LMDB Internals

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

Modules

 ID List Management
 Compatibility Macros
 Debug Macros
 Reader Lock Table
 Page Flags
 Node Flags
 Transaction DB Flags
 Transaction Flags
 Cursor Flags

Defines

#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)
#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   (0x40000000U >> (sizeof(ssize_t) == 4))
#define TXN_DBI_EXIST(txn, dbi, validity)   ((txn) && (dbi)<(txn)->mt_numdbs && ((txn)->mt_dbflags[dbi] & (validity)))
#define TXN_DBI_CHANGED(txn, dbi)   ((txn)->mt_dbiseqs[dbi] != (txn)->mt_env->me_dbiseqs[dbi])
#define MDB_END_NAMES
#define MDB_END_OPMASK   0x0F
#define MDB_END_UPDATE   0x10
#define MDB_END_FREE   0x20
#define MDB_END_SLOT   MDB_NOTLS
#define MDB_PS_MODIFY   1
#define MDB_PS_ROOTONLY   2
#define MDB_PS_FIRST   4
#define MDB_PS_LAST   8
#define MDB_SPLIT_REPLACE   MDB_APPENDDUP
#define mdb_env_close0(env, excl)   mdb_env_close1(env)

Typedefs

typedef MDB_ID pgno_t
typedef MDB_ID txnid_t
typedef uint16_t indx_t
typedef unsigned long long mdb_hash_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, Pidset = F_SETLK, Pidcheck = F_GETLK }
enum  Pidlock_op { Pidset = F_SETLK, Pidcheck = F_GETLK, 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_metamdb_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_nodemdb_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)
static int utf8_to_utf16 (const char *src, int srcsize, wchar_t **dst, int *dstsize)
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)
static pgno_t mdb_dbg_pgno (MDB_page *mp)
char * mdb_dkey (MDB_val *key, char *buf)
static const char * mdb_leafnode_type (MDB_node *n)
void mdb_page_list (MDB_page *mp)
void mdb_cursor_chk (MDB_cursor *mc)
static void mdb_audit (MDB_txn *txn)
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_pagemdb_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_envmdb_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 void NTAPI mdb_tls_callback (PVOID module, DWORD reason, PVOID ptr)
const PIMAGE_TLS_CALLBACK
mdb_tls_cbp 
__attribute__ ((section(".CRT$XLB"))) = mdb_tls_callback
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 mdb_hash_t mdb_hash_val (MDB_val *val, mdb_hash_t hval)
static void ESECT mdb_pack85 (unsigned long l, char *out)
static void ESECT mdb_hash_enc (MDB_val *val, char *encbuf)
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 void mdb_cursor_adjust (MDB_cursor *mc, func)
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_txnmdb_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.
static int ESECT mdb_mutex_failed (MDB_env *env, mdb_mutexref_t mutex, int rc)

Variables

static SECURITY_DESCRIPTOR mdb_null_sd
static SECURITY_ATTRIBUTES mdb_all_sa
static int mdb_sec_inited
static char *const mdb_errstr []
static pthread_key_t mdb_tls_keys [MAX_TLS_KEYS]
static int mdb_tls_nkeys
const PIMAGE_TLS_CALLBACK mdb_tls_cbp = mdb_tls_callback
static const char mdb_a85 [] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~"

Define 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,
 )     (((w) & (f)) == (f))

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

#define EVEN (  )     (((n) + 1U) & -2)

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 (  )     ((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)->mp_lower - (PAGEHDRSZ-PAGEBASE)) >> 1)

Number of nodes on a page

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

The amount of space remaining in the page

#define PAGEFILL ( env,
 ) 
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 (  )     F_ISSET((p)->mp_flags, P_LEAF)

Test if a page is a leaf page

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

Test if a page is a LEAF2 page

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

Test if a page is a branch page

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

Test if a page is an overflow page

#define IS_SUBP (  )     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 (  )     (*(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 (  )     (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,
 )     (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,
 )     ((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
#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   (0x40000000U >> (sizeof(ssize_t) == 4))

max bytes to write in one call

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

Check txn and dbi arguments to a function

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

Check for misused dbi handles

#define MDB_END_NAMES
Value:
{"committed", "empty-commit", "abort", "reset", \
    "reset-tmp", "fail-begin", "fail-beginchild"}
#define MDB_END_OPMASK   0x0F

mask for mdb_txn_end() operation number

#define MDB_END_UPDATE   0x10

update env state (DBIs)

#define MDB_END_FREE   0x20

free txn unless it is MDB_env.me_txn0

#define MDB_END_SLOT   MDB_NOTLS

release any reader slot if MDB_NOTLS

#define MDB_SPLIT_REPLACE   MDB_APPENDDUP

newkey is not new


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

HACK: pad 4KB on stack over the buf. Return system msgs in buf. This works as long as no function between the call to mdb_strerror and the actual use of the message uses more than 4K of stack.

static pgno_t mdb_dbg_pgno ( MDB_page mp  )  [static]

Return the page number of mp which may be sub-page, for debug output

char* mdb_dkey ( MDB_val key,
char *  buf 
)

Display a key in hexadecimal and return the address of the result.

Parameters:
[in] key the key to display
[in] buf the buffer to write into. Should always be DKBUF.
Returns:
The key in hexadecimal form.
void mdb_page_list ( MDB_page mp  ) 

Display all the keys in the page.

static void mdb_audit ( MDB_txn txn  )  [static]

Count all the pages in each DB and in the freelist and make sure it matches the actual number of pages being used. All named DBs must be open for a correct count.

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_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 mdb_hash_t mdb_hash_val ( MDB_val val,
mdb_hash_t  hval 
) [static]

perform a 64 bit Fowler/Noll/Vo FNV-1a hash on a buffer

Parameters:
[in] val value to hash
[in] hval initial value for hash
Returns:
64 bit hash

NOTE: To use the recommended 64 bit FNV-1a hash, use MDB_HASH_INIT as the hval arg on the first call.

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 uses fewer mallocs but loses protection from application bugs like wild pointer writes and other bad updates into the database. This may be slightly faster for DBs that fit entirely in RAM, but is slower for DBs larger than RAM. Incompatible with nested transactions. Do not mix processes with and without MDB_WRITEMAP on the same environment. This can defeat durability (mdb_env_sync etc).
  • MDB_NOMETASYNC Flush system buffers to disk only once per transaction, omit the metadata flush. Defer that until the system flushes files to disk, or next non-MDB_RDONLY commit or mdb_env_sync(). This optimization maintains database integrity, but a system crash may undo the last committed transaction. I.e. it preserves the ACI (atomicity, consistency, isolation) but not D (durability) database property. This flag may be changed at any time using mdb_env_set_flags().
  • MDB_NOSYNC Don't flush system buffers to disk when committing a transaction. This optimization means a system crash can corrupt the database or lose the last transactions if buffers are not yet flushed to disk. The risk is governed by how often the system flushes dirty buffers to disk and how often mdb_env_sync() is called. However, if the filesystem preserves write order and the MDB_WRITEMAP flag is not used, transactions exhibit ACI (atomicity, consistency, isolation) properties and only lose D (durability). I.e. database integrity is maintained, but a system crash may undo the final transactions. Note that (MDB_NOSYNC | MDB_WRITEMAP) leaves the system with no hint for when to write transactions to disk, unless mdb_env_sync() is called. (MDB_MAPASYNC | MDB_WRITEMAP) may be preferable. This flag may be changed at any time using mdb_env_set_flags().
  • MDB_MAPASYNC When using MDB_WRITEMAP, use asynchronous flushes to disk. As with MDB_NOSYNC, a system crash can then corrupt the database or lose the last transactions. Calling mdb_env_sync() ensures on-disk database integrity until next commit. This flag may be changed at any time using mdb_env_set_flags().
  • MDB_NOTLS Don't use Thread-Local Storage. Tie reader locktable slots to MDB_txn objects instead of to threads. I.e. mdb_txn_reset() keeps the slot reseved for the MDB_txn object. A thread may use parallel read-only transactions. A read-only transaction may span threads if the user synchronizes its use. Applications that multiplex many user threads over individual OS threads need this option. Such an application must also serialize the write transactions in an OS thread, since LMDB's write locking is unaware of the user threads.
  • MDB_NOLOCK Don't do any locking. If concurrent access is anticipated, the caller must manage all concurrency itself. For proper operation the caller must enforce single-writer semantics, and must ensure that no readers are using old transactions while a writer is active. The simplest approach is to use an exclusive lock so that no readers may be active at all when a writer begins.
  • MDB_NORDAHEAD Turn off readahead. Most operating systems perform readahead on read requests by default. This option turns it off if the OS supports it. Turning it off may help random read performance when the DB is larger than RAM and system RAM is full. The option is not implemented on Windows.
  • MDB_NOMEMINIT Don't initialize malloc'd memory before writing to unused spaces in the data file. By default, memory for pages written to the data file is obtained using malloc. While these pages may be reused in subsequent transactions, freshly malloc'd pages will be initialized to zeroes before use. This avoids persisting leftover data from other code (that used the heap and subsequently freed the memory) into the data file. Note that many other system libraries may allocate and free memory from the heap for arbitrary uses. E.g., stdio may use the heap for file I/O buffers. This initialization step has a modest performance cost so some applications may want to disable it using this flag. This option can be a problem for applications which handle sensitive data like passwords, and it makes memory checkers like Valgrind noisy. This flag is not needed with MDB_WRITEMAP, which writes directly to the mmap instead of using malloc for pages. The initialization is also skipped if MDB_RESERVE is used; the caller is expected to overwrite all of the memory that was reserved in that case. This flag may be changed at any time using mdb_env_set_flags().
[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 - before the next update operation or the transaction ends. This saves an extra memcpy if the data is being generated later. This flag must not be specified if the database was opened with MDB_DUPSORT.
  • MDB_APPEND - append the given key/data pair to the end of the database. No key comparisons are performed. This option allows fast bulk loading when keys are already known to be in the correct order. Loading unsorted keys with this flag will cause a MDB_KEYEXIST error.
  • MDB_APPENDDUP - as above, but for sorted dup data.
  • MDB_MULTIPLE - store multiple contiguous data elements in a single request. This flag may only be specified if the database was opened with MDB_DUPFIXED. The data argument must be an array of two MDB_vals. The mv_size of the first MDB_val must be the size of a single data element. The mv_data of the first MDB_val must point to the beginning of the array of contiguous data elements. The mv_size of the second MDB_val must be the count of the number of data elements to store. On return this field will be set to the count of the number of elements actually written. The mv_data of the second MDB_val is unused.
Returns:
A non-zero error value on failure and 0 on success. Some possible errors are:
  • MDB_MAP_FULL - the database is full, see mdb_env_set_mapsize().
  • MDB_TXN_FULL - the transaction has too many dirty pages.
  • EACCES - an attempt was made to write in a read-only transaction.
  • EINVAL - an invalid parameter was specified.
int mdb_cursor_del ( MDB_cursor cursor,
unsigned int  flags 
)

Delete current key/data pair.

This function deletes the key/data pair to which the cursor refers.

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:
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.
static int ESECT mdb_mutex_failed ( MDB_env env,
mdb_mutexref_t  mutex,
int  rc 
) [static]

Handle LOCK_MUTEX0() failure. Try to repair the lock file if the mutex owner died.

Parameters:
[in] env the environment handle
[in] mutex LOCK_MUTEX0() mutex
[in] rc LOCK_MUTEX0() error (nonzero)
Returns:
0 on success with the mutex locked, or an error code on failure.

Variable Documentation

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

Table of descriptions for LMDB Return Codes

const char mdb_a85[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~" [static]

Hash the string and output the encoded hash. This uses modified RFC1924 Ascii85 encoding to accommodate systems with very short name limits. We don't care about the encoding being reversible, we just want to preserve as many bits of the input as possible in a small printable string.

Parameters:
[in] str string to hash
[out] encbuf an array of 11 chars to hold the hash
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