Modules
	ID List Management

	Compatibility Macros

	Debug Macros

	Reader Lock Table

	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. More...

struct	MDB_cursor
	Opaque structure for navigating through a database. More...

struct	MDB_xcursor

struct	MDB_pgstate

struct	MDB_env
	Opaque structure for a database environment. More...

struct	MDB_ntxn

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	MDB_COMMIT_PAGES 64

#define	MAX_WRITE (0x80000000U >> (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	LOCKNAME "/lock.mdb"

#define	DATANAME "/data.mdb"

#define	LOCKSUFF "-lock"

#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)

Typedefs
typedef MDB_ID	pgno_t

typedef MDB_ID	txnid_t

typedef uint16_t	indx_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 }

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_txn txn, 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_txn txn, 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_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, char lpath, 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 st)

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 []

Detailed Description

Data Structure Documentation

struct MDB_page

Common header for all page types. Overflow records occupy a number of contiguous pages with no headers on any page after the first.

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_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.

Data Fields
unsigned short	mn_lo

unsigned short	mn_hi

unsigned short	mn_flags

unsigned short	mn_ksize

char	mn_data [1]

Field Documentation

unsigned short MDB_node::mn_lo

lo and hi are used for data size on leaf nodes and for child pgno on branch nodes. On 64 bit platforms, flags is also used for pgno. (Branch nodes have no flags). They are in host byte order in case that lets some accesses be optimized into a 32-bit word access.

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 file

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).

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

just for writing 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_copy

State needed for a compacting copy.

Data Fields
pthread_mutex_t	mc_mutex

pthread_cond_t	mc_cond

char *	mc_wbuf [2]

char *	mc_over [2]

MDB_env *	mc_env

MDB_txn *	mc_txn

int	mc_wlen [2]

int	mc_olen [2]

pgno_t	mc_next_pgno

HANDLE	mc_fd

int	mc_status

volatile int	mc_new

int	mc_toggle

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

#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

mdb_dbi_open flags 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)

#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 2^32 nodes with minimum of 2 keys per node. I.e., plenty. At 4 keys per node, enough for 2^64 nodes, so there's probably no need to raise this on a 64 bit machine.

#define MDB_COMMIT_PAGES 64

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

#define MAX_WRITE (0x80000000U >> (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 LOCKNAME "/lock.mdb"

The name of the lock file in the DB environment

#define DATANAME "/data.mdb"

The name of the data file in the DB environment

#define LOCKSUFF "-lock"

The suffix of the lock file when no subdir is used

#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

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.

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.

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

[in]	mc	cursor A cursor handle identifying the transaction and database for which we are allocating.
[in]	num	the number of pages to allocate.
[out]	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.

Parameters

[in]	mc	a cursor on the database being added to.
[in]	flags	flags defining what type of page is being allocated.
[in]	num	the number of pages to allocate. This is usually 1, unless allocating overflow pages for a large record.
[out]	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.

Parameters

[in] 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

[in]	txn	the transaction handle to end
[in]	mode	why and how to end the transaction

static int mdb_page_get	(	MDB_txn *	txn,
		pgno_t	pgno,
		MDB_page **	ret,
		int *	lvl
	)

static

Find the address of the page corresponding to a given page number.

Parameters

[in]	txn	the transaction for this access.
[in]	pgno	the page number for the page to retrieve.
[out]	ret	address of a pointer where the page's address will be stored.
[out]	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

[in,out]	mc	the cursor for this operation.
[in]	key	the key to search for, or NULL for first/last page.
[in]	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

[in]	csrc	Cursor pointing to the source page.
[in]	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.

Parameters

[in,out]	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.
[in]	newkey	The key for the newly inserted node.
[in]	newdata	The data for the newly inserted node.
[in]	newpgno	The page number, if the new node is a branch node.
[in]	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

[in]	env	the environment handle
[out]	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

[in] 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

[in] 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.

Parameters

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

[in]	mc	Cursor pointing to the node to delete.
[in]	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

[in]	mp	The main page to operate on.
[in]	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_txn *	txn,
		MDB_node *	leaf,
		MDB_val *	data
	)

static

Return the data associated with a given node.

Parameters

[in]	txn	The transaction for this operation.
[in]	leaf	The node being read.
[out]	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

[in]	env	The environment handle.
[in]	key	The key for the node.
[in]	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

[in]	env	The environment handle.
[in]	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

[in] 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.

Parameters

[in]	mc	Cursor pointing to the node to operate on.
[in]	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.

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

[in]	mc	The cursor for this operation.
[in]	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

[in] 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

[in]	mc	The main cursor whose sorted-dups cursor is to be initialized.
[in]	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,
		int	new_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

[in]	mc	The main cursor whose sorted-dups cursor is to be fixed up.
[in]	src_mx	The xcursor of an up-to-date cursor.
[in]	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

[in]	mc	Cursor on the DB to free.
[in]	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

[in]	txn	A transaction handle returned by mdb_txn_begin()
[in]	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 = <caller locked="" the="" reader="" mutex>="">.

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

[in] 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

[in]	txn	A transaction handle returned by mdb_txn_begin()
[in]	dbi	A database handle returned by mdb_dbi_open()
[in]	a	The first item to compare
[in]	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

[in]	txn	A transaction handle returned by mdb_txn_begin()
[in]	dbi	A database handle returned by mdb_dbi_open()
[in]	a	The first item to compare
[in]	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.

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

[in]	mc	A cursor handle for the current operation.
[in]	pflags	Flags of the pages to update: P_DIRTY to set P_KEEP, P_DIRTY\|P_KEEP to clear it.
[in]	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

[in]	txn	the transaction that's being committed
[in]	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

[in]	m0	cursor A cursor handle identifying the transaction and database for which we are checking space.
[in]	key	For a put operation, the key being stored.
[in]	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 int	psize
	)

static

Copy the used portions of a non-overflow page.

Parameters

[in]	dst	page to copy into
[in]	src	page to copy from
[in]	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

[in]	txn	the transaction handle.
[in]	mp	the page being referenced. It must not be dirty.
[out]	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

[in]	env	An environment handle returned by mdb_env_create()
[in]	force	If non-zero, force a synchronous flush. Otherwise if the environment has the MDB_NOSYNC flag set the flushes will be omitted, and with MDB_MAPASYNC they will be asynchronous.

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

[in]	txn	the transaction handle.
[in]	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

[in] 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

[in] 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

[in]	env	An environment handle returned by mdb_env_create()
[in]	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.
[in]	flags	Special options for this transaction. This parameter must be set to 0 or by bitwise OR'ing together one or more of the values described here. MDB_RDONLY This transaction will not perform any write operations.
[out]	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

[in] 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

[in] 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

[in] 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

[in] 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

[in] 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

[in]	env	the environment handle
[in]	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

[out] 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

[in]	env	An environment handle returned by mdb_env_create()
[in]	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

[in]	env	An environment handle returned by mdb_env_create()
[in]	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

[in]	env	An environment handle returned by mdb_env_create()
[in]	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

[in]	env	An environment handle returned by mdb_env_create()
[out]	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_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

[in] 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,
		char *	lpath,
		int	mode,
		int *	excl
	)

static

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

Parameters

[in]	env	The LMDB environment.
[in]	lpath	The pathname of the file used for the lock region.
[in]	mode	The Unix permissions for the file, if we create it.
[in,out]	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

[in]	env	An environment handle returned by mdb_env_create()
[in]	path	The directory in which the database files reside. This directory must already exist and be writable.
[in]	flags	Special options for this environment. This parameter must be set to 0 or by bitwise OR'ing together one or more of the values described here. Flags set by mdb_env_set_flags() are also used. 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 is faster and uses fewer mallocs, but loses protection from application bugs like wild pointer writes and other bad updates into the database. 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().
[in]	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

[in] 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

[in]	txn	A transaction handle returned by mdb_txn_begin()
[in]	dbi	A database handle returned by mdb_dbi_open()
[in]	key	The key to search for in the database
[out]	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

[in]	cursor	A cursor handle returned by mdb_cursor_open()
[in,out]	key	The key for a retrieved item
[in,out]	data	The data of a retrieved item
[in]	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

[in] 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

[in]	cursor	A cursor handle returned by mdb_cursor_open()
[in]	key	The key operated on.
[in]	data	The data operated on.
[in]	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. 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.

Parameters

[in]	cursor	A cursor handle returned by mdb_cursor_open()
[in]	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

[in]	txn	A transaction handle returned by mdb_txn_begin()
[in]	dbi	A database handle returned by mdb_dbi_open()
[out]	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

[in]	txn	A transaction handle returned by mdb_txn_begin()
[in]	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

[in]	cursor	A cursor handle returned by mdb_cursor_open()
[out]	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

[in] cursor A cursor handle returned by mdb_cursor_open()

MDB_txn* mdb_cursor_txn ( MDB_cursor * cursor )

Return the cursor's transaction handle.

Parameters

[in] cursor A cursor handle returned by mdb_cursor_open()

MDB_dbi mdb_cursor_dbi ( MDB_cursor * cursor )

Return the cursor's database handle.

Parameters

[in] 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

[in]	csrc	The cursor to copy from.
[out]	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

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

[in]	txn	A transaction handle returned by mdb_txn_begin()
[in]	dbi	A database handle returned by mdb_dbi_open()
[in]	key	The key to store in the database
[in,out]	data	The data to store
[in]	flags	Special options for this operation. This parameter must be set to 0 or by bitwise OR'ing together one or more of the values described here. 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	st
	)

static

Tell the writer thread there's a buffer ready to write

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

static

Depth-first tree traversal for compacting copy.

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 int	flags
	)

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

[in]	env	An environment handle returned by mdb_env_create(). It must have already been opened successfully.
[in]	path	The directory in which the copy will reside. This directory must already exist and be writable but must otherwise be empty.
[in]	flags	Special options for this operation. This parameter must be set to 0 or by bitwise OR'ing together one or more of the values described here. 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.

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

[in]	env	An environment handle returned by mdb_env_create(). It must have already been opened successfully.
[in]	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

[in]	env	An environment handle returned by mdb_env_create()
[in]	flags	The flags to change, bitwise OR'ed together
[in]	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

[in]	env	An environment handle returned by mdb_env_create()
[out]	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

[in]	env	An environment handle returned by mdb_env_create()
[in]	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

[in] 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

[in]	env	An environment handle returned by mdb_env_create().
[in]	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

[in]	env	An environment handle returned by mdb_env_create()
[out]	path	Address of a string pointer to contain the path. This is the actual string in the environment, not a copy. It should not be altered in any way.

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.

Parameters

[in]	env	An environment handle returned by mdb_env_create()
[out]	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

[in]	env	the environment to operate in.
[in]	db	the MDB_db record containing the stats to return.
[out]	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

[in]	env	An environment handle returned by mdb_env_create()
[out]	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

[in]	env	An environment handle returned by mdb_env_create()
[out]	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

[in]	txn	A transaction handle returned by mdb_txn_begin()
[in]	name	The name of the database to open. If only a single database is needed in the environment, this value may be NULL.
[in]	flags	Special options for this database. This parameter must be set to 0 or by bitwise OR'ing together one or more of the values described here. 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 and MDB_NEXT_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.
[out]	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

[in]	txn	A transaction handle returned by mdb_txn_begin()
[in]	dbi	A database handle returned by mdb_dbi_open()
[out]	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

[in]	env	An environment handle returned by mdb_env_create()
[in]	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

[in]	txn	A transaction handle returned by mdb_txn_begin()
[in]	dbi	A database handle returned by mdb_dbi_open()
[out]	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

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

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

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

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

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

[in] 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

[in]	env	An environment handle returned by mdb_env_create()
[in]	func	A MDB_msg_func function
[in]	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

[in]	env	An environment handle returned by mdb_env_create()
[out]	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",
}

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