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lmdb.h File Reference

Lightning memory-mapped database library. More...

`#include <sys/types.h>`

Go to the source code of this file.

## Data Structures

struct | MDB_val
| Generic structure used for passing keys and data in and out of the database. More...
struct | MDB_stat
| Statistics for a database in the environment. More...
struct | MDB_envinfo
| Information about the environment. More...

## Macros

#define | MDB_VERSION_MAJOR 0
#define | MDB_VERSION_MINOR 9
#define | MDB_VERSION_PATCH 35
#define | MDB_VERINT(a, b, c)
#define | MDB_VERSION_FULL MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
#define | MDB_VERSION_DATE "Jan 27, 2026"
#define | MDB_VERSTR(a, b, c, d)
#define | MDB_VERFOO(a, b, c, d)
#define | MDB_VERSION_STRING MDB_VERFOO(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH,MDB_VERSION_DATE)
#define | MDB_FIXEDMAP 0x01
#define | MDB_NOSUBDIR 0x4000
#define | MDB_NOSYNC 0x10000
#define | MDB_RDONLY 0x20000
#define | MDB_NOMETASYNC 0x40000
#define | MDB_WRITEMAP 0x80000
#define | MDB_MAPASYNC 0x100000
#define | MDB_NOTLS 0x200000
#define | MDB_NOLOCK 0x400000
#define | MDB_NORDAHEAD 0x800000
#define | MDB_NOMEMINIT 0x1000000
#define | MDB_REVERSEKEY 0x02
#define | MDB_DUPSORT 0x04
#define | MDB_INTEGERKEY 0x08
#define | MDB_DUPFIXED 0x10
#define | MDB_INTEGERDUP 0x20
#define | MDB_REVERSEDUP 0x40
#define | MDB_CREATE 0x40000
#define | MDB_NOOVERWRITE 0x10
#define | MDB_NODUPDATA 0x20
#define | MDB_CURRENT 0x40
#define | MDB_RESERVE 0x10000
#define | MDB_APPEND 0x20000
#define | MDB_APPENDDUP 0x40000
#define | MDB_MULTIPLE 0x80000
#define | MDB_CP_COMPACT 0x01
#define | MDB_SUCCESS 0
#define | MDB_KEYEXIST (-30799)
#define | MDB_NOTFOUND (-30798)
#define | MDB_PAGE_NOTFOUND (-30797)
#define | MDB_CORRUPTED (-30796)
#define | MDB_PANIC (-30795)
#define | MDB_VERSION_MISMATCH (-30794)
#define | MDB_INVALID (-30793)
#define | MDB_MAP_FULL (-30792)
#define | MDB_DBS_FULL (-30791)
#define | MDB_READERS_FULL (-30790)
#define | MDB_TLS_FULL (-30789)
#define | MDB_TXN_FULL (-30788)
#define | MDB_CURSOR_FULL (-30787)
#define | MDB_PAGE_FULL (-30786)
#define | MDB_MAP_RESIZED (-30785)
#define | MDB_INCOMPATIBLE (-30784)
#define | MDB_BAD_RSLOT (-30783)
#define | MDB_BAD_TXN (-30782)
#define | MDB_BAD_VALSIZE (-30781)
#define | MDB_BAD_DBI (-30780)
#define | MDB_LAST_ERRCODE MDB_BAD_DBI
#define | mdb_open(txn, name, flags, dbi)
#define | mdb_close(env, dbi)

## Typedefs

typedef mode_t | mdb_mode_t
typedef int | mdb_filehandle_t
typedef unsigned int | MDB_dbi
| A handle for an individual database in the DB environment.
typedef int | MDB_cmp_func(const MDB_val *a, const MDB_val *b)
| A callback function used to compare two keys in a database.
typedef void | MDB_rel_func(MDB_val *item, void *oldptr, void *newptr, void *relctx)
| A callback function used to relocate a position-dependent data item in a fixed-address database.
typedef void | MDB_assert_func(MDB_env *env, const char *msg)
| A callback function for most LMDB assert() failures, called before printing the message and aborting.
typedef int | MDB_msg_func(const char *msg, void *ctx)
| A callback function used to print a message from the library.

## Enumerations

enum | MDB_cursor_op { MDB_FIRST , MDB_FIRST_DUP , MDB_GET_BOTH , MDB_GET_BOTH_RANGE , MDB_GET_CURRENT , MDB_GET_MULTIPLE , MDB_LAST , MDB_LAST_DUP , MDB_NEXT , MDB_NEXT_DUP , MDB_NEXT_MULTIPLE , MDB_NEXT_NODUP , MDB_PREV , MDB_PREV_DUP , MDB_PREV_NODUP , MDB_SET , MDB_SET_KEY , MDB_SET_RANGE , MDB_PREV_MULTIPLE }
| Cursor Get operations. More...

## Functions

char * | mdb_version (int *major, int *minor, int *patch)
| Return the LMDB library version information.
char * | mdb_strerror (int err)
| Return a string describing a given error code.
int | mdb_env_create (MDB_env **env)
| Create an LMDB environment handle.
int | mdb_env_open (MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode)
| Open an environment handle.
int | mdb_env_copy (MDB_env *env, const char *path)
| Copy an LMDB environment to the specified path.
int | mdb_env_copyfd (MDB_env *env, mdb_filehandle_t fd)
| Copy an LMDB environment to the specified file descriptor.
int | mdb_env_copy2 (MDB_env *env, const char *path, unsigned int flags)
| Copy an LMDB environment to the specified path, with options.
int | mdb_env_copyfd2 (MDB_env *env, mdb_filehandle_t fd, unsigned int flags)
| Copy an LMDB environment to the specified file descriptor, with options.
int | mdb_env_stat (MDB_env *env, MDB_stat *stat)
| Return statistics about the LMDB environment.
int | mdb_env_info (MDB_env *env, MDB_envinfo *stat)
| Return information about the LMDB environment.
int | mdb_env_sync (MDB_env *env, int force)
| Flush the data buffers to disk.
void | mdb_env_close (MDB_env *env)
| Close the environment and release the memory map.
int | mdb_env_set_flags (MDB_env *env, unsigned int flags, int onoff)
| Set environment flags.
int | mdb_env_get_flags (MDB_env *env, unsigned int *flags)
| Get environment flags.
int | mdb_env_get_path (MDB_env *env, const char **path)
| Return the path that was used in mdb_env_open().
int | mdb_env_get_fd (MDB_env *env, mdb_filehandle_t *fd)
| Return the filedescriptor for the given environment.
int | mdb_env_set_mapsize (MDB_env *env, size_t size)
| Set the size of the memory map to use for this environment.
int | mdb_env_set_maxreaders (MDB_env *env, unsigned int readers)
| Set the maximum number of threads/reader slots for the environment.
int | mdb_env_get_maxreaders (MDB_env *env, unsigned int *readers)
| Get the maximum number of threads/reader slots for the environment.
int | mdb_env_set_maxdbs (MDB_env *env, MDB_dbi dbs)
| Set the maximum number of named databases for the environment.
int | mdb_env_get_maxkeysize (MDB_env *env)
| Get the maximum size of keys and MDB_DUPSORT data we can write.
int | mdb_env_set_userctx (MDB_env *env, void *ctx)
| Set application information associated with the MDB_env.
void * | mdb_env_get_userctx (MDB_env *env)
| Get the application information associated with the MDB_env.
int | mdb_env_set_assert (MDB_env *env, MDB_assert_func *func)
int | mdb_txn_begin (MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn)
| Create a transaction for use with the environment.
MDB_env * | mdb_txn_env (MDB_txn *txn)
| Returns the transaction's MDB_env.
size_t | mdb_txn_id (MDB_txn *txn)
| Return the transaction's ID.
int | mdb_txn_commit (MDB_txn *txn)
| Commit all the operations of a transaction into the database.
void | mdb_txn_abort (MDB_txn *txn)
| Abandon all the operations of the transaction instead of saving them.
void | mdb_txn_reset (MDB_txn *txn)
| Reset a read-only transaction.
int | mdb_txn_renew (MDB_txn *txn)
| Renew a read-only transaction.
int | mdb_dbi_open (MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi)
| Open a database in the environment.
int | mdb_stat (MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat)
| Retrieve statistics for a database.
int | mdb_dbi_flags (MDB_txn *txn, MDB_dbi dbi, unsigned int *flags)
| Retrieve the DB flags for a database handle.
void | mdb_dbi_close (MDB_env *env, MDB_dbi dbi)
| Close a database handle. Normally unnecessary. Use with care:
int | mdb_drop (MDB_txn *txn, MDB_dbi dbi, int del)
| Empty or delete+close a database.
int | mdb_set_compare (MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp)
| Set a custom key comparison function for a database.
int | mdb_set_dupsort (MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp)
| Set a custom data comparison function for a MDB_DUPSORT database.
int | mdb_set_relfunc (MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel)
| Set a relocation function for a MDB_FIXEDMAP database.
int | mdb_set_relctx (MDB_txn *txn, MDB_dbi dbi, void *ctx)
| Set a context pointer for a MDB_FIXEDMAP database's relocation function.
int | mdb_get (MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data)
| Get items from a database.
int | mdb_put (MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data, unsigned int flags)
| Store items into a database.
int | mdb_del (MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data)
| Delete items from a database.
int | mdb_cursor_open (MDB_txn *txn, MDB_dbi dbi, MDB_cursor **cursor)
| Create a cursor handle.
void | mdb_cursor_close (MDB_cursor *cursor)
| Close a cursor handle.
int | mdb_cursor_renew (MDB_txn *txn, MDB_cursor *cursor)
| Renew a cursor handle.
MDB_txn * | mdb_cursor_txn (MDB_cursor *cursor)
| Return the cursor's transaction handle.
MDB_dbi | mdb_cursor_dbi (MDB_cursor *cursor)
| Return the cursor's database handle.
int | mdb_cursor_get (MDB_cursor *cursor, MDB_val *key, MDB_val *data, MDB_cursor_op op)
| Retrieve by cursor.
int | mdb_cursor_put (MDB_cursor *cursor, MDB_val *key, MDB_val *data, unsigned int flags)
| Store by cursor.
int | mdb_cursor_del (MDB_cursor *cursor, unsigned int flags)
| Delete current key/data pair.
int | mdb_cursor_count (MDB_cursor *cursor, size_t *countp)
| Return count of duplicates for current key.
int | mdb_cmp (MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b)
| Compare two data items according to a particular database.
int | mdb_dcmp (MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b)
| Compare two data items according to a particular database.
int | mdb_reader_list (MDB_env *env, MDB_msg_func *func, void *ctx)
| Dump the entries in the reader lock table.
int | mdb_reader_check (MDB_env *env, int *dead)
| Check for stale entries in the reader lock table.

## Detailed Description

Lightning memory-mapped database library.

## Typedef Documentation

## mdb_mode_t

typedef mode_t mdb_mode_t

Unix permissions for creating files, or dummy definition for Windows

## mdb_filehandle_t

typedef int mdb_filehandle_t

An abstraction for a file handle. On POSIX systems file handles are small integers. On Windows they're opaque pointers.