internal

NAME

internal

SYNOPSIS

Modules

ID List Management
Compatibility Macros
A bunch of macros to minimize the amount of platform-specific ifdefs needed throughout the rest of the code. When the features this library needs are similar enough to POSIX to be hidden in a one-or-two line replacement, this macro approach is used.
Debug Macros
Reader Lock Table
Readers don’t acquire any locks for their data access. Instead, they simply record their transaction ID in the reader table. The reader mutex is needed just to find an empty slot in the reader table. The slot’s address is saved in thread-specific data so that subsequent read transactions started by the same thread need no further locking to proceed.
Page Flags
Node Flags
Transaction DB Flags
Transaction Flags
Cursor Flags

Data Structures

struct MDB_page
struct MDB_node
struct MDB_db
struct MDB_meta
union MDB_metabuf
struct MDB_dbx
struct MDB_txn
Opaque structure for a transaction handle.
struct MDB_cursor
Opaque structure for navigating through a database.
struct MDB_xcursor
struct MDB_pgstate
struct MDB_env
Opaque structure for a database environment.
struct MDB_ntxn
struct MDB_name
struct mdb_copy

Macros

#define LOCK_MUTEX(rc, env, mutex) ((rc) = LOCK_MUTEX0(mutex))
#define mdb_mutex_failed(env, mutex, rc) (rc)
#define MDB_DSYNC O_SYNC
#define MDB_FDATASYNC fdatasync
#define MDB_MSYNC(addr, len, flags) msync(addr,len,flags)
#define MS_SYNC 1
#define MS_ASYNC 0
#define MAX_PAGESIZE (PAGEBASE ? 0x10000 : 0x8000)
The maximum size of a database page.
#define MDB_MINKEYS 2
#define MDB_MAGIC 0xBEEFC0DE
#define MDB_DATA_VERSION ((MDB_DEVEL) ? 999 : 1)
#define MDB_LOCK_VERSION 1
#define MDB_MAXKEYSIZE ((MDB_DEVEL) ? 0 : 511)
The max size of a key we can write, or 0 for computed max.
#define ENV_MAXKEY(env) (MDB_MAXKEYSIZE)
#define MAXDATASIZE 0xffffffffUL
The maximum size of a data item.
#define DKBUF
#define DKEY(x) 0
#define P_INVALID (˜(pgno_t)0)
#define F_ISSET(w, f) (((w) & (f)) == (f))
#define EVEN(n) (((n) + 1U) & -2) /* sign-extending -2 to match n+1U */
#define DEFAULT_MAPSIZE 1048576
#define PAGEHDRSZ ((unsigned) offsetof(MDB_page, mp_ptrs))
#define METADATA(p) ((void *)((char *)(p) + PAGEHDRSZ))
#define PAGEBASE ((MDB_DEVEL) ? PAGEHDRSZ : 0)
#define NUMKEYS(p) (((p)->mp_lower - (PAGEHDRSZ-PAGEBASE)) >> 1)
#define SIZELEFT(p) (indx_t)((p)->mp_upper - (p)->mp_lower)
#define PAGEFILL(env, p)
#define FILL_THRESHOLD 250
#define IS_LEAF(p) F_ISSET((p)->mp_flags, P_LEAF)
#define IS_LEAF2(p) F_ISSET((p)->mp_flags, P_LEAF2)
#define IS_BRANCH(p) F_ISSET((p)->mp_flags, P_BRANCH)
#define IS_OVERFLOW(p) F_ISSET((p)->mp_flags, P_OVERFLOW)
#define IS_SUBP(p) F_ISSET((p)->mp_flags, P_SUBP)
#define OVPAGES(size, psize) ((PAGEHDRSZ-1 + (size)) / (psize) + 1)
#define NEXT_LOOSE_PAGE(p) (*(MDB_page **)((p) + 2))
#define NODESIZE offsetof(MDB_node, mn_data)
#define PGNO_TOPWORD ((pgno_t)-1 > 0xffffffffu ? 32 : 0)
#define INDXSIZE(k) (NODESIZE + ((k) == NULL ? 0 : (k)->mv_size))
#define LEAFSIZE(k, d) (NODESIZE + (k)->mv_size + (d)->mv_size)
#define NODEPTR(p, i) ((MDB_node *)((char *)(p) + (p)->mp_ptrs[i] + PAGEBASE))
#define NODEKEY(node) (void *)((node)->mn_data)
#define NODEDATA(node) (void *)((char *)(node)->mn_data + (node)->mn_ksize)
#define NODEPGNO(node)
#define SETPGNO(node, pgno)
#define NODEDSZ(node) ((node)->mn_lo | ((unsigned)(node)->mn_hi << 16))
#define SETDSZ(node, size)
#define NODEKSZ(node) ((node)->mn_ksize)
#define COPY_PGNO(dst, src)
#define LEAF2KEY(p, i, ks) ((char *)(p) + PAGEHDRSZ + ((i)*(ks)))
#define MDB_GET_KEY(node, keyptr)
#define MDB_GET_KEY2(node, key) { key.mv_size = NODEKSZ(node); key.mv_data = NODEKEY(node); }
#define MDB_VALID 0x8000
#define PERSISTENT_FLAGS (0xffff & ˜(MDB_VALID))
#define VALID_FLAGS
#define FREE_DBI 0
#define MAIN_DBI 1
#define CORE_DBS 2
#define NUM_METAS 2
#define CURSOR_STACK 32
#define XCURSOR_INITED(mc) ((mc)->mc_xcursor && ((mc)->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED))
#define XCURSOR_REFRESH(mc, top, mp)
#define MDB_COMMIT_PAGES 64
#define MAX_WRITE (0x40000000U >> (sizeof(ssize_t) == 4))
#define TXN_DBI_EXIST(txn, dbi, validity) ((txn) && (dbi)<(txn)->mt_numdbs && ((txn)->mt_dbflags[dbi] & (validity)))
#define TXN_DBI_CHANGED(txn, dbi) ((txn)->mt_dbiseqs[dbi] != (txn)->mt_env->me_dbiseqs[dbi])
#define MDB_END_NAMES
#define MDB_END_OPMASK 0x0F
#define MDB_END_UPDATE 0x10
#define MDB_END_FREE 0x20
#define MDB_END_SLOT MDB_NOTLS
#define MDB_PS_MODIFY 1
#define MDB_PS_ROOTONLY 2
#define MDB_PS_FIRST 4
#define MDB_PS_LAST 8
#define MDB_SPLIT_REPLACE MDB_APPENDDUP
#define mdb_env_close0(env, excl) mdb_env_close1(env)
#define mdb_cmp_clong mdb_cmp_cint
#define mdb_cassert(mc, expr) mdb_assert0((mc)->mc_txn->mt_env, expr, #expr)
#define mdb_tassert(txn, expr) mdb_assert0((txn)->mt_env, expr, #expr)
#define mdb_eassert(env, expr) mdb_assert0(env, expr, #expr)
#define mdb_assert0(env, expr, expr_txt)
#define MDB_NAME(str) str
#define mdb_name_cpy strcpy
#define MDB_SUFFLEN 9
#define mdb_fname_destroy(fname) do { if ((fname).mn_alloced) free((fname).mn_val); } while (0)
#define MDB_CLOEXEC 0
#define CHANGEABLE (MDB_NOSYNC|MDB_NOMETASYNC|MDB_MAPASYNC|MDB_NOMEMINIT)
#define CHANGELESS
#define MDB_NOSPILL 0x8000
#define WITH_CURSOR_TRACKING(mn, act)
#define MDB_WBUF (1024*1024)
#define MDB_EOF 0x10

Typedefs

typedef MDB_ID pgno_t
typedef MDB_ID txnid_t
typedef uint16_t indx_t
typedef char mdb_nchar_t

Enumerations

enum { MDB_END_COMMITTED, MDB_END_EMPTY_COMMIT, MDB_END_ABORT, MDB_END_RESET, MDB_END_RESET_TMP, MDB_END_FAIL_BEGIN, MDB_END_FAIL_BEGINCHILD }
enum Pidlock_op { Pidset = F_SETLK, Pidcheck = F_GETLK }
enum mdb_fopen_type { MDB_O_RDONLY = O_RDONLY, MDB_O_RDWR = O_RDWR |O_CREAT, MDB_O_META = O_WRONLY|MDB_DSYNC |MDB_CLOEXEC, MDB_O_COPY = O_WRONLY|O_CREAT|O_EXCL|MDB_CLOEXEC, MDB_O_MASK = MDB_O_RDWR|MDB_CLOEXEC | MDB_O_RDONLY|MDB_O_META|MDB_O_COPY, MDB_O_LOCKS = MDB_O_RDWR|MDB_CLOEXEC | ((MDB_O_MASK+1) & ˜MDB_O_MASK) }

Functions

static int mdb_page_alloc (MDB_cursor *mc, int num, MDB_page **mp)
static int mdb_page_new (MDB_cursor *mc, uint32_t flags, int num, MDB_page **mp)
static int mdb_page_touch (MDB_cursor *mc)
static void mdb_txn_end (MDB_txn *txn, unsigned mode)
static int mdb_page_get (MDB_cursor *mc, pgno_t pgno, MDB_page **mp, int *lvl)
static int mdb_page_search_root (MDB_cursor *mc, MDB_val *key, int modify)
static int mdb_page_search (MDB_cursor *mc, MDB_val *key, int flags)
static int mdb_page_merge (MDB_cursor *csrc, MDB_cursor *cdst)
static int mdb_page_split (MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata, pgno_t newpgno, unsigned int nflags)
static int mdb_env_read_header (MDB_env *env, MDB_meta *meta)
static MDB_meta * mdb_env_pick_meta (const MDB_env *env)
static int mdb_env_write_meta (MDB_txn *txn)
static void mdb_env_close0 (MDB_env *env, int excl)
static MDB_node * mdb_node_search (MDB_cursor *mc, MDB_val *key, int *exactp)
static int mdb_node_add (MDB_cursor *mc, indx_t indx, MDB_val *key, MDB_val *data, pgno_t pgno, unsigned int flags)
static void mdb_node_del (MDB_cursor *mc, int ksize)
static void mdb_node_shrink (MDB_page *mp, indx_t indx)
static int mdb_node_move (MDB_cursor *csrc, MDB_cursor *cdst, int fromleft)
static int mdb_node_read (MDB_cursor *mc, MDB_node *leaf, MDB_val *data)
static size_t mdb_leaf_size (MDB_env *env, MDB_val *key, MDB_val *data)
static size_t mdb_branch_size (MDB_env *env, MDB_val *key)
static int mdb_rebalance (MDB_cursor *mc)
static int mdb_update_key (MDB_cursor *mc, MDB_val *key)
static void mdb_cursor_pop (MDB_cursor *mc)
static int mdb_cursor_push (MDB_cursor *mc, MDB_page *mp)
static int mdb_cursor_del0 (MDB_cursor *mc)
static int mdb_del0 (MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data, unsigned flags)
static int mdb_cursor_sibling (MDB_cursor *mc, int move_right)
static int mdb_cursor_next (MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op)
static int mdb_cursor_prev (MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op)
static int mdb_cursor_set (MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op, int *exactp)
static int mdb_cursor_first (MDB_cursor *mc, MDB_val *key, MDB_val *data)
static int mdb_cursor_last (MDB_cursor *mc, MDB_val *key, MDB_val *data)
static void mdb_cursor_init (MDB_cursor *mc, MDB_txn *txn, MDB_dbi dbi, MDB_xcursor *mx)
static void mdb_xcursor_init0 (MDB_cursor *mc)
static void mdb_xcursor_init1 (MDB_cursor *mc, MDB_node *node)
static void mdb_xcursor_init2 (MDB_cursor *mc, MDB_xcursor *src_mx, int force)
static int mdb_drop0 (MDB_cursor *mc, int subs)
static void mdb_default_cmp (MDB_txn *txn, MDB_dbi dbi)
static int mdb_reader_check0 (MDB_env *env, int rlocked, int *dead)
char *ESECT 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.
static void ESECT mdb_assert_fail (MDB_env *env, const char *expr_txt, const char *func, const char *file, int line)
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.
static MDB_page * mdb_page_malloc (MDB_txn *txn, unsigned num)
static void mdb_page_free (MDB_env *env, MDB_page *mp)
static void mdb_dpage_free (MDB_env *env, MDB_page *dp)
static void mdb_dlist_free (MDB_txn *txn)
static int mdb_page_loose (MDB_cursor *mc, MDB_page *mp)
static int mdb_pages_xkeep (MDB_cursor *mc, unsigned pflags, int all)
static int mdb_page_flush (MDB_txn *txn, int keep)
static int mdb_page_spill (MDB_cursor *m0, MDB_val *key, MDB_val *data)
static txnid_t mdb_find_oldest (MDB_txn *txn)
static void mdb_page_dirty (MDB_txn *txn, MDB_page *mp)
static void mdb_page_copy (MDB_page *dst, MDB_page *src, unsigned int psize)
static int mdb_page_unspill (MDB_txn *txn, MDB_page *mp, MDB_page **ret)
int mdb_env_sync (MDB_env *env, int force)
Flush the data buffers to disk.
static int mdb_cursor_shadow (MDB_txn *src, MDB_txn *dst)
static void mdb_cursors_close (MDB_txn *txn, unsigned merge)
static int mdb_reader_pid (MDB_env *env, enum Pidlock_op op, MDB_PID_T pid)
static int mdb_txn_renew0 (MDB_txn *txn)
int mdb_txn_renew (MDB_txn *txn)
Renew a read-only transaction.
int mdb_txn_begin (MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **ret)
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.
static void mdb_dbis_update (MDB_txn *txn, int keep)
void mdb_txn_reset (MDB_txn *txn)
Reset a read-only transaction.
void mdb_txn_abort (MDB_txn *txn)
Abandon all the operations of the transaction instead of saving them.
static int mdb_freelist_save (MDB_txn *txn)
int mdb_txn_commit (MDB_txn *txn)
Commit all the operations of a transaction into the database.
static void ESECT mdb_env_init_meta0 (MDB_env *env, MDB_meta *meta)
static int ESECT mdb_env_init_meta (MDB_env *env, MDB_meta *meta)
int ESECT mdb_env_create (MDB_env **env)
Create an LMDB environment handle.
static int ESECT mdb_env_map (MDB_env *env, void *addr)
int ESECT mdb_env_set_mapsize (MDB_env *env, size_t size)
Set the size of the memory map to use for this environment.
int ESECT mdb_env_set_maxdbs (MDB_env *env, MDB_dbi dbs)
Set the maximum number of named databases for the environment.
int ESECT mdb_env_set_maxreaders (MDB_env *env, unsigned int readers)
Set the maximum number of threads/reader slots for the environment.
int ESECT mdb_env_get_maxreaders (MDB_env *env, unsigned int *readers)
Get the maximum number of threads/reader slots for the environment.
static int ESECT mdb_fsize (HANDLE fd, size_t *size)
static int ESECT mdb_fname_init (const char *path, unsigned envflags, MDB_name *fname)
static int ESECT mdb_fopen (const MDB_env *env, MDB_name *fname, enum mdb_fopen_type which, mdb_mode_t mode, HANDLE *res)
static int ESECT mdb_env_open2 (MDB_env *env)
static void mdb_env_reader_dest (void *ptr)
static int ESECT mdb_env_share_locks (MDB_env *env, int *excl)
static int ESECT mdb_env_excl_lock (MDB_env *env, int *excl)
static int ESECT mdb_env_setup_locks (MDB_env *env, MDB_name *fname, int mode, int *excl)
int ESECT mdb_env_open (MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode)
Open an environment handle.
void ESECT mdb_env_close (MDB_env *env)
Close the environment and release the memory map.
static int mdb_cmp_long (const MDB_val *a, const MDB_val *b)
static int mdb_cmp_int (const MDB_val *a, const MDB_val *b)
static int mdb_cmp_cint (const MDB_val *a, const MDB_val *b)
static int mdb_cmp_memn (const MDB_val *a, const MDB_val *b)
static int mdb_cmp_memnr (const MDB_val *a, const MDB_val *b)
static int mdb_page_search_lowest (MDB_cursor *mc)
static int mdb_ovpage_free (MDB_cursor *mc, MDB_page *mp)
int mdb_get (MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data)
Get items from a database.
int mdb_cursor_get (MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op)
Retrieve by cursor.
static int mdb_cursor_touch (MDB_cursor *mc)
int mdb_cursor_put (MDB_cursor *mc, MDB_val *key, MDB_val *data, unsigned int flags)
Store by cursor.
int mdb_cursor_del (MDB_cursor *mc, unsigned int flags)
Delete current key/data pair.
int mdb_cursor_open (MDB_txn *txn, MDB_dbi dbi, MDB_cursor **ret)
Create a cursor handle.
int mdb_cursor_renew (MDB_txn *txn, MDB_cursor *mc)
Renew a cursor handle.
int mdb_cursor_count (MDB_cursor *mc, size_t *countp)
Return count of duplicates for current key.
void mdb_cursor_close (MDB_cursor *mc)
Close a cursor handle.
MDB_txn * mdb_cursor_txn (MDB_cursor *mc)
Return the cursor’s transaction handle.
MDB_dbi mdb_cursor_dbi (MDB_cursor *mc)
Return the cursor’s database handle.
static void mdb_cursor_copy (const MDB_cursor *csrc, MDB_cursor *cdst)
int mdb_del (MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data)
Delete 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.
static THREAD_RET ESECT CALL_CONV mdb_env_copythr (void *arg)
static int ESECT mdb_env_cthr_toggle (mdb_copy *my, int adjust)
static int ESECT mdb_env_cwalk (mdb_copy *my, pgno_t *pg, int flags)
static int ESECT mdb_env_copyfd1 (MDB_env *env, HANDLE fd)
static int ESECT mdb_env_copyfd0 (MDB_env *env, HANDLE fd)
int ESECT mdb_env_copyfd2 (MDB_env *env, HANDLE fd, unsigned int flags)
int ESECT mdb_env_copyfd (MDB_env *env, HANDLE fd)
int ESECT mdb_env_copy2 (MDB_env *env, const char *path, unsigned int flags)
Copy an LMDB environment to the specified path, with options.
int ESECT mdb_env_copy (MDB_env *env, const char *path)
Copy an LMDB environment to the specified path.
int ESECT mdb_env_set_flags (MDB_env *env, unsigned int flag, int onoff)
Set environment flags.
int ESECT mdb_env_get_flags (MDB_env *env, unsigned int *arg)
Get environment flags.
int ESECT mdb_env_set_userctx (MDB_env *env, void *ctx)
Set application information associated with the MDB_env.
void *ESECT mdb_env_get_userctx (MDB_env *env)
Get the application information associated with the MDB_env.
int ESECT mdb_env_set_assert (MDB_env *env, MDB_assert_func *func)
int ESECT mdb_env_get_path (MDB_env *env, const char **arg)
Return the path that was used in mdb_env_open().
int ESECT mdb_env_get_fd (MDB_env *env, mdb_filehandle_t *arg)
Return the filedescriptor for the given environment.
static int ESECT mdb_stat0 (MDB_env *env, MDB_db *db, MDB_stat *arg)
int ESECT mdb_env_stat (MDB_env *env, MDB_stat *arg)
Return statistics about the LMDB environment.
int ESECT mdb_env_info (MDB_env *env, MDB_envinfo *arg)
Return information about the LMDB environment.
int mdb_dbi_open (MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi)
Open a database in the environment.
int ESECT mdb_stat (MDB_txn *txn, MDB_dbi dbi, MDB_stat *arg)
Retrieve statistics for a database.
void mdb_dbi_close (MDB_env *env, MDB_dbi dbi)
Close a database handle. Normally unnecessary. Use with care:
int mdb_dbi_flags (MDB_txn *txn, MDB_dbi dbi, unsigned int *flags)
Retrieve the DB flags for a database handle.
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 ESECT mdb_env_get_maxkeysize (MDB_env *env)
Get the maximum size of keys and MDB_DUPSORT data we can write.
int ESECT mdb_reader_list (MDB_env *env, MDB_msg_func *func, void *ctx)
Dump the entries in the reader lock table.
static int ESECT mdb_pid_insert (MDB_PID_T *ids, MDB_PID_T pid)
int ESECT mdb_reader_check (MDB_env *env, int *dead)
Check for stale entries in the reader lock table.

Variables

static char *const mdb_errstr []
static const mdb_nchar_t *const mdb_suffixes [2][2]

Detailed Description

Data Structure Documentation

struct MDB_page

Common header for all page types. The page type depends on mp_flags.

P_BRANCH and P_LEAF pages have unsorted ’MDB_node’s at the end, with sorted mp_ptrs[] entries referring to them. Exception: P_LEAF2 pages omit mp_ptrs and pack sorted MDB_DUPFIXED values after the page header.

P_OVERFLOW records occupy one or more contiguous pages where only the first has a page header. They hold the real data of F_BIGDATA nodes.

P_SUBP sub-pages are small leaf ’pages’ with duplicate data. A node with flag F_DUPDATA but not F_SUBDATA contains a sub-page. (Duplicate data can also go in sub-databases, which use normal pages.)

P_META pages contain MDB_meta, the start point of an LMDB snapshot.

Each non-metapage up to MDB_meta.mm_last_pg is reachable exactly once in the snapshot: Either used by a database or listed in a freeDB record.

Data Fields

union {
pgno_t p_pgno
struct MDB_page * p_next
} mp_p
uint16_t mp_pad
uint16_t mp_flags
union {
struct {
indx_t pb_lower
indx_t pb_upper
} pb
uint32_t pb_pages
} mp_pb
indx_t mp_ptrs [1]

Field Documentation

pgno_t MDB_page::p_pgno

page number

struct MDB_page* MDB_page::p_next

for in-memory list of freed pages

uint16_t MDB_page::mp_pad

key size if this is a LEAF2 page

uint16_t MDB_page::mp_flags

Page Flags

indx_t MDB_page::pb_lower

lower bound of free space

indx_t MDB_page::pb_upper

upper bound of free space

uint32_t MDB_page::pb_pages

number of overflow pages

indx_t MDB_page::mp_ptrs[1]

dynamic size

struct MDB_node

Header for a single key/data pair within a page. Used in pages of type P_BRANCH and P_LEAF without P_LEAF2. We guarantee 2-byte alignment for ’MDB_node’s.

mn_lo and mn_hi are used for data size on leaf nodes, and for child pgno on branch nodes. On 64 bit platforms, mn_flags is also used for pgno. (Branch nodes have no flags). Lo and hi are in host byte order in case some accesses can be optimized to 32-bit word access.

Leaf node flags describe node contents. F_BIGDATA says the node’s data part is the page number of an overflow page with actual data. F_DUPDATA and F_SUBDATA can be combined giving duplicate data in a sub-page/sub-database, and named databases (just F_SUBDATA).

Data Fields

unsigned short mn_flags
unsigned short mn_ksize
char mn_data [1]

unsigned short mn_lo
unsigned short mn_hi

Field Documentation

unsigned short MDB_node::mn_lo

part of data size or pgno

unsigned short MDB_node::mn_hi

part of data size or pgno

unsigned short MDB_node::mn_flags

Node Flags

unsigned short MDB_node::mn_ksize

key size

char MDB_node::mn_data[1]

key and data are appended here

struct MDB_db

Information about a single database in the environment.

Data Fields

uint32_t md_pad
uint16_t md_flags
uint16_t md_depth
pgno_t md_branch_pages
pgno_t md_leaf_pages
pgno_t md_overflow_pages
size_t md_entries
pgno_t md_root

Field Documentation

uint32_t MDB_db::md_pad

also ksize for LEAF2 pages

uint16_t MDB_db::md_flags

Database Flags

uint16_t MDB_db::md_depth

depth of this tree

pgno_t MDB_db::md_branch_pages

number of internal pages

pgno_t MDB_db::md_leaf_pages

number of leaf pages

pgno_t MDB_db::md_overflow_pages

number of overflow pages

size_t MDB_db::md_entries

number of data items

pgno_t MDB_db::md_root

the root page of this tree

struct MDB_meta

Meta page content. A meta page is the start point for accessing a database snapshot. Pages 0-1 are meta pages. Transaction N writes meta page #(N % 2).

Data Fields

uint32_t mm_magic
uint32_t mm_version
void * mm_address
size_t mm_mapsize
MDB_db mm_dbs [CORE_DBS]
pgno_t mm_last_pg
volatile txnid_t mm_txnid

Field Documentation

uint32_t MDB_meta::mm_magic

Stamp identifying this as an LMDB file. It must be set to MDB_MAGIC.

uint32_t MDB_meta::mm_version

Version number of this file. Must be set to MDB_DATA_VERSION.

void* MDB_meta::mm_address

address for fixed mapping

size_t MDB_meta::mm_mapsize

size of mmap region

MDB_db MDB_meta::mm_dbs[CORE_DBS]

first is free space, 2nd is main db

pgno_t MDB_meta::mm_last_pg

Last used page in the datafile. Actually the file may be shorter if the freeDB lists the final pages.

volatile txnid_t MDB_meta::mm_txnid

txnid that committed this page

union MDB_metabuf

Buffer for a stack-allocated meta page. The members define size and alignment, and silence type aliasing warnings. They are not used directly; that could mean incorrectly using several union members in parallel.

Data Fields

MDB_page mb_page
struct {
char mm_pad [PAGEHDRSZ]
MDB_meta mm_meta
} mb_metabuf

struct MDB_dbx

Auxiliary DB info. The information here is mostly static/read-only. There is only a single copy of this record in the environment.

Data Fields

MDB_val md_name
MDB_cmp_func * md_cmp
MDB_cmp_func * md_dcmp
MDB_rel_func * md_rel
void * md_relctx

Field Documentation

MDB_val MDB_dbx::md_name

name of the database

MDB_cmp_func* MDB_dbx::md_cmp

function for comparing keys

MDB_cmp_func* MDB_dbx::md_dcmp

function for comparing data items

MDB_rel_func* MDB_dbx::md_rel

user relocate function

void* MDB_dbx::md_relctx

user-provided context for md_rel

struct MDB_txn

Opaque structure for a transaction handle.

A database transaction. Every operation requires a transaction handle.

All database operations require a transaction handle. Transactions may be read-only or read-write.

Data Fields

MDB_txn * mt_parent
MDB_txn * mt_child
pgno_t mt_next_pgno
txnid_t mt_txnid
MDB_env * mt_env
MDB_IDL mt_free_pgs
MDB_page * mt_loose_pgs
int mt_loose_count
MDB_IDL mt_spill_pgs
union {
MDB_ID2L dirty_list
MDB_reader * reader
} mt_u
MDB_dbx * mt_dbxs
MDB_db * mt_dbs
unsigned int * mt_dbiseqs
MDB_cursor ** mt_cursors
unsigned char * mt_dbflags
MDB_dbi mt_numdbs
unsigned int mt_flags
unsigned int mt_dirty_room

Field Documentation

MDB_txn* MDB_txn::mt_parent

parent of a nested txn

MDB_txn* MDB_txn::mt_child

Nested txn under this txn, set together with flag MDB_TXN_HAS_CHILD

pgno_t MDB_txn::mt_next_pgno

next unallocated page

txnid_t MDB_txn::mt_txnid

The ID of this transaction. IDs are integers incrementing from 1. Only committed write transactions increment the ID. If a transaction aborts, the ID may be re-used by the next writer.

MDB_env* MDB_txn::mt_env

the DB environment

MDB_IDL MDB_txn::mt_free_pgs

The list of pages that became unused during this transaction.

MDB_page* MDB_txn::mt_loose_pgs

The list of loose pages that became unused and may be reused in this transaction, linked through NEXT_LOOSE_PAGE(page).

int MDB_txn::mt_loose_count

Number of loose pages (mt_loose_pgs)

MDB_IDL MDB_txn::mt_spill_pgs

The sorted list of dirty pages we temporarily wrote to disk because the dirty list was full. page numbers in here are shifted left by 1, deleted slots have the LSB set.

MDB_ID2L MDB_txn::dirty_list

For write txns: Modified pages. Sorted when not MDB_WRITEMAP.

MDB_reader* MDB_txn::reader

For read txns: This thread/txn’s reader table slot, or NULL.

MDB_dbx* MDB_txn::mt_dbxs

Array of records for each DB known in the environment.

MDB_db* MDB_txn::mt_dbs

Array of MDB_db records for each known DB

unsigned int* MDB_txn::mt_dbiseqs

Array of sequence numbers for each DB handle

MDB_cursor** MDB_txn::mt_cursors

In write txns, array of cursors for each DB

unsigned char* MDB_txn::mt_dbflags

Array of flags for each DB

MDB_dbi MDB_txn::mt_numdbs

Number of DB records in use, or 0 when the txn is finished. This number only ever increments until the txn finishes; we don’t decrement it when individual DB handles are closed.

unsigned int MDB_txn::mt_flags

Transaction Flags

unsigned int MDB_txn::mt_dirty_room

dirty_list room: Array size - #dirty pages visible to this txn. Includes ancestor txns’ dirty pages not hidden by other txns’ dirty/spilled pages. Thus commit(nested txn) has room to merge dirty_list into mt_parent after freeing hidden mt_parent pages.

struct MDB_cursor

Opaque structure for navigating through a database.

Cursors are used for all DB operations. A cursor holds a path of (page pointer, key index) from the DB root to a position in the DB, plus other state. MDB_DUPSORT cursors include an xcursor to the current data item. Write txns track their cursors and keep them up to date when data moves. Exception: An xcursor’s pointer to a P_SUBP page can be stale. (A node with F_DUPDATA but no F_SUBDATA contains a subpage).

Data Fields

MDB_cursor * mc_next
MDB_cursor * mc_backup
struct MDB_xcursor * mc_xcursor
MDB_txn * mc_txn
MDB_dbi mc_dbi
MDB_db * mc_db
MDB_dbx * mc_dbx
unsigned char * mc_dbflag
unsigned short mc_snum
unsigned short mc_top
unsigned int mc_flags
MDB_page * mc_pg [CURSOR_STACK]
indx_t mc_ki [CURSOR_STACK]

Field Documentation

MDB_cursor* MDB_cursor::mc_next

Next cursor on this DB in this txn

MDB_cursor* MDB_cursor::mc_backup

Backup of the original cursor if this cursor is a shadow

struct MDB_xcursor* MDB_cursor::mc_xcursor

Context used for databases with MDB_DUPSORT, otherwise NULL

MDB_txn* MDB_cursor::mc_txn

The transaction that owns this cursor

MDB_dbi MDB_cursor::mc_dbi

The database handle this cursor operates on

MDB_db* MDB_cursor::mc_db

The database record for this cursor

MDB_dbx* MDB_cursor::mc_dbx

The database auxiliary record for this cursor

unsigned char* MDB_cursor::mc_dbflag

The Transaction DB Flags for this database

unsigned short MDB_cursor::mc_snum

number of pushed pages

unsigned short MDB_cursor::mc_top

index of top page, normally mc_snum-1

unsigned int MDB_cursor::mc_flags

Cursor Flags

MDB_page* MDB_cursor::mc_pg[CURSOR_STACK]

stack of pushed pages

indx_t MDB_cursor::mc_ki[CURSOR_STACK]

stack of page indices

struct MDB_xcursor

Context for sorted-dup records. We could have gone to a fully recursive design, with arbitrarily deep nesting of sub-databases. But for now we only handle these levels - main DB, optional sub-DB, sorted-duplicate DB.

Data Fields

MDB_cursor mx_cursor
MDB_db mx_db
MDB_dbx mx_dbx
unsigned char mx_dbflag

Field Documentation

MDB_cursor MDB_xcursor::mx_cursor

A sub-cursor for traversing the Dup DB

MDB_db MDB_xcursor::mx_db

The database record for this Dup DB

MDB_dbx MDB_xcursor::mx_dbx

The auxiliary DB record for this Dup DB

unsigned char MDB_xcursor::mx_dbflag

The Transaction DB Flags for this Dup DB

struct MDB_pgstate

State of FreeDB old pages, stored in the MDB_env

Data Fields

pgno_t * mf_pghead
txnid_t mf_pglast

Field Documentation

pgno_t* MDB_pgstate::mf_pghead

Reclaimed freeDB pages, or NULL before use

txnid_t MDB_pgstate::mf_pglast

ID of last used record, or 0 if !mf_pghead

struct MDB_env

Opaque structure for a database environment.

The database environment.

A DB environment supports multiple databases, all residing in the same shared-memory map.

Data Fields

HANDLE me_fd
HANDLE me_lfd
HANDLE me_mfd
uint32_t me_flags
unsigned int me_psize
unsigned int me_os_psize
unsigned int me_maxreaders
volatile int me_close_readers
MDB_dbi me_numdbs
MDB_dbi me_maxdbs
MDB_PID_T me_pid
char * me_path
char * me_map
MDB_txninfo * me_txns
MDB_meta * me_metas [NUM_METAS]
void * me_pbuf
MDB_txn * me_txn
MDB_txn * me_txn0
size_t me_mapsize
off_t me_size
pgno_t me_maxpg
MDB_dbx * me_dbxs
uint16_t * me_dbflags
unsigned int * me_dbiseqs
pthread_key_t me_txkey
txnid_t me_pgoldest
MDB_pgstate me_pgstate
MDB_page * me_dpages
MDB_IDL me_free_pgs
MDB_ID2L me_dirty_list
int me_maxfree_1pg
unsigned int me_nodemax
int me_live_reader
void * me_userctx
MDB_assert_func * me_assert_func

Field Documentation

HANDLE MDB_env::me_fd

The main data file

HANDLE MDB_env::me_lfd

The lock file

HANDLE MDB_env::me_mfd

For writing and syncing the meta pages

uint32_t MDB_env::me_flags

Environment Flags

unsigned int MDB_env::me_psize

DB page size, inited from me_os_psize

unsigned int MDB_env::me_os_psize

OS page size, from GET_PAGESIZE

unsigned int MDB_env::me_maxreaders

size of the reader table

volatile int MDB_env::me_close_readers

Max MDB_txninfo.mti_numreaders of interest to mdb_env_close()

MDB_dbi MDB_env::me_numdbs

number of DBs opened

MDB_dbi MDB_env::me_maxdbs

size of the DB table

MDB_PID_T MDB_env::me_pid

process ID of this env

char* MDB_env::me_path

path to the DB files

char* MDB_env::me_map

the memory map of the data file

MDB_txninfo* MDB_env::me_txns

the memory map of the lock file or NULL

MDB_meta* MDB_env::me_metas[NUM_METAS]

pointers to the two meta pages

void* MDB_env::me_pbuf

scratch area for DUPSORT put()

MDB_txn* MDB_env::me_txn

current write transaction

MDB_txn* MDB_env::me_txn0

prealloc’d write transaction

size_t MDB_env::me_mapsize

size of the data memory map

off_t MDB_env::me_size

current file size

pgno_t MDB_env::me_maxpg

me_mapsize / me_psize

MDB_dbx* MDB_env::me_dbxs

array of static DB info

uint16_t* MDB_env::me_dbflags

array of flags from MDB_db.md_flags

unsigned int* MDB_env::me_dbiseqs

array of dbi sequence numbers

pthread_key_t MDB_env::me_txkey

thread-key for readers

txnid_t MDB_env::me_pgoldest

ID of oldest reader last time we looked

MDB_pgstate MDB_env::me_pgstate

state of old pages from freeDB

MDB_page* MDB_env::me_dpages

list of malloc’d blocks for re-use

MDB_IDL MDB_env::me_free_pgs

IDL of pages that became unused in a write txn

MDB_ID2L MDB_env::me_dirty_list

ID2L of pages written during a write txn. Length MDB_IDL_UM_SIZE.

int MDB_env::me_maxfree_1pg

Max number of freelist items that can fit in a single overflow page

unsigned int MDB_env::me_nodemax

Max size of a node on a page

int MDB_env::me_live_reader

have liveness lock in reader table

void* MDB_env::me_userctx

User-settable context

MDB_assert_func* MDB_env::me_assert_func

Callback for assertion failures

struct MDB_ntxn

Nested transaction

Data Fields

MDB_txn mnt_txn
MDB_pgstate mnt_pgstate

Field Documentation

MDB_txn MDB_ntxn::mnt_txn

the transaction

MDB_pgstate MDB_ntxn::mnt_pgstate

parent transaction’s saved freestate

struct MDB_name

Filename - string of mdb_nchar_t[]

Data Fields

int mn_len
int mn_alloced
mdb_nchar_t * mn_val

Field Documentation

int MDB_name::mn_len

Length

int MDB_name::mn_alloced

True if mn_val was malloced

mdb_nchar_t* MDB_name::mn_val

Contents

struct mdb_copy

State needed for a double-buffering compacting copy.

Data Fields

MDB_env * mc_env
MDB_txn * mc_txn
pthread_mutex_t mc_mutex
pthread_cond_t mc_cond
char * mc_wbuf [2]
char * mc_over [2]
int mc_wlen [2]
int mc_olen [2]
pgno_t mc_next_pgno
HANDLE mc_fd
int mc_toggle
int mc_new
volatile int mc_error

Field Documentation

pthread_cond_t mdb_copy::mc_cond

Condition variable for mc_new

int mdb_copy::mc_toggle

Buffer number in provider

int mdb_copy::mc_new

(0-2 buffers to write) | (MDB_EOF at end)

volatile int mdb_copy::mc_error

Error code. Never cleared if set. Both threads can set nonzero to fail the copy. Not mutex-protected, LMDB expects atomic int.

Macro Definition Documentation

#define MDB_DSYNC O_SYNC

A flag for opening a file and requesting synchronous data writes. This is only used when writing a meta page. It’s not strictly needed; we could just do a normal write and then immediately perform a flush. But if this flag is available it saves us an extra system call.

Note

If O_DSYNC is undefined but exists in /usr/include, preferably set some compiler flag to get the definition.

#define MDB_FDATASYNC fdatasync

Function for flushing the data of a file. Define this to fsync if fdatasync() is not supported.

#define MAX_PAGESIZE (PAGEBASE ? 0x10000 : 0x8000)

The maximum size of a database page. It is 32k or 64k, since value-PAGEBASE must fit in MDB_page.mp_upper.

LMDB will use database pages < OS pages if needed. That causes more I/O in write transactions: The OS must know (read) the whole page before writing a partial page.

Note that we don’t currently support Huge pages. On Linux, regular data files cannot use Huge pages, and in general Huge pages aren’t actually pageable. We rely on the OS demand-pager to read our data and page it out when memory pressure from other processes is high. So until OSs have actual paging support for Huge pages, they’re not viable.

#define MDB_MINKEYS 2

The minimum number of keys required in a database page. Setting this to a larger value will place a smaller bound on the maximum size of a data item. Data items larger than this size will be pushed into overflow pages instead of being stored directly in the B-tree node. This value used to default to 4. With a page size of 4096 bytes that meant that any item larger than 1024 bytes would go into an overflow page. That also meant that on average 2-3KB of each overflow page was wasted space. The value cannot be lower than 2 because then there would no longer be a tree structure. With this value, items larger than 2KB will go into overflow pages, and on average only 1KB will be wasted.

#define MDB_MAGIC 0xBEEFC0DE

A stamp that identifies a file as an LMDB file. There’s nothing special about this value other than that it is easily recognizable, and it will reflect any byte order mismatches.

#define MDB_DATA_VERSION ((MDB_DEVEL) ? 999 : 1)

The version number for a database’s datafile format.

#define MDB_LOCK_VERSION 1

The version number for a database’s lockfile format.

#define MDB_MAXKEYSIZE ((MDB_DEVEL) ? 0 : 511)

The max size of a key we can write, or 0 for computed max. This macro should normally be left alone or set to 0. Note that a database with big keys or dupsort data cannot be reliably modified by a liblmdb which uses a smaller max. The default is 511 for backwards compat, or 0 when MDB_DEVEL.

Other values are allowed, for backwards compat. However: A value bigger than the computed max can break if you do not know what you are doing, and liblmdb <= 0.9.10 can break when modifying a DB with keys/dupsort data bigger than its max.

Data items in an MDB_DUPSORT database are also limited to this size, since they’re actually keys of a sub-DB. Keys and MDB_DUPSORT data items must fit on a node in a regular page.

#define ENV_MAXKEY(env) (MDB_MAXKEYSIZE)

The maximum size of a key we can write to the environment.

#define MAXDATASIZE 0xffffffffUL

The maximum size of a data item. We only store a 32 bit value for node sizes.

#define P_INVALID (˜(pgno_t)0)

An invalid page number. Mainly used to denote an empty tree.

#define F_ISSET(w, f) (((w) & (f)) == (f))

Test if the flags f are set in a flag word w.

#define EVEN(n) (((n) + 1U) & -2) /* sign-extending -2 to match n+1U */

Round n up to an even number.

#define DEFAULT_MAPSIZE 1048576

Default size of memory map. This is certainly too small for any actual applications. Apps should always set the size explicitly using mdb_env_set_mapsize().

#define PAGEHDRSZ ((unsigned) offsetof(MDB_page, mp_ptrs))

Size of the page header, excluding dynamic data at the end

#define METADATA(p) ((void *)((char *)(p) + PAGEHDRSZ))

Address of first usable data byte in a page, after the header

#define PAGEBASE ((MDB_DEVEL) ? PAGEHDRSZ : 0)

ITS#7713, change PAGEBASE to handle 65536 byte pages

#define NUMKEYS(p) (((p)->mp_lower - (PAGEHDRSZ-PAGEBASE)) >> 1)

Number of nodes on a page

#define SIZELEFT(p) (indx_t)((p)->mp_upper - (p)->mp_lower)

The amount of space remaining in the page

#define PAGEFILL(env, p)

Value:

(1000L * ((env)->me_psize - PAGEHDRSZ - SIZELEFT(p)) / ((env)->me_psize - PAGEHDRSZ))
The percentage of space used in the page, in tenths of a percent.

#define FILL_THRESHOLD 250

The minimum page fill factor, in tenths of a percent. Pages emptier than this are candidates for merging.

#define IS_LEAF(p) F_ISSET((p)->mp_flags, P_LEAF)

Test if a page is a leaf page

#define IS_LEAF2(p) F_ISSET((p)->mp_flags, P_LEAF2)

Test if a page is a LEAF2 page

#define IS_BRANCH(p) F_ISSET((p)->mp_flags, P_BRANCH)

Test if a page is a branch page

#define IS_OVERFLOW(p) F_ISSET((p)->mp_flags, P_OVERFLOW)

Test if a page is an overflow page

#define IS_SUBP(p) F_ISSET((p)->mp_flags, P_SUBP)

Test if a page is a sub page

#define OVPAGES(size, psize) ((PAGEHDRSZ-1 + (size)) / (psize) + 1)

The number of overflow pages needed to store the given size.

#define NEXT_LOOSE_PAGE(p) (*(MDB_page **)((p) + 2))

Link in MDB_txn.mt_loose_pgs list. Kept outside the page header, which is needed when reusing the page.

#define NODESIZE offsetof(MDB_node, mn_data)

Size of the node header, excluding dynamic data at the end

#define PGNO_TOPWORD ((pgno_t)-1 > 0xffffffffu ? 32 : 0)

Bit position of top word in page number, for shifting mn_flags

#define INDXSIZE(k) (NODESIZE + ((k) == NULL ? 0 : (k)->mv_size))

Size of a node in a branch page with a given key. This is just the node header plus the key, there is no data.

#define LEAFSIZE(k, d) (NODESIZE + (k)->mv_size + (d)->mv_size)

Size of a node in a leaf page with a given key and data. This is node header plus key plus data size.

#define NODEPTR(p, i) ((MDB_node *)((char *)(p) + (p)->mp_ptrs[i] +PAGEBASE))

Address of node i in page p

#define NODEKEY(node) (void *)((node)->mn_data)

Address of the key for the node

#define NODEDATA(node) (void *)((char *)(node)->mn_data + (node)->mn_ksize)

Address of the data for a node

#define NODEPGNO(node)

Value:

((node)->mn_lo | ((pgno_t) (node)->mn_hi << 16) | (PGNO_TOPWORD ? ((pgno_t) (node)->mn_flags << PGNO_TOPWORD) : 0))
Get the page number pointed to by a branch node

#define SETPGNO(node, pgno)

Value:

do { (node)->mn_lo = (pgno) & 0xffff; (node)->mn_hi = (pgno) >> 16; if (PGNO_TOPWORD) (node)->mn_flags = (pgno) >> PGNO_TOPWORD; } while(0)
Set the page number in a branch node

#define NODEDSZ(node) ((node)->mn_lo | ((unsigned)(node)->mn_hi << 16))

Get the size of the data in a leaf node

#define SETDSZ(node, size)

Value:

do { (node)->mn_lo = (size) & 0xffff; (node)->mn_hi = (size) >> 16;} while(0)
Set the size of the data for a leaf node

#define NODEKSZ(node) ((node)->mn_ksize)

The size of a key in a node

#define COPY_PGNO(dst, src)

Value:

do { unsigned short *s, *d; s = (unsigned short *)&(src); d = (unsigned short *)&(dst); *d++ = *s++; *d = *s; } while (0)
Copy a page number from src to dst

#define LEAF2KEY(p, i, ks) ((char *)(p) + PAGEHDRSZ + ((i)*(ks)))

The address of a key in a LEAF2 page. LEAF2 pages are used for MDB_DUPFIXED sorted-duplicate sub-DBs. There are no node headers, keys are stored contiguously.

#define MDB_GET_KEY(node, keyptr)

Value:

{ if ((keyptr) != NULL) { (keyptr)->mv_size = NODEKSZ(node); (keyptr)->mv_data = NODEKEY(node); } }
Set the node’s key into keyptr, if requested.

#define MDB_GET_KEY2(node, key) { key.mv_size = NODEKSZ(node); key.mv_data= NODEKEY(node); }

Set the node’s key into key.

#define MDB_VALID 0x8000

DB handle is valid, for me_dbflags

#define VALID_FLAGS

Value:

(MDB_REVERSEKEY|MDB_DUPSORT|MDB_INTEGERKEY|MDB_DUPFIXED| MDB_INTEGERDUP|MDB_REVERSEDUP|MDB_CREATE)
mdb_dbi_open() flags

#define FREE_DBI 0

Handle for the DB used to track free pages.

#define MAIN_DBI 1

Handle for the default DB.

#define CORE_DBS 2

Number of DBs in metapage (free and main) - also hardcoded elsewhere

#define NUM_METAS 2

Number of meta pages - also hardcoded elsewhere

#define CURSOR_STACK 32

Enough space for 2ˆ32 nodes with minimum of 2 keys per node. I.e., plenty. At 4 keys per node, enough for 2ˆ64 nodes, so there’s probably no need to raise this on a 64 bit machine.

#define XCURSOR_INITED(mc) ((mc)->mc_xcursor &&((mc)->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED))

Check if there is an inited xcursor

#define XCURSOR_REFRESH(mc, top, mp)

Value:

do { MDB_page *xr_pg = (mp); MDB_node *xr_node; if (!XCURSOR_INITED(mc) || (mc)->mc_ki[top] >= NUMKEYS(xr_pg)) break; xr_node = NODEPTR(xr_pg, (mc)->mc_ki[top]); if ((xr_node->mn_flags & (F_DUPDATA|F_SUBDATA)) == F_DUPDATA) (mc)->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(xr_node); } while (0)
Update the xcursor’s sub-page pointer, if any, in mc. Needed when the node which contains the sub-page may have moved. Called with leaf page mp = mc->mc_pg[top].

#define MDB_COMMIT_PAGES 64

max number of pages to commit in one writev() call

#define MAX_WRITE (0x40000000U >> (sizeof(ssize_t) == 4))

max bytes to write in one call

#define TXN_DBI_EXIST(txn, dbi, validity) ((txn) && (dbi)<(txn)->mt_numdbs&& ((txn)->mt_dbflags[dbi] & (validity)))

Check txn and dbi arguments to a function

#define TXN_DBI_CHANGED(txn, dbi) ((txn)->mt_dbiseqs[dbi] !=(txn)->mt_env->me_dbiseqs[dbi])

Check for misused dbi handles

#define MDB_END_NAMES

Value:

{"committed", "empty-commit", "abort", "reset", "reset-tmp", "fail-begin", "fail-beginchild"}

#define MDB_END_OPMASK 0x0F

mask for mdb_txn_end() operation number

#define MDB_END_UPDATE 0x10

update env state (DBIs)

#define MDB_END_FREE 0x20

free txn unless it is MDB_env.me_txn0

#define MDB_END_SLOT MDB_NOTLS

release any reader slot if MDB_NOTLS

#define MDB_SPLIT_REPLACE MDB_APPENDDUP

newkey is not new

#define mdb_cmp_clong mdb_cmp_cint

Compare two items pointing at size_t’s of unknown alignment.

#define mdb_cassert(mc, expr) mdb_assert0((mc)->mc_txn->mt_env, expr,#expr)

assert(3) variant in cursor context

#define mdb_tassert(txn, expr) mdb_assert0((txn)->mt_env, expr, #expr)

assert(3) variant in transaction context

#define mdb_eassert(env, expr) mdb_assert0(env, expr, #expr)

assert(3) variant in environment context

#define mdb_assert0(env, expr, expr_txt)

Value:

((expr) ? (void)0 : mdb_assert_fail(env, expr_txt, mdb_func_, __FILE__, __LINE__))

#define MDB_NAME(str) str

mdb_nchar_t[] string literal

#define mdb_name_cpy strcpy

Copy name (mdb_nchar_t string)

#define MDB_SUFFLEN 9

Max string length in mdb_suffixes[]

#define mdb_fname_destroy(fname) do { if ((fname).mn_alloced)free((fname).mn_val); } while (0)

Destroy fname from mdb_fname_init()

#define CHANGEABLE (MDB_NOSYNC|MDB_NOMETASYNC|MDB_MAPASYNC|MDB_NOMEMINIT)

Only a subset of the Environment Flags flags can be changed at runtime. Changing other flags requires closing the environment and re-opening it with the new flags.

#define CHANGELESS

Value:

(MDB_FIXEDMAP|MDB_NOSUBDIR|MDB_RDONLY| MDB_WRITEMAP|MDB_NOTLS|MDB_NOLOCK|MDB_NORDAHEAD)

#define MDB_NOSPILL 0x8000

Do not spill pages to disk if txn is getting full, may fail instead

#define WITH_CURSOR_TRACKING(mn, act)

Value:

do { MDB_cursor dummy, *tracked, **tp = &(mn).mc_txn->mt_cursors[mn.mc_dbi]; if ((mn).mc_flags & C_SUB) { dummy.mc_flags = C_INITIALIZED; dummy.mc_xcursor = (MDB_xcursor *)&(mn); tracked = &dummy; } else { tracked = &(mn); } tracked->mc_next = *tp; *tp = tracked; { act; } *tp = tracked->mc_next; } while (0)
Perform act while tracking temporary cursor mn

#define MDB_EOF 0x10

mdb_env_copyfd1() is done reading

Typedef Documentation

typedef MDB_ID pgno_t

A page number in the database. Note that 64 bit page numbers are overkill, since pages themselves already represent 12-13 bits of addressable memory, and the OS will always limit applications to a maximum of 63 bits of address space.

Note

In the MDB_node structure, we only store 48 bits of this value, which thus limits us to only 60 bits of addressable data.

typedef MDB_ID txnid_t

A transaction ID. See struct MDB_txn.mt_txnid for details.

typedef uint16_t indx_t

Used for offsets within a single page. Since memory pages are typically 4 or 8KB in size, 12-13 bits, this is plenty.

typedef char mdb_nchar_t

Character type for file names: char on Unix, wchar_t on Windows

Enumeration Type Documentation

enum mdb_fopen_type

File type, access mode etc. for mdb_fopen()

Enumerator
MDB_O_RDONLY

for RDONLY me_fd

MDB_O_RDWR

for me_fd

MDB_O_META

for me_mfd

MDB_O_COPY

for mdb_env_copy()

MDB_O_MASK

Bitmask for open() flags in enum mdb_fopen_type. The other bits distinguish otherwise-equal MDB_O_* constants from each other.

MDB_O_LOCKS

for me_lfd

Function Documentation

static int mdb_page_alloc (MDB_cursor * mc, int num, MDB_page ** mp) [static]

Allocate page numbers and memory for writing. Maintain me_pglast, me_pghead and mt_next_pgno. Set MDB_TXN_ERROR on failure.

If there are free pages available from older transactions, they are re-used first. Otherwise allocate a new page at mt_next_pgno. Do not modify the freedB, just merge freeDB records into me_pghead[] and move me_pglast to say which records were consumed. Only this function can create me_pghead and move me_pglast/mt_next_pgno.

Parameters

mc cursor A cursor handle identifying the transaction and database for which we are allocating.
num the number of pages to allocate.
mp Address of the allocated page(s). Requests for multiple pages will always be satisfied by a single contiguous chunk of memory.

Returns

0 on success, non-zero on failure.

static int mdb_page_new (MDB_cursor * mc, uint32_t flags, int num, MDB_page** mp) [static]

Allocate and initialize new pages for a database. Set MDB_TXN_ERROR on failure.

Parameters

mc a cursor on the database being added to.
flags flags defining what type of page is being allocated.
num the number of pages to allocate. This is usually 1, unless allocating overflow pages for a large record.
mp Address of a page, or NULL on failure.

Returns

0 on success, non-zero on failure.

static int mdb_page_touch (MDB_cursor * mc) [static]

Touch a page: make it dirty and re-insert into tree with updated pgno. Set MDB_TXN_ERROR on failure.

Parameters

mc cursor pointing to the page to be touched

Returns

0 on success, non-zero on failure.

static void mdb_txn_end (MDB_txn * txn, unsigned mode) [static]

End a transaction, except successful commit of a nested transaction. May be called twice for readonly txns: First reset it, then abort.

Parameters

txn the transaction handle to end
mode why and how to end the transaction

static int mdb_page_get (MDB_cursor * mc, pgno_t pgno, MDB_page ** ret, int *lvl) [static]

Find the address of the page corresponding to a given page number. Set MDB_TXN_ERROR on failure.

Parameters

mc the cursor accessing the page.
pgno the page number for the page to retrieve.
ret address of a pointer where the page’s address will be stored.
lvl dirty_list inheritance level of found page. 1=current txn, 0=mapped page.

Returns

0 on success, non-zero on failure.

static int mdb_page_search_root (MDB_cursor * mc, MDB_val * key, int flags)[static]

Finish mdb_page_search() / mdb_page_search_lowest(). The cursor is at the root page, set up the rest of it.

static int mdb_page_search (MDB_cursor * mc, MDB_val * key, int flags)[static]

Search for the page a given key should be in. Push it and its parent pages on the cursor stack.

Parameters

mc the cursor for this operation.
key the key to search for, or NULL for first/last page.
flags If MDB_PS_MODIFY is set, visited pages in the DB are touched (updated with new page numbers). If MDB_PS_FIRST or MDB_PS_LAST is set, find first or last leaf. This is used by mdb_cursor_first() and mdb_cursor_last(). If MDB_PS_ROOTONLY set, just fetch root node, no further lookups.

Returns

0 on success, non-zero on failure.

static int mdb_page_merge (MDB_cursor * csrc, MDB_cursor * cdst) [static]

Merge one page into another. The nodes from the page pointed to by csrc will be copied to the page pointed to by cdst and then the csrc page will be freed.

Parameters

csrc Cursor pointing to the source page.
cdst Cursor pointing to the destination page.

Returns

0 on success, non-zero on failure.

static int mdb_page_split (MDB_cursor * mc, MDB_val * newkey, MDB_val *newdata, pgno_t newpgno, unsigned int nflags) [static]

Split a page and insert a new node. Set MDB_TXN_ERROR on failure.

Parameters

mc Cursor pointing to the page and desired insertion index. The cursor will be updated to point to the actual page and index where the node got inserted after the split.
newkey The key for the newly inserted node.
newdata The data for the newly inserted node.
newpgno The page number, if the new node is a branch node.
nflags The NODE_ADD_FLAGS for the new node.

Returns

0 on success, non-zero on failure.

static int ESECT mdb_env_read_header (MDB_env * env, MDB_meta * meta)[static]

Read the environment parameters of a DB environment before mapping it into memory.

Parameters

env the environment handle
meta address of where to store the meta information

Returns

0 on success, non-zero on failure.

static MDB_meta * mdb_env_pick_meta (const MDB_env * env) [static]

Check both meta pages to see which one is newer.

Parameters

env the environment handle

Returns

newest MDB_meta.

static int mdb_env_write_meta (MDB_txn * txn) [static]

Update the environment info to commit a transaction.

Parameters

txn the transaction that’s being committed

Returns

0 on success, non-zero on failure.

static void ESECT mdb_env_close0 (MDB_env * env, int excl) [static]

Destroy resources from mdb_env_open(), clear our readers & DBIs

static MDB_node * mdb_node_search (MDB_cursor * mc, MDB_val * key, int *exactp) [static]

Search for key within a page, using binary search. Returns the smallest entry larger or equal to the key. If exactp is non-null, stores whether the found entry was an exact match in *exactp (1 or 0). Updates the cursor index with the index of the found entry. If no entry larger or equal to the key is found, returns NULL.

static int mdb_node_add (MDB_cursor * mc, indx_t indx, MDB_val * key, MDB_val* data, pgno_t pgno, unsigned int flags) [static]

Add a node to the page pointed to by the cursor. Set MDB_TXN_ERROR on failure.

Parameters

mc The cursor for this operation.
indx The index on the page where the new node should be added.
key The key for the new node.
data The data for the new node, if any.
pgno The page number, if adding a branch node.
flags Flags for the node.

Returns

0 on success, non-zero on failure. Possible errors are:

	•		ENOMEM - failed to allocate overflow pages for the node.
	•		MDB_PAGE_FULL - there is insufficient room in the page. This error should never happen since all callers already calculate the page’s free space before calling this function.

static void mdb_node_del (MDB_cursor * mc, int ksize) [static]

Delete the specified node from a page.
Parameters

mc Cursor pointing to the node to delete.
ksize The size of a node. Only used if the page is part of a MDB_DUPFIXED database.

static void mdb_node_shrink (MDB_page * mp, indx_t indx) [static]

Compact the main page after deleting a node on a subpage.
Parameters

mp The main page to operate on.
indx The index of the subpage on the main page.

static int mdb_node_move (MDB_cursor * csrc, MDB_cursor * cdst, int fromleft)[static]

Move a node from csrc to cdst.

static int mdb_node_read (MDB_cursor * mc, MDB_node * leaf, MDB_val * data)[static]

Return the data associated with a given node.
Parameters

mc The cursor for this operation.
leaf The node being read.
data Updated to point to the node’s data.

Returns

0 on success, non-zero on failure.

static size_t mdb_leaf_size (MDB_env * env, MDB_val * key, MDB_val * data)[static]

Calculate the size of a leaf node. The size depends on the environment’s page size; if a data item is too large it will be put onto an overflow page and the node size will only include the key and not the data. Sizes are always rounded up to an even number of bytes, to guarantee 2-byte alignment of the MDB_node headers.
Parameters

env The environment handle.
key The key for the node.
data The data for the node.

Returns

The number of bytes needed to store the node.

static size_t mdb_branch_size (MDB_env * env, MDB_val * key) [static]

Calculate the size of a branch node. The size should depend on the environment’s page size but since we currently don’t support spilling large keys onto overflow pages, it’s simply the size of the MDB_node header plus the size of the key. Sizes are always rounded up to an even number of bytes, to guarantee 2-byte alignment of the MDB_node headers.
Parameters

env The environment handle.
key The key for the node.

Returns

The number of bytes needed to store the node.

static int mdb_rebalance (MDB_cursor * mc) [static]

Rebalance the tree after a delete operation.
Parameters

mc Cursor pointing to the page where rebalancing should begin.

Returns

0 on success, non-zero on failure.

static int mdb_update_key (MDB_cursor * mc, MDB_val * key) [static]

Replace the key for a branch node with a new key. Set MDB_TXN_ERROR on failure.
Parameters

mc Cursor pointing to the node to operate on.
key The new key to use.

Returns

0 on success, non-zero on failure.

static void mdb_cursor_pop (MDB_cursor * mc) [static]

Pop a page off the top of the cursor’s stack.

static int mdb_cursor_push (MDB_cursor * mc, MDB_page * mp) [static]

Push a page onto the top of the cursor’s stack. Set MDB_TXN_ERROR on failure.

static int mdb_cursor_del0 (MDB_cursor * mc) [static]

Complete a delete operation started by mdb_cursor_del().

static int mdb_cursor_sibling (MDB_cursor * mc, int move_right) [static]

Find a sibling for a page. Replaces the page at the top of the cursor’s stack with the specified sibling, if one exists.
Parameters

mc The cursor for this operation.
move_right Non-zero if the right sibling is requested, otherwise the left sibling.

Returns

0 on success, non-zero on failure.

static int mdb_cursor_next (MDB_cursor * mc, MDB_val * key, MDB_val * data,MDB_cursor_op op) [static]

Move the cursor to the next data item.

static int mdb_cursor_prev (MDB_cursor * mc, MDB_val * key, MDB_val * data,MDB_cursor_op op) [static]

Move the cursor to the previous data item.

static int mdb_cursor_set (MDB_cursor * mc, MDB_val * key, MDB_val * data,MDB_cursor_op op, int * exactp) [static]

Set the cursor on a specific data item.

static int mdb_cursor_first (MDB_cursor * mc, MDB_val * key, MDB_val * data)[static]

Move the cursor to the first item in the database.

static int mdb_cursor_last (MDB_cursor * mc, MDB_val * key, MDB_val * data)[static]

Move the cursor to the last item in the database.

static void mdb_cursor_init (MDB_cursor * mc, MDB_txn * txn, MDB_dbi dbi,MDB_xcursor * mx) [static]

Initialize a cursor for a given transaction and database.

static void mdb_xcursor_init0 (MDB_cursor * mc) [static]

Initial setup of a sorted-dups cursor. Sorted duplicates are implemented as a sub-database for the given key. The duplicate data items are actually keys of the sub-database. Operations on the duplicate data items are performed using a sub-cursor initialized when the sub-database is first accessed. This function does the preliminary setup of the sub-cursor, filling in the fields that depend only on the parent DB.
Parameters

mc The main cursor whose sorted-dups cursor is to be initialized.

static void mdb_xcursor_init1 (MDB_cursor * mc, MDB_node * node) [static]

Final setup of a sorted-dups cursor. Sets up the fields that depend on the data from the main cursor.
Parameters

mc The main cursor whose sorted-dups cursor is to be initialized.
node The data containing the MDB_db record for the sorted-dup database.

static void mdb_xcursor_init2 (MDB_cursor * mc, MDB_xcursor * src_mx, intnew_dupdata) [static]

Fixup a sorted-dups cursor due to underlying update. Sets up some fields that depend on the data from the main cursor. Almost the same as init1, but skips initialization steps if the xcursor had already been used.
Parameters

mc The main cursor whose sorted-dups cursor is to be fixed up.
src_mx The xcursor of an up-to-date cursor.
new_dupdata True if converting from a non-F_DUPDATA item.

static int mdb_drop0 (MDB_cursor * mc, int subs) [static]

Add all the DB’s pages to the free list.
Parameters

mc Cursor on the DB to free.
subs non-Zero to check for sub-DBs in this DB.

Returns

0 on success, non-zero on failure.

static void mdb_default_cmp (MDB_txn * txn, MDB_dbi dbi) [static]

Set the default comparison functions for a database. Called immediately after a database is opened to set the defaults. The user can then override them with mdb_set_compare() or mdb_set_dupsort().
Parameters

txn A transaction handle returned by mdb_txn_begin()
dbi A database handle returned by mdb_dbi_open()

static int ESECT mdb_reader_check0 (MDB_env * env, int rlocked, int * dead)[static]

As mdb_reader_check(). rlocked is set if caller locked me_rmutex.

char* ESECT mdb_version (int * major, int * minor, int * patch)

Return the LMDB library version information. Return the library version info.

char* mdb_strerror (int err)

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 Return Codes for a list of LMDB-specific error codes.
Parameters

err The error code

Return values

error message The description of the error

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. This returns a comparison as if the two data items were keys in the specified database.
Parameters

txn A transaction handle returned by mdb_txn_begin()
dbi A database handle returned by mdb_dbi_open()
a The first item to compare
b The second item to compare

Returns

< 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)

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.
Parameters

txn A transaction handle returned by mdb_txn_begin()
dbi A database handle returned by mdb_dbi_open()
a The first item to compare
b The second item to compare

Returns

< 0 if a < b, 0 if a == b, > 0 if a > b

static MDB_page* mdb_page_malloc (MDB_txn * txn, unsigned num) [static]

Allocate memory for a page. Re-use old malloc’d pages first for singletons, otherwise just malloc. Set MDB_TXN_ERROR on failure.

static void mdb_page_free (MDB_env * env, MDB_page * mp) [static]

Free a single page. Saves single pages to a list, for future reuse. (This is not used for multi-page overflow pages.)

static void mdb_dpage_free (MDB_env * env, MDB_page * dp) [static]

Free a dirty page

static void mdb_dlist_free (MDB_txn * txn) [static]

Return all dirty pages to dpage list

static int mdb_page_loose (MDB_cursor * mc, MDB_page * mp) [static]

Loosen or free a single page. Saves single pages to a list for future reuse in this same txn. It has been pulled from the freeDB and already resides on the dirty list, but has been deleted. Use these pages first before pulling again from the freeDB.
If the page wasn’t dirtied in this txn, just add it to this txn’s free list.

static int mdb_pages_xkeep (MDB_cursor * mc, unsigned pflags, int all)[static]

Set or clear P_KEEP in dirty, non-overflow, non-sub pages watched by txn.
Parameters

mc A cursor handle for the current operation.
pflags Flags of the pages to update: P_DIRTY to set P_KEEP, P_DIRTY|P_KEEP to clear it.
all No shortcuts. Needed except after a full mdb_page_flush().

Returns

0 on success, non-zero on failure.

static int mdb_page_flush (MDB_txn * txn, int keep) [static]

Flush (some) dirty pages to the map, after clearing their dirty flag.
Parameters

txn the transaction that’s being committed
keep number of initial pages in dirty_list to keep dirty.

Returns

0 on success, non-zero on failure.

static int mdb_page_spill (MDB_cursor * m0, MDB_val * key, MDB_val * data)[static]

Spill pages from the dirty list back to disk. This is intended to prevent running into MDB_TXN_FULL situations, but note that they may still occur in a few cases: 1) our estimate of the txn size could be too small. Currently this seems unlikely, except with a large number of MDB_MULTIPLE items. 2) child txns may run out of space if their parents dirtied a lot of pages and never spilled them. TODO: we probably should do a preemptive spill during mdb_txn_begin() of a child txn, if the parent’s dirty_room is below a given threshold.
Otherwise, if not using nested txns, it is expected that apps will not run into MDB_TXN_FULL any more. The pages are flushed to disk the same way as for a txn commit, e.g. their P_DIRTY flag is cleared. If the txn never references them again, they can be left alone. If the txn only reads them, they can be used without any fuss. If the txn writes them again, they can be dirtied immediately without going thru all of the work of mdb_page_touch(). Such references are handled by mdb_page_unspill().
Also note, we never spill DB root pages, nor pages of active cursors, because we’ll need these back again soon anyway. And in nested txns, we can’t spill a page in a child txn if it was already spilled in a parent txn. That would alter the parent txns’ data even though the child hasn’t committed yet, and we’d have no way to undo it if the child aborted.
Parameters

m0 cursor A cursor handle identifying the transaction and database for which we are checking space.
key For a put operation, the key being stored.
data For a put operation, the data being stored.

Returns

0 on success, non-zero on failure.

static txnid_t mdb_find_oldest (MDB_txn * txn) [static]

Find oldest txnid still referenced. Expects txn->mt_txnid > 0.

static void mdb_page_dirty (MDB_txn * txn, MDB_page * mp) [static]

Add a page to the txn’s dirty list

static void mdb_page_copy (MDB_page * dst, MDB_page * src, unsigned intpsize) [static]

Copy the used portions of a non-overflow page.
Parameters

dst page to copy into
src page to copy from
psize size of a page

static int mdb_page_unspill (MDB_txn * txn, MDB_page * mp, MDB_page ** ret)[static]

Pull a page off the txn’s spill list, if present. If a page being referenced was spilled to disk in this txn, bring it back and make it dirty/writable again.
Parameters

txn the transaction handle.
mp the page being referenced. It must not be dirty.
ret the writable page, if any. ret is unchanged if mp wasn’t spilled.

int mdb_env_sync (MDB_env * env, int force)

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.
Parameters

env An environment handle returned by mdb_env_create()
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.

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

	•		EACCES - the environment is read-only.
	•		EINVAL - an invalid parameter was specified.
	•		EIO - an error occurred during synchronization.

static int mdb_cursor_shadow (MDB_txn * src, MDB_txn * dst) [static]

Back up parent txn’s cursors, then grab the originals for tracking

static void mdb_cursors_close (MDB_txn * txn, unsigned merge) [static]

Close this write txn’s cursors, give parent txn’s cursors back to parent.
Parameters

txn the transaction handle.
merge true to keep changes to parent cursors, false to revert.

Returns

0 on success, non-zero on failure.

static int mdb_reader_pid (MDB_env * env, enum Pidlock_op op, MDB_PID_T pid)[static]

Set or check a pid lock. Set returns 0 on success. Check returns 0 if the process is certainly dead, nonzero if it may be alive (the lock exists or an error happened so we do not know).
On Windows Pidset is a no-op, we merely check for the existence of the process with the given pid. On POSIX we use a single byte lock on the lockfile, set at an offset equal to the pid.

static int mdb_txn_renew0 (MDB_txn * txn) [static]

Common code for mdb_txn_begin() and mdb_txn_renew().
Parameters

txn the transaction handle to initialize

Returns

0 on success, non-zero on failure.

int mdb_txn_renew (MDB_txn * txn)

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.
Parameters

txn A transaction handle returned by mdb_txn_begin()

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

	•		MDB_PANIC - a fatal error occurred earlier and the environment must be shut down.
	•		EINVAL - an invalid parameter was specified.

int mdb_txn_begin (MDB_env * env, MDB_txn * parent, unsigned int flags,MDB_txn ** txn)

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.
Cursors may not span transactions.

Parameters

env An environment handle returned by mdb_env_create()
parent If this parameter is non-NULL, the new transaction will be a nested transaction, with the transaction indicated by 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.
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.

•

MDB_RDONLY This transaction will not perform any write operations.

txn Address where the new MDB_txn handle will be stored

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

	•		MDB_PANIC - a fatal error occurred earlier and the environment must be shut down.
	•		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().
	•		MDB_READERS_FULL - a read-only transaction was requested and the reader lock table is full. See mdb_env_set_maxreaders().
	•		ENOMEM - out of memory.

MDB_env* mdb_txn_env (MDB_txn * txn)

Returns the transaction’s MDB_env.
Parameters

txn A transaction handle returned by mdb_txn_begin()

size_t mdb_txn_id (MDB_txn * txn)

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.
Parameters

txn A transaction handle returned by mdb_txn_begin()

Returns

A transaction ID, valid if input is an active transaction.

static void mdb_dbis_update (MDB_txn * txn, int keep) [static]

Export or close DBI handles opened in this txn.

void mdb_txn_reset (MDB_txn * txn)

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.
Parameters

txn A transaction handle returned by mdb_txn_begin()

void mdb_txn_abort (MDB_txn * txn)

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.

Parameters

txn A transaction handle returned by mdb_txn_begin()

static int mdb_freelist_save (MDB_txn * txn) [static]

Save the freelist as of this transaction to the freeDB. This changes the freelist. Keep trying until it stabilizes.

int mdb_txn_commit (MDB_txn * txn)

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.

Parameters

txn A transaction handle returned by mdb_txn_begin()

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

	•		EINVAL - an invalid parameter was specified.
	•		ENOSPC - no more disk space.
	•		EIO - a low-level I/O error occurred while writing.
	•		ENOMEM - out of memory.

static void ESECT mdb_env_init_meta0 (MDB_env * env, MDB_meta * meta)[static]

Fill in most of the zeroed MDB_meta for an empty database environment

static int ESECT mdb_env_init_meta (MDB_env * env, MDB_meta * meta) [static]

Write the environment parameters of a freshly created DB environment.
Parameters

env the environment handle
meta the MDB_meta to write

Returns

0 on success, non-zero on failure.

int ESECT mdb_env_create (MDB_env ** env)

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.
Parameters

env The address where the new handle will be stored

Returns

A non-zero error value on failure and 0 on success.

int ESECT mdb_env_set_mapsize (MDB_env * env, size_t size)

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.
Parameters

env An environment handle returned by mdb_env_create()
size The size in bytes

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - an invalid parameter was specified, or the environment has an active write transaction.

int ESECT mdb_env_set_maxdbs (MDB_env * env, MDB_dbi dbs)

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.
Parameters

env An environment handle returned by mdb_env_create()
dbs The maximum number of databases

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - an invalid parameter was specified, or the environment is already open.

int ESECT mdb_env_set_maxreaders (MDB_env * env, unsigned int readers)

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().
Parameters

env An environment handle returned by mdb_env_create()
readers The maximum number of reader lock table slots

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - an invalid parameter was specified, or the environment is already open.

int ESECT mdb_env_get_maxreaders (MDB_env * env, unsigned int * readers)

Get the maximum number of threads/reader slots for the environment.
Parameters

env An environment handle returned by mdb_env_create()
readers Address of an integer to store the number of readers

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - an invalid parameter was specified.

static int ESECT mdb_fname_init (const char * path, unsigned envflags,MDB_name * fname) [static]

Set up filename + scratch area for filename suffix, for opening files. It should be freed with mdb_fname_destroy(). On Windows, paths are converted from char *UTF-8 to wchar_t *UTF-16.
Parameters

path Pathname for mdb_env_open().
envflags Whether a subdir and/or lockfile will be used.
fname Resulting filename, with room for a suffix if necessary.

static int ESECT mdb_fopen (const MDB_env * env, MDB_name * fname, enummdb_fopen_type which, mdb_mode_t mode, HANDLE * res) [static]

Open an LMDB file.
Parameters

env The LMDB environment.
fname Path from from mdb_fname_init(). A suffix is appended if necessary to create the filename, without changing mn_len.
which Determines file type, access mode, etc.
mode The Unix permissions for the file, if we create it.
res Resulting file handle.

Returns

0 on success, non-zero on failure.

static int ESECT mdb_env_open2 (MDB_env * env) [static]

Further setup required for opening an LMDB environment

static void mdb_env_reader_dest (void * ptr) [static]

Release a reader thread’s slot in the reader lock table. This function is called automatically when a thread exits.
Parameters

ptr This points to the slot in the reader lock table.

static int ESECT mdb_env_share_locks (MDB_env * env, int * excl) [static]

Downgrade the exclusive lock on the region back to shared

static int ESECT mdb_env_excl_lock (MDB_env * env, int * excl) [static]

Try to get exclusive lock, otherwise shared. Maintain *excl = -1: no/unknown lock, 0: shared, 1: exclusive.

static int ESECT mdb_env_setup_locks (MDB_env * env, MDB_name * fname, intmode, int * excl) [static]

Open and/or initialize the lock region for the environment.
Parameters

env The LMDB environment.
fname Filename + scratch area, from mdb_fname_init().
mode The Unix permissions for the file, if we create it.
excl In -1, out lock type: -1 none, 0 shared, 1 exclusive

Returns

0 on success, non-zero on failure.

int ESECT mdb_env_open (MDB_env * env, const char * path, unsigned int flags,mdb_mode_t mode)

Open an environment handle. If this function fails, mdb_env_close() must be called to discard the MDB_env handle.
Parameters

env An environment handle returned by mdb_env_create()
path The directory in which the database files reside. This directory must already exist and be writable.
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.

	•		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.
	•		MDB_NOSUBDIR By default, LMDB creates its environment in a directory whose pathname is given in path, and creates its data and lock files under that directory. With this option, path is used as-is for the database main data file. The database lock file is the path with ’-lock’ appended.
	•		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.
	•		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).
	•		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().
	•		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().
	•		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().
	•		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.
	•		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.
	•		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.
	•		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().

mode The UNIX permissions to set on created files and semaphores. This parameter is ignored on Windows.

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

	•		MDB_VERSION_MISMATCH - the version of the LMDB library doesn’t match the version that created the database environment.
	•		MDB_INVALID - the environment file headers are corrupted.
	•		ENOENT - the directory specified by the path parameter doesn’t exist.
	•		EACCES - the user didn’t have permission to access the environment files.
	•		EAGAIN - the environment was locked by another process.

void ESECT mdb_env_close (MDB_env * env)

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.
Parameters

env An environment handle returned by mdb_env_create()

static int mdb_cmp_long (const MDB_val * a, const MDB_val * b) [static]

Compare two items pointing at aligned size_t’s

static int mdb_cmp_int (const MDB_val * a, const MDB_val * b) [static]

Compare two items pointing at aligned unsigned int’s.
This is also set as MDB_INTEGERDUP|MDB_DUPFIXED’s MDB_dbx.md_dcmp, but mdb_cmp_clong() is called instead if the data type is size_t.

static int mdb_cmp_cint (const MDB_val * a, const MDB_val * b) [static]

Compare two items pointing at unsigned ints of unknown alignment. Nodes and keys are guaranteed to be 2-byte aligned.

static int mdb_cmp_memn (const MDB_val * a, const MDB_val * b) [static]

Compare two items lexically

static int mdb_cmp_memnr (const MDB_val * a, const MDB_val * b) [static]

Compare two items in reverse byte order

static int mdb_page_search_lowest (MDB_cursor * mc) [static]

Search for the lowest key under the current branch page. This just bypasses a NUMKEYS check in the current page before calling mdb_page_search_root(), because the callers are all in situations where the current page is known to be underfilled.

int mdb_get (MDB_txn * txn, MDB_dbi dbi, MDB_val * key, MDB_val * data)

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 key are returned in the structure to which 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.
Values returned from the database are valid only until a subsequent update operation, or the end of the transaction.

Parameters

txn A transaction handle returned by mdb_txn_begin()
dbi A database handle returned by mdb_dbi_open()
key The key to search for in the database
data The data corresponding to the key

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

	•		MDB_NOTFOUND - the key was not in the database.
	•		EINVAL - an invalid parameter was specified.

int mdb_cursor_get (MDB_cursor * cursor, MDB_val * key, MDB_val * data,MDB_cursor_op op)

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 key refers (except for the case of the MDB_SET option, in which the key object is unchanged), and the address and length of the data are returned in the object to which data refers. See mdb_get() for restrictions on using the output values.
Parameters

cursor A cursor handle returned by mdb_cursor_open()
key The key for a retrieved item
data The data of a retrieved item
op A cursor operation MDB_cursor_op

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

	•		MDB_NOTFOUND - no matching key found.
	•		EINVAL - an invalid parameter was specified.

static int mdb_cursor_touch (MDB_cursor * mc) [static]

Touch all the pages in the cursor stack. Set mc_top. Makes sure all the pages are writable, before attempting a write operation.
Parameters

mc The cursor to operate on.

int mdb_cursor_put (MDB_cursor * cursor, MDB_val * key, MDB_val * data,unsigned int flags)

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.

Parameters

cursor A cursor handle returned by mdb_cursor_open()
key The key operated on.
data The data operated on.
flags Options for this operation. This parameter must be set to 0 or one of the values described here.

	•		MDB_CURRENT - replace the item at the current cursor position. The 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.
	•		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.
	•		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).
	•		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.
	•		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.
	•		MDB_APPENDDUP - as above, but for sorted dup data.
	•		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 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.

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

	•		MDB_MAP_FULL - the database is full, see mdb_env_set_mapsize().
	•		MDB_TXN_FULL - the transaction has too many dirty pages.
	•		EACCES - an attempt was made to write in a read-only transaction.
	•		EINVAL - an invalid parameter was specified.

int mdb_cursor_del (MDB_cursor * cursor, unsigned int flags)

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.
Parameters

cursor A cursor handle returned by mdb_cursor_open()
flags Options for this operation. This parameter must be set to 0 or one of the values described here.

•

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.

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

	•		EACCES - an attempt was made to write in a read-only transaction.
	•		EINVAL - an invalid parameter was specified.

int mdb_cursor_open (MDB_txn * txn, MDB_dbi dbi, MDB_cursor ** cursor)

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.

Parameters

txn A transaction handle returned by mdb_txn_begin()
dbi A database handle returned by mdb_dbi_open()
cursor Address where the new MDB_cursor handle will be stored

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - an invalid parameter was specified.

int mdb_cursor_renew (MDB_txn * txn, MDB_cursor * cursor)

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.
Parameters

txn A transaction handle returned by mdb_txn_begin()
cursor A cursor handle returned by mdb_cursor_open()

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - an invalid parameter was specified.

int mdb_cursor_count (MDB_cursor * cursor, size_t * countp)

Return count of duplicates for current key. This call is only valid on databases that support sorted duplicate data items MDB_DUPSORT.
Parameters

cursor A cursor handle returned by mdb_cursor_open()
countp Address where the count will be stored

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - cursor is not initialized, or an invalid parameter was specified.

void mdb_cursor_close (MDB_cursor * cursor)

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.
Parameters

cursor A cursor handle returned by mdb_cursor_open()

MDB_txn* mdb_cursor_txn (MDB_cursor * cursor)

Return the cursor’s transaction handle.
Parameters

cursor A cursor handle returned by mdb_cursor_open()

MDB_dbi mdb_cursor_dbi (MDB_cursor * cursor)

Return the cursor’s database handle.
Parameters

cursor A cursor handle returned by mdb_cursor_open()

static void mdb_cursor_copy (const MDB_cursor * csrc, MDB_cursor * cdst)[static]

Copy the contents of a cursor.
Parameters

csrc The cursor to copy from.
cdst The cursor to copy to.

int mdb_del (MDB_txn * txn, MDB_dbi dbi, MDB_val * key, MDB_val * data)

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.
Parameters

txn A transaction handle returned by mdb_txn_begin()
dbi A database handle returned by mdb_dbi_open()
key The key to delete from the database
data The data to delete

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

	•		EACCES - an attempt was made to write in a read-only transaction.
	•		EINVAL - an invalid parameter was specified.

int mdb_put (MDB_txn * txn, MDB_dbi dbi, MDB_val * key, MDB_val * data,unsigned int flags)

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).
Parameters

txn A transaction handle returned by mdb_txn_begin()
dbi A database handle returned by mdb_dbi_open()
key The key to store in the database
data The data to store
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.

	•		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.
	•		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 data parameter will be set to point to the existing item.
	•		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.
	•		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.
	•		MDB_APPENDDUP - as above, but for sorted dup data.

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

	•		MDB_MAP_FULL - the database is full, see mdb_env_set_mapsize().
	•		MDB_TXN_FULL - the transaction has too many dirty pages.
	•		EACCES - an attempt was made to write in a read-only transaction.
	•		EINVAL - an invalid parameter was specified.

static THREAD_RET ESECT CALL_CONV mdb_env_copythr (void * arg) [static]

Dedicated writer thread for compacting copy.

static int ESECT mdb_env_cthr_toggle (mdb_copy * my, int adjust) [static]

Give buffer and/or MDB_EOF to writer thread, await unused buffer.
Parameters

my control structure.
adjust (1 to hand off 1 buffer) | (MDB_EOF when ending).

static int ESECT mdb_env_cwalk (mdb_copy * my, pgno_t * pg, int flags)[static]

Depth-first tree traversal for compacting copy.
Parameters

my control structure.
pg database root.
flags includes F_DUPDATA if it is a sorted-duplicate sub-DB.

static int ESECT mdb_env_copyfd1 (MDB_env * env, HANDLE fd) [static]

Copy environment with compaction.

static int ESECT mdb_env_copyfd0 (MDB_env * env, HANDLE fd) [static]

Copy environment as-is.

int ESECT mdb_env_copy2 (MDB_env * env, const char * path, unsigned intflags)

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 Caveats.

Parameters

env An environment handle returned by mdb_env_create(). It must have already been opened successfully.
path The directory in which the copy will reside. This directory must already exist and be writable but must otherwise be empty.
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.

•

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.

Returns

A non-zero error value on failure and 0 on success.

int ESECT mdb_env_copy (MDB_env * env, const char * path)

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 Caveats.

Parameters

env An environment handle returned by mdb_env_create(). It must have already been opened successfully.
path The directory in which the copy will reside. This directory must already exist and be writable but must otherwise be empty.

Returns

A non-zero error value on failure and 0 on success.

int ESECT mdb_env_set_flags (MDB_env * env, unsigned int flags, int onoff)

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.
Parameters

env An environment handle returned by mdb_env_create()
flags The flags to change, bitwise OR’ed together
onoff A non-zero value sets the flags, zero clears them.

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - an invalid parameter was specified.

int ESECT mdb_env_get_flags (MDB_env * env, unsigned int * flags)

Get environment flags.
Parameters

env An environment handle returned by mdb_env_create()
flags The address of an integer to store the flags

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - an invalid parameter was specified.

int ESECT mdb_env_set_userctx (MDB_env * env, void * ctx)

Set application information associated with the MDB_env.
Parameters

env An environment handle returned by mdb_env_create()
ctx An arbitrary pointer for whatever the application needs.

Returns

A non-zero error value on failure and 0 on success.

void* ESECT mdb_env_get_userctx (MDB_env * env)

Get the application information associated with the MDB_env.
Parameters

env An environment handle returned by mdb_env_create()

Returns

The pointer set by mdb_env_set_userctx().

int ESECT mdb_env_set_assert (MDB_env * env, MDB_assert_func * func)

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.

Parameters

env An environment handle returned by mdb_env_create().
func An MDB_assert_func function, or 0.

Returns

A non-zero error value on failure and 0 on success.

int ESECT mdb_env_get_path (MDB_env * env, const char ** path)

Return the path that was used in mdb_env_open().
Parameters

env An environment handle returned by mdb_env_create()
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.

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - an invalid parameter was specified.

int ESECT mdb_env_get_fd (MDB_env * env, mdb_filehandle_t * fd)

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.)
Parameters

env An environment handle returned by mdb_env_create()
fd Address of a mdb_filehandle_t to contain the descriptor.

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - an invalid parameter was specified.

static int ESECT mdb_stat0 (MDB_env * env, MDB_db * db, MDB_stat * arg)[static]

Common code for mdb_stat() and mdb_env_stat().
Parameters

env the environment to operate in.
db the MDB_db record containing the stats to return.
arg the address of an MDB_stat structure to receive the stats.

Returns

0, this function always succeeds.

int ESECT mdb_env_stat (MDB_env * env, MDB_stat * stat)

Return statistics about the LMDB environment.
Parameters

env An environment handle returned by mdb_env_create()
stat The address of an MDB_stat structure where the statistics will be copied

int ESECT mdb_env_info (MDB_env * env, MDB_envinfo * stat)

Return information about the LMDB environment.
Parameters

env An environment handle returned by mdb_env_create()
stat The address of an MDB_envinfo structure where the information will be copied

int mdb_dbi_open (MDB_txn * txn, const char * name, unsigned int flags,MDB_dbi * dbi)

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.
Parameters

txn A transaction handle returned by mdb_txn_begin()
name The name of the database to open. If only a single database is needed in the environment, this value may be NULL.
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.

	•		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.
	•		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.
	•		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.
	•		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.
	•		MDB_INTEGERDUP This option specifies that duplicate data items are binary integers, similar to MDB_INTEGERKEY keys.
	•		MDB_REVERSEDUP This option specifies that duplicate data items should be compared as strings in reverse order.
	•		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.

dbi Address where the new MDB_dbi handle will be stored

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

	•		MDB_NOTFOUND - the specified database doesn’t exist in the environment and MDB_CREATE was not specified.
	•		MDB_DBS_FULL - too many databases have been opened. See mdb_env_set_maxdbs().

int ESECT mdb_stat (MDB_txn * txn, MDB_dbi dbi, MDB_stat * stat)

Retrieve statistics for a database.
Parameters

txn A transaction handle returned by mdb_txn_begin()
dbi A database handle returned by mdb_dbi_open()
stat The address of an MDB_stat structure where the statistics will be copied

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - an invalid parameter was specified.

void mdb_dbi_close (MDB_env * env, MDB_dbi dbi)

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.
Parameters

env An environment handle returned by mdb_env_create()
dbi A database handle returned by mdb_dbi_open()

int mdb_dbi_flags (MDB_txn * txn, MDB_dbi dbi, unsigned int * flags)

Retrieve the DB flags for a database handle.
Parameters

txn A transaction handle returned by mdb_txn_begin()
dbi A database handle returned by mdb_dbi_open()
flags Address where the flags will be returned.

Returns

A non-zero error value on failure and 0 on success.

int mdb_drop (MDB_txn * txn, MDB_dbi dbi, int del)

Empty or delete+close a database. See mdb_dbi_close() for restrictions about closing the DB handle.
Parameters

txn A transaction handle returned by mdb_txn_begin()
dbi A database handle returned by mdb_dbi_open()
del 0 to empty the DB, 1 to delete it from the environment and close the DB handle.

Returns

A non-zero error value on failure and 0 on success.

int mdb_set_compare (MDB_txn * txn, MDB_dbi dbi, MDB_cmp_func * cmp)

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.

Parameters

txn A transaction handle returned by mdb_txn_begin()
dbi A database handle returned by mdb_dbi_open()
cmp A MDB_cmp_func function

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - an invalid parameter was specified.

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. 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.

Parameters

txn A transaction handle returned by mdb_txn_begin()
dbi A database handle returned by mdb_dbi_open()
cmp A MDB_cmp_func function

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - an invalid parameter was specified.

int mdb_set_relfunc (MDB_txn * txn, MDB_dbi dbi, MDB_rel_func * rel)

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.

Parameters

txn A transaction handle returned by mdb_txn_begin()
dbi A database handle returned by mdb_dbi_open()
rel A MDB_rel_func function

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - an invalid parameter was specified.

int mdb_set_relctx (MDB_txn * txn, MDB_dbi dbi, void * ctx)

Set a context pointer for a MDB_FIXEDMAP database’s relocation function. See mdb_set_relfunc and MDB_rel_func for more details.
Parameters

txn A transaction handle returned by mdb_txn_begin()
dbi A database handle returned by mdb_dbi_open()
ctx An arbitrary pointer for whatever the application needs. It will be passed to the callback function set by mdb_set_relfunc as its relctx parameter whenever the callback is invoked.

Returns

A non-zero error value on failure and 0 on success. Some possible errors are:

•

EINVAL - an invalid parameter was specified.

int ESECT mdb_env_get_maxkeysize (MDB_env * env)

Get the maximum size of keys and MDB_DUPSORT data we can write. Depends on the compile-time constant MDB_MAXKEYSIZE. Default 511. See MDB_val.
Parameters

env An environment handle returned by mdb_env_create()

Returns

The maximum size of a key we can write

int ESECT mdb_reader_list (MDB_env * env, MDB_msg_func * func, void * ctx)

Dump the entries in the reader lock table.
Parameters

env An environment handle returned by mdb_env_create()
func A MDB_msg_func function
ctx Anything the message function needs

Returns

< 0 on failure, >= 0 on success.

static int ESECT mdb_pid_insert (MDB_PID_T * ids, MDB_PID_T pid) [static]

Insert pid into list if not already present. return -1 if already present.

int ESECT mdb_reader_check (MDB_env * env, int * dead)

Check for stale entries in the reader lock table.
Parameters

env An environment handle returned by mdb_env_create()
dead Number of stale slots that were cleared

Returns

0 on success, non-zero on failure.

Variable Documentation

char* const mdb_errstr[] [static]

Initial value:
= {
"MDB_KEYEXIST: Key/data pair already exists",
"MDB_NOTFOUND: No matching key/data pair found",
"MDB_PAGE_NOTFOUND: Requested page not found",
"MDB_CORRUPTED: Located page was wrong type",
"MDB_PANIC: Update of meta page failed or environment had fatal error",
"MDB_VERSION_MISMATCH: Database environment version mismatch",
"MDB_INVALID: File is not an LMDB file",
"MDB_MAP_FULL: Environment mapsize limit reached",
"MDB_DBS_FULL: Environment maxdbs limit reached",
"MDB_READERS_FULL: Environment maxreaders limit reached",
"MDB_TLS_FULL: Thread-local storage keys full - too many environments open",
"MDB_TXN_FULL: Transaction has too many dirty pages - transaction too big",
"MDB_CURSOR_FULL: Internal error - cursor stack limit reached",
"MDB_PAGE_FULL: Internal error - page has no more space",
"MDB_MAP_RESIZED: Database contents grew beyond environment mapsize",
"MDB_INCOMPATIBLE: Operation and DB incompatible, or DB flags changed",
"MDB_BAD_RSLOT: Invalid reuse of reader locktable slot",
"MDB_BAD_TXN: Transaction must abort, has a child, or is invalid",
"MDB_BAD_VALSIZE: Unsupported size of key/DB name/data, or wrong DUPFIXED size",
"MDB_BAD_DBI: The specified DBI handle was closed/changed unexpectedly",
}
Table of descriptions for LMDB Return Codes

const mdb_nchar_t* const mdb_suffixes[2][2] [static]

Initial value:
= {
{ MDB_NAME("/data.mdb"), MDB_NAME("") },
{ MDB_NAME("/lock.mdb"), MDB_NAME("-lock") }
}
Filename suffixes [datafile,lockfile][without,with MDB_NOSUBDIR]

Author

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