transaction must not be used
1074 * again after this call, except with #mdb_cursor_renew().
1075 * Reader locks generally don't interfere with writers, but they keep old
1076 * versions of database pages allocated. Thus they prevent the old pages
1077 * from being reused when writers commit new data, and so under heavy load
1078 * the database size may grow much more rapidly than otherwise.
1079 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1080 */
1081void mdb_txn_reset(MDB_txn *txn);
1082
1083 /** @brief Renew a read-only transaction.
1084 *
1085 * This acquires a new reader lock for a transaction handle that had been
1086 * released by #mdb_txn_reset(). It must be called before a reset transaction
1087 * may be used again.
1088 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1089 * @return A non-zero error value on failure and 0 on success. Some possible
1090 * errors are:
1091 * <ul>
1092 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment
1093 * must be shut down.
1094 * <li>EINVAL - an invalid parameter was specified.
1095 * </ul>
1096 */
1097int mdb_txn_renew(MDB_txn *txn);
1098
1099/** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
1100#define mdb_open(txn,name,flags,dbi) mdb_dbi_open(txn,name,flags,dbi)
1101/** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */
1102#define mdb_close(env,dbi) mdb_dbi_close(env,dbi)
1103
1104 /** @brief Open a database in the environment.
1105 *
1106 * A database handle denotes the name and parameters of a database,
1107 * independently of whether such a database exists.
1108 * The database handle may be discarded by calling #mdb_dbi_close().
1109 * The old database handle is returned if the database was already open.
1110 * The handle may only be closed once.
1111 *
1112 * The database handle will be private to the current transaction until
1113 * the transaction is successfully committed. If the transaction is
1114 * aborted the handle will be closed automatically.
1115 * After a successful commit the handle will reside in the shared
1116 * environment, and may be used by other transactions.
1117 *
1118 * This function must not be called from multiple concurrent
1119 * transactions in the same process. A transaction that uses
1120 * this function must finish (either commit or abort) before
1121 * any other transaction in the process may use this function.
1122 *
1123 * To use named databases (with name != NULL), #mdb_env_set_maxdbs()
1124 * must be called before opening the environment. Database names are
1125 * keys in the unnamed database, and may be read but not written.
1126 *
1127 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1128 * @param[in] name The name of the database to open. If only a single
1129 * database is needed in the environment, this value may be NULL.
1130 * @param[in] flags Special options for this database. This parameter
1131 * must be set to 0 or by bitwise OR'ing together one or more of the
1132 * values described here.
1133 * <ul>
1134 * <li>#MDB_REVERSEKEY
1135 * Keys are strings to be compared in reverse order, from the end
1136 * of the strings to the beginning. By default, Keys are treated as strings and
1137 * compared from beginning to end.
1138 * <li>#MDB_DUPSORT
1139 * Duplicate keys may be used in the database. (Or, from another perspective,
1140 * keys may have multiple data items, stored in sorted order.) By default
1141 * keys must be unique and may have only a single data item.
1142 * <li>#MDB_INTEGERKEY
1143 * Keys are binary integers in native byte order, either unsigned int
1144 * or #mdb_size_t, and will be sorted as such.
1145 * (lmdb expects 32-bit int <= size_t <= 32/64-bit mdb_size_t.)
1146 * The keys must all be of the same size.
1147 * <li>#MDB_DUPFIXED
1148 * This flag may only be used in combination with #MDB_DUPSORT. This option
1149 * tells the library that the data items for this database are all the same
1150 * size, which allows further optimizations in storage and retrieval. When
1151 * all data items are the same size, the #MDB_GET_MULTIPLE, #MDB_NEXT_MULTIPLE
1152 * and #MDB_PREV_MULTIPLE cursor operations may be used to retrieve multiple
1153 * items at once.
1154 * <li>#MDB_INTEGERDUP
1155 * This option specifies that duplicate data items are binary integers,
1156 * similar to #MDB_INTEGERKEY keys.
1157 * <li>#MDB_REVERSEDUP
1158 * This option specifies that duplicate data items should be compared as
1159 * strings in reverse order.
1160 * <li>#MDB_CREATE
1161 * Create the named database if it doesn't exist. This option is not
1162 * allowed in a read-only transaction or a read-only environment.
1163 * </ul>
1164 * @param[out] dbi Address where the new #MDB_dbi handle will be stored
1165 * @return A non-zero error value on failure and 0 on success. Some possible
1166 * errors are:
1167 * <ul>
1168 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment
1169 * and #MDB_CREATE was not specified.
1170 * <li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs().
1171 * </ul>
1172 */
1173int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi);
1174
1175 /** @brief Retrieve statistics for a database.
1176 *
1177 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1178 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1179 * @param[out] stat The address of an #MDB_stat structure
1180 * where the statistics will be copied
1181 * @return A non-zero error value on failure and 0 on success. Some possible
1182 * errors are:
1183 * <ul>
1184 * <li>EINVAL - an invalid parameter was specified.
1185 * </ul>
1186 */
1187int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
1188
1189 /** @brief Retrieve the DB flags for a database handle.
1190 *
1191 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1192 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1193 * @param[out] flags Address where the flags will be returned.
1194 * @return A non-zero error value on failure and 0 on success.
1195 */
1196int mdb_dbi_flags(MDB_txn *txn, MDB_dbi dbi, unsigned int *flags);
1197
1198 /** @brief Close a database handle. Normally unnecessary. Use with care:
1199 *
1200 * This call is not mutex protected. Handles should only be closed by
1201 * a single thread, and only if no other threads are going to reference
1202 * the database handle or one of its cursors any further. Do not close
1203 * a handle if an existing transaction has modified its database.
1204 * Doing so can cause misbehavior from database corruption to errors
1205 * like MDB_BAD_VALSIZE (since the DB name is gone).
1206 *
1207 * Closing a database handle is not necessary, but lets #mdb_dbi_open()
1208 * reuse the handle value. Usually it's better to set a bigger
1209 * #mdb_env_set_maxdbs(), unless that value would be large.
1210 *
1211 * @param[in] env An environment handle returned by #mdb_env_create()
1212 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1213 */
1214void mdb_dbi_close(MDB_env *env, MDB_dbi dbi);
1215
1216 /** @brief Empty or delete+close a database.
1217 *
1218 * See #mdb_dbi_close() for restrictions about closing the DB handle.
1219 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1220 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1221 * @param[in] del 0 to empty the DB, 1 to delete it from the
1222 * environment and close the DB handle.
1223 * @return A non-zero error value on failure and 0 on success.
1224 */
1225int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
1226
1227 /** @brief Set a custom key comparison function for a database.
1228 *
1229 * The comparison function is called whenever it is necessary to compare a
1230 * key specified by the application with a key currently stored in the database.
1231 * If no comparison function is specified, and no special key flags were specified
1232 * with #mdb_dbi_open(), the keys are compared lexically, with shorter keys collating
1233 * before longer keys.
1234 * @warning This function must be called before any data access functions are used,
1235 * otherwise data corruption may occur. The same comparison function must be used by every
1236 * program accessing the database, every time the database is used.
1237 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1238 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1239 * @param[in] cmp A #MDB_cmp_func function
1240 * @return A non-zero error value on failure and 0 on success. Some possible
1241 * errors are:
1242 * <ul>
1243 * <li>EINVAL - an invalid parameter was specified.
1244 * </ul>
1245 */
1246int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
1247
1248 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database.
1249 *
1250 * This comparison function is called whenever it is necessary to compare a data
1251 * item specified by the application with a data item currently stored in the database.
1252 * This function only takes effect if the database was opened with the #MDB_DUPSORT
1253 * flag.
1254 * If no comparison function is specified, and no special key flags were specified
1255 * with #mdb_dbi_open(), the data items are compared lexically, with shorter items collating
1256 * before longer items.
1257 * @warning This function must be called before any data access functions are used,
1258 * otherwise data corruption may occur. The same comparison function must be used by every
1259 * program accessing the database, every time the database is used.
1260 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1261 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1262 * @param[in] cmp A #MDB_cmp_func function
1263 * @return A non-zero error value on failure and 0 on success. Some possible
1264 * errors are:
1265 * <ul>
1266 * <li>EINVAL - an invalid parameter was specified.
1267 * </ul>
1268 */
1269int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp);
1270
1271 /** @brief Set a relocation function for a #MDB_FIXEDMAP database.
1272 *
1273 * @todo The relocation function is called whenever it is necessary to move the data
1274 * of an item to a different position in the database (e.g. through tree
1275 * balancing operations, shifts as a result of adds or deletes, etc.). It is
1276 * intended to allow address/position-dependent data items to be stored in
1277 * a database in an environment opened with the #MDB_FIXEDMAP option.
1278 * Currently the relocation feature is unimplemented and setting
1279 * this function has no effect.
1280 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1281 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1282 * @param[in] rel A #MDB_rel_func function
1283 * @return A non-zero error value on failure and 0 on success. Some possible
1284 * errors are:
1285 * <ul>
1286 * <li>EINVAL - an invalid parameter was specified.
1287 * </ul>
1288 */
1289int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel);
1290
1291 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function.
1292 *
1293 * See #mdb_set_relfunc and #MDB_rel_func for more details.
1294 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1295 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1296 * @param[in] ctx An arbitrary pointer for whatever the application needs.
1297 * It will be passed to the callback function set by #mdb_set_relfunc
1298 * as its \b relctx parameter whenever the callback is invoked.
1299 * @return A non-zero error value on failure and 0 on success. Some possible
1300 * errors are:
1301 * <ul>
1302 * <li>EINVAL - an invalid parameter was specified.
1303 * </ul>
1304 */
1305int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx);
1306
1307 /** @brief Get items from a database.
1308 *
1309 * This function retrieves key/data pairs from the database. The address
1310 * and length of the data associated with the specified \b key are returned
1311 * in the structure to which \b data refers.
1312 * If the database supports duplicate keys (#MDB_DUPSORT) then the
1313 * first data item for the key will be returned. Retrieval of other
1314 * items requires the use of #mdb_cursor_get().
1315 *
1316 * @note The memory pointed to by the returned values is owned by the
1317 * database. The caller need not dispose of the memory, and may not
1318 * modify it in any way. For values returned in a read-only transaction
1319 * any modification attempts will cause a SIGSEGV.
1320 * @note Values returned from the database are valid only until a
1321 * subsequent update operation, or the end of the transaction.
1322 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1323 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1324 * @param[in] key The key to search for in the database
1325 * @param[out] data The data corresponding to the key
1326 * @return A non-zero error value on failure and 0 on success. Some possible
1327 * errors are:
1328 * <ul>
1329 * <li>#MDB_NOTFOUND - the key was not in the database.
1330 * <li>EINVAL - an invalid parameter was specified.
1331 * </ul>
1332 */
1333int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1334
1335 /** @brief Store items into a database.
1336 *
1337 * This function stores key/data pairs in the database. The default behavior
1338 * is to enter the new key/data pair, replacing any previously existing key
1339 * if duplicates are disallowed, or adding a duplicate data item if
1340 * duplicates are allowed (#MDB_DUPSORT).
1341 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1342 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1343 * @param[in] key The key to store in the database
1344 * @param[in,out] data The data to store
1345 * @param[in] flags Special options for this operation. This parameter
1346 * must be set to 0 or by bitwise OR'ing together one or more of the
1347 * values described here.
1348 * <ul>
1349 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1350 * already appear in the database. This flag may only be specified
1351 * if the database was opened with #MDB_DUPSORT. The function will
1352 * return #MDB_KEYEXIST if the key/data pair already appears in the
1353 * database.
1354 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1355 * does not already appear in the database. The function will return
1356 * #MDB_KEYEXIST if the key already appears in the database, even if
1357 * the database supports duplicates (#MDB_DUPSORT). The \b data
1358 * parameter will be set to point to the existing item.
1359 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1360 * don't copy the given data. Instead, return a pointer to the
1361 * reserved space, which the caller can fill in later - before
1362 * the next update operation or the transaction ends. This saves
1363 * an extra memcpy if the data is being generated later.
1364 * LMDB does nothing else with this memory, the caller is expected
1365 * to modify all of the space requested. This flag must not be
1366 * specified if the database was opened with #MDB_DUPSORT.
1367 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1368 * database. This option allows fast bulk loading when keys are
1369 * already known to be in the correct order. Loading unsorted keys
1370 * with this flag will cause a #MDB_KEYEXIST error.
1371 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1372 * </ul>
1373 * @return A non-zero error value on failure and 0 on success. Some possible
1374 * errors are:
1375 * <ul>
1376 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1377 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1378 * <li>EACCES - an attempt was made to write in a read-only transaction.
1379 * <li>EINVAL - an invalid parameter was specified.
1380 * </ul>
1381 */
1382int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data,
1383 unsigned int flags);
1384
1385 /** @brief Delete items from a database.
1386 *
1387 * This function removes key/data pairs from the database.
1388 * If the database does not support sorted duplicate data items
1389 * (#MDB_DUPSORT) the data parameter is ignored.
1390 * If the database supports sorted duplicates and the data parameter
1391 * is NULL, all of the duplicate data items for the key will be
1392 * deleted. Otherwise, if the data parameter is non-NULL
1393 * only the matching data item will be deleted.
1394 * This function will return #MDB_NOTFOUND if the specified key/data
1395 * pair is not in the database.
1396 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1397 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1398 * @param[in] key The key to delete from the database
1399 * @param[in] data The data to delete
1400 * @return A non-zero error value on failure and 0 on success. Some possible
1401 * errors are:
1402 * <ul>
1403 * <li>EACCES - an attempt was made to write in a read-only transaction.
1404 * <li>EINVAL - an invalid parameter was specified.
1405 * </ul>
1406 */
1407int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data);
1408
1409 /** @brief Create a cursor handle.
1410 *
1411 * A cursor is associated with a specific transaction and database.
1412 * A cursor cannot be used when its database handle is closed. Nor
1413 * when its transaction has ended, except with #mdb_cursor_renew().
1414 * It can be discarded with #mdb_cursor_close().
1415 * A cursor in a write-transaction can be closed before its transaction
1416 * ends, and will otherwise be closed when its transaction ends.
1417 * A cursor in a read-only transaction must be closed explicitly, before
1418 * or after its transaction ends. It can be reused with
1419 * #mdb_cursor_renew() before finally closing it.
1420 * @note Earlier documentation said that cursors in every transaction
1421 * were closed when the transaction committed or aborted.
1422 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1423 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1424 * @param[out] cursor Address where the new #MDB_cursor handle will be stored
1425 * @return A non-zero error value on failure and 0 on success. Some possible
1426 * errors are:
1427 * <ul>
1428 * <li>EINVAL - an invalid parameter was specified.
1429 * </ul>
1430 */
1431int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor);
1432
1433 /** @brief Close a cursor handle.
1434 *
1435 * The cursor handle will be freed and must not be used again after this call.
1436 * Its transaction must still be live if it is a write-transaction.
1437 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1438 */
1439void mdb_cursor_close(MDB_cursor *cursor);
1440
1441 /** @brief Renew a cursor handle.
1442 *
1443 * A cursor is associated with a specific transaction and database.
1444 * Cursors that are only used in read-only
1445 * transactions may be re-used, to avoid unnecessary malloc/free overhead.
1446 * The cursor may be associated with a new read-only transaction, and
1447 * referencing the same database handle as it was created with.
1448 * This may be done whether the previous transaction is live or dead.
1449 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1450 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1451 * @return A non-zero error value on failure and 0 on success. Some possible
1452 * errors are:
1453 * <ul>
1454 * <li>EINVAL - an invalid parameter was specified.
1455 * </ul>
1456 */
1457int mdb_cursor_renew(MDB_txn *txn, MDB_cursor *cursor);
1458
1459 /** @brief Return the cursor's transaction handle.
1460 *
1461 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1462 */
1463MDB_txn *mdb_cursor_txn(MDB_cursor *cursor);
1464
1465 /** @brief Return the cursor's database handle.
1466 *
1467 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1468 */
1469MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor);
1470
1471 /** @brief Retrieve by cursor.
1472 *
1473 * This function retrieves key/data pairs from the database. The address and length
1474 * of the key are returned in the object to which \b key refers (except for the
1475 * case of the #MDB_SET option, in which the \b key object is unchanged), and
1476 * the address and length of the data are returned in the object to which \b data
1477 * refers.
1478 * See #mdb_get() for restrictions on using the output values.
1479 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1480 * @param[in,out] key The key for a retrieved item
1481 * @param[in,out] data The data of a retrieved item
1482 * @param[in] op A cursor operation #MDB_cursor_op
1483 * @return A non-zero error value on failure and 0 on success. Some possible
1484 * errors are:
1485 * <ul>
1486 * <li>#MDB_NOTFOUND - no matching key found.
1487 * <li>EINVAL - an invalid parameter was specified.
1488 * </ul>
1489 */
1490int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1491 MDB_cursor_op op);
1492
1493 /** @brief Store by cursor.
1494 *
1495 * This function stores key/data pairs into the database.
1496 * The cursor is positioned at the new item, or on failure usually near it.
1497 * @note Earlier documentation incorrectly said errors would leave the
1498 * state of the cursor unchanged.
1499 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1500 * @param[in] key The key operated on.
1501 * @param[in] data The data operated on.
1502 * @param[in] flags Options for this operation. This parameter
1503 * must be set to 0 or one of the values described here.
1504 * <ul>
1505 * <li>#MDB_CURRENT - replace the item at the current cursor position.
1506 * The \b key parameter must still be provided, and must match it.
1507 * If using sorted duplicates (#MDB_DUPSORT) the data item must still
1508 * sort into the same place. This is intended to be used when the
1509 * new data is the same size as the old. Otherwise it will simply
1510 * perform a delete of the old record followed by an insert.
1511 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not
1512 * already appear in the database. This flag may only be specified
1513 * if the database was opened with #MDB_DUPSORT. The function will
1514 * return #MDB_KEYEXIST if the key/data pair already appears in the
1515 * database.
1516 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key
1517 * does not already appear in the database. The function will return
1518 * #MDB_KEYEXIST if the key already appears in the database, even if
1519 * the database supports duplicates (#MDB_DUPSORT).
1520 * <li>#MDB_RESERVE - reserve space for data of the given size, but
1521 * don't copy the given data. Instead, return a pointer to the
1522 * reserved space, which the caller can fill in later - before
1523 * the next update operation or the transaction ends. This saves
1524 * an extra memcpy if the data is being generated later. This flag
1525 * must not be specified if the database was opened with #MDB_DUPSORT.
1526 * <li>#MDB_APPEND - append the given key/data pair to the end of the
1527 * database. No key comparisons are performed. This option allows
1528 * fast bulk loading when keys are already known to be in the
1529 * correct order. Loading unsorted keys with this flag will cause
1530 * a #MDB_KEYEXIST error.
1531 * <li>#MDB_APPENDDUP - as above, but for sorted dup data.
1532 * <li>#MDB_MULTIPLE - store multiple contiguous data elements in a
1533 * single request. This flag may only be specified if the database
1534 * was opened with #MDB_DUPFIXED. The \b data argument must be an
1535 * array of two MDB_vals. The mv_size of the first MDB_val must be
1536 * the size of a single data element. The mv_data of the first MDB_val
1537 * must point to the beginning of the array of contiguous data elements.
1538 * The mv_size of the second MDB_val must be the count of the number
1539 * of data elements to store. On return this field will be set to
1540 * the count of the number of elements actually written. The mv_data
1541 * of the second MDB_val is unused.
1542 * </ul>
1543 * @return A non-zero error value on failure and 0 on success. Some possible
1544 * errors are:
1545 * <ul>
1546 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
1547 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
1548 * <li>EACCES - an attempt was made to write in a read-only transaction.
1549 * <li>EINVAL - an invalid parameter was specified.
1550 * </ul>
1551 */
1552int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
1553 unsigned int flags);
1554
1555 /** @brief Delete current key/data pair
1556 *
1557 * This function deletes the key/data pair to which the cursor refers.
1558 * This does not invalidate the cursor, so operations such as MDB_NEXT
1559 * can still be used on it.
1560 * Both MDB_NEXT and MDB_GET_CURRENT will return the same record after
1561 * this operation.
1562 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1563 * @param[in] flags Options for this operation. This parameter
1564 * must be set to 0 or one of the values described here.
1565 * <ul>
1566 * <li>#MDB_NODUPDATA - delete all of the data items for the current key.
1567 * This flag may only be specified if the database was opened with #MDB_DUPSORT.
1568 * </ul>
1569 * @return A non-zero error value on failure and 0 on success. Some possible
1570 * errors are:
1571 * <ul>
1572 * <li>EACCES - an attempt was made to write in a read-only transaction.
1573 * <li>EINVAL - an invalid parameter was specified.
1574 * </ul>
1575 */
1576int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags);
1577
1578 /** @brief Return count of duplicates for current key.
1579 *
1580 * This call is only valid on databases that support sorted duplicate
1581 * data items #MDB_DUPSORT.
1582 * @param[in] cursor A cursor handle returned by #mdb_cursor_open()
1583 * @param[out] countp Address where the count will be stored
1584 * @return A non-zero error value on failure and 0 on success. Some possible
1585 * errors are:
1586 * <ul>
1587 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified.
1588 * </ul>
1589 */
1590int mdb_cursor_count(MDB_cursor *cursor, mdb_size_t *countp);
1591
1592 /** @brief Compare two data items according to a particular database.
1593 *
1594 * This returns a comparison as if the two data items were keys in the
1595 * specified database.
1596 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1597 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1598 * @param[in] a The first item to compare
1599 * @param[in] b The second item to compare
1600 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1601 */
1602int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1603
1604 /** @brief Compare two data items according to a particular database.
1605 *
1606 * This returns a comparison as if the two items were data items of
1607 * the specified database. The database must have the #MDB_DUPSORT flag.
1608 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
1609 * @param[in] dbi A database handle returned by #mdb_dbi_open()
1610 * @param[in] a The first item to compare
1611 * @param[in] b The second item to compare
1612 * @return < 0 if a < b, 0 if a == b, > 0 if a > b
1613 */
1614int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
1615
1616 /** @brief A callback function used to print a message from the library.
1617 *
1618 * @param[in] msg The string to be printed.
1619 * @param[in] ctx An arbitrary context pointer for the callback.
1620 * @return < 0 on failure, >= 0 on success.
1621 */
1622typedef int (MDB_msg_func)(const char *msg, void *ctx);
1623
1624 /** @brief Dump the entries in the reader lock table.
1625 *
1626 * @param[in] env An environment handle returned by #mdb_env_create()
1627 * @param[in] func A #MDB_msg_func function
1628 * @param[in] ctx Anything the message function needs
1629 * @return < 0 on failure, >= 0 on success.
1630 */
1631int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx);
1632
1633 /** @brief Check for stale entries in the reader lock table.
1634 *
1635 * @param[in] env An environment handle returned by #mdb_env_create()
1636 * @param[out] dead Number of stale slots that were cleared
1637 * @return 0 on success, non-zero on failure.
1638 */
1639int mdb_reader_check(MDB_env *env, int *dead);
1640/** @} */
1641
1642#ifdef __cplusplus
1643}
1644#endif
1645/** @page tools LMDB Command Line Tools
1646 The following describes the command line tools that are available for LMDB.
1647 \li \ref mdb_copy_1
1648 \li \ref mdb_dump_1
1649 \li \ref mdb_load_1
1650 \li \ref mdb_stat_1
1651*/
1652
1653#endif /* _LMDB_H_ */
1654