JezK

Edit File: lmdb.h

/** @file lmdb.h * @brief Lightning memory-mapped database library * * @mainpage Lightning Memory-Mapped Database Manager (LMDB) * * @section intro_sec Introduction * LMDB is a Btree-based database management library modeled loosely on the * BerkeleyDB API, but much simplified. The entire database is exposed * in a memory map, and all data fetches return data directly * from the mapped memory, so no malloc's or memcpy's occur during * data fetches. As such, the library is extremely simple because it * requires no page caching layer of its own, and it is extremely high * performance and memory-efficient. It is also fully transactional with * full ACID semantics, and when the memory map is read-only, the * database integrity cannot be corrupted by stray pointer writes from * application code. * * The library is fully thread-aware and supports concurrent read/write * access from multiple processes and threads. Data pages use a copy-on- * write strategy so no active data pages are ever overwritten, which * also provides resistance to corruption and eliminates the need of any * special recovery procedures after a system crash. Writes are fully * serialized; only one write transaction may be active at a time, which * guarantees that writers can never deadlock. The database structure is * multi-versioned so readers run with no locks; writers cannot block * readers, and readers don't block writers. * * Unlike other well-known database mechanisms which use either write-ahead * transaction logs or append-only data writes, LMDB requires no maintenance * during operation. Both write-ahead loggers and append-only databases * require periodic checkpointing and/or compaction of their log or database * files otherwise they grow without bound. LMDB tracks free pages within * the database and re-uses them for new write operations, so the database * size does not grow without bound in normal use. * * The memory map can be used as a read-only or read-write map. It is * read-only by default as this provides total immunity to corruption. * Using read-write mode offers much higher write performance, but adds * the possibility for stray application writes thru pointers to silently * corrupt the database. Of course if your application code is known to * be bug-free (...) then this is not an issue. * * If this is your first time using a transactional embedded key/value * store, you may find the \ref starting page to be helpful. * * @section caveats_sec Caveats * Troubleshooting the lock file, plus semaphores on BSD systems: * * - A broken lockfile can cause sync issues. * Stale reader transactions left behind by an aborted program * cause further writes to grow the database quickly, and * stale locks can block further operation. * * Fix: Check for stale readers periodically, using the * #mdb_reader_check function or the \ref mdb_stat_1 "mdb_stat" tool. * Stale writers will be cleared automatically on some systems: * - Windows - automatic * - Linux, systems using POSIX mutexes with Robust option - automatic * - not on BSD, systems using POSIX semaphores. * Otherwise just make all programs using the database close it; * the lockfile is always reset on first open of the environment. * * - On BSD systems or others configured with MDB_USE_POSIX_SEM, * startup can fail due to semaphores owned by another userid. * * Fix: Open and close the database as the user which owns the * semaphores (likely last user) or as root, while no other * process is using the database. * * Restrictions/caveats (in addition to those listed for some functions): * * - Only the database owner should normally use the database on * BSD systems or when otherwise configured with MDB_USE_POSIX_SEM. * Multiple users can cause startup to fail later, as noted above. * * - There is normally no pure read-only mode, since readers need write * access to locks and lock file. Exceptions: On read-only filesystems * or with the #MDB_NOLOCK flag described under #mdb_env_open(). * * - An LMDB configuration will often reserve considerable \b unused * memory address space and maybe file size for future growth. * This does not use actual memory or disk space, but users may need * to understand the difference so they won't be scared off. * * - By default, in versions before 0.9.10, unused portions of the data * file might receive garbage data from memory freed by other code. * (This does not happen when using the #MDB_WRITEMAP flag.) As of * 0.9.10 the default behavior is to initialize such memory before * writing to the data file. Since there may be a slight performance * cost due to this initialization, applications may disable it using * the #MDB_NOMEMINIT flag. Applications handling sensitive data * which must not be written should not use this flag. This flag is * irrelevant when using #MDB_WRITEMAP. * * - A thread can only use one transaction at a time, plus any child * transactions. Each transaction belongs to one thread. See below. * The #MDB_NOTLS flag changes this for read-only transactions. * * - Use an MDB_env* in the process which opened it, not after fork(). * * - Do not have open an LMDB database twice in the same process at * the same time. Not even from a plain open() call - close()ing it * breaks fcntl() advisory locking. (It is OK to reopen it after * fork() - exec*(), since the lockfile has FD_CLOEXEC set.) * * - Avoid long-lived transactions. Read transactions prevent * reuse of pages freed by newer write transactions, thus the * database can grow quickly. Write transactions prevent * other write transactions, since writes are serialized. * * - Avoid suspending a process with active transactions. These * would then be "long-lived" as above. Also read transactions * suspended when writers commit could sometimes see wrong data. * * ...when several processes can use a database concurrently: * * - Avoid aborting a process with an active transaction. * The transaction becomes "long-lived" as above until a check * for stale readers is performed or the lockfile is reset, * since the process may not remove it from the lockfile. * * This does not apply to write transactions if the system clears * stale writers, see above. * * - If you do that anyway, do a periodic check for stale readers. Or * close the environment once in a while, so the lockfile can get reset. * * - Do not use LMDB databases on remote filesystems, even between * processes on the same host. This breaks flock() on some OSes, * possibly memory map sync, and certainly sync between programs * on different hosts. * * - Opening a database can fail if another process is opening or * closing it at exactly the same time. * * @author Howard Chu, Symas Corporation. * * @copyright Copyright 2011-2021 Howard Chu, Symas Corp. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted only as authorized by the OpenLDAP * Public License. * * A copy of this license is available in the file LICENSE in the * top-level directory of the distribution or, alternatively, at * <http://www.OpenLDAP.org/license.html>. * * @par Derived From: * This code is derived from btree.c written by Martin Hedenfalk. * * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se> * * Permission to use, copy, modify, and distribute this software for any * purpose with or without fee is hereby granted, provided that the above * copyright notice and this permission notice appear in all copies. * * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */ #ifndef _LMDB_H_ #define _LMDB_H_ #include <sys/types.h> #ifdef __cplusplus extern "C" { #endif /** Unix permissions for creating files, or dummy definition for Windows */ #ifdef _MSC_VER typedef int mdb_mode_t; #else typedef mode_t mdb_mode_t; #endif /** An abstraction for a file handle. * On POSIX systems file handles are small integers. On Windows * they're opaque pointers. */ #ifdef _WIN32 typedef void *mdb_filehandle_t; #else typedef int mdb_filehandle_t; #endif /** @defgroup mdb LMDB API * @{ * @brief OpenLDAP Lightning Memory-Mapped Database Manager */ /** @defgroup Version Version Macros * @{ */ /** Library major version */ #define MDB_VERSION_MAJOR 0 /** Library minor version */ #define MDB_VERSION_MINOR 9 /** Library patch version */ #define MDB_VERSION_PATCH 29 /** Combine args a,b,c into a single integer for easy version comparisons */ #define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c)) /** The full library version as a single integer */ #define MDB_VERSION_FULL \ MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH) /** The release date of this library version */ #define MDB_VERSION_DATE "March 16, 2021" /** A stringifier for the version info */ #define MDB_VERSTR(a,b,c,d) "LMDB " #a "." #b "." #c ": (" d ")" /** A helper for the stringifier macro */ #define MDB_VERFOO(a,b,c,d) MDB_VERSTR(a,b,c,d) /** The full library version as a C string */ #define MDB_VERSION_STRING \ MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE) /** @} */ /** @brief Opaque structure for a database environment. * * A DB environment supports multiple databases, all residing in the same * shared-memory map. */ typedef struct MDB_env MDB_env; /** @brief Opaque structure for a transaction handle. * * All database operations require a transaction handle. Transactions may be * read-only or read-write. */ typedef struct MDB_txn MDB_txn; /** @brief A handle for an individual database in the DB environment. */ typedef unsigned int MDB_dbi; /** @brief Opaque structure for navigating through a database */ typedef struct MDB_cursor MDB_cursor; /** @brief Generic structure used for passing keys and data in and out * of the database. * * Values returned from the database are valid only until a subsequent * update operation, or the end of the transaction. Do not modify or * free them, they commonly point into the database itself. * * Key sizes must be between 1 and #mdb_env_get_maxkeysize() inclusive. * The same applies to data sizes in databases with the #MDB_DUPSORT flag. * Other data items can in theory be from 0 to 0xffffffff bytes long. */ typedef struct MDB_val { size_t mv_size; /**< size of the data item */ void *mv_data; /**< address of the data item */ } MDB_val; /** @brief A callback function used to compare two keys in a database */ typedef int (MDB_cmp_func)(const MDB_val *a, const MDB_val *b); /** @brief A callback function used to relocate a position-dependent data item * in a fixed-address database. * * The \b newptr gives the item's desired address in * the memory map, and \b oldptr gives its previous address. The item's actual * data resides at the address in \b item. This callback is expected to walk * through the fields of the record in \b item and modify any * values based at the \b oldptr address to be relative to the \b newptr address. * @param[in,out] item The item that is to be relocated. * @param[in] oldptr The previous address. * @param[in] newptr The new address to relocate to. * @param[in] relctx An application-provided context, set by #mdb_set_relctx(). * @todo This feature is currently unimplemented. */ typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx); /** @defgroup mdb_env Environment Flags * @{ */ /** mmap at a fixed address (experimental) */ #define MDB_FIXEDMAP 0x01 /** no environment directory */ #define MDB_NOSUBDIR 0x4000 /** don't fsync after commit */ #define MDB_NOSYNC 0x10000 /** read only */ #define MDB_RDONLY 0x20000 /** don't fsync metapage after commit */ #define MDB_NOMETASYNC 0x40000 /** use writable mmap */ #define MDB_WRITEMAP 0x80000 /** use asynchronous msync when #MDB_WRITEMAP is used */ #define MDB_MAPASYNC 0x100000 /** tie reader locktable slots to #MDB_txn objects instead of to threads */ #define MDB_NOTLS 0x200000 /** don't do any locking, caller must manage their own locks */ #define MDB_NOLOCK 0x400000 /** don't do readahead (no effect on Windows) */ #define MDB_NORDAHEAD 0x800000 /** don't initialize malloc'd memory before writing to datafile */ #define MDB_NOMEMINIT 0x1000000 /** @} */ /** @defgroup mdb_dbi_open Database Flags * @{ */ /** use reverse string keys */ #define MDB_REVERSEKEY 0x02 /** use sorted duplicates */ #define MDB_DUPSORT 0x04 /** numeric keys in native byte order: either unsigned int or size_t. * The keys must all be of the same size. */ #define MDB_INTEGERKEY 0x08 /** with #MDB_DUPSORT, sorted dup items have fixed size */ #define MDB_DUPFIXED 0x10 /** with #MDB_DUPSORT, dups are #MDB_INTEGERKEY-style integers */ #define MDB_INTEGERDUP 0x20 /** with #MDB_DUPSORT, use reverse string dups */ #define MDB_REVERSEDUP 0x40 /** create DB if not already existing */ #define MDB_CREATE 0x40000 /** @} */ /** @defgroup mdb_put Write Flags * @{ */ /** For put: Don't write if the key already exists. */ #define MDB_NOOVERWRITE 0x10 /** Only for #MDB_DUPSORT<br> * For put: don't write if the key and data pair already exist.<br> * For mdb_cursor_del: remove all duplicate data items. */ #define MDB_NODUPDATA 0x20 /** For mdb_cursor_put: overwrite the current key/data pair */ #define MDB_CURRENT 0x40 /** For put: Just reserve space for data, don't copy it. Return a * pointer to the reserved space. */ #define MDB_RESERVE 0x10000 /** Data is being appended, don't split full pages. */ #define MDB_APPEND 0x20000 /** Duplicate data is being appended, don't split full pages. */ #define MDB_APPENDDUP 0x40000 /** Store multiple data items in one call. Only for #MDB_DUPFIXED. */ #define MDB_MULTIPLE 0x80000 /* @} */ /** @defgroup mdb_copy Copy Flags * @{ */ /** Compacting copy: Omit free space from copy, and renumber all * pages sequentially. */ #define MDB_CP_COMPACT 0x01 /* @} */ /** @brief Cursor Get operations. * * This is the set of all operations for retrieving data * using a cursor. */ typedef enum MDB_cursor_op { MDB_FIRST, /**< Position at first key/data item */ MDB_FIRST_DUP, /**< Position at first data item of current key. Only for #MDB_DUPSORT */ MDB_GET_BOTH, /**< Position at key/data pair. Only for #MDB_DUPSORT */ MDB_GET_BOTH_RANGE, /**< position at key, nearest data. Only for #MDB_DUPSORT */ MDB_GET_CURRENT, /**< Return key/data at current cursor position */ MDB_GET_MULTIPLE, /**< Return up to a page of duplicate data items from current cursor position. Move cursor to prepare for #MDB_NEXT_MULTIPLE. Only for #MDB_DUPFIXED */ MDB_LAST, /**< Position at last key/data item */ MDB_LAST_DUP, /**< Position at last data item of current key. Only for #MDB_DUPSORT */ MDB_NEXT, /**< Position at next data item */ MDB_NEXT_DUP, /**< Position at next data item of current key. Only for #MDB_DUPSORT */ MDB_NEXT_MULTIPLE, /**< Return up to a page of duplicate data items from next cursor position. Move cursor to prepare for #MDB_NEXT_MULTIPLE. Only for #MDB_DUPFIXED */ MDB_NEXT_NODUP, /**< Position at first data item of next key */ MDB_PREV, /**< Position at previous data item */ MDB_PREV_DUP, /**< Position at previous data item of current key. Only for #MDB_DUPSORT */ MDB_PREV_NODUP, /**< Position at last data item of previous key */ MDB_SET, /**< Position at specified key */ MDB_SET_KEY, /**< Position at specified key, return key + data */ MDB_SET_RANGE, /**< Position at first key greater than or equal to specified key. */ MDB_PREV_MULTIPLE /**< Position at previous page and return up to a page of duplicate data items. Only for #MDB_DUPFIXED */ } MDB_cursor_op; /** @defgroup errors Return Codes * * BerkeleyDB uses -30800 to -30999, we'll go under them * @{ */ /** Successful result */ #define MDB_SUCCESS 0 /** key/data pair already exists */ #define MDB_KEYEXIST (-30799) /** key/data pair not found (EOF) */ #define MDB_NOTFOUND (-30798) /** Requested page not found - this usually indicates corruption */ #define MDB_PAGE_NOTFOUND (-30797) /** Located page was wrong type */ #define MDB_CORRUPTED (-30796) /** Update of meta page failed or environment had fatal error */ #define MDB_PANIC (-30795) /** Environment version mismatch */ #define MDB_VERSION_MISMATCH (-30794) /** File is not a valid LMDB file */ #define MDB_INVALID (-30793) /** Environment mapsize reached */ #define MDB_MAP_FULL (-30792) /** Environment maxdbs reached */ #define MDB_DBS_FULL (-30791) /** Environment maxreaders reached */ #define MDB_READERS_FULL (-30790) /** Too many TLS keys in use - Windows only */ #define MDB_TLS_FULL (-30789) /** Txn has too many dirty pages */ #define MDB_TXN_FULL (-30788) /** Cursor stack too deep - internal error */ #define MDB_CURSOR_FULL (-30787) /** Page has not enough space - internal error */ #define MDB_PAGE_FULL (-30786) /** Database contents grew beyond environment mapsize */ #define MDB_MAP_RESIZED (-30785) /** Operation and DB incompatible, or DB type changed. This can mean: * <ul> * <li>The operation expects an #MDB_DUPSORT / #MDB_DUPFIXED database. * <li>Opening a named DB when the unnamed DB has #MDB_DUPSORT / #MDB_INTEGERKEY. * <li>Accessing a data record as a database, or vice versa. * <li>The database was dropped and recreated with different flags. * </ul> */ #define MDB_INCOMPATIBLE (-30784) /** Invalid reuse of reader locktable slot */ #define MDB_BAD_RSLOT (-30783) /** Transaction must abort, has a child, or is invalid */ #define MDB_BAD_TXN (-30782) /** Unsupported size of key/DB name/data, or wrong DUPFIXED size */ #define MDB_BAD_VALSIZE (-30781) /** The specified DBI was changed unexpectedly */ #define MDB_BAD_DBI (-30780) /** The last defined error code */ #define MDB_LAST_ERRCODE MDB_BAD_DBI /** @} */ /** @brief Statistics for a database in the environment */ typedef struct MDB_stat { unsigned int ms_psize; /**< Size of a database page. This is currently the same for all databases. */ unsigned int ms_depth; /**< Depth (height) of the B-tree */ size_t ms_branch_pages; /**< Number of internal (non-leaf) pages */ size_t ms_leaf_pages; /**< Number of leaf pages */ size_t ms_overflow_pages; /**< Number of overflow pages */ size_t ms_entries; /**< Number of data items */ } MDB_stat; /** @brief Information about the environment */ typedef struct MDB_envinfo { void *me_mapaddr; /**< Address of map, if fixed */ size_t me_mapsize; /**< Size of the data memory map */ size_t me_last_pgno; /**< ID of the last used page */ size_t me_last_txnid; /**< ID of the last committed transaction */ unsigned int me_maxreaders; /**< max reader slots in the environment */ unsigned int me_numreaders; /**< max reader slots used in the environment */ } MDB_envinfo; /** @brief Return the LMDB library version information. * * @param[out] major if non-NULL, the library major version number is copied here * @param[out] minor if non-NULL, the library minor version number is copied here * @param[out] patch if non-NULL, the library patch version number is copied here * @retval "version string" The library version as a string */ char *mdb_version(int *major, int *minor, int *patch); /** @brief Return a string describing a given error code. * * This function is a superset of the ANSI C X3.159-1989 (ANSI C) strerror(3) * function. If the error code is greater than or equal to 0, then the string * returned by the system function strerror(3) is returned. If the error code * is less than 0, an error string corresponding to the LMDB library error is * returned. See @ref errors for a list of LMDB-specific error codes. * @param[in] err The error code * @retval "error message" The description of the error */ char *mdb_strerror(int err); /** @brief Create an LMDB environment handle. * * This function allocates memory for a #MDB_env structure. To release * the allocated memory and discard the handle, call #mdb_env_close(). * Before the handle may be used, it must be opened using #mdb_env_open(). * Various other options may also need to be set before opening the handle, * e.g. #mdb_env_set_mapsize(), #mdb_env_set_maxreaders(), #mdb_env_set_maxdbs(), * depending on usage requirements. * @param[out] env The address where the new handle will be stored * @return A non-zero error value on failure and 0 on success. */ int mdb_env_create(MDB_env **env); /** @brief Open an environment handle. * * If this function fails, #mdb_env_close() must be called to discard the #MDB_env handle. * @param[in] env An environment handle returned by #mdb_env_create() * @param[in] path The directory in which the database files reside. This * directory must already exist and be writable. * @param[in] flags Special options for this environment. This parameter * must be set to 0 or by bitwise OR'ing together one or more of the * values described here. * Flags set by mdb_env_set_flags() are also used. * <ul> * <li>#MDB_FIXEDMAP * use a fixed address for the mmap region. This flag must be specified * when creating the environment, and is stored persistently in the environment. * If successful, the memory map will always reside at the same virtual address * and pointers used to reference data items in the database will be constant * across multiple invocations. This option may not always work, depending on * how the operating system has allocated memory to shared libraries and other uses. * The feature is highly experimental. * <li>#MDB_NOSUBDIR * By default, LMDB creates its environment in a directory whose * pathname is given in \b path, and creates its data and lock files * under that directory. With this option, \b path is used as-is for * the database main data file. The database lock file is the \b path * with "-lock" appended. * <li>#MDB_RDONLY * Open the environment in read-only mode. No write operations will be * allowed. LMDB will still modify the lock file - except on read-only * filesystems, where LMDB does not use locks. * <li>#MDB_WRITEMAP * Use a writeable memory map unless MDB_RDONLY is set. This uses * fewer mallocs but loses protection from application bugs * like wild pointer writes and other bad updates into the database. * This may be slightly faster for DBs that fit entirely in RAM, but * is slower for DBs larger than RAM. * Incompatible with nested transactions. * Do not mix processes with and without MDB_WRITEMAP on the same * environment. This can defeat durability (#mdb_env_sync etc). * <li>#MDB_NOMETASYNC * Flush system buffers to disk only once per transaction, omit the * metadata flush. Defer that until the system flushes files to disk, * or next non-MDB_RDONLY commit or #mdb_env_sync(). This optimization * maintains database integrity, but a system crash may undo the last * committed transaction. I.e. it preserves the ACI (atomicity, * consistency, isolation) but not D (durability) database property. * This flag may be changed at any time using #mdb_env_set_flags(). * <li>#MDB_NOSYNC * Don't flush system buffers to disk when committing a transaction. * This optimization means a system crash can corrupt the database or * lose the last transactions if buffers are not yet flushed to disk. * The risk is governed by how often the system flushes dirty buffers * to disk and how often #mdb_env_sync() is called. However, if the * filesystem preserves write order and the #MDB_WRITEMAP flag is not * used, transactions exhibit ACI (atomicity, consistency, isolation) * properties and only lose D (durability). I.e. database integrity * is maintained, but a system crash may undo the final transactions. * Note that (#MDB_NOSYNC | #MDB_WRITEMAP) leaves the system with no * hint for when to write transactions to disk, unless #mdb_env_sync() * is called. (#MDB_MAPASYNC | #MDB_WRITEMAP) may be preferable. * This flag may be changed at any time using #mdb_env_set_flags(). * <li>#MDB_MAPASYNC * When using #MDB_WRITEMAP, use asynchronous flushes to disk. * As with #MDB_NOSYNC, a system crash can then corrupt the * database or lose the last transactions. Calling #mdb_env_sync() * ensures on-disk database integrity until next commit. * This flag may be changed at any time using #mdb_env_set_flags(). * <li>#MDB_NOTLS * Don't use Thread-Local Storage. Tie reader locktable slots to * #MDB_txn objects instead of to threads. I.e. #mdb_txn_reset() keeps * the slot reserved for the #MDB_txn object. A thread may use parallel * read-only transactions. A read-only transaction may span threads if * the user synchronizes its use. Applications that multiplex many * user threads over individual OS threads need this option. Such an * application must also serialize the write transactions in an OS * thread, since LMDB's write locking is unaware of the user threads. * <li>#MDB_NOLOCK * Don't do any locking. If concurrent access is anticipated, the * caller must manage all concurrency itself. For proper operation * the caller must enforce single-writer semantics, and must ensure * that no readers are using old transactions while a writer is * active. The simplest approach is to use an exclusive lock so that * no readers may be active at all when a writer begins. * <li>#MDB_NORDAHEAD * Turn off readahead. Most operating systems perform readahead on * read requests by default. This option turns it off if the OS * supports it. Turning it off may help random read performance * when the DB is larger than RAM and system RAM is full. * The option is not implemented on Windows. * <li>#MDB_NOMEMINIT * Don't initialize malloc'd memory before writing to unused spaces * in the data file. By default, memory for pages written to the data * file is obtained using malloc. While these pages may be reused in * subsequent transactions, freshly malloc'd pages will be initialized * to zeroes before use. This avoids persisting leftover data from other * code (that used the heap and subsequently freed the memory) into the * data file. Note that many other system libraries may allocate * and free memory from the heap for arbitrary uses. E.g., stdio may * use the heap for file I/O buffers. This initialization step has a * modest performance cost so some applications may want to disable * it using this flag. This option can be a problem for applications * which handle sensitive data like passwords, and it makes memory * checkers like Valgrind noisy. This flag is not needed with #MDB_WRITEMAP, * which writes directly to the mmap instead of using malloc for pages. The * initialization is also skipped if #MDB_RESERVE is used; the * caller is expected to overwrite all of the memory that was * reserved in that case. * This flag may be changed at any time using #mdb_env_set_flags(). * </ul> * @param[in] mode The UNIX permissions to set on created files and semaphores. * This parameter is ignored on Windows. * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>#MDB_VERSION_MISMATCH - the version of the LMDB library doesn't match the * version that created the database environment. * <li>#MDB_INVALID - the environment file headers are corrupted. * <li>ENOENT - the directory specified by the path parameter doesn't exist. * <li>EACCES - the user didn't have permission to access the environment files. * <li>EAGAIN - the environment was locked by another process. * </ul> */ int mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode); /** @brief Copy an LMDB environment to the specified path. * * This function may be used to make a backup of an existing environment. * No lockfile is created, since it gets recreated at need. * @note This call can trigger significant file size growth if run in * parallel with write transactions, because it employs a read-only * transaction. See long-lived transactions under @ref caveats_sec. * @param[in] env An environment handle returned by #mdb_env_create(). It * must have already been opened successfully. * @param[in] path The directory in which the copy will reside. This * directory must already exist and be writable but must otherwise be * empty. * @return A non-zero error value on failure and 0 on success. */ int mdb_env_copy(MDB_env *env, const char *path); /** @brief Copy an LMDB environment to the specified file descriptor. * * This function may be used to make a backup of an existing environment. * No lockfile is created, since it gets recreated at need. * @note This call can trigger significant file size growth if run in * parallel with write transactions, because it employs a read-only * transaction. See long-lived transactions under @ref caveats_sec. * @param[in] env An environment handle returned by #mdb_env_create(). It * must have already been opened successfully. * @param[in] fd The filedescriptor to write the copy to. It must * have already been opened for Write access. * @return A non-zero error value on failure and 0 on success. */ int mdb_env_copyfd(MDB_env *env, mdb_filehandle_t fd); /** @brief Copy an LMDB environment to the specified path, with options. * * This function may be used to make a backup of an existing environment. * No lockfile is created, since it gets recreated at need. * @note This call can trigger significant file size growth if run in * parallel with write transactions, because it employs a read-only * transaction. See long-lived transactions under @ref caveats_sec. * @param[in] env An environment handle returned by #mdb_env_create(). It * must have already been opened successfully. * @param[in] path The directory in which the copy will reside. This * directory must already exist and be writable but must otherwise be * empty. * @param[in] flags Special options for this operation. This parameter * must be set to 0 or by bitwise OR'ing together one or more of the * values described here. * <ul> * <li>#MDB_CP_COMPACT - Perform compaction while copying: omit free * pages and sequentially renumber all pages in output. This option * consumes more CPU and runs more slowly than the default. * Currently it fails if the environment has suffered a page leak. * </ul> * @return A non-zero error value on failure and 0 on success. */ int mdb_env_copy2(MDB_env *env, const char *path, unsigned int flags); /** @brief Copy an LMDB environment to the specified file descriptor, * with options. * * This function may be used to make a backup of an existing environment. * No lockfile is created, since it gets recreated at need. See * #mdb_env_copy2() for further details. * @note This call can trigger significant file size growth if run in * parallel with write transactions, because it employs a read-only * transaction. See long-lived transactions under @ref caveats_sec. * @param[in] env An environment handle returned by #mdb_env_create(). It * must have already been opened successfully. * @param[in] fd The filedescriptor to write the copy to. It must * have already been opened for Write access. * @param[in] flags Special options for this operation. * See #mdb_env_copy2() for options. * @return A non-zero error value on failure and 0 on success. */ int mdb_env_copyfd2(MDB_env *env, mdb_filehandle_t fd, unsigned int flags); /** @brief Return statistics about the LMDB environment. * * @param[in] env An environment handle returned by #mdb_env_create() * @param[out] stat The address of an #MDB_stat structure * where the statistics will be copied */ int mdb_env_stat(MDB_env *env, MDB_stat *stat); /** @brief Return information about the LMDB environment. * * @param[in] env An environment handle returned by #mdb_env_create() * @param[out] stat The address of an #MDB_envinfo structure * where the information will be copied */ int mdb_env_info(MDB_env *env, MDB_envinfo *stat); /** @brief Flush the data buffers to disk. * * Data is always written to disk when #mdb_txn_commit() is called, * but the operating system may keep it buffered. LMDB always flushes * the OS buffers upon commit as well, unless the environment was * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC. This call is * not valid if the environment was opened with #MDB_RDONLY. * @param[in] env An environment handle returned by #mdb_env_create() * @param[in] force If non-zero, force a synchronous flush. Otherwise * if the environment has the #MDB_NOSYNC flag set the flushes * will be omitted, and with #MDB_MAPASYNC they will be asynchronous. * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EACCES - the environment is read-only. * <li>EINVAL - an invalid parameter was specified. * <li>EIO - an error occurred during synchronization. * </ul> */ int mdb_env_sync(MDB_env *env, int force); /** @brief Close the environment and release the memory map. * * Only a single thread may call this function. All transactions, databases, * and cursors must already be closed before calling this function. Attempts to * use any such handles after calling this function will cause a SIGSEGV. * The environment handle will be freed and must not be used again after this call. * @param[in] env An environment handle returned by #mdb_env_create() */ void mdb_env_close(MDB_env *env); /** @brief Set environment flags. * * This may be used to set some flags in addition to those from * #mdb_env_open(), or to unset these flags. If several threads * change the flags at the same time, the result is undefined. * @param[in] env An environment handle returned by #mdb_env_create() * @param[in] flags The flags to change, bitwise OR'ed together * @param[in] onoff A non-zero value sets the flags, zero clears them. * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_env_set_flags(MDB_env *env, unsigned int flags, int onoff); /** @brief Get environment flags. * * @param[in] env An environment handle returned by #mdb_env_create() * @param[out] flags The address of an integer to store the flags * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_env_get_flags(MDB_env *env, unsigned int *flags); /** @brief Return the path that was used in #mdb_env_open(). * * @param[in] env An environment handle returned by #mdb_env_create() * @param[out] path Address of a string pointer to contain the path. This * is the actual string in the environment, not a copy. It should not be * altered in any way. * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_env_get_path(MDB_env *env, const char **path); /** @brief Return the filedescriptor for the given environment. * * This function may be called after fork(), so the descriptor can be * closed before exec*(). Other LMDB file descriptors have FD_CLOEXEC. * (Until LMDB 0.9.18, only the lockfile had that.) * * @param[in] env An environment handle returned by #mdb_env_create() * @param[out] fd Address of a mdb_filehandle_t to contain the descriptor. * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_env_get_fd(MDB_env *env, mdb_filehandle_t *fd); /** @brief Set the size of the memory map to use for this environment. * * The size should be a multiple of the OS page size. The default is * 10485760 bytes. The size of the memory map is also the maximum size * of the database. The value should be chosen as large as possible, * to accommodate future growth of the database. * This function should be called after #mdb_env_create() and before #mdb_env_open(). * It may be called at later times if no transactions are active in * this process. Note that the library does not check for this condition, * the caller must ensure it explicitly. * * The new size takes effect immediately for the current process but * will not be persisted to any others until a write transaction has been * committed by the current process. Also, only mapsize increases are * persisted into the environment. * * If the mapsize is increased by another process, and data has grown * beyond the range of the current mapsize, #mdb_txn_begin() will * return #MDB_MAP_RESIZED. This function may be called with a size * of zero to adopt the new size. * * Any attempt to set a size smaller than the space already consumed * by the environment will be silently changed to the current size of the used space. * @param[in] env An environment handle returned by #mdb_env_create() * @param[in] size The size in bytes * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified, or the environment has * an active write transaction. * </ul> */ int mdb_env_set_mapsize(MDB_env *env, size_t size); /** @brief Set the maximum number of threads/reader slots for the environment. * * This defines the number of slots in the lock table that is used to track readers in the * the environment. The default is 126. * Starting a read-only transaction normally ties a lock table slot to the * current thread until the environment closes or the thread exits. If * MDB_NOTLS is in use, #mdb_txn_begin() instead ties the slot to the * MDB_txn object until it or the #MDB_env object is destroyed. * This function may only be called after #mdb_env_create() and before #mdb_env_open(). * @param[in] env An environment handle returned by #mdb_env_create() * @param[in] readers The maximum number of reader lock table slots * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified, or the environment is already open. * </ul> */ int mdb_env_set_maxreaders(MDB_env *env, unsigned int readers); /** @brief Get the maximum number of threads/reader slots for the environment. * * @param[in] env An environment handle returned by #mdb_env_create() * @param[out] readers Address of an integer to store the number of readers * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers); /** @brief Set the maximum number of named databases for the environment. * * This function is only needed if multiple databases will be used in the * environment. Simpler applications that use the environment as a single * unnamed database can ignore this option. * This function may only be called after #mdb_env_create() and before #mdb_env_open(). * * Currently a moderate number of slots are cheap but a huge number gets * expensive: 7-120 words per transaction, and every #mdb_dbi_open() * does a linear search of the opened slots. * @param[in] env An environment handle returned by #mdb_env_create() * @param[in] dbs The maximum number of databases * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified, or the environment is already open. * </ul> */ int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs); /** @brief Get the maximum size of keys and #MDB_DUPSORT data we can write. * * Depends on the compile-time constant #MDB_MAXKEYSIZE. Default 511. * See @ref MDB_val. * @param[in] env An environment handle returned by #mdb_env_create() * @return The maximum size of a key we can write */ int mdb_env_get_maxkeysize(MDB_env *env); /** @brief Set application information associated with the #MDB_env. * * @param[in] env An environment handle returned by #mdb_env_create() * @param[in] ctx An arbitrary pointer for whatever the application needs. * @return A non-zero error value on failure and 0 on success. */ int mdb_env_set_userctx(MDB_env *env, void *ctx); /** @brief Get the application information associated with the #MDB_env. * * @param[in] env An environment handle returned by #mdb_env_create() * @return The pointer set by #mdb_env_set_userctx(). */ void *mdb_env_get_userctx(MDB_env *env); /** @brief A callback function for most LMDB assert() failures, * called before printing the message and aborting. * * @param[in] env An environment handle returned by #mdb_env_create(). * @param[in] msg The assertion message, not including newline. */ typedef void MDB_assert_func(MDB_env *env, const char *msg); /** Set or reset the assert() callback of the environment. * Disabled if liblmdb is built with NDEBUG. * @note This hack should become obsolete as lmdb's error handling matures. * @param[in] env An environment handle returned by #mdb_env_create(). * @param[in] func An #MDB_assert_func function, or 0. * @return A non-zero error value on failure and 0 on success. */ int mdb_env_set_assert(MDB_env *env, MDB_assert_func *func); /** @brief Create a transaction for use with the environment. * * The transaction handle may be discarded using #mdb_txn_abort() or #mdb_txn_commit(). * @note A transaction and its cursors must only be used by a single * thread, and a thread may only have a single transaction at a time. * If #MDB_NOTLS is in use, this does not apply to read-only transactions. * @note Cursors may not span transactions. * @param[in] env An environment handle returned by #mdb_env_create() * @param[in] parent If this parameter is non-NULL, the new transaction * will be a nested transaction, with the transaction indicated by \b parent * as its parent. Transactions may be nested to any level. A parent * transaction and its cursors may not issue any other operations than * mdb_txn_commit and mdb_txn_abort while it has active child transactions. * @param[in] flags Special options for this transaction. This parameter * must be set to 0 or by bitwise OR'ing together one or more of the * values described here. * <ul> * <li>#MDB_RDONLY * This transaction will not perform any write operations. * </ul> * @param[out] txn Address where the new #MDB_txn handle will be stored * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>#MDB_PANIC - a fatal error occurred earlier and the environment * must be shut down. * <li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's * mapsize and this environment's map must be resized as well. * See #mdb_env_set_mapsize(). * <li>#MDB_READERS_FULL - a read-only transaction was requested and * the reader lock table is full. See #mdb_env_set_maxreaders(). * <li>ENOMEM - out of memory. * </ul> */ int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn); /** @brief Returns the transaction's #MDB_env * * @param[in] txn A transaction handle returned by #mdb_txn_begin() */ MDB_env *mdb_txn_env(MDB_txn *txn); /** @brief Return the transaction's ID. * * This returns the identifier associated with this transaction. For a * read-only transaction, this corresponds to the snapshot being read; * concurrent readers will frequently have the same transaction ID. * * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @return A transaction ID, valid if input is an active transaction. */ size_t mdb_txn_id(MDB_txn *txn); /** @brief Commit all the operations of a transaction into the database. * * The transaction handle is freed. It and its cursors must not be used * again after this call, except with #mdb_cursor_renew(). * @note Earlier documentation incorrectly said all cursors would be freed. * Only write-transactions free cursors. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified. * <li>ENOSPC - no more disk space. * <li>EIO - a low-level I/O error occurred while writing. * <li>ENOMEM - out of memory. * </ul> */ int mdb_txn_commit(MDB_txn *txn); /** @brief Abandon all the operations of the transaction instead of saving them. * * The transaction handle is freed. It and its cursors must not be used * again after this call, except with #mdb_cursor_renew(). * @note Earlier documentation incorrectly said all cursors would be freed. * Only write-transactions free cursors. * @param[in] txn A transaction handle returned by #mdb_txn_begin() */ void mdb_txn_abort(MDB_txn *txn); /** @brief Reset a read-only transaction. * * Abort the transaction like #mdb_txn_abort(), but keep the transaction * handle. #mdb_txn_renew() may reuse the handle. This saves allocation * overhead if the process will start a new read-only transaction soon, * and also locking overhead if #MDB_NOTLS is in use. The reader table * lock is released, but the table slot stays tied to its thread or * #MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free * its lock table slot if MDB_NOTLS is in use. * Cursors opened within the transaction must not be used * again after this call, except with #mdb_cursor_renew(). * Reader locks generally don't interfere with writers, but they keep old * versions of database pages allocated. Thus they prevent the old pages * from being reused when writers commit new data, and so under heavy load * the database size may grow much more rapidly than otherwise. * @param[in] txn A transaction handle returned by #mdb_txn_begin() */ void mdb_txn_reset(MDB_txn *txn); /** @brief Renew a read-only transaction. * * This acquires a new reader lock for a transaction handle that had been * released by #mdb_txn_reset(). It must be called before a reset transaction * may be used again. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>#MDB_PANIC - a fatal error occurred earlier and the environment * must be shut down. * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_txn_renew(MDB_txn *txn); /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */ #define mdb_open(txn,name,flags,dbi) mdb_dbi_open(txn,name,flags,dbi) /** Compat with version <= 0.9.4, avoid clash with libmdb from MDB Tools project */ #define mdb_close(env,dbi) mdb_dbi_close(env,dbi) /** @brief Open a database in the environment. * * A database handle denotes the name and parameters of a database, * independently of whether such a database exists. * The database handle may be discarded by calling #mdb_dbi_close(). * The old database handle is returned if the database was already open. * The handle may only be closed once. * * The database handle will be private to the current transaction until * the transaction is successfully committed. If the transaction is * aborted the handle will be closed automatically. * After a successful commit the handle will reside in the shared * environment, and may be used by other transactions. * * This function must not be called from multiple concurrent * transactions in the same process. A transaction that uses * this function must finish (either commit or abort) before * any other transaction in the process may use this function. * * To use named databases (with name != NULL), #mdb_env_set_maxdbs() * must be called before opening the environment. Database names are * keys in the unnamed database, and may be read but not written. * * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] name The name of the database to open. If only a single * database is needed in the environment, this value may be NULL. * @param[in] flags Special options for this database. This parameter * must be set to 0 or by bitwise OR'ing together one or more of the * values described here. * <ul> * <li>#MDB_REVERSEKEY * Keys are strings to be compared in reverse order, from the end * of the strings to the beginning. By default, Keys are treated as strings and * compared from beginning to end. * <li>#MDB_DUPSORT * Duplicate keys may be used in the database. (Or, from another perspective, * keys may have multiple data items, stored in sorted order.) By default * keys must be unique and may have only a single data item. * <li>#MDB_INTEGERKEY * Keys are binary integers in native byte order, either unsigned int * or size_t, and will be sorted as such. * The keys must all be of the same size. * <li>#MDB_DUPFIXED * This flag may only be used in combination with #MDB_DUPSORT. This option * tells the library that the data items for this database are all the same * size, which allows further optimizations in storage and retrieval. When * all data items are the same size, the #MDB_GET_MULTIPLE, #MDB_NEXT_MULTIPLE * and #MDB_PREV_MULTIPLE cursor operations may be used to retrieve multiple * items at once. * <li>#MDB_INTEGERDUP * This option specifies that duplicate data items are binary integers, * similar to #MDB_INTEGERKEY keys. * <li>#MDB_REVERSEDUP * This option specifies that duplicate data items should be compared as * strings in reverse order. * <li>#MDB_CREATE * Create the named database if it doesn't exist. This option is not * allowed in a read-only transaction or a read-only environment. * </ul> * @param[out] dbi Address where the new #MDB_dbi handle will be stored * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>#MDB_NOTFOUND - the specified database doesn't exist in the environment * and #MDB_CREATE was not specified. * <li>#MDB_DBS_FULL - too many databases have been opened. See #mdb_env_set_maxdbs(). * </ul> */ int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi); /** @brief Retrieve statistics for a database. * * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_dbi_open() * @param[out] stat The address of an #MDB_stat structure * where the statistics will be copied * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat); /** @brief Retrieve the DB flags for a database handle. * * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_dbi_open() * @param[out] flags Address where the flags will be returned. * @return A non-zero error value on failure and 0 on success. */ int mdb_dbi_flags(MDB_txn *txn, MDB_dbi dbi, unsigned int *flags); /** @brief Close a database handle. Normally unnecessary. Use with care: * * This call is not mutex protected. Handles should only be closed by * a single thread, and only if no other threads are going to reference * the database handle or one of its cursors any further. Do not close * a handle if an existing transaction has modified its database. * Doing so can cause misbehavior from database corruption to errors * like MDB_BAD_VALSIZE (since the DB name is gone). * * Closing a database handle is not necessary, but lets #mdb_dbi_open() * reuse the handle value. Usually it's better to set a bigger * #mdb_env_set_maxdbs(), unless that value would be large. * * @param[in] env An environment handle returned by #mdb_env_create() * @param[in] dbi A database handle returned by #mdb_dbi_open() */ void mdb_dbi_close(MDB_env *env, MDB_dbi dbi); /** @brief Empty or delete+close a database. * * See #mdb_dbi_close() for restrictions about closing the DB handle. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_dbi_open() * @param[in] del 0 to empty the DB, 1 to delete it from the * environment and close the DB handle. * @return A non-zero error value on failure and 0 on success. */ int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del); /** @brief Set a custom key comparison function for a database. * * The comparison function is called whenever it is necessary to compare a * key specified by the application with a key currently stored in the database. * If no comparison function is specified, and no special key flags were specified * with #mdb_dbi_open(), the keys are compared lexically, with shorter keys collating * before longer keys. * @warning This function must be called before any data access functions are used, * otherwise data corruption may occur. The same comparison function must be used by every * program accessing the database, every time the database is used. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_dbi_open() * @param[in] cmp A #MDB_cmp_func function * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp); /** @brief Set a custom data comparison function for a #MDB_DUPSORT database. * * This comparison function is called whenever it is necessary to compare a data * item specified by the application with a data item currently stored in the database. * This function only takes effect if the database was opened with the #MDB_DUPSORT * flag. * If no comparison function is specified, and no special key flags were specified * with #mdb_dbi_open(), the data items are compared lexically, with shorter items collating * before longer items. * @warning This function must be called before any data access functions are used, * otherwise data corruption may occur. The same comparison function must be used by every * program accessing the database, every time the database is used. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_dbi_open() * @param[in] cmp A #MDB_cmp_func function * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp); /** @brief Set a relocation function for a #MDB_FIXEDMAP database. * * @todo The relocation function is called whenever it is necessary to move the data * of an item to a different position in the database (e.g. through tree * balancing operations, shifts as a result of adds or deletes, etc.). It is * intended to allow address/position-dependent data items to be stored in * a database in an environment opened with the #MDB_FIXEDMAP option. * Currently the relocation feature is unimplemented and setting * this function has no effect. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_dbi_open() * @param[in] rel A #MDB_rel_func function * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel); /** @brief Set a context pointer for a #MDB_FIXEDMAP database's relocation function. * * See #mdb_set_relfunc and #MDB_rel_func for more details. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_dbi_open() * @param[in] ctx An arbitrary pointer for whatever the application needs. * It will be passed to the callback function set by #mdb_set_relfunc * as its \b relctx parameter whenever the callback is invoked. * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx); /** @brief Get items from a database. * * This function retrieves key/data pairs from the database. The address * and length of the data associated with the specified \b key are returned * in the structure to which \b data refers. * If the database supports duplicate keys (#MDB_DUPSORT) then the * first data item for the key will be returned. Retrieval of other * items requires the use of #mdb_cursor_get(). * * @note The memory pointed to by the returned values is owned by the * database. The caller need not dispose of the memory, and may not * modify it in any way. For values returned in a read-only transaction * any modification attempts will cause a SIGSEGV. * @note Values returned from the database are valid only until a * subsequent update operation, or the end of the transaction. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_dbi_open() * @param[in] key The key to search for in the database * @param[out] data The data corresponding to the key * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>#MDB_NOTFOUND - the key was not in the database. * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_get(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data); /** @brief Store items into a database. * * This function stores key/data pairs in the database. The default behavior * is to enter the new key/data pair, replacing any previously existing key * if duplicates are disallowed, or adding a duplicate data item if * duplicates are allowed (#MDB_DUPSORT). * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_dbi_open() * @param[in] key The key to store in the database * @param[in,out] data The data to store * @param[in] flags Special options for this operation. This parameter * must be set to 0 or by bitwise OR'ing together one or more of the * values described here. * <ul> * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not * already appear in the database. This flag may only be specified * if the database was opened with #MDB_DUPSORT. The function will * return #MDB_KEYEXIST if the key/data pair already appears in the * database. * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key * does not already appear in the database. The function will return * #MDB_KEYEXIST if the key already appears in the database, even if * the database supports duplicates (#MDB_DUPSORT). The \b data * parameter will be set to point to the existing item. * <li>#MDB_RESERVE - reserve space for data of the given size, but * don't copy the given data. Instead, return a pointer to the * reserved space, which the caller can fill in later - before * the next update operation or the transaction ends. This saves * an extra memcpy if the data is being generated later. * LMDB does nothing else with this memory, the caller is expected * to modify all of the space requested. This flag must not be * specified if the database was opened with #MDB_DUPSORT. * <li>#MDB_APPEND - append the given key/data pair to the end of the * database. This option allows fast bulk loading when keys are * already known to be in the correct order. Loading unsorted keys * with this flag will cause a #MDB_KEYEXIST error. * <li>#MDB_APPENDDUP - as above, but for sorted dup data. * </ul> * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize(). * <li>#MDB_TXN_FULL - the transaction has too many dirty pages. * <li>EACCES - an attempt was made to write in a read-only transaction. * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_put(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data, unsigned int flags); /** @brief Delete items from a database. * * This function removes key/data pairs from the database. * If the database does not support sorted duplicate data items * (#MDB_DUPSORT) the data parameter is ignored. * If the database supports sorted duplicates and the data parameter * is NULL, all of the duplicate data items for the key will be * deleted. Otherwise, if the data parameter is non-NULL * only the matching data item will be deleted. * This function will return #MDB_NOTFOUND if the specified key/data * pair is not in the database. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_dbi_open() * @param[in] key The key to delete from the database * @param[in] data The data to delete * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EACCES - an attempt was made to write in a read-only transaction. * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_del(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data); /** @brief Create a cursor handle. * * A cursor is associated with a specific transaction and database. * A cursor cannot be used when its database handle is closed. Nor * when its transaction has ended, except with #mdb_cursor_renew(). * It can be discarded with #mdb_cursor_close(). * A cursor in a write-transaction can be closed before its transaction * ends, and will otherwise be closed when its transaction ends. * A cursor in a read-only transaction must be closed explicitly, before * or after its transaction ends. It can be reused with * #mdb_cursor_renew() before finally closing it. * @note Earlier documentation said that cursors in every transaction * were closed when the transaction committed or aborted. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_dbi_open() * @param[out] cursor Address where the new #MDB_cursor handle will be stored * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor); /** @brief Close a cursor handle. * * The cursor handle will be freed and must not be used again after this call. * Its transaction must still be live if it is a write-transaction. * @param[in] cursor A cursor handle returned by #mdb_cursor_open() */ void mdb_cursor_close(MDB_cursor *cursor); /** @brief Renew a cursor handle. * * A cursor is associated with a specific transaction and database. * Cursors that are only used in read-only * transactions may be re-used, to avoid unnecessary malloc/free overhead. * The cursor may be associated with a new read-only transaction, and * referencing the same database handle as it was created with. * This may be done whether the previous transaction is live or dead. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] cursor A cursor handle returned by #mdb_cursor_open() * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_cursor_renew(MDB_txn *txn, MDB_cursor *cursor); /** @brief Return the cursor's transaction handle. * * @param[in] cursor A cursor handle returned by #mdb_cursor_open() */ MDB_txn *mdb_cursor_txn(MDB_cursor *cursor); /** @brief Return the cursor's database handle. * * @param[in] cursor A cursor handle returned by #mdb_cursor_open() */ MDB_dbi mdb_cursor_dbi(MDB_cursor *cursor); /** @brief Retrieve by cursor. * * This function retrieves key/data pairs from the database. The address and length * of the key are returned in the object to which \b key refers (except for the * case of the #MDB_SET option, in which the \b key object is unchanged), and * the address and length of the data are returned in the object to which \b data * refers. * See #mdb_get() for restrictions on using the output values. * @param[in] cursor A cursor handle returned by #mdb_cursor_open() * @param[in,out] key The key for a retrieved item * @param[in,out] data The data of a retrieved item * @param[in] op A cursor operation #MDB_cursor_op * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>#MDB_NOTFOUND - no matching key found. * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data, MDB_cursor_op op); /** @brief Store by cursor. * * This function stores key/data pairs into the database. * The cursor is positioned at the new item, or on failure usually near it. * @note Earlier documentation incorrectly said errors would leave the * state of the cursor unchanged. * @param[in] cursor A cursor handle returned by #mdb_cursor_open() * @param[in] key The key operated on. * @param[in] data The data operated on. * @param[in] flags Options for this operation. This parameter * must be set to 0 or one of the values described here. * <ul> * <li>#MDB_CURRENT - replace the item at the current cursor position. * The \b key parameter must still be provided, and must match it. * If using sorted duplicates (#MDB_DUPSORT) the data item must still * sort into the same place. This is intended to be used when the * new data is the same size as the old. Otherwise it will simply * perform a delete of the old record followed by an insert. * <li>#MDB_NODUPDATA - enter the new key/data pair only if it does not * already appear in the database. This flag may only be specified * if the database was opened with #MDB_DUPSORT. The function will * return #MDB_KEYEXIST if the key/data pair already appears in the * database. * <li>#MDB_NOOVERWRITE - enter the new key/data pair only if the key * does not already appear in the database. The function will return * #MDB_KEYEXIST if the key already appears in the database, even if * the database supports duplicates (#MDB_DUPSORT). * <li>#MDB_RESERVE - reserve space for data of the given size, but * don't copy the given data. Instead, return a pointer to the * reserved space, which the caller can fill in later - before * the next update operation or the transaction ends. This saves * an extra memcpy if the data is being generated later. This flag * must not be specified if the database was opened with #MDB_DUPSORT. * <li>#MDB_APPEND - append the given key/data pair to the end of the * database. No key comparisons are performed. This option allows * fast bulk loading when keys are already known to be in the * correct order. Loading unsorted keys with this flag will cause * a #MDB_KEYEXIST error. * <li>#MDB_APPENDDUP - as above, but for sorted dup data. * <li>#MDB_MULTIPLE - store multiple contiguous data elements in a * single request. This flag may only be specified if the database * was opened with #MDB_DUPFIXED. The \b data argument must be an * array of two MDB_vals. The mv_size of the first MDB_val must be * the size of a single data element. The mv_data of the first MDB_val * must point to the beginning of the array of contiguous data elements. * The mv_size of the second MDB_val must be the count of the number * of data elements to store. On return this field will be set to * the count of the number of elements actually written. The mv_data * of the second MDB_val is unused. * </ul> * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize(). * <li>#MDB_TXN_FULL - the transaction has too many dirty pages. * <li>EACCES - an attempt was made to write in a read-only transaction. * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_cursor_put(MDB_cursor *cursor, MDB_val *key, MDB_val *data, unsigned int flags); /** @brief Delete current key/data pair * * This function deletes the key/data pair to which the cursor refers. * This does not invalidate the cursor, so operations such as MDB_NEXT * can still be used on it. * Both MDB_NEXT and MDB_GET_CURRENT will return the same record after * this operation. * @param[in] cursor A cursor handle returned by #mdb_cursor_open() * @param[in] flags Options for this operation. This parameter * must be set to 0 or one of the values described here. * <ul> * <li>#MDB_NODUPDATA - delete all of the data items for the current key. * This flag may only be specified if the database was opened with #MDB_DUPSORT. * </ul> * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EACCES - an attempt was made to write in a read-only transaction. * <li>EINVAL - an invalid parameter was specified. * </ul> */ int mdb_cursor_del(MDB_cursor *cursor, unsigned int flags); /** @brief Return count of duplicates for current key. * * This call is only valid on databases that support sorted duplicate * data items #MDB_DUPSORT. * @param[in] cursor A cursor handle returned by #mdb_cursor_open() * @param[out] countp Address where the count will be stored * @return A non-zero error value on failure and 0 on success. Some possible * errors are: * <ul> * <li>EINVAL - cursor is not initialized, or an invalid parameter was specified. * </ul> */ int mdb_cursor_count(MDB_cursor *cursor, size_t *countp); /** @brief Compare two data items according to a particular database. * * This returns a comparison as if the two data items were keys in the * specified database. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_dbi_open() * @param[in] a The first item to compare * @param[in] b The second item to compare * @return < 0 if a < b, 0 if a == b, > 0 if a > b */ int mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b); /** @brief Compare two data items according to a particular database. * * This returns a comparison as if the two items were data items of * the specified database. The database must have the #MDB_DUPSORT flag. * @param[in] txn A transaction handle returned by #mdb_txn_begin() * @param[in] dbi A database handle returned by #mdb_dbi_open() * @param[in] a The first item to compare * @param[in] b The second item to compare * @return < 0 if a < b, 0 if a == b, > 0 if a > b */ int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b); /** @brief A callback function used to print a message from the library. * * @param[in] msg The string to be printed. * @param[in] ctx An arbitrary context pointer for the callback. * @return < 0 on failure, >= 0 on success. */ typedef int (MDB_msg_func)(const char *msg, void *ctx); /** @brief Dump the entries in the reader lock table. * * @param[in] env An environment handle returned by #mdb_env_create() * @param[in] func A #MDB_msg_func function * @param[in] ctx Anything the message function needs * @return < 0 on failure, >= 0 on success. */ int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx); /** @brief Check for stale entries in the reader lock table. * * @param[in] env An environment handle returned by #mdb_env_create() * @param[out] dead Number of stale slots that were cleared * @return 0 on success, non-zero on failure. */ int mdb_reader_check(MDB_env *env, int *dead); /** @} */ #ifdef __cplusplus } #endif /** @page tools LMDB Command Line Tools The following describes the command line tools that are available for LMDB. \li \ref mdb_copy_1 \li \ref mdb_dump_1 \li \ref mdb_load_1 \li \ref mdb_stat_1 */ #endif /* _LMDB_H_ */