1 /* $NetBSD: lmdb.h,v 1.1.1.1 2014/05/28 09:58:42 tron Exp $ */ 2 3 /** @file lmdb.h 4 * @brief Lightning memory-mapped database library 5 * 6 * @mainpage Lightning Memory-Mapped Database Manager (MDB) 7 * 8 * @section intro_sec Introduction 9 * MDB is a Btree-based database management library modeled loosely on the 10 * BerkeleyDB API, but much simplified. The entire database is exposed 11 * in a memory map, and all data fetches return data directly 12 * from the mapped memory, so no malloc's or memcpy's occur during 13 * data fetches. As such, the library is extremely simple because it 14 * requires no page caching layer of its own, and it is extremely high 15 * performance and memory-efficient. It is also fully transactional with 16 * full ACID semantics, and when the memory map is read-only, the 17 * database integrity cannot be corrupted by stray pointer writes from 18 * application code. 19 * 20 * The library is fully thread-aware and supports concurrent read/write 21 * access from multiple processes and threads. Data pages use a copy-on- 22 * write strategy so no active data pages are ever overwritten, which 23 * also provides resistance to corruption and eliminates the need of any 24 * special recovery procedures after a system crash. Writes are fully 25 * serialized; only one write transaction may be active at a time, which 26 * guarantees that writers can never deadlock. The database structure is 27 * multi-versioned so readers run with no locks; writers cannot block 28 * readers, and readers don't block writers. 29 * 30 * Unlike other well-known database mechanisms which use either write-ahead 31 * transaction logs or append-only data writes, MDB requires no maintenance 32 * during operation. Both write-ahead loggers and append-only databases 33 * require periodic checkpointing and/or compaction of their log or database 34 * files otherwise they grow without bound. MDB tracks free pages within 35 * the database and re-uses them for new write operations, so the database 36 * size does not grow without bound in normal use. 37 * 38 * The memory map can be used as a read-only or read-write map. It is 39 * read-only by default as this provides total immunity to corruption. 40 * Using read-write mode offers much higher write performance, but adds 41 * the possibility for stray application writes thru pointers to silently 42 * corrupt the database. Of course if your application code is known to 43 * be bug-free (...) then this is not an issue. 44 * 45 * @section caveats_sec Caveats 46 * Troubleshooting the lock file, plus semaphores on BSD systems: 47 * 48 * - A broken lockfile can cause sync issues. 49 * Stale reader transactions left behind by an aborted program 50 * cause further writes to grow the database quickly, and 51 * stale locks can block further operation. 52 * 53 * Fix: Check for stale readers periodically, using the 54 * #mdb_reader_check function or the mdb_stat tool. Or just 55 * make all programs using the database close it; the lockfile 56 * is always reset on first open of the environment. 57 * 58 * - On BSD systems or others configured with MDB_USE_POSIX_SEM, 59 * startup can fail due to semaphores owned by another userid. 60 * 61 * Fix: Open and close the database as the user which owns the 62 * semaphores (likely last user) or as root, while no other 63 * process is using the database. 64 * 65 * Restrictions/caveats (in addition to those listed for some functions): 66 * 67 * - Only the database owner should normally use the database on 68 * BSD systems or when otherwise configured with MDB_USE_POSIX_SEM. 69 * Multiple users can cause startup to fail later, as noted above. 70 * 71 * - There is normally no pure read-only mode, since readers need write 72 * access to locks and lock file. Exceptions: On read-only filesystems 73 * or with the #MDB_NOLOCK flag described under #mdb_env_open(). 74 * 75 * - By default, in versions before 0.9.10, unused portions of the data 76 * file might receive garbage data from memory freed by other code. 77 * (This does not happen when using the #MDB_WRITEMAP flag.) As of 78 * 0.9.10 the default behavior is to initialize such memory before 79 * writing to the data file. Since there may be a slight performance 80 * cost due to this initialization, applications may disable it using 81 * the #MDB_NOMEMINIT flag. Applications handling sensitive data 82 * which must not be written should not use this flag. This flag is 83 * irrelevant when using #MDB_WRITEMAP. 84 * 85 * - A thread can only use one transaction at a time, plus any child 86 * transactions. Each transaction belongs to one thread. See below. 87 * The #MDB_NOTLS flag changes this for read-only transactions. 88 * 89 * - Use an MDB_env* in the process which opened it, without fork()ing. 90 * 91 * - Do not have open an MDB database twice in the same process at 92 * the same time. Not even from a plain open() call - close()ing it 93 * breaks flock() advisory locking. 94 * 95 * - Avoid long-lived transactions. Read transactions prevent 96 * reuse of pages freed by newer write transactions, thus the 97 * database can grow quickly. Write transactions prevent 98 * other write transactions, since writes are serialized. 99 * 100 * - Avoid suspending a process with active transactions. These 101 * would then be "long-lived" as above. Also read transactions 102 * suspended when writers commit could sometimes see wrong data. 103 * 104 * ...when several processes can use a database concurrently: 105 * 106 * - Avoid aborting a process with an active transaction. 107 * The transaction becomes "long-lived" as above until a check 108 * for stale readers is performed or the lockfile is reset, 109 * since the process may not remove it from the lockfile. 110 * 111 * - If you do that anyway, do a periodic check for stale readers. Or 112 * close the environment once in a while, so the lockfile can get reset. 113 * 114 * - Do not use MDB databases on remote filesystems, even between 115 * processes on the same host. This breaks flock() on some OSes, 116 * possibly memory map sync, and certainly sync between programs 117 * on different hosts. 118 * 119 * - Opening a database can fail if another process is opening or 120 * closing it at exactly the same time. 121 * 122 * @author Howard Chu, Symas Corporation. 123 * 124 * @copyright Copyright 2011-2013 Howard Chu, Symas Corp. All rights reserved. 125 * 126 * Redistribution and use in source and binary forms, with or without 127 * modification, are permitted only as authorized by the OpenLDAP 128 * Public License. 129 * 130 * A copy of this license is available in the file LICENSE in the 131 * top-level directory of the distribution or, alternatively, at 132 * <http://www.OpenLDAP.org/license.html>. 133 * 134 * @par Derived From: 135 * This code is derived from btree.c written by Martin Hedenfalk. 136 * 137 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se> 138 * 139 * Permission to use, copy, modify, and distribute this software for any 140 * purpose with or without fee is hereby granted, provided that the above 141 * copyright notice and this permission notice appear in all copies. 142 * 143 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 144 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 145 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 146 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 147 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 148 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 149 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 150 */ 151 #ifndef _LMDB_H_ 152 #define _LMDB_H_ 153 154 #include <sys/types.h> 155 156 #ifdef __cplusplus 157 extern "C" { 158 #endif 159 160 /** Unix permissions for creating files, or dummy definition for Windows */ 161 #ifdef _MSC_VER 162 typedef int mdb_mode_t; 163 #else 164 typedef mode_t mdb_mode_t; 165 #endif 166 167 /** An abstraction for a file handle. 168 * On POSIX systems file handles are small integers. On Windows 169 * they're opaque pointers. 170 */ 171 #ifdef _WIN32 172 typedef void *mdb_filehandle_t; 173 #else 174 typedef int mdb_filehandle_t; 175 #endif 176 177 /** @defgroup mdb MDB API 178 * @{ 179 * @brief OpenLDAP Lightning Memory-Mapped Database Manager 180 */ 181 /** @defgroup Version Version Macros 182 * @{ 183 */ 184 /** Library major version */ 185 #define MDB_VERSION_MAJOR 0 186 /** Library minor version */ 187 #define MDB_VERSION_MINOR 9 188 /** Library patch version */ 189 #define MDB_VERSION_PATCH 11 190 191 /** Combine args a,b,c into a single integer for easy version comparisons */ 192 #define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c)) 193 194 /** The full library version as a single integer */ 195 #define MDB_VERSION_FULL \ 196 MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH) 197 198 /** The release date of this library version */ 199 #define MDB_VERSION_DATE "January 15, 2014" 200 201 /** A stringifier for the version info */ 202 #define MDB_VERSTR(a,b,c,d) "MDB " #a "." #b "." #c ": (" d ")" 203 204 /** A helper for the stringifier macro */ 205 #define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d) 206 207 /** The full library version as a C string */ 208 #define MDB_VERSION_STRING \ 209 MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE) 210 /** @} */ 211 212 /** @brief Opaque structure for a database environment. 213 * 214 * A DB environment supports multiple databases, all residing in the same 215 * shared-memory map. 216 */ 217 typedef struct MDB_env MDB_env; 218 219 /** @brief Opaque structure for a transaction handle. 220 * 221 * All database operations require a transaction handle. Transactions may be 222 * read-only or read-write. 223 */ 224 typedef struct MDB_txn MDB_txn; 225 226 /** @brief A handle for an individual database in the DB environment. */ 227 typedef unsigned int MDB_dbi; 228 229 /** @brief Opaque structure for navigating through a database */ 230 typedef struct MDB_cursor MDB_cursor; 231 232 /** @brief Generic structure used for passing keys and data in and out 233 * of the database. 234 * 235 * Values returned from the database are valid only until a subsequent 236 * update operation, or the end of the transaction. Do not modify or 237 * free them, they commonly point into the database itself. 238 * 239 * Key sizes must be between 1 and #mdb_env_get_maxkeysize() inclusive. 240 * The same applies to data sizes in databases with the #MDB_DUPSORT flag. 241 * Other data items can in theory be from 0 to 0xffffffff bytes long. 242 */ 243 typedef struct MDB_val { 244 size_t mv_size; /**< size of the data item */ 245 void *mv_data; /**< address of the data item */ 246 } MDB_val; 247 248 /** @brief A callback function used to compare two keys in a database */ 249 typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b); 250 251 /** @brief A callback function used to relocate a position-dependent data item 252 * in a fixed-address database. 253 * 254 * The \b newptr gives the item's desired address in 255 * the memory map, and \b oldptr gives its previous address. The item's actual 256 * data resides at the address in \b item. This callback is expected to walk 257 * through the fields of the record in \b item and modify any 258 * values based at the \b oldptr address to be relative to the \b newptr address. 259 * @param[in,out] item The item that is to be relocated. 260 * @param[in] oldptr The previous address. 261 * @param[in] newptr The new address to relocate to. 262 * @param[in] relctx An application-provided context, set by #mdb_set_relctx(). 263 * @todo This feature is currently unimplemented. 264 */ 265 typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx); 266 267 /** @defgroup mdb_env Environment Flags 268 * @{ 269 */ 270 /** mmap at a fixed address (experimental) */ 271 #define MDB_FIXEDMAP 0x01 272 /** no environment directory */ 273 #define MDB_NOSUBDIR 0x4000 274 /** don't fsync after commit */ 275 #define MDB_NOSYNC 0x10000 276 /** read only */ 277 #define MDB_RDONLY 0x20000 278 /** don't fsync metapage after commit */ 279 #define MDB_NOMETASYNC 0x40000 280 /** use writable mmap */ 281 #define MDB_WRITEMAP 0x80000 282 /** use asynchronous msync when #MDB_WRITEMAP is used */ 283 #define MDB_MAPASYNC 0x100000 284 /** tie reader locktable slots to #MDB_txn objects instead of to threads */ 285 #define MDB_NOTLS 0x200000 286 /** don't do any locking, caller must manage their own locks */ 287 #define MDB_NOLOCK 0x400000 288 /** don't do readahead (no effect on Windows) */ 289 #define MDB_NORDAHEAD 0x800000 290 /** don't initialize malloc'd memory before writing to datafile */ 291 #define MDB_NOMEMINIT 0x1000000 292 /** @} */ 293 294 /** @defgroup mdb_dbi_open Database Flags 295 * @{ 296 */ 297 /** use reverse string keys */ 298 #define MDB_REVERSEKEY 0x02 299 /** use sorted duplicates */ 300 #define MDB_DUPSORT 0x04 301 /** numeric keys in native byte order. 302 * The keys must all be of the same size. */ 303 #define MDB_INTEGERKEY 0x08 304 /** with #MDB_DUPSORT, sorted dup items have fixed size */ 305 #define MDB_DUPFIXED 0x10 306 /** with #MDB_DUPSORT, dups are numeric in native byte order */ 307 #define MDB_INTEGERDUP 0x20 308 /** with #MDB_DUPSORT, use reverse string dups */ 309 #define MDB_REVERSEDUP 0x40 310 /** create DB if not already existing */ 311 #define MDB_CREATE 0x40000 312 /** @} */ 313 314 /** @defgroup mdb_put Write Flags 315 * @{ 316 */ 317 /** For put: Don't write if the key already exists. */ 318 #define MDB_NOOVERWRITE 0x10 319 /** Only for #MDB_DUPSORT<br> 320 * For put: don't write if the key and data pair already exist.<br> 321 * For mdb_cursor_del: remove all duplicate data items. 322 */ 323 #define MDB_NODUPDATA 0x20 324 /** For mdb_cursor_put: overwrite the current key/data pair */ 325 #define MDB_CURRENT 0x40 326 /** For put: Just reserve space for data, don't copy it. Return a 327 * pointer to the reserved space. 328 */ 329 #define MDB_RESERVE 0x10000 330 /** Data is being appended, don't split full pages. */ 331 #define MDB_APPEND 0x20000 332 /** Duplicate data is being appended, don't split full pages. */ 333 #define MDB_APPENDDUP 0x40000 334 /** Store multiple data items in one call. Only for #MDB_DUPFIXED. */ 335 #define MDB_MULTIPLE 0x80000 336 /* @} */ 337 338 /** @brief Cursor Get operations. 339 * 340 * This is the set of all operations for retrieving data 341 * using a cursor. 342 */ 343 typedef enum MDB_cursor_op { 344 MDB_FIRST, /**< Position at first key/data item */ 345 MDB_FIRST_DUP, /**< Position at first data item of current key. 346 Only for #MDB_DUPSORT */ 347 MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */ 348 MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */ 349 MDB_GET_CURRENT, /**< Return key/data at current cursor position */ 350 MDB_GET_MULTIPLE, /**< Return all the duplicate data items at the current 351 cursor position. Only for #MDB_DUPFIXED */ 352 MDB_LAST, /**< Position at last key/data item */ 353 MDB_LAST_DUP, /**< Position at last data item of current key. 354 Only for #MDB_DUPSORT */ 355 MDB_NEXT, /**< Position at next data item */ 356 MDB_NEXT_DUP, /**< Position at next data item of current key. 357 Only for #MDB_DUPSORT */ 358 MDB_NEXT_MULTIPLE, /**< Return all duplicate data items at the next 359 cursor position. Only for #MDB_DUPFIXED */ 360 MDB_NEXT_NODUP, /**< Position at first data item of next key */ 361 MDB_PREV, /**< Position at previous data item */ 362 MDB_PREV_DUP, /**< Position at previous data item of current key. 363 Only for #MDB_DUPSORT */ 364 MDB_PREV_NODUP, /**< Position at last data item of previous key */ 365 MDB_SET, /**< Position at specified key */ 366 MDB_SET_KEY, /**< Position at specified key, return key + data */ 367 MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */ 368 } MDB_cursor_op; 369 370 /** @defgroup errors Return Codes 371 * 372 * BerkeleyDB uses -30800 to -30999, we'll go under them 373 * @{ 374 */ 375 /** Successful result */ 376 #define MDB_SUCCESS 0 377 /** key/data pair already exists */ 378 #define MDB_KEYEXIST (-30799) 379 /** key/data pair not found (EOF) */ 380 #define MDB_NOTFOUND (-30798) 381 /** Requested page not found - this usually indicates corruption */ 382 #define MDB_PAGE_NOTFOUND (-30797) 383 /** Located page was wrong type */ 384 #define MDB_CORRUPTED (-30796) 385 /** Update of meta page failed, probably I/O error */ 386 #define MDB_PANIC (-30795) 387 /** Environment version mismatch */ 388 #define MDB_VERSION_MISMATCH (-30794) 389 /** File is not a valid MDB file */ 390 #define MDB_INVALID (-30793) 391 /** Environment mapsize reached */ 392 #define MDB_MAP_FULL (-30792) 393 /** Environment maxdbs reached */ 394 #define MDB_DBS_FULL (-30791) 395 /** Environment maxreaders reached */ 396 #define MDB_READERS_FULL (-30790) 397 /** Too many TLS keys in use - Windows only */ 398 #define MDB_TLS_FULL (-30789) 399 /** Txn has too many dirty pages */ 400 #define MDB_TXN_FULL (-30788) 401 /** Cursor stack too deep - internal error */ 402 #define MDB_CURSOR_FULL (-30787) 403 /** Page has not enough space - internal error */ 404 #define MDB_PAGE_FULL (-30786) 405 /** Database contents grew beyond environment mapsize */ 406 #define MDB_MAP_RESIZED (-30785) 407 /** MDB_INCOMPATIBLE: Operation and DB incompatible, or DB flags changed */ 408 #define MDB_INCOMPATIBLE (-30784) 409 /** Invalid reuse of reader locktable slot */ 410 #define MDB_BAD_RSLOT (-30783) 411 /** Transaction cannot recover - it must be aborted */ 412 #define MDB_BAD_TXN (-30782) 413 /** Too big key/data, key is empty, or wrong DUPFIXED size */ 414 #define MDB_BAD_VALSIZE (-30781) 415 #define MDB_LAST_ERRCODE MDB_BAD_VALSIZE 416 /** @} */ 417 418 /** @brief Statistics for a database in the environment */ 419 typedef struct MDB_stat { 420 unsigned int ms_psize; /**< Size of a database page. 421 This is currently the same for all databases. */ 422 unsigned int ms_depth; /**< Depth (height) of the B-tree */ 423 size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */ 424 size_t ms_leaf_pages; /**< Number of leaf pages */ 425 size_t ms_overflow_pages; /**< Number of overflow pages */ 426 size_t ms_entries; /**< Number of data items */ 427 } MDB_stat; 428 429 /** @brief Information about the environment */ 430 typedef struct MDB_envinfo { 431 void *me_mapaddr; /**< Address of map, if fixed */ 432 size_t me_mapsize; /**< Size of the data memory map */ 433 size_t me_last_pgno; /**< ID of the last used page */ 434 size_t me_last_txnid; /**< ID of the last committed transaction */ 435 unsigned int me_maxreaders; /**< max reader slots in the environment */ 436 unsigned int me_numreaders; /**< max reader slots used in the environment */ 437 } MDB_envinfo; 438 439 /** @brief Return the mdb library version information. 440 * 441 * @param[out] major if non-NULL, the library major version number is copied here 442 * @param[out] minor if non-NULL, the library minor version number is copied here 443 * @param[out] patch if non-NULL, the library patch version number is copied here 444 * @retval "version string" The library version as a string 445 */ 446 char *mdb_version(int *major, int *minor, int *patch); 447 448 /** @brief Return a string describing a given error code. 449 * 450 * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3) 451 * function. If the error code is greater than or equal to 0, then the string 452 * returned by the system function strerror(3) is returned. If the error code 453 * is less than 0, an error string corresponding to the MDB library error is 454 * returned. See @ref errors for a list of MDB-specific error codes. 455 * @param[in] err The error code 456 * @retval "error message" The description of the error 457 */ 458 char *mdb_strerror(int err); 459 460 /** @brief Create an MDB environment handle. 461 * 462 * This function allocates memory for a #MDB_env structure. To release 463 * the allocated memory and discard the handle, call #mdb_env_close(). 464 * Before the handle may be used, it must be opened using #mdb_env_open(). 465 * Various other options may also need to be set before opening the handle, 466 * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(), 467 * depending on usage requirements. 468 * @param[out] env The address where the new handle will be stored 469 * @return A non-zero error value on failure and 0 on success. 470 */ 471 int mdb_env_create(MDB_env **env); 472 473 /** @brief Open an environment handle. 474 * 475 * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle. 476 * @param[in] env An environment handle returned by #mdb_env_create() 477 * @param[in] path The directory in which the database files reside. This 478 * directory must already exist and be writable. 479 * @param[in] flags Special options for this environment. This parameter 480 * must be set to 0 or by bitwise OR'ing together one or more of the 481 * values described here. 482 * Flags set by mdb_env_set_flags() are also used. 483 * <ul> 484 * <li>#MDB_FIXEDMAP 485 * use a fixed address for the mmap region. This flag must be specified 486 * when creating the environment, and is stored persistently in the environment. 487 * If successful, the memory map will always reside at the same virtual address 488 * and pointers used to reference data items in the database will be constant 489 * across multiple invocations. This option may not always work, depending on 490 * how the operating system has allocated memory to shared libraries and other uses. 491 * The feature is highly experimental. 492 * <li>#MDB_NOSUBDIR 493 * By default, MDB creates its environment in a directory whose 494 * pathname is given in \b path, and creates its data and lock files 495 * under that directory. With this option, \b path is used as-is for 496 * the database main data file. The database lock file is the \b path 497 * with "-lock" appended. 498 * <li>#MDB_RDONLY 499 * Open the environment in read-only mode. No write operations will be 500 * allowed. MDB will still modify the lock file - except on read-only 501 * filesystems, where MDB does not use locks. 502 * <li>#MDB_WRITEMAP 503 * Use a writeable memory map unless MDB_RDONLY is set. This is faster 504 * and uses fewer mallocs, but loses protection from application bugs 505 * like wild pointer writes and other bad updates into the database. 506 * Incompatible with nested transactions. 507 * Processes with and without MDB_WRITEMAP on the same environment do 508 * not cooperate well. 509 * <li>#MDB_NOMETASYNC 510 * Flush system buffers to disk only once per transaction, omit the 511 * metadata flush. Defer that until the system flushes files to disk, 512 * or next non-MDB_RDONLY commit or #mdb_env_sync(). This optimization 513 * maintains database integrity, but a system crash may undo the last 514 * committed transaction. I.e. it preserves the ACI (atomicity, 515 * consistency, isolation) but not D (durability) database property. 516 * This flag may be changed at any time using #mdb_env_set_flags(). 517 * <li>#MDB_NOSYNC 518 * Don't flush system buffers to disk when committing a transaction. 519 * This optimization means a system crash can corrupt the database or 520 * lose the last transactions if buffers are not yet flushed to disk. 521 * The risk is governed by how often the system flushes dirty buffers 522 * to disk and how often #mdb_env_sync() is called. However, if the 523 * filesystem preserves write order and the #MDB_WRITEMAP flag is not 524 * used, transactions exhibit ACI (atomicity, consistency, isolation) 525 * properties and only lose D (durability). I.e. database integrity 526 * is maintained, but a system crash may undo the final transactions. 527 * Note that (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no 528 * hint for when to write transactions to disk, unless #mdb_env_sync() 529 * is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable. 530 * This flag may be changed at any time using #mdb_env_set_flags(). 531 * <li>#MDB_MAPASYNC 532 * When using #MDB_WRITEMAP, use asynchronous flushes to disk. 533 * As with #MDB_NOSYNC, a system crash can then corrupt the 534 * database or lose the last transactions. Calling #mdb_env_sync() 535 * ensures on-disk database integrity until next commit. 536 * This flag may be changed at any time using #mdb_env_set_flags(). 537 * <li>#MDB_NOTLS 538 * Don't use Thread-Local Storage. Tie reader locktable slots to 539 * #MDB_txn objects instead of to threads. I.e. #mdb_txn_reset() keeps 540 * the slot reseved for the #MDB_txn object. A thread may use parallel 541 * read-only transactions. A read-only transaction may span threads if 542 * the user synchronizes its use. Applications that multiplex many 543 * user threads over individual OS threads need this option. Such an 544 * application must also serialize the write transactions in an OS 545 * thread, since MDB's write locking is unaware of the user threads. 546 * <li>#MDB_NOLOCK 547 * Don't do any locking. If concurrent access is anticipated, the 548 * caller must manage all concurrency itself. For proper operation 549 * the caller must enforce single-writer semantics, and must ensure 550 * that no readers are using old transactions while a writer is 551 * active. The simplest approach is to use an exclusive lock so that 552 * no readers may be active at all when a writer begins. 553 * <li>#MDB_NORDAHEAD 554 * Turn off readahead. Most operating systems perform readahead on 555 * read requests by default. This option turns it off if the OS 556 * supports it. Turning it off may help random read performance 557 * when the DB is larger than RAM and system RAM is full. 558 * The option is not implemented on Windows. 559 * <li>#MDB_NOMEMINIT 560 * Don't initialize malloc'd memory before writing to unused spaces 561 * in the data file. By default, memory for pages written to the data 562 * file is obtained using malloc. While these pages may be reused in 563 * subsequent transactions, freshly malloc'd pages will be initialized 564 * to zeroes before use. This avoids persisting leftover data from other 565 * code (that used the heap and subsequently freed the memory) into the 566 * data file. Note that many other system libraries may allocate 567 * and free memory from the heap for arbitrary uses. E.g., stdio may 568 * use the heap for file I/O buffers. This initialization step has a 569 * modest performance cost so some applications may want to disable 570 * it using this flag. This option can be a problem for applications 571 * which handle sensitive data like passwords, and it makes memory 572 * checkers like Valgrind noisy. This flag is not needed with #MDB_WRITEMAP, 573 * which writes directly to the mmap instead of using malloc for pages. The 574 * initialization is also skipped if #MDB_RESERVE is used; the 575 * caller is expected to overwrite all of the memory that was 576 * reserved in that case. 577 * This flag may be changed at any time using #mdb_env_set_flags(). 578 * </ul> 579 * @param[in] mode The UNIX permissions to set on created files. This parameter 580 * is ignored on Windows. 581 * @return A non-zero error value on failure and 0 on success. Some possible 582 * errors are: 583 * <ul> 584 * <li>#MDB_VERSION_MISMATCH - the version of the MDB library doesn't match the 585 * version that created the database environment. 586 * <li>#MDB_INVALID - the environment file headers are corrupted. 587 * <li>ENOENT - the directory specified by the path parameter doesn't exist. 588 * <li>EACCES - the user didn't have permission to access the environment files. 589 * <li>EAGAIN - the environment was locked by another process. 590 * </ul> 591 */ 592 int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode); 593 594 /** @brief Copy an MDB environment to the specified path. 595 * 596 * This function may be used to make a backup of an existing environment. 597 * No lockfile is created, since it gets recreated at need. 598 * @note This call can trigger significant file size growth if run in 599 * parallel with write transactions, because it employs a read-only 600 * transaction. See long-lived transactions under @ref caveats_sec. 601 * @param[in] env An environment handle returned by #mdb_env_create(). It 602 * must have already been opened successfully. 603 * @param[in] path The directory in which the copy will reside. This 604 * directory must already exist and be writable but must otherwise be 605 * empty. 606 * @return A non-zero error value on failure and 0 on success. 607 */ 608 int mdb_env_copy(MDB_env *env, const char *path); 609 610 /** @brief Copy an MDB environment to the specified file descriptor. 611 * 612 * This function may be used to make a backup of an existing environment. 613 * No lockfile is created, since it gets recreated at need. 614 * @note This call can trigger significant file size growth if run in 615 * parallel with write transactions, because it employs a read-only 616 * transaction. See long-lived transactions under @ref caveats_sec. 617 * @param[in] env An environment handle returned by #mdb_env_create(). It 618 * must have already been opened successfully. 619 * @param[in] fd The filedescriptor to write the copy to. It must 620 * have already been opened for Write access. 621 * @return A non-zero error value on failure and 0 on success. 622 */ 623 int mdb_env_copyfd(MDB_env *env, mdb_filehandle_t fd); 624 625 /** @brief Return statistics about the MDB environment. 626 * 627 * @param[in] env An environment handle returned by #mdb_env_create() 628 * @param[out] stat The address of an #MDB_stat structure 629 * where the statistics will be copied 630 */ 631 int mdb_env_stat(MDB_env *env, MDB_stat *stat); 632 633 /** @brief Return information about the MDB environment. 634 * 635 * @param[in] env An environment handle returned by #mdb_env_create() 636 * @param[out] stat The address of an #MDB_envinfo structure 637 * where the information will be copied 638 */ 639 int mdb_env_info(MDB_env *env, MDB_envinfo *stat); 640 641 /** @brief Flush the data buffers to disk. 642 * 643 * Data is always written to disk when #mdb_txn_commit() is called, 644 * but the operating system may keep it buffered. MDB always flushes 645 * the OS buffers upon commit as well, unless the environment was 646 * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC. 647 * @param[in] env An environment handle returned by #mdb_env_create() 648 * @param[in] force If non-zero, force a synchronous flush. Otherwise 649 * if the environment has the #MDB_NOSYNC flag set the flushes 650 * will be omitted, and with #MDB_MAPASYNC they will be asynchronous. 651 * @return A non-zero error value on failure and 0 on success. Some possible 652 * errors are: 653 * <ul> 654 * <li>EINVAL - an invalid parameter was specified. 655 * <li>EIO - an error occurred during synchronization. 656 * </ul> 657 */ 658 int mdb_env_sync(MDB_env *env, int force); 659 660 /** @brief Close the environment and release the memory map. 661 * 662 * Only a single thread may call this function. All transactions, databases, 663 * and cursors must already be closed before calling this function. Attempts to 664 * use any such handles after calling this function will cause a SIGSEGV. 665 * The environment handle will be freed and must not be used again after this call. 666 * @param[in] env An environment handle returned by #mdb_env_create() 667 */ 668 void mdb_env_close(MDB_env *env); 669 670 /** @brief Set environment flags. 671 * 672 * This may be used to set some flags in addition to those from 673 * #mdb_env_open(), or to unset these flags. 674 * @param[in] env An environment handle returned by #mdb_env_create() 675 * @param[in] flags The flags to change, bitwise OR'ed together 676 * @param[in] onoff A non-zero value sets the flags, zero clears them. 677 * @return A non-zero error value on failure and 0 on success. Some possible 678 * errors are: 679 * <ul> 680 * <li>EINVAL - an invalid parameter was specified. 681 * </ul> 682 */ 683 int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff); 684 685 /** @brief Get environment flags. 686 * 687 * @param[in] env An environment handle returned by #mdb_env_create() 688 * @param[out] flags The address of an integer to store the flags 689 * @return A non-zero error value on failure and 0 on success. Some possible 690 * errors are: 691 * <ul> 692 * <li>EINVAL - an invalid parameter was specified. 693 * </ul> 694 */ 695 int mdb_env_get_flags(MDB_env *env, unsigned int *flags); 696 697 /** @brief Return the path that was used in #mdb_env_open(). 698 * 699 * @param[in] env An environment handle returned by #mdb_env_create() 700 * @param[out] path Address of a string pointer to contain the path. This 701 * is the actual string in the environment, not a copy. It should not be 702 * altered in any way. 703 * @return A non-zero error value on failure and 0 on success. Some possible 704 * errors are: 705 * <ul> 706 * <li>EINVAL - an invalid parameter was specified. 707 * </ul> 708 */ 709 int mdb_env_get_path(MDB_env *env, const char **path); 710 711 /** @brief Return the filedescriptor for the given environment. 712 * 713 * @param[in] env An environment handle returned by #mdb_env_create() 714 * @param[out] fd Address of a mdb_filehandle_t to contain the descriptor. 715 * @return A non-zero error value on failure and 0 on success. Some possible 716 * errors are: 717 * <ul> 718 * <li>EINVAL - an invalid parameter was specified. 719 * </ul> 720 */ 721 int mdb_env_get_fd(MDB_env *env, mdb_filehandle_t *fd); 722 723 /** @brief Set the size of the memory map to use for this environment. 724 * 725 * The size should be a multiple of the OS page size. The default is 726 * 10485760 bytes. The size of the memory map is also the maximum size 727 * of the database. The value should be chosen as large as possible, 728 * to accommodate future growth of the database. 729 * This function should be called after #mdb_env_create() and before #mdb_env_open(). 730 * It may be called at later times if no transactions are active in 731 * this process. Note that the library does not check for this condition, 732 * the caller must ensure it explicitly. 733 * 734 * If the mapsize is changed by another process, #mdb_txn_begin() will 735 * return #MDB_MAP_RESIZED. This function may be called with a size 736 * of zero to adopt the new size. 737 * 738 * Any attempt to set a size smaller than the space already consumed 739 * by the environment will be silently changed to the current size of the used space. 740 * @param[in] env An environment handle returned by #mdb_env_create() 741 * @param[in] size The size in bytes 742 * @return A non-zero error value on failure and 0 on success. Some possible 743 * errors are: 744 * <ul> 745 * <li>EINVAL - an invalid parameter was specified, or the environment has 746 * an active write transaction. 747 * </ul> 748 */ 749 int mdb_env_set_mapsize(MDB_env *env, size_t size); 750 751 /** @brief Set the maximum number of threads/reader slots for the environment. 752 * 753 * This defines the number of slots in the lock table that is used to track readers in the 754 * the environment. The default is 126. 755 * Starting a read-only transaction normally ties a lock table slot to the 756 * current thread until the environment closes or the thread exits. If 757 * MDB_NOTLS is in use, #mdb_txn_begin() instead ties the slot to the 758 * MDB_txn object until it or the #MDB_env object is destroyed. 759 * This function may only be called after #mdb_env_create() and before #mdb_env_open(). 760 * @param[in] env An environment handle returned by #mdb_env_create() 761 * @param[in] readers The maximum number of reader lock table slots 762 * @return A non-zero error value on failure and 0 on success. Some possible 763 * errors are: 764 * <ul> 765 * <li>EINVAL - an invalid parameter was specified, or the environment is already open. 766 * </ul> 767 */ 768 int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers); 769 770 /** @brief Get the maximum number of threads/reader slots for the environment. 771 * 772 * @param[in] env An environment handle returned by #mdb_env_create() 773 * @param[out] readers Address of an integer to store the number of readers 774 * @return A non-zero error value on failure and 0 on success. Some possible 775 * errors are: 776 * <ul> 777 * <li>EINVAL - an invalid parameter was specified. 778 * </ul> 779 */ 780 int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers); 781 782 /** @brief Set the maximum number of named databases for the environment. 783 * 784 * This function is only needed if multiple databases will be used in the 785 * environment. Simpler applications that use the environment as a single 786 * unnamed database can ignore this option. 787 * This function may only be called after #mdb_env_create() and before #mdb_env_open(). 788 * @param[in] env An environment handle returned by #mdb_env_create() 789 * @param[in] dbs The maximum number of databases 790 * @return A non-zero error value on failure and 0 on success. Some possible 791 * errors are: 792 * <ul> 793 * <li>EINVAL - an invalid parameter was specified, or the environment is already open. 794 * </ul> 795 */ 796 int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs); 797 798 /** @brief Get the maximum size of keys and #MDB_DUPSORT data we can write. 799 * 800 * Depends on the compile-time constant #MDB_MAXKEYSIZE. Default 511. 801 * See @ref MDB_val. 802 * @param[in] env An environment handle returned by #mdb_env_create() 803 * @return The maximum size of a key we can write 804 */ 805 int mdb_env_get_maxkeysize(MDB_env *env); 806 807 /** @brief Set application information associated with the #MDB_env. 808 * 809 * @param[in] env An environment handle returned by #mdb_env_create() 810 * @param[in] ctx An arbitrary pointer for whatever the application needs. 811 * @return A non-zero error value on failure and 0 on success. 812 */ 813 int mdb_env_set_userctx(MDB_env *env, void *ctx); 814 815 /** @brief Get the application information associated with the #MDB_env. 816 * 817 * @param[in] env An environment handle returned by #mdb_env_create() 818 * @return The pointer set by #mdb_env_set_userctx(). 819 */ 820 void *mdb_env_get_userctx(MDB_env *env); 821 822 /** @brief A callback function for most MDB assert() failures, 823 * called before printing the message and aborting. 824 * 825 * @param[in] env An environment handle returned by #mdb_env_create(). 826 * @param[in] msg The assertion message, not including newline. 827 */ 828 typedef void MDB_assert_func(MDB_env *env, const char *msg); 829 830 /** Set or reset the assert() callback of the environment. 831 * Disabled if liblmdb is buillt with NDEBUG. 832 * @note This hack should become obsolete as lmdb's error handling matures. 833 * @param[in] env An environment handle returned by #mdb_env_create(). 834 * @parem[in] func An #MDB_assert_func function, or 0. 835 * @return A non-zero error value on failure and 0 on success. 836 */ 837 int mdb_env_set_assert(MDB_env *env, MDB_assert_func *func); 838 839 /** @brief Create a transaction for use with the environment. 840 * 841 * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit(). 842 * @note A transaction and its cursors must only be used by a single 843 * thread, and a thread may only have a single transaction at a time. 844 * If #MDB_NOTLS is in use, this does not apply to read-only transactions. 845 * @note Cursors may not span transactions. 846 * @param[in] env An environment handle returned by #mdb_env_create() 847 * @param[in] parent If this parameter is non-NULL, the new transaction 848 * will be a nested transaction, with the transaction indicated by \b parent 849 * as its parent. Transactions may be nested to any level. A parent 850 * transaction and its cursors may not issue any other operations than 851 * mdb_txn_commit and mdb_txn_abort while it has active child transactions. 852 * @param[in] flags Special options for this transaction. This parameter 853 * must be set to 0 or by bitwise OR'ing together one or more of the 854 * values described here. 855 * <ul> 856 * <li>#MDB_RDONLY 857 * This transaction will not perform any write operations. 858 * </ul> 859 * @param[out] txn Address where the new #MDB_txn handle will be stored 860 * @return A non-zero error value on failure and 0 on success. Some possible 861 * errors are: 862 * <ul> 863 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment 864 * must be shut down. 865 * <li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's 866 * mapsize and this environment's map must be resized as well. 867 * See #mdb_env_set_mapsize(). 868 * <li>#MDB_READERS_FULL - a read-only transaction was requested and 869 * the reader lock table is full. See #mdb_env_set_maxreaders(). 870 * <li>ENOMEM - out of memory. 871 * </ul> 872 */ 873 int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn); 874 875 /** @brief Returns the transaction's #MDB_env 876 * 877 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 878 */ 879 MDB_env *mdb_txn_env(MDB_txn *txn); 880 881 /** @brief Commit all the operations of a transaction into the database. 882 * 883 * The transaction handle is freed. It and its cursors must not be used 884 * again after this call, except with #mdb_cursor_renew(). 885 * @note Earlier documentation incorrectly said all cursors would be freed. 886 * Only write-transactions free cursors. 887 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 888 * @return A non-zero error value on failure and 0 on success. Some possible 889 * errors are: 890 * <ul> 891 * <li>EINVAL - an invalid parameter was specified. 892 * <li>ENOSPC - no more disk space. 893 * <li>EIO - a low-level I/O error occurred while writing. 894 * <li>ENOMEM - out of memory. 895 * </ul> 896 */ 897 int mdb_txn_commit(MDB_txn *txn); 898 899 /** @brief Abandon all the operations of the transaction instead of saving them. 900 * 901 * The transaction handle is freed. It and its cursors must not be used 902 * again after this call, except with #mdb_cursor_renew(). 903 * @note Earlier documentation incorrectly said all cursors would be freed. 904 * Only write-transactions free cursors. 905 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 906 */ 907 void mdb_txn_abort(MDB_txn *txn); 908 909 /** @brief Reset a read-only transaction. 910 * 911 * Abort the transaction like #mdb_txn_abort(), but keep the transaction 912 * handle. #mdb_txn_renew() may reuse the handle. This saves allocation 913 * overhead if the process will start a new read-only transaction soon, 914 * and also locking overhead if #MDB_NOTLS is in use. The reader table 915 * lock is released, but the table slot stays tied to its thread or 916 * #MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free 917 * its lock table slot if MDB_NOTLS is in use. 918 * Cursors opened within the transaction must not be used 919 * again after this call, except with #mdb_cursor_renew(). 920 * Reader locks generally don't interfere with writers, but they keep old 921 * versions of database pages allocated. Thus they prevent the old pages 922 * from being reused when writers commit new data, and so under heavy load 923 * the database size may grow much more rapidly than otherwise. 924 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 925 */ 926 void mdb_txn_reset(MDB_txn *txn); 927 928 /** @brief Renew a read-only transaction. 929 * 930 * This acquires a new reader lock for a transaction handle that had been 931 * released by #mdb_txn_reset(). It must be called before a reset transaction 932 * may be used again. 933 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 934 * @return A non-zero error value on failure and 0 on success. Some possible 935 * errors are: 936 * <ul> 937 * <li>#MDB_PANIC - a fatal error occurred earlier and the environment 938 * must be shut down. 939 * <li>EINVAL - an invalid parameter was specified. 940 * </ul> 941 */ 942 int mdb_txn_renew(MDB_txn *txn); 943 944 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */ 945 #define mdb_open(txn,name,flags,dbi) mdb_dbi_open(txn,name,flags,dbi) 946 /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */ 947 #define mdb_close(env,dbi) mdb_dbi_close(env,dbi) 948 949 /** @brief Open a database in the environment. 950 * 951 * A database handle denotes the name and parameters of a database, 952 * independently of whether such a database exists. 953 * The database handle may be discarded by calling #mdb_dbi_close(). 954 * The old database handle is returned if the database was already open. 955 * The handle must only be closed once. 956 * The database handle will be private to the current transaction until 957 * the transaction is successfully committed. If the transaction is 958 * aborted the handle will be closed automatically. 959 * After a successful commit the 960 * handle will reside in the shared environment, and may be used 961 * by other transactions. This function must not be called from 962 * multiple concurrent transactions. A transaction that uses this function 963 * must finish (either commit or abort) before any other transaction may 964 * use this function. 965 * 966 * To use named databases (with name != NULL), #mdb_env_set_maxdbs() 967 * must be called before opening the environment. 968 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 969 * @param[in] name The name of the database to open. If only a single 970 * database is needed in the environment, this value may be NULL. 971 * @param[in] flags Special options for this database. This parameter 972 * must be set to 0 or by bitwise OR'ing together one or more of the 973 * values described here. 974 * <ul> 975 * <li>#MDB_REVERSEKEY 976 * Keys are strings to be compared in reverse order, from the end 977 * of the strings to the beginning. By default, Keys are treated as strings and 978 * compared from beginning to end. 979 * <li>#MDB_DUPSORT 980 * Duplicate keys may be used in the database. (Or, from another perspective, 981 * keys may have multiple data items, stored in sorted order.) By default 982 * keys must be unique and may have only a single data item. 983 * <li>#MDB_INTEGERKEY 984 * Keys are binary integers in native byte order. Setting this option 985 * requires all keys to be the same size, typically sizeof(int) 986 * or sizeof(size_t). 987 * <li>#MDB_DUPFIXED 988 * This flag may only be used in combination with #MDB_DUPSORT. This option 989 * tells the library that the data items for this database are all the same 990 * size, which allows further optimizations in storage and retrieval. When 991 * all data items are the same size, the #MDB_GET_MULTIPLE and #MDB_NEXT_MULTIPLE 992 * cursor operations may be used to retrieve multiple items at once. 993 * <li>#MDB_INTEGERDUP 994 * This option specifies that duplicate data items are also integers, and 995 * should be sorted as such. 996 * <li>#MDB_REVERSEDUP 997 * This option specifies that duplicate data items should be compared as 998 * strings in reverse order. 999 * <li>#MDB_CREATE 1000 * Create the named database if it doesn't exist. This option is not 1001 * allowed in a read-only transaction or a read-only environment. 1002 * </ul> 1003 * @param[out] dbi Address where the new #MDB_dbi 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_NOTFOUND - the specified database doesn't exist in the environment 1008 * and #MDB_CREATE was not specified. 1009 * <li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs(). 1010 * </ul> 1011 */ 1012 int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi); 1013 1014 /** @brief Retrieve statistics for a database. 1015 * 1016 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1017 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1018 * @param[out] stat The address of an #MDB_stat structure 1019 * where the statistics will be copied 1020 * @return A non-zero error value on failure and 0 on success. Some possible 1021 * errors are: 1022 * <ul> 1023 * <li>EINVAL - an invalid parameter was specified. 1024 * </ul> 1025 */ 1026 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat); 1027 1028 /** @brief Retrieve the DB flags for a database handle. 1029 * 1030 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1031 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1032 * @param[out] flags Address where the flags will be returned. 1033 * @return A non-zero error value on failure and 0 on success. 1034 */ 1035 int mdb_dbi_flags(MDB_txn *txn, MDB_dbi dbi, unsigned int *flags); 1036 1037 /** @brief Close a database handle. 1038 * 1039 * This call is not mutex protected. Handles should only be closed by 1040 * a single thread, and only if no other threads are going to reference 1041 * the database handle or one of its cursors any further. Do not close 1042 * a handle if an existing transaction has modified its database. 1043 * @param[in] env An environment handle returned by #mdb_env_create() 1044 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1045 */ 1046 void mdb_dbi_close(MDB_env *env, MDB_dbi dbi); 1047 1048 /** @brief Empty or delete+close a database. 1049 * 1050 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1051 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1052 * @param[in] del 0 to empty the DB, 1 to delete it from the 1053 * environment and close the DB handle. 1054 * @return A non-zero error value on failure and 0 on success. 1055 */ 1056 int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del); 1057 1058 /** @brief Set a custom key comparison function for a database. 1059 * 1060 * The comparison function is called whenever it is necessary to compare a 1061 * key specified by the application with a key currently stored in the database. 1062 * If no comparison function is specified, and no special key flags were specified 1063 * with #mdb_dbi_open(), the keys are compared lexically, with shorter keys collating 1064 * before longer keys. 1065 * @warning This function must be called before any data access functions are used, 1066 * otherwise data corruption may occur. The same comparison function must be used by every 1067 * program accessing the database, every time the database is used. 1068 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1069 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1070 * @param[in] cmp A #MDB_cmp_func function 1071 * @return A non-zero error value on failure and 0 on success. Some possible 1072 * errors are: 1073 * <ul> 1074 * <li>EINVAL - an invalid parameter was specified. 1075 * </ul> 1076 */ 1077 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp); 1078 1079 /** @brief Set a custom data comparison function for a #MDB_DUPSORT database. 1080 * 1081 * This comparison function is called whenever it is necessary to compare a data 1082 * item specified by the application with a data item currently stored in the database. 1083 * This function only takes effect if the database was opened with the #MDB_DUPSORT 1084 * flag. 1085 * If no comparison function is specified, and no special key flags were specified 1086 * with #mdb_dbi_open(), the data items are compared lexically, with shorter items collating 1087 * before longer items. 1088 * @warning This function must be called before any data access functions are used, 1089 * otherwise data corruption may occur. The same comparison function must be used by every 1090 * program accessing the database, every time the database is used. 1091 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1092 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1093 * @param[in] cmp A #MDB_cmp_func function 1094 * @return A non-zero error value on failure and 0 on success. Some possible 1095 * errors are: 1096 * <ul> 1097 * <li>EINVAL - an invalid parameter was specified. 1098 * </ul> 1099 */ 1100 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp); 1101 1102 /** @brief Set a relocation function for a #MDB_FIXEDMAP database. 1103 * 1104 * @todo The relocation function is called whenever it is necessary to move the data 1105 * of an item to a different position in the database (e.g. through tree 1106 * balancing operations, shifts as a result of adds or deletes, etc.). It is 1107 * intended to allow address/position-dependent data items to be stored in 1108 * a database in an environment opened with the #MDB_FIXEDMAP option. 1109 * Currently the relocation feature is unimplemented and setting 1110 * this function has no effect. 1111 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1112 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1113 * @param[in] rel A #MDB_rel_func function 1114 * @return A non-zero error value on failure and 0 on success. Some possible 1115 * errors are: 1116 * <ul> 1117 * <li>EINVAL - an invalid parameter was specified. 1118 * </ul> 1119 */ 1120 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel); 1121 1122 /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function. 1123 * 1124 * See #mdb_set_relfunc and #MDB_rel_func for more details. 1125 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1126 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1127 * @param[in] ctx An arbitrary pointer for whatever the application needs. 1128 * It will be passed to the callback function set by #mdb_set_relfunc 1129 * as its \b relctx parameter whenever the callback is invoked. 1130 * @return A non-zero error value on failure and 0 on success. Some possible 1131 * errors are: 1132 * <ul> 1133 * <li>EINVAL - an invalid parameter was specified. 1134 * </ul> 1135 */ 1136 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx); 1137 1138 /** @brief Get items from a database. 1139 * 1140 * This function retrieves key/data pairs from the database. The address 1141 * and length of the data associated with the specified \b key are returned 1142 * in the structure to which \b data refers. 1143 * If the database supports duplicate keys (#MDB_DUPSORT) then the 1144 * first data item for the key will be returned. Retrieval of other 1145 * items requires the use of #mdb_cursor_get(). 1146 * 1147 * @note The memory pointed to by the returned values is owned by the 1148 * database. The caller need not dispose of the memory, and may not 1149 * modify it in any way. For values returned in a read-only transaction 1150 * any modification attempts will cause a SIGSEGV. 1151 * @note Values returned from the database are valid only until a 1152 * subsequent update operation, or the end of the transaction. 1153 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1154 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1155 * @param[in] key The key to search for in the database 1156 * @param[out] data The data corresponding to the key 1157 * @return A non-zero error value on failure and 0 on success. Some possible 1158 * errors are: 1159 * <ul> 1160 * <li>#MDB_NOTFOUND - the key was not in the database. 1161 * <li>EINVAL - an invalid parameter was specified. 1162 * </ul> 1163 */ 1164 int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data); 1165 1166 /** @brief Store items into a database. 1167 * 1168 * This function stores key/data pairs in the database. The default behavior 1169 * is to enter the new key/data pair, replacing any previously existing key 1170 * if duplicates are disallowed, or adding a duplicate data item if 1171 * duplicates are allowed (#MDB_DUPSORT). 1172 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1173 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1174 * @param[in] key The key to store in the database 1175 * @param[in,out] data The data to store 1176 * @param[in] flags Special options for this operation. This parameter 1177 * must be set to 0 or by bitwise OR'ing together one or more of the 1178 * values described here. 1179 * <ul> 1180 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not 1181 * already appear in the database. This flag may only be specified 1182 * if the database was opened with #MDB_DUPSORT. The function will 1183 * return #MDB_KEYEXIST if the key/data pair already appears in the 1184 * database. 1185 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key 1186 * does not already appear in the database. The function will return 1187 * #MDB_KEYEXIST if the key already appears in the database, even if 1188 * the database supports duplicates (#MDB_DUPSORT). The \b data 1189 * parameter will be set to point to the existing item. 1190 * <li>#MDB_RESERVE - reserve space for data of the given size, but 1191 * don't copy the given data. Instead, return a pointer to the 1192 * reserved space, which the caller can fill in later - before 1193 * the next update operation or the transaction ends. This saves 1194 * an extra memcpy if the data is being generated later. 1195 * MDB does nothing else with this memory, the caller is expected 1196 * to modify all of the space requested. 1197 * <li>#MDB_APPEND - append the given key/data pair to the end of the 1198 * database. No key comparisons are performed. This option allows 1199 * fast bulk loading when keys are already known to be in the 1200 * correct order. Loading unsorted keys with this flag will cause 1201 * data corruption. 1202 * <li>#MDB_APPENDDUP - as above, but for sorted dup data. 1203 * </ul> 1204 * @return A non-zero error value on failure and 0 on success. Some possible 1205 * errors are: 1206 * <ul> 1207 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize(). 1208 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages. 1209 * <li>EACCES - an attempt was made to write in a read-only transaction. 1210 * <li>EINVAL - an invalid parameter was specified. 1211 * </ul> 1212 */ 1213 int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data, 1214 unsigned int flags); 1215 1216 /** @brief Delete items from a database. 1217 * 1218 * This function removes key/data pairs from the database. 1219 * If the database does not support sorted duplicate data items 1220 * (#MDB_DUPSORT) the data parameter is ignored. 1221 * If the database supports sorted duplicates and the data parameter 1222 * is NULL, all of the duplicate data items for the key will be 1223 * deleted. Otherwise, if the data parameter is non-NULL 1224 * only the matching data item will be deleted. 1225 * This function will return #MDB_NOTFOUND if the specified key/data 1226 * pair is not in the database. 1227 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1228 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1229 * @param[in] key The key to delete from the database 1230 * @param[in] data The data to delete 1231 * @return A non-zero error value on failure and 0 on success. Some possible 1232 * errors are: 1233 * <ul> 1234 * <li>EACCES - an attempt was made to write in a read-only transaction. 1235 * <li>EINVAL - an invalid parameter was specified. 1236 * </ul> 1237 */ 1238 int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data); 1239 1240 /** @brief Create a cursor handle. 1241 * 1242 * A cursor is associated with a specific transaction and database. 1243 * A cursor cannot be used when its database handle is closed. Nor 1244 * when its transaction has ended, except with #mdb_cursor_renew(). 1245 * It can be discarded with #mdb_cursor_close(). 1246 * A cursor in a write-transaction can be closed before its transaction 1247 * ends, and will otherwise be closed when its transaction ends. 1248 * A cursor in a read-only transaction must be closed explicitly, before 1249 * or after its transaction ends. It can be reused with 1250 * #mdb_cursor_renew() before finally closing it. 1251 * @note Earlier documentation said that cursors in every transaction 1252 * were closed when the transaction committed or aborted. 1253 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1254 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1255 * @param[out] cursor Address where the new #MDB_cursor handle will be stored 1256 * @return A non-zero error value on failure and 0 on success. Some possible 1257 * errors are: 1258 * <ul> 1259 * <li>EINVAL - an invalid parameter was specified. 1260 * </ul> 1261 */ 1262 int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor); 1263 1264 /** @brief Close a cursor handle. 1265 * 1266 * The cursor handle will be freed and must not be used again after this call. 1267 * Its transaction must still be live if it is a write-transaction. 1268 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1269 */ 1270 void mdb_cursor_close(MDB_cursor *cursor); 1271 1272 /** @brief Renew a cursor handle. 1273 * 1274 * A cursor is associated with a specific transaction and database. 1275 * Cursors that are only used in read-only 1276 * transactions may be re-used, to avoid unnecessary malloc/free overhead. 1277 * The cursor may be associated with a new read-only transaction, and 1278 * referencing the same database handle as it was created with. 1279 * This may be done whether the previous transaction is live or dead. 1280 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1281 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1282 * @return A non-zero error value on failure and 0 on success. Some possible 1283 * errors are: 1284 * <ul> 1285 * <li>EINVAL - an invalid parameter was specified. 1286 * </ul> 1287 */ 1288 int mdb_cursor_renew(MDB_txn *txn, MDB_cursor *cursor); 1289 1290 /** @brief Return the cursor's transaction handle. 1291 * 1292 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1293 */ 1294 MDB_txn *mdb_cursor_txn(MDB_cursor *cursor); 1295 1296 /** @brief Return the cursor's database handle. 1297 * 1298 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1299 */ 1300 MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor); 1301 1302 /** @brief Retrieve by cursor. 1303 * 1304 * This function retrieves key/data pairs from the database. The address and length 1305 * of the key are returned in the object to which \b key refers (except for the 1306 * case of the #MDB_SET option, in which the \b key object is unchanged), and 1307 * the address and length of the data are returned in the object to which \b data 1308 * refers. 1309 * See #mdb_get() for restrictions on using the output values. 1310 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1311 * @param[in,out] key The key for a retrieved item 1312 * @param[in,out] data The data of a retrieved item 1313 * @param[in] op A cursor operation #MDB_cursor_op 1314 * @return A non-zero error value on failure and 0 on success. Some possible 1315 * errors are: 1316 * <ul> 1317 * <li>#MDB_NOTFOUND - no matching key found. 1318 * <li>EINVAL - an invalid parameter was specified. 1319 * </ul> 1320 */ 1321 int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data, 1322 MDB_cursor_op op); 1323 1324 /** @brief Store by cursor. 1325 * 1326 * This function stores key/data pairs into the database. 1327 * If the function fails for any reason, the state of the cursor will be 1328 * unchanged. If the function succeeds and an item is inserted into the 1329 * database, the cursor is always positioned to refer to the newly inserted item. 1330 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1331 * @param[in] key The key operated on. 1332 * @param[in] data The data operated on. 1333 * @param[in] flags Options for this operation. This parameter 1334 * must be set to 0 or one of the values described here. 1335 * <ul> 1336 * <li>#MDB_CURRENT - overwrite the data of the key/data pair to which 1337 * the cursor refers with the specified data item. The \b key 1338 * parameter is ignored. 1339 * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not 1340 * already appear in the database. This flag may only be specified 1341 * if the database was opened with #MDB_DUPSORT. The function will 1342 * return #MDB_KEYEXIST if the key/data pair already appears in the 1343 * database. 1344 * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key 1345 * does not already appear in the database. The function will return 1346 * #MDB_KEYEXIST if the key already appears in the database, even if 1347 * the database supports duplicates (#MDB_DUPSORT). 1348 * <li>#MDB_RESERVE - reserve space for data of the given size, but 1349 * don't copy the given data. Instead, return a pointer to the 1350 * reserved space, which the caller can fill in later. This saves 1351 * an extra memcpy if the data is being generated later. 1352 * <li>#MDB_APPEND - append the given key/data pair to the end of the 1353 * database. No key comparisons are performed. This option allows 1354 * fast bulk loading when keys are already known to be in the 1355 * correct order. Loading unsorted keys with this flag will cause 1356 * data corruption. 1357 * <li>#MDB_APPENDDUP - as above, but for sorted dup data. 1358 * <li>#MDB_MULTIPLE - store multiple contiguous data elements in a 1359 * single request. This flag may only be specified if the database 1360 * was opened with #MDB_DUPFIXED. The \b data argument must be an 1361 * array of two MDB_vals. The mv_size of the first MDB_val must be 1362 * the size of a single data element. The mv_data of the first MDB_val 1363 * must point to the beginning of the array of contiguous data elements. 1364 * The mv_size of the second MDB_val must be the count of the number 1365 * of data elements to store. On return this field will be set to 1366 * the count of the number of elements actually written. The mv_data 1367 * of the second MDB_val is unused. 1368 * </ul> 1369 * @return A non-zero error value on failure and 0 on success. Some possible 1370 * errors are: 1371 * <ul> 1372 * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize(). 1373 * <li>#MDB_TXN_FULL - the transaction has too many dirty pages. 1374 * <li>EACCES - an attempt was made to modify a read-only database. 1375 * <li>EINVAL - an invalid parameter was specified. 1376 * </ul> 1377 */ 1378 int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data, 1379 unsigned int flags); 1380 1381 /** @brief Delete current key/data pair 1382 * 1383 * This function deletes the key/data pair to which the cursor refers. 1384 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1385 * @param[in] flags Options for this operation. This parameter 1386 * must be set to 0 or one of the values described here. 1387 * <ul> 1388 * <li>#MDB_NODUPDATA - delete all of the data items for the current key. 1389 * This flag may only be specified if the database was opened with #MDB_DUPSORT. 1390 * </ul> 1391 * @return A non-zero error value on failure and 0 on success. Some possible 1392 * errors are: 1393 * <ul> 1394 * <li>EACCES - an attempt was made to modify a read-only database. 1395 * <li>EINVAL - an invalid parameter was specified. 1396 * </ul> 1397 */ 1398 int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags); 1399 1400 /** @brief Return count of duplicates for current key. 1401 * 1402 * This call is only valid on databases that support sorted duplicate 1403 * data items #MDB_DUPSORT. 1404 * @param[in] cursor A cursor handle returned by #mdb_cursor_open() 1405 * @param[out] countp Address where the count will be stored 1406 * @return A non-zero error value on failure and 0 on success. Some possible 1407 * errors are: 1408 * <ul> 1409 * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified. 1410 * </ul> 1411 */ 1412 int mdb_cursor_count(MDB_cursor *cursor, size_t *countp); 1413 1414 /** @brief Compare two data items according to a particular database. 1415 * 1416 * This returns a comparison as if the two data items were keys in the 1417 * specified database. 1418 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1419 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1420 * @param[in] a The first item to compare 1421 * @param[in] b The second item to compare 1422 * @return < 0 if a < b, 0 if a == b, > 0 if a > b 1423 */ 1424 int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b); 1425 1426 /** @brief Compare two data items according to a particular database. 1427 * 1428 * This returns a comparison as if the two items were data items of 1429 * the specified database. The database must have the #MDB_DUPSORT flag. 1430 * @param[in] txn A transaction handle returned by #mdb_txn_begin() 1431 * @param[in] dbi A database handle returned by #mdb_dbi_open() 1432 * @param[in] a The first item to compare 1433 * @param[in] b The second item to compare 1434 * @return < 0 if a < b, 0 if a == b, > 0 if a > b 1435 */ 1436 int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b); 1437 1438 /** @brief A callback function used to print a message from the library. 1439 * 1440 * @param[in] msg The string to be printed. 1441 * @param[in] ctx An arbitrary context pointer for the callback. 1442 * @return < 0 on failure, >= 0 on success. 1443 */ 1444 typedef int (MDB_msg_func)(const char *msg, void *ctx); 1445 1446 /** @brief Dump the entries in the reader lock table. 1447 * 1448 * @param[in] env An environment handle returned by #mdb_env_create() 1449 * @param[in] func A #MDB_msg_func function 1450 * @param[in] ctx Anything the message function needs 1451 * @return < 0 on failure, >= 0 on success. 1452 */ 1453 int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx); 1454 1455 /** @brief Check for stale entries in the reader lock table. 1456 * 1457 * @param[in] env An environment handle returned by #mdb_env_create() 1458 * @param[out] dead Number of stale slots that were cleared 1459 * @return 0 on success, non-zero on failure. 1460 */ 1461 int mdb_reader_check(MDB_env *env, int *dead); 1462 /** @} */ 1463 1464 #ifdef __cplusplus 1465 } 1466 #endif 1467 #endif /* _LMDB_H_ */ 1468