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lmdb.h 72.28 KiB
/** @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 2011-2020 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 25
/** 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 "January 30, 2020"
/** 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 reseved for the #MDB_txn object. A thread may use parallel
* read-only transactions. A read-only transaction may span threads if
* the user synchronizes its use. Applications that multiplex many
* user threads over individual OS threads need this option. Such an
* application must also serialize the write transactions in an OS
* 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 buillt with NDEBUG.
* @note This hack should become obsolete as lmdb's error handling matures.
* @param[in] env An environment handle returned by #mdb_env_create().
* @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_ */