1 /** @file lmdb.h 2 * @brief Lightning memory-mapped database library 3 * 4 * @mainpage Lightning Memory-Mapped Database Manager (LMDB) 5 * 6 * @section intro_sec Introduction 7 * LMDB is a Btree-based database management library modeled loosely on the 8 * BerkeleyDB API, but much simplified. The entire database is exposed 9 * in a memory map, and all data fetches return data directly 10 * from the mapped memory, so no malloc's or memcpy's occur during 11 * data fetches. As such, the library is extremely simple because it 12 * requires no page caching layer of its own, and it is extremely high 13 * performance and memory-efficient. It is also fully transactional with 14 * full ACID semantics, and when the memory map is read-only, the 15 * database integrity cannot be corrupted by stray pointer writes from 16 * application code. 17 * 18 * The library is fully thread-aware and supports concurrent read/write 19 * access from multiple processes and threads. Data pages use a copy-on- 20 * write strategy so no active data pages are ever overwritten, which 21 * also provides resistance to corruption and eliminates the need of any 22 * special recovery procedures after a system crash. Writes are fully 23 * serialized; only one write transaction may be active at a time, which 24 * guarantees that writers can never deadlock. The database structure is 25 * multi-versioned so readers run with no locks; writers cannot block 26 * readers, and readers don't block writers. 27 * 28 * Unlike other well-known database mechanisms which use either write-ahead 29 * transaction logs or append-only data writes, LMDB requires no maintenance 30 * during operation. Both write-ahead loggers and append-only databases 31 * require periodic checkpointing and/or compaction of their log or database 32 * files otherwise they grow without bound. LMDB tracks free pages within 33 * the database and re-uses them for new write operations, so the database 34 * size does not grow without bound in normal use. 35 * 36 * The memory map can be used as a read-only or read-write map. It is 37 * read-only by default as this provides total immunity to corruption. 38 * Using read-write mode offers much higher write performance, but adds 39 * the possibility for stray application writes thru pointers to silently 40 * corrupt the database. Of course if your application code is known to 41 * be bug-free (...) then this is not an issue. 42 * 43 * If this is your first time using a transactional embedded key/value 44 * store, you may find the \ref starting page to be helpful. 45 * 46 * @section caveats_sec Caveats 47 * Troubleshooting the lock file, plus semaphores on BSD systems: 48 * 49 * - A broken lockfile can cause sync issues. 50 * Stale reader transactions left behind by an aborted program 51 * cause further writes to grow the database quickly, and 52 * stale locks can block further operation. 53 * 54 * Fix: Check for stale readers periodically, using the 55 * #mdb_reader_check function or the \ref mdb_stat_1 "mdb_stat" tool. 56 * Stale writers will be cleared automatically on some systems: 57 * - Windows - automatic 58 * - Linux, systems using POSIX mutexes with Robust option - automatic 59 * - not on BSD, systems using POSIX semaphores. 60 * Otherwise just make all programs using the database close it; 61 * the lockfile is always reset on first open of the environment. 62 * 63 * - On BSD systems or others configured with MDB_USE_POSIX_SEM, 64 * startup can fail due to semaphores owned by another userid. 65 * 66 * Fix: Open and close the database as the user which owns the 67 * semaphores (likely last user) or as root, while no other 68 * process is using the database. 69 * 70 * Restrictions/caveats (in addition to those listed for some functions): 71 * 72 * - Only the database owner should normally use the database on 73 * BSD systems or when otherwise configured with MDB_USE_POSIX_SEM. 74 * Multiple users can cause startup to fail later, as noted above. 75 * 76 * - There is normally no pure read-only mode, since readers need write 77 * access to locks and lock file. Exceptions: On read-only filesystems 78 * or with the #MDB_NOLOCK flag described under #mdb_env_open(). 79 * 80 * - An LMDB configuration will often reserve considerable \b unused 81 * memory address space and maybe file size for future growth. 82 * This does not use actual memory or disk space, but users may need 83 * to understand the difference so they won't be scared off. 84 * 85 * - By default, in versions before 0.9.10, unused portions of the data 86 * file might receive garbage data from memory freed by other code. 87 * (This does not happen when using the #MDB_WRITEMAP flag.) As of 88 * 0.9.10 the default behavior is to initialize such memory before 89 * writing to the data file. Since there may be a slight performance 90 * cost due to this initialization, applications may disable it using 91 * the #MDB_NOMEMINIT flag. Applications handling sensitive data 92 * which must not be written should not use this flag. This flag is 93 * irrelevant when using #MDB_WRITEMAP. 94 * 95 * - A thread can only use one transaction at a time, plus any child 96 * transactions. Each transaction belongs to one thread. See below. 97 * The #MDB_NOTLS flag changes this for read-only transactions. 98 * 99 * - Use an MDB_env* in the process which opened it, not after fork(). 100 * 101 * - Do not have open an LMDB database twice in the same process at 102 * the same time. Not even from a plain open() call - close()ing it 103 * breaks fcntl() advisory locking. (It is OK to reopen it after 104 * fork() - exec*(), since the lockfile has FD_CLOEXEC set.) 105 * 106 * - Avoid long-lived transactions. Read transactions prevent 107 * reuse of pages freed by newer write transactions, thus the 108 * database can grow quickly. Write transactions prevent 109 * other write transactions, since writes are serialized. 110 * 111 * - Avoid suspending a process with active transactions. These 112 * would then be "long-lived" as above. Also read transactions 113 * suspended when writers commit could sometimes see wrong data. 114 * 115 * ...when several processes can use a database concurrently: 116 * 117 * - Avoid aborting a process with an active transaction. 118 * The transaction becomes "long-lived" as above until a check 119 * for stale readers is performed or the lockfile is reset, 120 * since the process may not remove it from the lockfile. 121 * 122 * This does not apply to write transactions if the system clears 123 * stale writers, see above. 124 * 125 * - If you do that anyway, do a periodic check for stale readers. Or 126 * close the environment once in a while, so the lockfile can get reset. 127 * 128 * - Do not use LMDB databases on remote filesystems, even between 129 * processes on the same host. This breaks flock() on some OSes, 130 * possibly memory map sync, and certainly sync between programs 131 * on different hosts. 132 * 133 * - Opening a database can fail if another process is opening or 134 * closing it at exactly the same time. 135 * 136 * @author Howard Chu, Symas Corporation. 137 * 138 * @copyright Copyright 2011-2021 Howard Chu, Symas Corp. All rights reserved. 139 * 140 * Redistribution and use in source and binary forms, with or without 141 * modification, are permitted only as authorized by the OpenLDAP 142 * Public License. 143 * 144 * A copy of this license is available in the file LICENSE in the 145 * top-level directory of the distribution or, alternatively, at 146 * <http://www.OpenLDAP.org/license.html>. 147 * 148 * @par Derived From: 149 * This code is derived from btree.c written by Martin Hedenfalk. 150 * 151 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se> 152 * 153 * Permission to use, copy, modify, and distribute this software for any 154 * purpose with or without fee is hereby granted, provided that the above 155 * copyright notice and this permission notice appear in all copies. 156 * 157 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 158 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 159 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 160 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 161 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 162 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 163 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 164 */ 165 #ifndef _LMDB_H_ 166 #define _LMDB_H_ 167 168 #include <sys/types.h> 169 170 #ifdef __cplusplus 171 extern "C" { 172 #endif 173 174 /** Unix permissions for creating files, or dummy definition for Windows */ 175 #ifdef _MSC_VER 176 typedef int mdb_mode_t; 177 #else 178 typedef mode_t mdb_mode_t; 179 #endif 180 181 /** An abstraction for a file handle. 182 * On POSIX systems file handles are small integers. On Windows 183 * they're opaque pointers. 184 */ 185 #ifdef _WIN32 186 typedef void *mdb_filehandle_t; 187 #else 188 typedef int mdb_filehandle_t; 189 #endif 190 191 /** @defgroup mdb LMDB API 192 * @{ 193 * @brief OpenLDAP Lightning Memory-Mapped Database Manager 194 */ 195 /** @defgroup Version Version Macros 196 * @{ 197 */ 198 /** Library major version */ 199 #define MDB_VERSION_MAJOR 0 200 /** Library minor version */ 201 #define MDB_VERSION_MINOR 9 202 /** Library patch version */ 203 #define MDB_VERSION_PATCH 29 204 205 /** Combine args a,b,c into a single integer for easy version comparisons */ 206 #define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c)) 207 208 /** The full library version as a single integer */ 209 #define MDB_VERSION_FULL \ 210 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH) 211 212 /** The release date of this library version */ 213 #define MDB_VERSION_DATE "March 16, 2021" 214 215 /** A stringifier for the version info */ 216 #define MDB_VERSTR(a,b,c,d) "LMDB " #a "." #b "." #c ": (" d ")" 217 218 /** A helper for the stringifier macro */ 219 #define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d) 220 221 /** The full library version as a C string */ 222 #define MDB_VERSION_STRING \ 223 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE) 224 /** @} */ 225 226 /** @brief Opaque structure for a database environment. 227 * 228 * A DB environment supports multiple databases, all residing in the same 229 * shared-memory map. 230 */ 231 typedef struct MDB_env MDB_env; 232 233 /** @brief Opaque structure for a transaction handle. 234 * 235 * All database operations require a transaction handle. Transactions may be 236 * read-only or read-write. 237 */ 238 typedef struct MDB_txn MDB_txn; 239 240 /** @brief A handle for an individual database in the DB environment. */ 241 typedef unsigned int MDB_dbi; 242 243 /** @brief Opaque structure for navigating through a database */ 244 typedef struct MDB_cursor MDB_cursor; 245 246 /** @brief Generic structure used for passing keys and data in and out 247 * of the database. 248 * 249 * Values returned from the database are valid only until a subsequent 250 * update operation, or the end of the transaction. Do not modify or 251 * free them, they commonly point into the database itself. 252 * 253 * Key sizes must be between 1 and #mdb_env_get_maxkeysize() inclusive. 254 * The same applies to data sizes in databases with the #MDB_DUPSORT flag. 255 * Other data items can in theory be from 0 to 0xffffffff bytes long. 256 */ 257 typedef struct MDB_val { 258 size_t mv_size; /**< size of the data item */ 259 void *mv_data; /**< address of the data item */ 260 } MDB_val; 261 262 /** @brief A callback function used to compare two keys in a database */ 263 typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b); 264 265 /** @brief A callback function used to relocate a position-dependent data item 266 * in a fixed-address database. 267 * 268 * The \b newptr gives the item's desired address in 269 * the memory map, and \b oldptr gives its previous address. The item's actual 270 * data resides at the address in \b item. This callback is expected to walk 271 * through the fields of the record in \b item and modify any 272 * values based at the \b oldptr address to be relative to the \b newptr address. 273 * @param[in,out] item The item that is to be relocated. 274 * @param[in] oldptr The previous address. 275 * @param[in] newptr The new address to relocate to. 276 * @param[in] relctx An application-provided context, set by #mdb_set_relctx(). 277 * @todo This feature is currently unimplemented. 278 */ 279 typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx); 280 281 /** @defgroup mdb_env Environment Flags 282 * @{ 283 */ 284 /** mmap at a fixed address (experimental) */ 285 #define MDB_FIXEDMAP 0x01 286 /** no environment directory */ 287 #define MDB_NOSUBDIR 0x4000 288 /** don't fsync after commit */ 289 #define MDB_NOSYNC 0x10000 290 /** read only */ 291 #define MDB_RDONLY 0x20000 292 /** don't fsync metapage after commit */ 293 #define MDB_NOMETASYNC 0x40000 294 /** use writable mmap */ 295 #define MDB_WRITEMAP 0x80000 296 /** use asynchronous msync when #MDB_WRITEMAP is used */ 297 #define MDB_MAPASYNC 0x100000 298 /** tie reader locktable slots to #MDB_txn objects instead of to threads */ 299 #define MDB_NOTLS 0x200000 300 /** don't do any locking, caller must manage their own locks */ 301 #define MDB_NOLOCK 0x400000 302 /** don't do readahead (no effect on Windows) */ 303 #define MDB_NORDAHEAD 0x800000 304 /** don't initialize malloc'd memory before writing to datafile */ 305 #define MDB_NOMEMINIT 0x1000000 306 /** @} */ 307 308 /** @defgroup mdb_dbi_open Database Flags 309 * @{ 310 */ 311 /** use reverse string keys */ 312 #define MDB_REVERSEKEY 0x02 313 /** use sorted duplicates */ 314 #define MDB_DUPSORT 0x04 315 /** numeric keys in native byte order: either unsigned int or size_t. 316 * The keys must all be of the same size. */ 317 #define MDB_INTEGERKEY 0x08 318 /** with #MDB_DUPSORT, sorted dup items have fixed size */ 319 #define MDB_DUPFIXED 0x10 320 /** with #MDB_DUPSORT, dups are #MDB_INTEGERKEY-style integers */ 321 #define MDB_INTEGERDUP 0x20 322 /** with #MDB_DUPSORT, use reverse string dups */ 323 #define MDB_REVERSEDUP 0x40 324 /** create DB if not already existing */ 325 #define MDB_CREATE 0x40000 326 /** @} */ 327 328 /** @defgroup mdb_put Write Flags 329 * @{ 330 */ 331 /** For put: Don't write if the key already exists. */ 332 #define MDB_NOOVERWRITE 0x10 333 /** Only for #MDB_DUPSORT<br> 334 * For put: don't write if the key and data pair already exist.<br> 335 * For mdb_cursor_del: remove all duplicate data items. 336 */ 337 #define MDB_NODUPDATA 0x20 338 /** For mdb_cursor_put: overwrite the current key/data pair */ 339 #define MDB_CURRENT 0x40 340 /** For put: Just reserve space for data, don't copy it. Return a 341 * pointer to the reserved space. 342 */ 343 #define MDB_RESERVE 0x10000 344 /** Data is being appended, don't split full pages. */ 345 #define MDB_APPEND 0x20000 346 /** Duplicate data is being appended, don't split full pages. */ 347 #define MDB_APPENDDUP 0x40000 348 /** Store multiple data items in one call. Only for #MDB_DUPFIXED. */ 349 #define MDB_MULTIPLE 0x80000 350 /* @} */ 351 352 /** @defgroup mdb_copy Copy Flags 353 * @{ 354 */ 355 /** Compacting copy: Omit free space from copy, and renumber all 356 * pages sequentially. 357 */ 358 #define MDB_CP_COMPACT 0x01 359 /* @} */ 360 361 /** @brief Cursor Get operations. 362 * 363 * This is the set of all operations for retrieving data 364 * using a cursor. 365 */ 366 typedef enum MDB_cursor_op { 367 MDB_FIRST, /**< Position at first key/data item */ 368 MDB_FIRST_DUP, /**< Position at first data item of current key. 369 Only for #MDB_DUPSORT */ 370 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */ 371 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */ 372 MDB_GET_CURRENT, /**< Return key/data at current cursor position */ 373 MDB_GET_MULTIPLE, /**< Return up to a page of duplicate data items 374 from current cursor position. Move cursor to prepare 375 for #MDB_NEXT_MULTIPLE. Only for #MDB_DUPFIXED */ 376 MDB_LAST, /**< Position at last key/data item */ 377 MDB_LAST_DUP, /**< Position at last data item of current key. 378 Only for #MDB_DUPSORT */ 379 MDB_NEXT, /**< Position at next data item */ 380 MDB_NEXT_DUP, /**< Position at next data item of current key. 381 Only for #MDB_DUPSORT */ 382 MDB_NEXT_MULTIPLE, /**< Return up to a page of duplicate data items 383 from next cursor position. Move cursor to prepare 384 for #MDB_NEXT_MULTIPLE. Only for #MDB_DUPFIXED */ 385 MDB_NEXT_NODUP, /**< Position at first data item of next key */ 386 MDB_PREV, /**< Position at previous data item */ 387 MDB_PREV_DUP, /**< Position at previous data item of current key. 388 Only for #MDB_DUPSORT */ 389 MDB_PREV_NODUP, /**< Position at last data item of previous key */ 390 MDB_SET, /**< Position at specified key */ 391 MDB_SET_KEY, /**< Position at specified key, return key + data */ 392 MDB_SET_RANGE, /**< Position at first key greater than or equal to specified key. */ 393 MDB_PREV_MULTIPLE /**< Position at previous page and return up to 394 a page of duplicate data items. Only for #MDB_DUPFIXED */ 395 } MDB_cursor_op; 396 397 /** @defgroup errors Return Codes 398 * 399 * BerkeleyDB uses -30800 to -30999, we'll go under them 400 * @{ 401 */ 402 /** Successful result */ 403 #define MDB_SUCCESS 0 404 /** key/data pair already exists */ 405 #define MDB_KEYEXIST (-30799) 406 /** key/data pair not found (EOF) */ 407 #define MDB_NOTFOUND (-30798) 408 /** Requested page not found - this usually indicates corruption */ 409 #define MDB_PAGE_NOTFOUND (-30797) 410 /** Located page was wrong type */ 411 #define MDB_CORRUPTED (-30796) 412 /** Update of meta page failed or environment had fatal error */ 413 #define MDB_PANIC (-30795) 414 /** Environment version mismatch */ 415 #define MDB_VERSION_MISMATCH (-30794) 416 /** File is not a valid LMDB file */ 417 #define MDB_INVALID (-30793) 418 /** Environment mapsize reached */ 419 #define MDB_MAP_FULL (-30792) 420 /** Environment maxdbs reached */ 421 #define MDB_DBS_FULL (-30791) 422 /** Environment maxreaders reached */ 423 #define MDB_READERS_FULL (-30790) 424 /** Too many TLS keys in use - Windows only */ 425 #define MDB_TLS_FULL (-30789) 426 /** Txn has too many dirty pages */ 427 #define MDB_TXN_FULL (-30788) 428 /** Cursor stack too deep - internal error */ 429 #define MDB_CURSOR_FULL (-30787) 430 /** Page has not enough space - internal error */ 431 #define MDB_PAGE_FULL (-30786) 432 /** Database contents grew beyond environment mapsize */ 433 #define MDB_MAP_RESIZED (-30785) 434 /** Operation and DB incompatible, or DB type changed. This can mean: 435 * <ul> 436 * <li>The operation expects an #MDB_DUPSORT / #MDB_DUPFIXED database. 437 * <li>Opening a named DB when the unnamed DB has #MDB_DUPSORT / #MDB_INTEGERKEY. 438 * <li>Accessing a data record as a database, or vice versa. 439 * <li>The database was dropped and recreated with different flags. 440 * </ul> 441 */ 442 #define MDB_INCOMPATIBLE (-30784) 443 /** Invalid reuse of reader locktable slot */ 444 #define MDB_BAD_RSLOT (-30783) 445 /** Transaction must abort, has a child, or is invalid */ 446 #define MDB_BAD_TXN (-30782) 447 /** Unsupported size of key/DB name/data, or wrong DUPFIXED size */ 448 #define MDB_BAD_VALSIZE (-30781) 449 /** The specified DBI was changed unexpectedly */ 450 #define MDB_BAD_DBI (-30780) 451 /** The last defined error code */ 452 #define MDB_LAST_ERRCODE MDB_BAD_DBI 453 /** @} */ 454 455 /** @brief Statistics for a database in the environment */ 456 typedef struct MDB_stat { 457 unsigned int ms_psize; /**< Size of a database page. 458 This is currently the same for all databases. */ 459 unsigned int ms_depth; /**< Depth (height) of the B-tree */ 460 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */ 461 size_t ms_leaf_pages; /**< Number of leaf pages */ 462 size_t ms_overflow_pages; /**< Number of overflow pages */ 463 size_t ms_entries; /**< Number of data items */ 464 } MDB_stat; 465 466 /** @brief Information about the environment */ 467 typedef struct MDB_envinfo { 468 void *me_mapaddr; /**< Address of map, if fixed */ 469 size_t me_mapsize; /**< Size of the data memory map */ 470 size_t me_last_pgno; /**< ID of the last used page */ 471 size_t me_last_txnid; /**< ID of the last committed transaction */ 472 unsigned int me_maxreaders; /**< max reader slots in the environment */ 473 unsigned int me_numreaders; /**< max reader slots used in the environment */ 474 } MDB_envinfo; 475 476 /** @brief Return the LMDB library version information. 477 * 478 * @param[out] major if non-NULL, the library major version number is copied here 479 * @param[out] minor if non-NULL, the library minor version number is copied here 480 * @param[out] patch if non-NULL, the library patch version number is copied here 481 * @retval "version string" The library version as a string 482 */ 483 char *mdb_version(int *major, int *minor, int *patch); 484 485 /** @brief Return a string describing a given error code. 486 * 487 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3) 488 * function. If the error code is greater than or equal to 0, then the string 489 * returned by the system function strerror(3) is returned. If the error code 490 * is less than 0, an error string corresponding to the LMDB library error is 491 * returned. See @ref errors for a list of LMDB-specific error codes. 492 * @param[in] err The error code 493 * @retval "error message" The description of the error 494 */ 495 char *mdb_strerror(int err); 496 497 /** @brief Create an LMDB environment handle. 498 * 499 * This function allocates memory for a #MDB_env structure. To release 500 * the allocated memory and discard the handle, call #mdb_env_close(). 501 * Before the handle may be used, it must be opened using #mdb_env_open(). 502 * Various other options may also need to be set before opening the handle, 503 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(), 504 * depending on usage requirements. 505 * @param[out] env The address where the new handle will be stored 506 * @return A non-zero error value on failure and 0 on success. 507 */ 508 int mdb_env_create(MDB_env **env); 509 510 /** @brief Open an environment handle. 511 * 512 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle. 513 * @param[in] env An environment handle returned by #mdb_env_create() 514 * @param[in] path The directory in which the database files reside. This 515 * directory must already exist and be writable. 516 * @param[in] flags Special options for this environment. This parameter 517 * must be set to 0 or by bitwise OR'ing together one or more of the 518 * values described here. 519 * Flags set by mdb_env_set_flags() are also used. 520 * <ul> 521 * <li>#MDB_FIXEDMAP 522 * use a fixed address for the mmap region. This flag must be specified 523 * when creating the environment, and is stored persistently in the environment. 524 * If successful, the memory map will always reside at the same virtual address 525 * and pointers used to reference data items in the database will be constant 526 * across multiple invocations. This option may not always work, depending on 527 * how the operating system has allocated memory to shared libraries and other uses. 528 * The feature is highly experimental. 529 * <li>#MDB_NOSUBDIR 530 * By default, LMDB creates its environment in a directory whose 531 * pathname is given in \b path, and creates its data and lock files 532 * under that directory. With this option, \b path is used as-is for 533 * the database main data file. The database lock file is the \b path 534 * with "-lock" appended. 535 * <li>#MDB_RDONLY 536 * Open the environment in read-only mode. No write operations will be 537 * allowed. LMDB will still modify the lock file - except on read-only 538 * filesystems, where LMDB does not use locks. 539 * <li>#MDB_WRITEMAP 540 * Use a writeable memory map unless MDB_RDONLY is set. This uses 541 * fewer mallocs but loses protection from application bugs 542 * like wild pointer writes and other bad updates into the database. 543 * This may be slightly faster for DBs that fit entirely in RAM, but 544 * is slower for DBs larger than RAM. 545 * Incompatible with nested transactions. 546 * Do not mix processes with and without MDB_WRITEMAP on the same 547 * environment. This can defeat durability (#mdb_env_sync etc). 548 * <li>#MDB_NOMETASYNC 549 * Flush system buffers to disk only once per transaction, omit the 550 * metadata flush. Defer that until the system flushes files to disk, 551 * or next non-MDB_RDONLY commit or #mdb_env_sync(). This optimization 552 * maintains database integrity, but a system crash may undo the last 553 * committed transaction. I.e. it preserves the ACI (atomicity, 554 * consistency, isolation) but not D (durability) database property. 555 * This flag may be changed at any time using #mdb_env_set_flags(). 556 * <li>#MDB_NOSYNC 557 * Don't flush system buffers to disk when committing a transaction. 558 * This optimization means a system crash can corrupt the database or 559 * lose the last transactions if buffers are not yet flushed to disk. 560 * The risk is governed by how often the system flushes dirty buffers 561 * to disk and how often #mdb_env_sync() is called. However, if the 562 * filesystem preserves write order and the #MDB_WRITEMAP flag is not 563 * used, transactions exhibit ACI (atomicity, consistency, isolation) 564 * properties and only lose D (durability). I.e. database integrity 565 * is maintained, but a system crash may undo the final transactions. 566 * Note that (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no 567 * hint for when to write transactions to disk, unless #mdb_env_sync() 568 * is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable. 569 * This flag may be changed at any time using #mdb_env_set_flags(). 570 * <li>#MDB_MAPASYNC 571 * When using #MDB_WRITEMAP, use asynchronous flushes to disk. 572 * As with #MDB_NOSYNC, a system crash can then corrupt the 573 * database or lose the last transactions. Calling #mdb_env_sync() 574 * ensures on-disk database integrity until next commit. 575 * This flag may be changed at any time using #mdb_env_set_flags(). 576 * <li>#MDB_NOTLS 577 * Don't use Thread-Local Storage. Tie reader locktable slots to 578 * #MDB_txn objects instead of to threads. I.e. #mdb_txn_reset() keeps 579 * the slot reserved for the #MDB_txn object. A thread may use parallel 580 * read-only transactions. A read-only transaction may span threads if 581 * the user synchronizes its use. Applications that multiplex many 582 * user threads over individual OS threads need this option. Such an 583 * application must also serialize the write transactions in an OS 584 * thread, since LMDB's write locking is unaware of the user threads. 585 * <li>#MDB_NOLOCK 586 * Don't do any locking. If concurrent access is anticipated, the 587 * caller must manage all concurrency itself. For proper operation 588 * the caller must enforce single-writer semantics, and must ensure 589 * that no readers are using old transactions while a writer is 590 * active. The simplest approach is to use an exclusive lock so that 591 * no readers may be active at all when a writer begins. 592 * <li>#MDB_NORDAHEAD 593 * Turn off readahead. Most operating systems perform readahead on 594 * read requests by default. This option turns it off if the OS 595 * supports it. Turning it off may help random read performance 596 * when the DB is larger than RAM and system RAM is full. 597 * The option is not implemented on Windows. 598 * <li>#MDB_NOMEMINIT 599 * Don't initialize malloc'd memory before writing to unused spaces 600 * in the data file. By default, memory for pages written to the data 601 * file is obtained using malloc. While these pages may be reused in 602 * subsequent transactions, freshly malloc'd pages will be initialized 603 * to zeroes before use. This avoids persisting leftover data from other 604 * code (that used the heap and subsequently freed the memory) into the 605 * data file. Note that many other system libraries may allocate 606 * and free memory from the heap for arbitrary uses. E.g., stdio may 607 * use the heap for file I/O buffers. This initialization step has a 608 * modest performance cost so some applications may want to disable 609 * it using this flag. This option can be a problem for applications 610 * which handle sensitive data like passwords, and it makes memory 611 * checkers like Valgrind noisy. This flag is not needed with #MDB_WRITEMAP, 612 * which writes directly to the mmap instead of using malloc for pages. The 613 * initialization is also skipped if #MDB_RESERVE is used; the 614 * caller is expected to overwrite all of the memory that was 615 * reserved in that case. 616 * This flag may be changed at any time using #mdb_env_set_flags(). 617 * </ul> 618 * @param[in] mode The UNIX permissions to set on created files and semaphores. 619 * This parameter is ignored on Windows. 620 * @return A non-zero error value on failure and 0 on success. Some possible 621 * errors are: 622 * <ul> 623 * <li>#MDB_VERSION_MISMATCH - the version of the LMDB library doesn't match the 624 * version that created the database environment. 625 * <li>#MDB_INVALID - the environment file headers are corrupted. 626 * <li>ENOENT - the directory specified by the path parameter doesn't exist. 627 * <li>EACCES - the user didn't have permission to access the environment files. 628 * <li>EAGAIN - the environment was locked by another process. 629 * </ul> 630 */ 631 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode); 632 633 /** @brief Copy an LMDB environment to the specified path. 634 * 635 * This function may be used to make a backup of an existing environment. 636 * No lockfile is created, since it gets recreated at need. 637 * @note This call can trigger significant file size growth if run in 638 * parallel with write transactions, because it employs a read-only 639 * transaction. See long-lived transactions under @ref caveats_sec. 640 * @param[in] env An environment handle returned by #mdb_env_create(). It 641 * must have already been opened successfully. 642 * @param[in] path The directory in which the copy will reside. This 643 * directory must already exist and be writable but must otherwise be 644 * empty. 645 * @return A non-zero error value on failure and 0 on success. 646 */ 647 int mdb_env_copy(MDB_env *env, const char *path); 648 649 /** @brief Copy an LMDB environment to the specified file descriptor. 650 * 651 * This function may be used to make a backup of an existing environment. 652 * No lockfile is created, since it gets recreated at need. 653 * @note This call can trigger significant file size growth if run in 654 * parallel with write transactions, because it employs a read-only 655 * transaction. See long-lived transactions under @ref caveats_sec. 656 * @param[in] env An environment handle returned by #mdb_env_create(). It 657 * must have already been opened successfully. 658 * @param[in] fd The filedescriptor to write the copy to. It must 659 * have already been opened for Write access. 660 * @return A non-zero error value on failure and 0 on success. 661 */ 662 int mdb_env_copyfd(MDB_env *env, mdb_filehandle_t fd); 663 664 /** @brief Copy an LMDB environment to the specified path, with options. 665 * 666 * This function may be used to make a backup of an existing environment. 667 * No lockfile is created, since it gets recreated at need. 668 * @note This call can trigger significant file size growth if run in 669 * parallel with write transactions, because it employs a read-only 670 * transaction. See long-lived transactions under @ref caveats_sec. 671 * @param[in] env An environment handle returned by #mdb_env_create(). It 672 * must have already been opened successfully. 673 * @param[in] path The directory in which the copy will reside. This 674 * directory must already exist and be writable but must otherwise be 675 * empty. 676 * @param[in] flags Special options for this operation. This parameter 677 * must be set to 0 or by bitwise OR'ing together one or more of the 678 * values described here. 679 * <ul> 680 * <li>#MDB_CP_COMPACT - Perform compaction while copying: omit free 681 * pages and sequentially renumber all pages in output. This option 682 * consumes more CPU and runs more slowly than the default. 683 * Currently it fails if the environment has suffered a page leak. 684 * </ul> 685 * @return A non-zero error value on failure and 0 on success. 686 */ 687 int mdb_env_copy2(MDB_env *env, const char *path, unsigned int flags); 688 689 /** @brief Copy an LMDB environment to the specified file descriptor, 690 * with options. 691 * 692 * This function may be used to make a backup of an existing environment. 693 * No lockfile is created, since it gets recreated at need. See 694 * #mdb_env_copy2() for further details. 695 * @note This call can trigger significant file size growth if run in 696 * parallel with write transactions, because it employs a read-only 697 * transaction. See long-lived transactions under @ref caveats_sec. 698 * @param[in] env An environment handle returned by #mdb_env_create(). It 699 * must have already been opened successfully. 700 * @param[in] fd The filedescriptor to write the copy to. It must 701 * have already been opened for Write access. 702 * @param[in] flags Special options for this operation. 703 * See #mdb_env_copy2() for options. 704 * @return A non-zero error value on failure and 0 on success. 705 */ 706 int mdb_env_copyfd2(MDB_env *env, mdb_filehandle_t fd, unsigned int flags); 707 708 /** @brief Return statistics about the LMDB environment. 709 * 710 * @param[in] env An environment handle returned by #mdb_env_create() 711 * @param[out] stat The address of an #MDB_stat structure 712 * where the statistics will be copied 713 */ 714 int mdb_env_stat(MDB_env *env, MDB_stat *stat); 715 716 /** @brief Return information about the LMDB environment. 717 * 718 * @param[in] env An environment handle returned by #mdb_env_create() 719 * @param[out] stat The address of an #MDB_envinfo structure 720 * where the information will be copied 721 */ 722 int mdb_env_info(MDB_env *env, MDB_envinfo *stat); 723 724 /** @brief Flush the data buffers to disk. 725 * 726 * Data is always written to disk when #mdb_txn_commit() is called, 727 * but the operating system may keep it buffered. LMDB always flushes 728 * the OS buffers upon commit as well, unless the environment was 729 * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC. This call is 730 * not valid if the environment was opened with #MDB_RDONLY. 731 * @param[in] env An environment handle returned by #mdb_env_create() 732 * @param[in] force If non-zero, force a synchronous flush. Otherwise 733 * if the environment has the #MDB_NOSYNC flag set the flushes 734 * will be omitted, and with #MDB_MAPASYNC they will be asynchronous. 735 * @return A non-zero error value on failure and 0 on success. Some possible 736 * errors are: 737 * <ul> 738 * <li>EACCES - the environment is read-only. 739 * <li>EINVAL - an invalid parameter was specified. 740 * <li>EIO - an error occurred during synchronization. 741 * </ul> 742 */ 743 int mdb_env_sync(MDB_env *env, int force); 744 745 /** @brief Close the environment and release the memory map. 746 * 747 * Only a single thread may call this function. All transactions, databases, 748 * and cursors must already be closed before calling this function. Attempts to 749 * use any such handles after calling this function will cause a SIGSEGV. 750 * The environment handle will be freed and must not be used again after this call. 751 * @param[in] env An environment handle returned by #mdb_env_create() 752 */ 753 void mdb_env_close(MDB_env *env); 754 755 /** @brief Set environment flags. 756 * 757 * This may be used to set some flags in addition to those from 758 * #mdb_env_open(), or to unset these flags. If several threads 759 * change the flags at the same time, the result is undefined. 760 * @param[in] env An environment handle returned by #mdb_env_create() 761 * @param[in] flags The flags to change, bitwise OR'ed together 762 * @param[in] onoff A non-zero value sets the flags, zero clears them. 763 * @return A non-zero error value on failure and 0 on success. Some possible 764 * errors are: 765 * <ul> 766 * <li>EINVAL - an invalid parameter was specified. 767 * </ul> 768 */ 769 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff); 770 771 /** @brief Get environment flags. 772 * 773 * @param[in] env An environment handle returned by #mdb_env_create() 774 * @param[out] flags The address of an integer to store the flags 775 * @return A non-zero error value on failure and 0 on success. Some possible 776 * errors are: 777 * <ul> 778 * <li>EINVAL - an invalid parameter was specified. 779 * </ul> 780 */ 781 int mdb_env_get_flags(MDB_env *env, unsigned int *flags); 782 783 /** @brief Return the path that was used in #mdb_env_open(). 784 * 785 * @param[in] env An environment handle returned by #mdb_env_create() 786 * @param[out] path Address of a string pointer to contain the path. This 787 * is the actual string in the environment, not a copy. It should not be 788 * altered in any way. 789 * @return A non-zero error value on failure and 0 on success. Some possible 790 * errors are: 791 * <ul> 792 * <li>EINVAL - an invalid parameter was specified. 793 * </ul> 794 */ 795 int mdb_env_get_path(MDB_env *env, const char **path); 796 797 /** @brief Return the filedescriptor for the given environment. 798 * 799 * This function may be called after fork(), so the descriptor can be 800 * closed before exec*(). Other LMDB file descriptors have FD_CLOEXEC. 801 * (Until LMDB 0.9.18, only the lockfile had that.) 802 * 803 * @param[in] env An environment handle returned by #mdb_env_create() 804 * @param[out] fd Address of a mdb_filehandle_t to contain the descriptor. 805 * @return A non-zero error value on failure and 0 on success. Some possible 806 * errors are: 807 * <ul> 808 * <li>EINVAL - an invalid parameter was specified. 809 * </ul> 810 */ 811 int mdb_env_get_fd(MDB_env *env, mdb_filehandle_t *fd); 812 813 /** @brief Set the size of the memory map to use for this environment. 814 * 815 * The size should be a multiple of the OS page size. The default is 816 * 10485760 bytes. The size of the memory map is also the maximum size 817 * of the database. The value should be chosen as large as possible, 818 * to accommodate future growth of the database. 819 * This function should be called after #mdb_env_create() and before #mdb_env_open(). 820 * It may be called at later times if no transactions are active in 821 * this process. Note that the library does not check for this condition, 822 * the caller must ensure it explicitly. 823 * 824 * The new size takes effect immediately for the current process but 825 * will not be persisted to any others until a write transaction has been 826 * committed by the current process. Also, only mapsize increases are 827 * persisted into the environment. 828 * 829 * If the mapsize is increased by another process, and data has grown 830 * beyond the range of the current mapsize, #mdb_txn_begin() will 831 * return #MDB_MAP_RESIZED. This function may be called with a size 832 * of zero to adopt the new size. 833 * 834 * Any attempt to set a size smaller than the space already consumed 835 * by the environment will be silently changed to the current size of the used space. 836 * @param[in] env An environment handle returned by #mdb_env_create() 837 * @param[in] size The size in bytes 838 * @return A non-zero error value on failure and 0 on success. Some possible 839 * errors are: 840 * <ul> 841 * <li>EINVAL - an invalid parameter was specified, or the environment has 842 * an active write transaction. 843 * </ul> 844 */ 845 int mdb_env_set_mapsize(MDB_env *env, size_t size); 846 847 /** @brief Set the maximum number of threads/reader slots for the environment. 848 * 849 * This defines the number of slots in the lock table that is used to track readers in the 850 * the environment. The default is 126. 851 * Starting a read-only transaction normally ties a lock table slot to the 852 * current thread until the environment closes or the thread exits. If 853 * MDB_NOTLS is in use, #mdb_txn_begin() instead ties the slot to the 854 * MDB_txn object until it or the #MDB_env object is destroyed. 855 * This function may only be called after #mdb_env_create() and before #mdb_env_open(). 856 * @param[in] env An environment handle returned by #mdb_env_create() 857 * @param[in] readers The maximum number of reader lock table slots 858 * @return A non-zero error value on failure and 0 on success. Some possible 859 * errors are: 860 * <ul> 861 * <li>EINVAL - an invalid parameter was specified, or the environment is already open. 862 * </ul> 863 */ 864 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers); 865 866 /** @brief Get the maximum number of threads/reader slots for the environment. 867 * 868 * @param[in] env An environment handle returned by #mdb_env_create() 869 * @param[out] readers Address of an integer to store the number of readers 870 * @return A non-zero error value on failure and 0 on success. Some possible 871 * errors are: 872 * <ul> 873 * <li>EINVAL - an invalid parameter was specified. 874 * </ul> 875 */ 876 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers); 877 878 /** @brief Set the maximum number of named databases for the environment. 879 * 880 * This function is only needed if multiple databases will be used in the 881 * environment. Simpler applications that use the environment as a single 882 * unnamed database can ignore this option. 883 * This function may only be called after #mdb_env_create() and before #mdb_env_open(). 884 * 885 * Currently a moderate number of slots are cheap but a huge number gets 886 * expensive: 7-120 words per transaction, and every #mdb_dbi_open() 887 * does a linear search of the opened slots. 888 * @param[in] env An environment handle returned by #mdb_env_create() 889 * @param[in] dbs The maximum number of databases 890 * @return A non-zero error value on failure and 0 on success. Some possible 891 * errors are: 892 * <ul> 893 * <li>EINVAL - an invalid parameter was specified, or the environment is already open. 894 * </ul> 895 */ 896 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs); 897 898 /** @brief Get the maximum size of keys and #MDB_DUPSORT data we can write. 899 * 900 * Depends on the compile-time constant #MDB_MAXKEYSIZE. Default 511. 901 * See @ref MDB_val. 902 * @param[in] env An environment handle returned by #mdb_env_create() 903 * @return The maximum size of a key we can write 904 */ 905 int mdb_env_get_maxkeysize(MDB_env *env); 906 907 /** @brief Set application information associated with the #MDB_env. 908 * 909 * @param[in] env An environment handle returned by #mdb_env_create() 910 * @param[in] ctx An arbitrary pointer for whatever the application needs. 911 * @return A non-zero error value on failure and 0 on success. 912 */ 913 int mdb_env_set_userctx(MDB_env *env, void *ctx); 914 915 /** @brief Get the application information associated with the #MDB_env. 916 * 917 * @param[in] env An environment handle returned by #mdb_env_create() 918 * @return The pointer set by #mdb_env_set_userctx(). 919 */ 920 void *mdb_env_get_userctx(MDB_env *env); 921 922 /** @brief A callback function for most LMDB assert() failures, 923 * called before printing the message and aborting. 924 * 925 * @param[in] env An environment handle returned by #mdb_env_create(). 926 * @param[in] msg The assertion message, not including newline. 927 */ 928 typedef void MDB_assert_func(MDB_env *env, const char *msg); 929 930 /** Set or reset the assert() callback of the environment. 931 * Disabled if liblmdb is built with NDEBUG. 932 * @note This hack should become obsolete as lmdb's error handling matures. 933 * @param[in] env An environment handle returned by #mdb_env_create(). 934 * @param[in] func An #MDB_assert_func function, or 0. 935 * @return A non-zero error value on failure and 0 on success. 936 */ 937 int mdb_env_set_assert(MDB_env *env, MDB_assert_func *func); 938 939 /** @brief Create a transaction for use with the environment. 940 * 941 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit(). 942 * @note A transaction and its cursors must only be used by a single 943 * thread, and a thread may only have a single transaction at a time. 944 * If #MDB_NOTLS is in use, this does not apply to read-only transactions. 945 * @note Cursors may not span transactions. 946 * @param[in] env An environment handle returned by #mdb_env_create() 947 * @param[in] parent If this parameter is non-NULL, the new transaction 948 * will be a nested transaction, with the transaction indicated by \b parent 949 * as its parent. Transactions may be nested to any level. A parent 950 * transaction and its cursors may not issue any other operations than 951 * mdb_txn_commit and mdb_txn_abort while it has active child transactions. 952 * @param[in] flags Special options for this transaction. This parameter 953 * must be set to 0 or by bitwise OR'ing together one or more of the 954 * values described here. 955 * <ul> 956 * <li>#MDB_RDONLY 957 * This transaction will not perform any write operations. 958 * </ul> 959 * @param[out] txn Address where the new #MDB_txn handle will be stored 960 * @return A non-zero error value on failure and 0 on success. Some possible 961 * errors are: 962 * <ul> 963 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment 964 * must be shut down. 965 * <li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's 966 * mapsize and this environment's map must be resized as well. 967 * See #mdb_env_set_mapsize(). 968 * <li>#MDB_READERS_FULL - a read-only transaction was requested and 969 * the reader lock table is full. See #mdb_env_set_maxreaders(). 970 * <li>ENOMEM - out of memory. 971 * </ul> 972 */ 973 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn); 974 975 /** @brief Returns the transaction's #MDB_env 976 * 977 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 978 */ 979 MDB_env *mdb_txn_env(MDB_txn *txn); 980 981 /** @brief Return the transaction's ID. 982 * 983 * This returns the identifier associated with this transaction. For a 984 * read-only transaction, this corresponds to the snapshot being read; 985 * concurrent readers will frequently have the same transaction ID. 986 * 987 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 988 * @return A transaction ID, valid if input is an active transaction. 989 */ 990 size_t mdb_txn_id(MDB_txn *txn); 991 992 /** @brief Commit all the operations of a transaction into the database. 993 * 994 * The transaction handle is freed. It and its cursors must not be used 995 * again after this call, except with #mdb_cursor_renew(). 996 * @note Earlier documentation incorrectly said all cursors would be freed. 997 * Only write-transactions free cursors. 998 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 999 * @return A non-zero error value on failure and 0 on success. Some possible 1000 * errors are: 1001 * <ul> 1002 * <li>EINVAL - an invalid parameter was specified. 1003 * <li>ENOSPC - no more disk space. 1004 * <li>EIO - a low-level I/O error occurred while writing. 1005 * <li>ENOMEM - out of memory. 1006 * </ul> 1007 */ 1008 int mdb_txn_commit(MDB_txn *txn); 1009 1010 /** @brief Abandon all the operations of the transaction instead of saving them. 1011 * 1012 * The transaction handle is freed. It and its cursors must not be used 1013 * again after this call, except with #mdb_cursor_renew(). 1014 * @note Earlier documentation incorrectly said all cursors would be freed. 1015 * Only write-transactions free cursors. 1016 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1017 */ 1018 void mdb_txn_abort(MDB_txn *txn); 1019 1020 /** @brief Reset a read-only transaction. 1021 * 1022 * Abort the transaction like #mdb_txn_abort(), but keep the transaction 1023 * handle. #mdb_txn_renew() may reuse the handle. This saves allocation 1024 * overhead if the process will start a new read-only transaction soon, 1025 * and also locking overhead if #MDB_NOTLS is in use. The reader table 1026 * lock is released, but the table slot stays tied to its thread or 1027 * #MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free 1028 * its lock table slot if MDB_NOTLS is in use. 1029 * Cursors opened within the transaction must not be used 1030 * again after this call, except with #mdb_cursor_renew(). 1031 * Reader locks generally don't interfere with writers, but they keep old 1032 * versions of database pages allocated. Thus they prevent the old pages 1033 * from being reused when writers commit new data, and so under heavy load 1034 * the database size may grow much more rapidly than otherwise. 1035 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1036 */ 1037 void mdb_txn_reset(MDB_txn *txn); 1038 1039 /** @brief Renew a read-only transaction. 1040 * 1041 * This acquires a new reader lock for a transaction handle that had been 1042 * released by #mdb_txn_reset(). It must be called before a reset transaction 1043 * may be used again. 1044 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1045 * @return A non-zero error value on failure and 0 on success. Some possible 1046 * errors are: 1047 * <ul> 1048 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment 1049 * must be shut down. 1050 * <li>EINVAL - an invalid parameter was specified. 1051 * </ul> 1052 */ 1053 int mdb_txn_renew(MDB_txn *txn); 1054 1055 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */ 1056 #define mdb_open(txn,name,flags,dbi) mdb_dbi_open(txn,name,flags,dbi) 1057 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */ 1058 #define mdb_close(env,dbi) mdb_dbi_close(env,dbi) 1059 1060 /** @brief Open a database in the environment. 1061 * 1062 * A database handle denotes the name and parameters of a database, 1063 * independently of whether such a database exists. 1064 * The database handle may be discarded by calling #mdb_dbi_close(). 1065 * The old database handle is returned if the database was already open. 1066 * The handle may only be closed once. 1067 * 1068 * The database handle will be private to the current transaction until 1069 * the transaction is successfully committed. If the transaction is 1070 * aborted the handle will be closed automatically. 1071 * After a successful commit the handle will reside in the shared 1072 * environment, and may be used by other transactions. 1073 * 1074 * This function must not be called from multiple concurrent 1075 * transactions in the same process. A transaction that uses 1076 * this function must finish (either commit or abort) before 1077 * any other transaction in the process may use this function. 1078 * 1079 * To use named databases (with name != NULL), #mdb_env_set_maxdbs() 1080 * must be called before opening the environment. Database names are 1081 * keys in the unnamed database, and may be read but not written. 1082 * 1083 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1084 * @param[in] name The name of the database to open. If only a single 1085 * database is needed in the environment, this value may be NULL. 1086 * @param[in] flags Special options for this database. This parameter 1087 * must be set to 0 or by bitwise OR'ing together one or more of the 1088 * values described here. 1089 * <ul> 1090 * <li>#MDB_REVERSEKEY 1091 * Keys are strings to be compared in reverse order, from the end 1092 * of the strings to the beginning. By default, Keys are treated as strings and 1093 * compared from beginning to end. 1094 * <li>#MDB_DUPSORT 1095 * Duplicate keys may be used in the database. (Or, from another perspective, 1096 * keys may have multiple data items, stored in sorted order.) By default 1097 * keys must be unique and may have only a single data item. 1098 * <li>#MDB_INTEGERKEY 1099 * Keys are binary integers in native byte order, either unsigned int 1100 * or size_t, and will be sorted as such. 1101 * The keys must all be of the same size. 1102 * <li>#MDB_DUPFIXED 1103 * This flag may only be used in combination with #MDB_DUPSORT. This option 1104 * tells the library that the data items for this database are all the same 1105 * size, which allows further optimizations in storage and retrieval. When 1106 * all data items are the same size, the #MDB_GET_MULTIPLE, #MDB_NEXT_MULTIPLE 1107 * and #MDB_PREV_MULTIPLE cursor operations may be used to retrieve multiple 1108 * items at once. 1109 * <li>#MDB_INTEGERDUP 1110 * This option specifies that duplicate data items are binary integers, 1111 * similar to #MDB_INTEGERKEY keys. 1112 * <li>#MDB_REVERSEDUP 1113 * This option specifies that duplicate data items should be compared as 1114 * strings in reverse order. 1115 * <li>#MDB_CREATE 1116 * Create the named database if it doesn't exist. This option is not 1117 * allowed in a read-only transaction or a read-only environment. 1118 * </ul> 1119 * @param[out] dbi Address where the new #MDB_dbi handle will be stored 1120 * @return A non-zero error value on failure and 0 on success. Some possible 1121 * errors are: 1122 * <ul> 1123 * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment 1124 * and #MDB_CREATE was not specified. 1125 * <li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs(). 1126 * </ul> 1127 */ 1128 int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi); 1129 1130 /** @brief Retrieve statistics for a database. 1131 * 1132 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1133 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1134 * @param[out] stat The address of an #MDB_stat structure 1135 * where the statistics will be copied 1136 * @return A non-zero error value on failure and 0 on success. Some possible 1137 * errors are: 1138 * <ul> 1139 * <li>EINVAL - an invalid parameter was specified. 1140 * </ul> 1141 */ 1142 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat); 1143 1144 /** @brief Retrieve the DB flags for a database handle. 1145 * 1146 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1147 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1148 * @param[out] flags Address where the flags will be returned. 1149 * @return A non-zero error value on failure and 0 on success. 1150 */ 1151 int mdb_dbi_flags(MDB_txn *txn, MDB_dbi dbi, unsigned int *flags); 1152 1153 /** @brief Close a database handle. Normally unnecessary. Use with care: 1154 * 1155 * This call is not mutex protected. Handles should only be closed by 1156 * a single thread, and only if no other threads are going to reference 1157 * the database handle or one of its cursors any further. Do not close 1158 * a handle if an existing transaction has modified its database. 1159 * Doing so can cause misbehavior from database corruption to errors 1160 * like MDB_BAD_VALSIZE (since the DB name is gone). 1161 * 1162 * Closing a database handle is not necessary, but lets #mdb_dbi_open() 1163 * reuse the handle value. Usually it's better to set a bigger 1164 * #mdb_env_set_maxdbs(), unless that value would be large. 1165 * 1166 * @param[in] env An environment handle returned by #mdb_env_create() 1167 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1168 */ 1169 void mdb_dbi_close(MDB_env *env, MDB_dbi dbi); 1170 1171 /** @brief Empty or delete+close a database. 1172 * 1173 * See #mdb_dbi_close() for restrictions about closing the DB handle. 1174 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1175 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1176 * @param[in] del 0 to empty the DB, 1 to delete it from the 1177 * environment and close the DB handle. 1178 * @return A non-zero error value on failure and 0 on success. 1179 */ 1180 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del); 1181 1182 /** @brief Set a custom key comparison function for a database. 1183 * 1184 * The comparison function is called whenever it is necessary to compare a 1185 * key specified by the application with a key currently stored in the database. 1186 * If no comparison function is specified, and no special key flags were specified 1187 * with #mdb_dbi_open(), the keys are compared lexically, with shorter keys collating 1188 * before longer keys. 1189 * @warning This function must be called before any data access functions are used, 1190 * otherwise data corruption may occur. The same comparison function must be used by every 1191 * program accessing the database, every time the database is used. 1192 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1193 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1194 * @param[in] cmp A #MDB_cmp_func function 1195 * @return A non-zero error value on failure and 0 on success. Some possible 1196 * errors are: 1197 * <ul> 1198 * <li>EINVAL - an invalid parameter was specified. 1199 * </ul> 1200 */ 1201 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp); 1202 1203 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database. 1204 * 1205 * This comparison function is called whenever it is necessary to compare a data 1206 * item specified by the application with a data item currently stored in the database. 1207 * This function only takes effect if the database was opened with the #MDB_DUPSORT 1208 * flag. 1209 * If no comparison function is specified, and no special key flags were specified 1210 * with #mdb_dbi_open(), the data items are compared lexically, with shorter items collating 1211 * before longer items. 1212 * @warning This function must be called before any data access functions are used, 1213 * otherwise data corruption may occur. The same comparison function must be used by every 1214 * program accessing the database, every time the database is used. 1215 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1216 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1217 * @param[in] cmp A #MDB_cmp_func function 1218 * @return A non-zero error value on failure and 0 on success. Some possible 1219 * errors are: 1220 * <ul> 1221 * <li>EINVAL - an invalid parameter was specified. 1222 * </ul> 1223 */ 1224 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp); 1225 1226 /** @brief Set a relocation function for a #MDB_FIXEDMAP database. 1227 * 1228 * @todo The relocation function is called whenever it is necessary to move the data 1229 * of an item to a different position in the database (e.g. through tree 1230 * balancing operations, shifts as a result of adds or deletes, etc.). It is 1231 * intended to allow address/position-dependent data items to be stored in 1232 * a database in an environment opened with the #MDB_FIXEDMAP option. 1233 * Currently the relocation feature is unimplemented and setting 1234 * this function has no effect. 1235 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1236 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1237 * @param[in] rel A #MDB_rel_func function 1238 * @return A non-zero error value on failure and 0 on success. Some possible 1239 * errors are: 1240 * <ul> 1241 * <li>EINVAL - an invalid parameter was specified. 1242 * </ul> 1243 */ 1244 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel); 1245 1246 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function. 1247 * 1248 * See #mdb_set_relfunc and #MDB_rel_func for more details. 1249 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1250 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1251 * @param[in] ctx An arbitrary pointer for whatever the application needs. 1252 * It will be passed to the callback function set by #mdb_set_relfunc 1253 * as its \b relctx parameter whenever the callback is invoked. 1254 * @return A non-zero error value on failure and 0 on success. Some possible 1255 * errors are: 1256 * <ul> 1257 * <li>EINVAL - an invalid parameter was specified. 1258 * </ul> 1259 */ 1260 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx); 1261 1262 /** @brief Get items from a database. 1263 * 1264 * This function retrieves key/data pairs from the database. The address 1265 * and length of the data associated with the specified \b key are returned 1266 * in the structure to which \b data refers. 1267 * If the database supports duplicate keys (#MDB_DUPSORT) then the 1268 * first data item for the key will be returned. Retrieval of other 1269 * items requires the use of #mdb_cursor_get(). 1270 * 1271 * @note The memory pointed to by the returned values is owned by the 1272 * database. The caller need not dispose of the memory, and may not 1273 * modify it in any way. For values returned in a read-only transaction 1274 * any modification attempts will cause a SIGSEGV. 1275 * @note Values returned from the database are valid only until a 1276 * subsequent update operation, or the end of the transaction. 1277 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1278 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1279 * @param[in] key The key to search for in the database 1280 * @param[out] data The data corresponding to the key 1281 * @return A non-zero error value on failure and 0 on success. Some possible 1282 * errors are: 1283 * <ul> 1284 * <li>#MDB_NOTFOUND - the key was not in the database. 1285 * <li>EINVAL - an invalid parameter was specified. 1286 * </ul> 1287 */ 1288 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data); 1289 1290 /** @brief Store items into a database. 1291 * 1292 * This function stores key/data pairs in the database. The default behavior 1293 * is to enter the new key/data pair, replacing any previously existing key 1294 * if duplicates are disallowed, or adding a duplicate data item if 1295 * duplicates are allowed (#MDB_DUPSORT). 1296 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1297 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1298 * @param[in] key The key to store in the database 1299 * @param[in,out] data The data to store 1300 * @param[in] flags Special options for this operation. This parameter 1301 * must be set to 0 or by bitwise OR'ing together one or more of the 1302 * values described here. 1303 * <ul> 1304 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not 1305 * already appear in the database. This flag may only be specified 1306 * if the database was opened with #MDB_DUPSORT. The function will 1307 * return #MDB_KEYEXIST if the key/data pair already appears in the 1308 * database. 1309 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key 1310 * does not already appear in the database. The function will return 1311 * #MDB_KEYEXIST if the key already appears in the database, even if 1312 * the database supports duplicates (#MDB_DUPSORT). The \b data 1313 * parameter will be set to point to the existing item. 1314 * <li>#MDB_RESERVE - reserve space for data of the given size, but 1315 * don't copy the given data. Instead, return a pointer to the 1316 * reserved space, which the caller can fill in later - before 1317 * the next update operation or the transaction ends. This saves 1318 * an extra memcpy if the data is being generated later. 1319 * LMDB does nothing else with this memory, the caller is expected 1320 * to modify all of the space requested. This flag must not be 1321 * specified if the database was opened with #MDB_DUPSORT. 1322 * <li>#MDB_APPEND - append the given key/data pair to the end of the 1323 * database. This option allows fast bulk loading when keys are 1324 * already known to be in the correct order. Loading unsorted keys 1325 * with this flag will cause a #MDB_KEYEXIST error. 1326 * <li>#MDB_APPENDDUP - as above, but for sorted dup data. 1327 * </ul> 1328 * @return A non-zero error value on failure and 0 on success. Some possible 1329 * errors are: 1330 * <ul> 1331 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize(). 1332 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages. 1333 * <li>EACCES - an attempt was made to write in a read-only transaction. 1334 * <li>EINVAL - an invalid parameter was specified. 1335 * </ul> 1336 */ 1337 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data, 1338 unsigned int flags); 1339 1340 /** @brief Delete items from a database. 1341 * 1342 * This function removes key/data pairs from the database. 1343 * If the database does not support sorted duplicate data items 1344 * (#MDB_DUPSORT) the data parameter is ignored. 1345 * If the database supports sorted duplicates and the data parameter 1346 * is NULL, all of the duplicate data items for the key will be 1347 * deleted. Otherwise, if the data parameter is non-NULL 1348 * only the matching data item will be deleted. 1349 * This function will return #MDB_NOTFOUND if the specified key/data 1350 * pair is not in the database. 1351 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1352 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1353 * @param[in] key The key to delete from the database 1354 * @param[in] data The data to delete 1355 * @return A non-zero error value on failure and 0 on success. Some possible 1356 * errors are: 1357 * <ul> 1358 * <li>EACCES - an attempt was made to write in a read-only transaction. 1359 * <li>EINVAL - an invalid parameter was specified. 1360 * </ul> 1361 */ 1362 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data); 1363 1364 /** @brief Create a cursor handle. 1365 * 1366 * A cursor is associated with a specific transaction and database. 1367 * A cursor cannot be used when its database handle is closed. Nor 1368 * when its transaction has ended, except with #mdb_cursor_renew(). 1369 * It can be discarded with #mdb_cursor_close(). 1370 * A cursor in a write-transaction can be closed before its transaction 1371 * ends, and will otherwise be closed when its transaction ends. 1372 * A cursor in a read-only transaction must be closed explicitly, before 1373 * or after its transaction ends. It can be reused with 1374 * #mdb_cursor_renew() before finally closing it. 1375 * @note Earlier documentation said that cursors in every transaction 1376 * were closed when the transaction committed or aborted. 1377 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1378 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1379 * @param[out] cursor Address where the new #MDB_cursor handle will be stored 1380 * @return A non-zero error value on failure and 0 on success. Some possible 1381 * errors are: 1382 * <ul> 1383 * <li>EINVAL - an invalid parameter was specified. 1384 * </ul> 1385 */ 1386 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor); 1387 1388 /** @brief Close a cursor handle. 1389 * 1390 * The cursor handle will be freed and must not be used again after this call. 1391 * Its transaction must still be live if it is a write-transaction. 1392 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1393 */ 1394 void mdb_cursor_close(MDB_cursor *cursor); 1395 1396 /** @brief Renew a cursor handle. 1397 * 1398 * A cursor is associated with a specific transaction and database. 1399 * Cursors that are only used in read-only 1400 * transactions may be re-used, to avoid unnecessary malloc/free overhead. 1401 * The cursor may be associated with a new read-only transaction, and 1402 * referencing the same database handle as it was created with. 1403 * This may be done whether the previous transaction is live or dead. 1404 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1405 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1406 * @return A non-zero error value on failure and 0 on success. Some possible 1407 * errors are: 1408 * <ul> 1409 * <li>EINVAL - an invalid parameter was specified. 1410 * </ul> 1411 */ 1412 int mdb_cursor_renew(MDB_txn *txn, MDB_cursor *cursor); 1413 1414 /** @brief Return the cursor's transaction handle. 1415 * 1416 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1417 */ 1418 MDB_txn *mdb_cursor_txn(MDB_cursor *cursor); 1419 1420 /** @brief Return the cursor's database handle. 1421 * 1422 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1423 */ 1424 MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor); 1425 1426 /** @brief Retrieve by cursor. 1427 * 1428 * This function retrieves key/data pairs from the database. The address and length 1429 * of the key are returned in the object to which \b key refers (except for the 1430 * case of the #MDB_SET option, in which the \b key object is unchanged), and 1431 * the address and length of the data are returned in the object to which \b data 1432 * refers. 1433 * See #mdb_get() for restrictions on using the output values. 1434 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1435 * @param[in,out] key The key for a retrieved item 1436 * @param[in,out] data The data of a retrieved item 1437 * @param[in] op A cursor operation #MDB_cursor_op 1438 * @return A non-zero error value on failure and 0 on success. Some possible 1439 * errors are: 1440 * <ul> 1441 * <li>#MDB_NOTFOUND - no matching key found. 1442 * <li>EINVAL - an invalid parameter was specified. 1443 * </ul> 1444 */ 1445 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data, 1446 MDB_cursor_op op); 1447 1448 /** @brief Store by cursor. 1449 * 1450 * This function stores key/data pairs into the database. 1451 * The cursor is positioned at the new item, or on failure usually near it. 1452 * @note Earlier documentation incorrectly said errors would leave the 1453 * state of the cursor unchanged. 1454 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1455 * @param[in] key The key operated on. 1456 * @param[in] data The data operated on. 1457 * @param[in] flags Options for this operation. This parameter 1458 * must be set to 0 or one of the values described here. 1459 * <ul> 1460 * <li>#MDB_CURRENT - replace the item at the current cursor position. 1461 * The \b key parameter must still be provided, and must match it. 1462 * If using sorted duplicates (#MDB_DUPSORT) the data item must still 1463 * sort into the same place. This is intended to be used when the 1464 * new data is the same size as the old. Otherwise it will simply 1465 * perform a delete of the old record followed by an insert. 1466 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not 1467 * already appear in the database. This flag may only be specified 1468 * if the database was opened with #MDB_DUPSORT. The function will 1469 * return #MDB_KEYEXIST if the key/data pair already appears in the 1470 * database. 1471 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key 1472 * does not already appear in the database. The function will return 1473 * #MDB_KEYEXIST if the key already appears in the database, even if 1474 * the database supports duplicates (#MDB_DUPSORT). 1475 * <li>#MDB_RESERVE - reserve space for data of the given size, but 1476 * don't copy the given data. Instead, return a pointer to the 1477 * reserved space, which the caller can fill in later - before 1478 * the next update operation or the transaction ends. This saves 1479 * an extra memcpy if the data is being generated later. This flag 1480 * must not be specified if the database was opened with #MDB_DUPSORT. 1481 * <li>#MDB_APPEND - append the given key/data pair to the end of the 1482 * database. No key comparisons are performed. This option allows 1483 * fast bulk loading when keys are already known to be in the 1484 * correct order. Loading unsorted keys with this flag will cause 1485 * a #MDB_KEYEXIST error. 1486 * <li>#MDB_APPENDDUP - as above, but for sorted dup data. 1487 * <li>#MDB_MULTIPLE - store multiple contiguous data elements in a 1488 * single request. This flag may only be specified if the database 1489 * was opened with #MDB_DUPFIXED. The \b data argument must be an 1490 * array of two MDB_vals. The mv_size of the first MDB_val must be 1491 * the size of a single data element. The mv_data of the first MDB_val 1492 * must point to the beginning of the array of contiguous data elements. 1493 * The mv_size of the second MDB_val must be the count of the number 1494 * of data elements to store. On return this field will be set to 1495 * the count of the number of elements actually written. The mv_data 1496 * of the second MDB_val is unused. 1497 * </ul> 1498 * @return A non-zero error value on failure and 0 on success. Some possible 1499 * errors are: 1500 * <ul> 1501 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize(). 1502 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages. 1503 * <li>EACCES - an attempt was made to write in a read-only transaction. 1504 * <li>EINVAL - an invalid parameter was specified. 1505 * </ul> 1506 */ 1507 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data, 1508 unsigned int flags); 1509 1510 /** @brief Delete current key/data pair 1511 * 1512 * This function deletes the key/data pair to which the cursor refers. 1513 * This does not invalidate the cursor, so operations such as MDB_NEXT 1514 * can still be used on it. 1515 * Both MDB_NEXT and MDB_GET_CURRENT will return the same record after 1516 * this operation. 1517 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1518 * @param[in] flags Options for this operation. This parameter 1519 * must be set to 0 or one of the values described here. 1520 * <ul> 1521 * <li>#MDB_NODUPDATA - delete all of the data items for the current key. 1522 * This flag may only be specified if the database was opened with #MDB_DUPSORT. 1523 * </ul> 1524 * @return A non-zero error value on failure and 0 on success. Some possible 1525 * errors are: 1526 * <ul> 1527 * <li>EACCES - an attempt was made to write in a read-only transaction. 1528 * <li>EINVAL - an invalid parameter was specified. 1529 * </ul> 1530 */ 1531 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags); 1532 1533 /** @brief Return count of duplicates for current key. 1534 * 1535 * This call is only valid on databases that support sorted duplicate 1536 * data items #MDB_DUPSORT. 1537 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1538 * @param[out] countp Address where the count will be stored 1539 * @return A non-zero error value on failure and 0 on success. Some possible 1540 * errors are: 1541 * <ul> 1542 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified. 1543 * </ul> 1544 */ 1545 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp); 1546 1547 /** @brief Compare two data items according to a particular database. 1548 * 1549 * This returns a comparison as if the two data items were keys in the 1550 * specified database. 1551 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1552 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1553 * @param[in] a The first item to compare 1554 * @param[in] b The second item to compare 1555 * @return < 0 if a < b, 0 if a == b, > 0 if a > b 1556 */ 1557 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b); 1558 1559 /** @brief Compare two data items according to a particular database. 1560 * 1561 * This returns a comparison as if the two items were data items of 1562 * the specified database. The database must have the #MDB_DUPSORT flag. 1563 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1564 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1565 * @param[in] a The first item to compare 1566 * @param[in] b The second item to compare 1567 * @return < 0 if a < b, 0 if a == b, > 0 if a > b 1568 */ 1569 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b); 1570 1571 /** @brief A callback function used to print a message from the library. 1572 * 1573 * @param[in] msg The string to be printed. 1574 * @param[in] ctx An arbitrary context pointer for the callback. 1575 * @return < 0 on failure, >= 0 on success. 1576 */ 1577 typedef int (MDB_msg_func)(const char *msg, void *ctx); 1578 1579 /** @brief Dump the entries in the reader lock table. 1580 * 1581 * @param[in] env An environment handle returned by #mdb_env_create() 1582 * @param[in] func A #MDB_msg_func function 1583 * @param[in] ctx Anything the message function needs 1584 * @return < 0 on failure, >= 0 on success. 1585 */ 1586 int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx); 1587 1588 /** @brief Check for stale entries in the reader lock table. 1589 * 1590 * @param[in] env An environment handle returned by #mdb_env_create() 1591 * @param[out] dead Number of stale slots that were cleared 1592 * @return 0 on success, non-zero on failure. 1593 */ 1594 int mdb_reader_check(MDB_env *env, int *dead); 1595 /** @} */ 1596 1597 #ifdef __cplusplus 1598 } 1599 #endif 1600 /** @page tools LMDB Command Line Tools 1601 The following describes the command line tools that are available for LMDB. 1602 \li \ref mdb_copy_1 1603 \li \ref mdb_dump_1 1604 \li \ref mdb_load_1 1605 \li \ref mdb_stat_1 1606 */ 1607 1608 #endif /* _LMDB_H_ */ 1609