Provided by: lmdb-doc_0.9.17-3_all bug

NAME

       internal - LMDB Internals

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

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

   Macros
       #define LOCK_MUTEX(rc,  env,  mutex)   ((rc) = LOCK_MUTEX0(mutex))
       #define mdb_mutex_failed(env,  mutex,  rc)   (rc)
       #define MDB_DSYNC   O_SYNC
       #define MDB_FDATASYNC   fdatasync
       #define MDB_MSYNC(addr,  len,  flags)   msync(addr,len,flags)
       #define MS_SYNC   1
       #define MS_ASYNC   0
       #define MAX_PAGESIZE   (PAGEBASE ? 0x10000 : 0x8000)
           The maximum size of a database page.
       #define MDB_MINKEYS   2
       #define MDB_MAGIC   0xBEEFC0DE
       #define MDB_DATA_VERSION   ((MDB_DEVEL) ? 999 : 1)
       #define MDB_LOCK_VERSION   1
       #define MDB_MAXKEYSIZE   ((MDB_DEVEL) ? 0 : 511)
           The max size of a key we can write, or 0 for computed max.
       #define ENV_MAXKEY(env)   (MDB_MAXKEYSIZE)
       #define MAXDATASIZE   0xffffffffUL
           The maximum size of a data item.
       #define DKBUF
       #define DKEY(x)   0
       #define P_INVALID   (~(pgno_t)0)
       #define F_ISSET(w,  f)   (((w) & (f)) == (f))
       #define EVEN(n)   (((n) + 1U) & -2) /* sign-extending -2 to match n+1U */
       #define DEFAULT_MAPSIZE   1048576
       #define PAGEHDRSZ   ((unsigned) offsetof(MDB_page, mp_ptrs))
       #define METADATA(p)   ((void *)((char *)(p) + PAGEHDRSZ))
       #define PAGEBASE   ((MDB_DEVEL) ? PAGEHDRSZ : 0)
       #define NUMKEYS(p)   (((p)->mp_lower - (PAGEHDRSZ-PAGEBASE)) >> 1)
       #define SIZELEFT(p)   (indx_t)((p)->mp_upper - (p)->mp_lower)
       #define PAGEFILL(env,  p)
       #define FILL_THRESHOLD   250
       #define IS_LEAF(p)   F_ISSET((p)->mp_flags, P_LEAF)
       #define IS_LEAF2(p)   F_ISSET((p)->mp_flags, P_LEAF2)
       #define IS_BRANCH(p)   F_ISSET((p)->mp_flags, P_BRANCH)
       #define IS_OVERFLOW(p)   F_ISSET((p)->mp_flags, P_OVERFLOW)
       #define IS_SUBP(p)   F_ISSET((p)->mp_flags, P_SUBP)
       #define OVPAGES(size,  psize)   ((PAGEHDRSZ-1 + (size)) / (psize) + 1)
       #define NEXT_LOOSE_PAGE(p)   (*(MDB_page **)((p) + 2))
       #define NODESIZE   offsetof(MDB_node, mn_data)
       #define PGNO_TOPWORD   ((pgno_t)-1 > 0xffffffffu ? 32 : 0)
       #define INDXSIZE(k)   (NODESIZE + ((k) == NULL ? 0 : (k)->mv_size))
       #define LEAFSIZE(k,  d)   (NODESIZE + (k)->mv_size + (d)->mv_size)
       #define NODEPTR(p,  i)   ((MDB_node *)((char *)(p) + (p)->mp_ptrs[i] + PAGEBASE))
       #define NODEKEY(node)   (void *)((node)->mn_data)
       #define NODEDATA(node)   (void *)((char *)(node)->mn_data + (node)->mn_ksize)
       #define NODEPGNO(node)
       #define SETPGNO(node,  pgno)
       #define NODEDSZ(node)   ((node)->mn_lo | ((unsigned)(node)->mn_hi << 16))
       #define SETDSZ(node,  size)
       #define NODEKSZ(node)   ((node)->mn_ksize)
       #define COPY_PGNO(dst,  src)
       #define LEAF2KEY(p,  i,  ks)   ((char *)(p) + PAGEHDRSZ + ((i)*(ks)))
       #define MDB_GET_KEY(node,  keyptr)
       #define MDB_GET_KEY2(node,  key)   { key.mv_size = NODEKSZ(node); key.mv_data =
           NODEKEY(node); }
       #define MDB_VALID   0x8000
       #define PERSISTENT_FLAGS   (0xffff & ~(MDB_VALID))
       #define VALID_FLAGS
       #define FREE_DBI   0
       #define MAIN_DBI   1
       #define CORE_DBS   2
       #define NUM_METAS   2
       #define CURSOR_STACK   32
       #define MDB_COMMIT_PAGES   64
       #define MAX_WRITE   (0x80000000U >> (sizeof(ssize_t) == 4))
       #define TXN_DBI_EXIST(txn,  dbi,  validity)   ((txn) && (dbi)<(txn)->mt_numdbs &&
           ((txn)->mt_dbflags[dbi] & (validity)))
       #define TXN_DBI_CHANGED(txn,  dbi)   ((txn)->mt_dbiseqs[dbi] !=
           (txn)->mt_env->me_dbiseqs[dbi])
       #define MDB_END_NAMES
       #define MDB_END_OPMASK   0x0F
       #define MDB_END_UPDATE   0x10
       #define MDB_END_FREE   0x20
       #define MDB_END_SLOT   MDB_NOTLS
       #define MDB_PS_MODIFY   1
       #define MDB_PS_ROOTONLY   2
       #define MDB_PS_FIRST   4
       #define MDB_PS_LAST   8
       #define MDB_SPLIT_REPLACE   MDB_APPENDDUP
       #define mdb_env_close0(env,  excl)   mdb_env_close1(env)
       #define mdb_cmp_clong   mdb_cmp_cint
       #define mdb_cassert(mc,  expr)   mdb_assert0((mc)->mc_txn->mt_env, expr, #expr)
       #define mdb_tassert(txn,  expr)   mdb_assert0((txn)->mt_env, expr, #expr)
       #define mdb_eassert(env,  expr)   mdb_assert0(env, expr, #expr)
       #define mdb_assert0(env,  expr,  expr_txt)
       #define LOCKNAME   '/lock.mdb'
       #define DATANAME   '/data.mdb'
       #define LOCKSUFF   '-lock'
       #define CHANGEABLE   (MDB_NOSYNC|MDB_NOMETASYNC|MDB_MAPASYNC|MDB_NOMEMINIT)
       #define CHANGELESS
       #define MDB_NOSPILL   0x8000
       #define WITH_CURSOR_TRACKING(mn,  act)
       #define MDB_WBUF   (1024*1024)

   Typedefs
       typedef MDB_ID pgno_t
       typedef MDB_ID txnid_t
       typedef uint16_t indx_t

   Enumerations
       enum { MDB_END_COMMITTED, MDB_END_EMPTY_COMMIT, MDB_END_ABORT, MDB_END_RESET,
           MDB_END_RESET_TMP, MDB_END_FAIL_BEGIN, MDB_END_FAIL_BEGINCHILD }
       enum Pidlock_op { Pidset = F_SETLK, Pidcheck = F_GETLK }

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

   Variables
       static char *const mdb_errstr []

Detailed Description

Data Structure Documentation

struct MDB_page

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

   Data Fields

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

Field Documentation

   pgno_t MDB_page::p_pgno
       page number

   struct MDB_page* MDB_page::p_next
       for in-memory list of freed pages

   uint16_t MDB_page::mp_flags
       Page Flags

   indx_t MDB_page::pb_lower
       lower bound of free space

   indx_t MDB_page::pb_upper
       upper bound of free space

   uint32_t MDB_page::pb_pages
       number of overflow pages

   indx_t MDB_page::mp_ptrs[1]
       dynamic size

struct MDB_node

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

   Data Fields

       unsigned short mn_lo
       unsigned short mn_hi
       unsigned short mn_flags
       unsigned short mn_ksize
       char mn_data [1]

Field Documentation

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

   unsigned short MDB_node::mn_hi
       part of data size or pgno

   unsigned short MDB_node::mn_flags
       Node Flags

   unsigned short MDB_node::mn_ksize
       key size

   char MDB_node::mn_data[1]
       key and data are appended here

struct MDB_db

       Information about a single database in the environment.

   Data Fields

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

Field Documentation

   uint32_t MDB_db::md_pad
       also ksize for LEAF2 pages

   uint16_t MDB_db::md_flags
       Database Flags

   uint16_t MDB_db::md_depth
       depth of this tree

   pgno_t MDB_db::md_branch_pages
       number of internal pages

   pgno_t MDB_db::md_leaf_pages
       number of leaf pages

   pgno_t MDB_db::md_overflow_pages
       number of overflow pages

   size_t MDB_db::md_entries
       number of data items

   pgno_t MDB_db::md_root
       the root page of this tree

struct MDB_meta

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

   Data Fields

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

Field Documentation

   uint32_t MDB_meta::mm_magic
       Stamp identifying this as an LMDB file. It must be set to MDB_MAGIC.

   uint32_t MDB_meta::mm_version
       Version number of this file. Must be set to MDB_DATA_VERSION.

   void* MDB_meta::mm_address
       address for fixed mapping

   size_t MDB_meta::mm_mapsize
       size of mmap region

   MDB_db MDB_meta::mm_dbs[CORE_DBS]
       first is free space, 2nd is main db

   pgno_t MDB_meta::mm_last_pg
       last used page in file

   volatile txnid_t MDB_meta::mm_txnid
       txnid that committed this page

union MDB_metabuf

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

   Data Fields

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

struct MDB_dbx

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

   Data Fields

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

Field Documentation

   MDB_val MDB_dbx::md_name
       name of the database

   MDB_cmp_func* MDB_dbx::md_cmp
       function for comparing keys

   MDB_cmp_func* MDB_dbx::md_dcmp
       function for comparing data items

   MDB_rel_func* MDB_dbx::md_rel
       user relocate function

   void* MDB_dbx::md_relctx
       user-provided context for md_rel

struct MDB_txn

       Opaque structure for a transaction handle.

       A database transaction. Every operation requires a transaction handle.

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

   Data Fields

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

Field Documentation

   MDB_txn* MDB_txn::mt_parent
       parent of a nested txn

   MDB_txn* MDB_txn::mt_child
       Nested txn under this txn, set together with flag MDB_TXN_HAS_CHILD

   pgno_t MDB_txn::mt_next_pgno
       next unallocated page

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

   MDB_env* MDB_txn::mt_env
       the DB environment

   MDB_IDL MDB_txn::mt_free_pgs
       The list of pages that became unused during this transaction.

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

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

   MDB_ID2L MDB_txn::dirty_list
       For write txns: Modified pages. Sorted when not MDB_WRITEMAP.

   MDB_reader* MDB_txn::reader
       For read txns: This thread/txn's reader table slot, or NULL.

   MDB_dbx* MDB_txn::mt_dbxs
       Array of records for each DB known in the environment.

   MDB_db* MDB_txn::mt_dbs
       Array of MDB_db records for each known DB

   unsigned int* MDB_txn::mt_dbiseqs
       Array of sequence numbers for each DB handle

   MDB_cursor** MDB_txn::mt_cursors
       In write txns, array of cursors for each DB

   unsigned char* MDB_txn::mt_dbflags
       Array of flags for each DB

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

   unsigned int MDB_txn::mt_flags
       Transaction Flags

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

struct MDB_cursor

       Opaque structure for navigating through a database.

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

   Data Fields

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

Field Documentation

   MDB_cursor* MDB_cursor::mc_next
       Next cursor on this DB in this txn

   MDB_cursor* MDB_cursor::mc_backup
       Backup of the original cursor if this cursor is a shadow

   struct MDB_xcursor* MDB_cursor::mc_xcursor
       Context used for databases with MDB_DUPSORT, otherwise NULL

   MDB_txn* MDB_cursor::mc_txn
       The transaction that owns this cursor

   MDB_dbi MDB_cursor::mc_dbi
       The database handle this cursor operates on

   MDB_db* MDB_cursor::mc_db
       The database record for this cursor

   MDB_dbx* MDB_cursor::mc_dbx
       The database auxiliary record for this cursor

   unsigned char* MDB_cursor::mc_dbflag
       The Transaction DB Flags for this database

   unsigned short MDB_cursor::mc_snum
       number of pushed pages

   unsigned short MDB_cursor::mc_top
       index of top page, normally mc_snum-1

   unsigned int MDB_cursor::mc_flags
       Cursor Flags

   MDB_page* MDB_cursor::mc_pg[CURSOR_STACK]
       stack of pushed pages

   indx_t MDB_cursor::mc_ki[CURSOR_STACK]
       stack of page indices

struct MDB_xcursor

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

   Data Fields

       MDB_cursor mx_cursor
       MDB_db mx_db
       MDB_dbx mx_dbx
       unsigned char mx_dbflag

Field Documentation

   MDB_cursor MDB_xcursor::mx_cursor
       A sub-cursor for traversing the Dup DB

   MDB_db MDB_xcursor::mx_db
       The database record for this Dup DB

   MDB_dbx MDB_xcursor::mx_dbx
       The auxiliary DB record for this Dup DB

   unsigned char MDB_xcursor::mx_dbflag
       The Transaction DB Flags for this Dup DB

struct MDB_pgstate

       State of FreeDB old pages, stored in the MDB_env

   Data Fields

       pgno_t * mf_pghead
       txnid_t mf_pglast

Field Documentation

   pgno_t* MDB_pgstate::mf_pghead
       Reclaimed freeDB pages, or NULL before use

   txnid_t MDB_pgstate::mf_pglast
       ID of last used record, or 0 if !mf_pghead

struct MDB_env

       Opaque structure for a database environment.

       The database environment.

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

   Data Fields

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

Field Documentation

   HANDLE MDB_env::me_fd
       The main data file

   HANDLE MDB_env::me_lfd
       The lock file

   HANDLE MDB_env::me_mfd
       just for writing the meta pages

   uint32_t MDB_env::me_flags
       Environment Flags

   unsigned int MDB_env::me_psize
       DB page size, inited from me_os_psize

   unsigned int MDB_env::me_os_psize
       OS page size, from GET_PAGESIZE

   unsigned int MDB_env::me_maxreaders
       size of the reader table

   volatile int MDB_env::me_close_readers
       Max MDB_txninfo.mti_numreaders of interest to mdb_env_close()

   MDB_dbi MDB_env::me_numdbs
       number of DBs opened

   MDB_dbi MDB_env::me_maxdbs
       size of the DB table

   MDB_PID_T MDB_env::me_pid
       process ID of this env

   char* MDB_env::me_path
       path to the DB files

   char* MDB_env::me_map
       the memory map of the data file

   MDB_txninfo* MDB_env::me_txns
       the memory map of the lock file or NULL

   MDB_meta* MDB_env::me_metas[NUM_METAS]
       pointers to the two meta pages

   void* MDB_env::me_pbuf
       scratch area for DUPSORT put()

   MDB_txn* MDB_env::me_txn
       current write transaction

   MDB_txn* MDB_env::me_txn0
       prealloc'd write transaction

   size_t MDB_env::me_mapsize
       size of the data memory map

   off_t MDB_env::me_size
       current file size

   pgno_t MDB_env::me_maxpg
       me_mapsize / me_psize

   MDB_dbx* MDB_env::me_dbxs
       array of static DB info

   uint16_t* MDB_env::me_dbflags
       array of flags from MDB_db.md_flags

   unsigned int* MDB_env::me_dbiseqs
       array of dbi sequence numbers

   pthread_key_t MDB_env::me_txkey
       thread-key for readers

   txnid_t MDB_env::me_pgoldest
       ID of oldest reader last time we looked

   MDB_pgstate MDB_env::me_pgstate
       state of old pages from freeDB

   MDB_page* MDB_env::me_dpages
       list of malloc'd blocks for re-use

   MDB_IDL MDB_env::me_free_pgs
       IDL of pages that became unused in a write txn

   MDB_ID2L MDB_env::me_dirty_list
       ID2L of pages written during a write txn. Length MDB_IDL_UM_SIZE.

   int MDB_env::me_maxfree_1pg
       Max number of freelist items that can fit in a single overflow page

   unsigned int MDB_env::me_nodemax
       Max size of a node on a page

   int MDB_env::me_live_reader
       have liveness lock in reader table

   void* MDB_env::me_userctx
       User-settable context

   MDB_assert_func* MDB_env::me_assert_func
       Callback for assertion failures

struct MDB_ntxn

       Nested transaction

   Data Fields

       MDB_txn mnt_txn
       MDB_pgstate mnt_pgstate

Field Documentation

   MDB_txn MDB_ntxn::mnt_txn
       the transaction

   MDB_pgstate MDB_ntxn::mnt_pgstate
       parent transaction's saved freestate

struct mdb_copy

       State needed for a compacting copy.

   Data Fields

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

Macro Definition Documentation

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

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

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

   #define MAX_PAGESIZE   (PAGEBASE ? 0x10000 : 0x8000)
       The maximum size of a database page. It is 32k or 64k, since value-PAGEBASE must fit in
       MDB_page.mp_upper.

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

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

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

   #define MDB_MAGIC   0xBEEFC0DE
       A stamp that identifies a file as an LMDB file. There's nothing special about this value
       other than that it is easily recognizable, and it will reflect any byte order mismatches.

   #define MDB_DATA_VERSION   ((MDB_DEVEL) ? 999 : 1)
       The version number for a database's datafile format.

   #define MDB_LOCK_VERSION   1
       The version number for a database's lockfile format.

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

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

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

   #define ENV_MAXKEY(env)   (MDB_MAXKEYSIZE)
       The maximum size of a key we can write to the environment.

   #define MAXDATASIZE   0xffffffffUL
       The maximum size of a data item. We only store a 32 bit value for node sizes.

   #define P_INVALID   (~(pgno_t)0)
       An invalid page number. Mainly used to denote an empty tree.

   #define F_ISSET(w, f)   (((w) & (f)) == (f))
       Test if the flags f are set in a flag word w.

   #define EVEN(n)   (((n) + 1U) & -2) /* sign-extending -2 to match n+1U */
       Round n up to an even number.

   #define DEFAULT_MAPSIZE   1048576
       Default size of memory map. This is certainly too small for any actual applications. Apps
       should always set the size explicitly using mdb_env_set_mapsize().

   #define PAGEHDRSZ   ((unsigned) offsetof(MDB_page, mp_ptrs))
       Size of the page header, excluding dynamic data at the end

   #define METADATA(p)   ((void *)((char *)(p) + PAGEHDRSZ))
       Address of first usable data byte in a page, after the header

   #define PAGEBASE   ((MDB_DEVEL) ? PAGEHDRSZ : 0)
       ITS#7713, change PAGEBASE to handle 65536 byte pages

   #define NUMKEYS(p)   (((p)->mp_lower - (PAGEHDRSZ-PAGEBASE)) >> 1)
       Number of nodes on a page

   #define SIZELEFT(p)   (indx_t)((p)->mp_upper - (p)->mp_lower)
       The amount of space remaining in the page

   #define PAGEFILL(env, p)
       Value:

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

   #define FILL_THRESHOLD   250
       The minimum page fill factor, in tenths of a percent. Pages emptier than this are
       candidates for merging.

   #define IS_LEAF(p)   F_ISSET((p)->mp_flags, P_LEAF)
       Test if a page is a leaf page

   #define IS_LEAF2(p)   F_ISSET((p)->mp_flags, P_LEAF2)
       Test if a page is a LEAF2 page

   #define IS_BRANCH(p)   F_ISSET((p)->mp_flags, P_BRANCH)
       Test if a page is a branch page

   #define IS_OVERFLOW(p)   F_ISSET((p)->mp_flags, P_OVERFLOW)
       Test if a page is an overflow page

   #define IS_SUBP(p)   F_ISSET((p)->mp_flags, P_SUBP)
       Test if a page is a sub page

   #define OVPAGES(size, psize)   ((PAGEHDRSZ-1 + (size)) / (psize) + 1)
       The number of overflow pages needed to store the given size.

   #define NEXT_LOOSE_PAGE(p)   (*(MDB_page **)((p) + 2))
       Link in MDB_txn.mt_loose_pgs list

   #define NODESIZE   offsetof(MDB_node, mn_data)
       Size of the node header, excluding dynamic data at the end

   #define PGNO_TOPWORD   ((pgno_t)-1 > 0xffffffffu ? 32 : 0)
       Bit position of top word in page number, for shifting mn_flags

   #define INDXSIZE(k)   (NODESIZE + ((k) == NULL ? 0 : (k)->mv_size))
       Size of a node in a branch page with a given key. This is just the node header plus the
       key, there is no data.

   #define LEAFSIZE(k, d)   (NODESIZE + (k)->mv_size + (d)->mv_size)
       Size of a node in a leaf page with a given key and data. This is node header plus key plus
       data size.

   #define NODEPTR(p, i)   ((MDB_node *)((char *)(p) + (p)->mp_ptrs[i] + PAGEBASE))
       Address of node i in page p

   #define NODEKEY(node)   (void *)((node)->mn_data)
       Address of the key for the node

   #define NODEDATA(node)   (void *)((char *)(node)->mn_data + (node)->mn_ksize)
       Address of the data for a node

   #define NODEPGNO(node)
       Value:

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

   #define SETPGNO(node, pgno)
       Value:

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

   #define NODEDSZ(node)   ((node)->mn_lo | ((unsigned)(node)->mn_hi << 16))
       Get the size of the data in a leaf node

   #define SETDSZ(node, size)
       Value:

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

   #define NODEKSZ(node)   ((node)->mn_ksize)
       The size of a key in a node

   #define COPY_PGNO(dst, src)
       Value:

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

   #define LEAF2KEY(p, i, ks)   ((char *)(p) + PAGEHDRSZ + ((i)*(ks)))
       The address of a key in a LEAF2 page. LEAF2 pages are used for MDB_DUPFIXED sorted-
       duplicate sub-DBs. There are no node headers, keys are stored contiguously.

   #define MDB_GET_KEY(node, keyptr)
       Value:

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

   #define MDB_GET_KEY2(node, key)   { key.mv_size = NODEKSZ(node); key.mv_data = NODEKEY(node);
       }
       Set the node's key into key.

   #define MDB_VALID   0x8000
       mdb_dbi_open flags DB handle is valid, for me_dbflags

   #define VALID_FLAGS
       Value:

       (MDB_REVERSEKEY|MDB_DUPSORT|MDB_INTEGERKEY|MDB_DUPFIXED|\
            MDB_INTEGERDUP|MDB_REVERSEDUP|MDB_CREATE)

   #define FREE_DBI   0
       Handle for the DB used to track free pages.

   #define MAIN_DBI   1
       Handle for the default DB.

   #define CORE_DBS   2
       Number of DBs in metapage (free and main) - also hardcoded elsewhere

   #define NUM_METAS   2
       Number of meta pages - also hardcoded elsewhere

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

   #define MDB_COMMIT_PAGES   64
       max number of pages to commit in one writev() call

   #define MAX_WRITE   (0x80000000U >> (sizeof(ssize_t) == 4))
       max bytes to write in one call

   #define TXN_DBI_EXIST(txn, dbi, validity)   ((txn) && (dbi)<(txn)->mt_numdbs &&
       ((txn)->mt_dbflags[dbi] & (validity)))
       Check txn and dbi arguments to a function

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

   #define MDB_END_NAMES
       Value:

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

   #define MDB_END_OPMASK   0x0F
       mask for mdb_txn_end() operation number

   #define MDB_END_UPDATE   0x10
       update env state (DBIs)

   #define MDB_END_FREE   0x20
       free txn unless it is MDB_env.me_txn0

   #define MDB_END_SLOT   MDB_NOTLS
       release any reader slot if MDB_NOTLS

   #define MDB_SPLIT_REPLACE   MDB_APPENDDUP
       newkey is not new

   #define mdb_cmp_clong   mdb_cmp_cint
       Compare two items pointing at size_t's of unknown alignment.

   #define mdb_cassert(mc, expr)   mdb_assert0((mc)->mc_txn->mt_env, expr, #expr)
       assert(3) variant in cursor context

   #define mdb_tassert(txn, expr)   mdb_assert0((txn)->mt_env, expr, #expr)
       assert(3) variant in transaction context

   #define mdb_eassert(env, expr)   mdb_assert0(env, expr, #expr)
       assert(3) variant in environment context

   #define mdb_assert0(env, expr, expr_txt)
       Value:

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

   #define LOCKNAME   '/lock.mdb'
       The name of the lock file in the DB environment

   #define DATANAME   '/data.mdb'
       The name of the data file in the DB environment

   #define LOCKSUFF   '-lock'
       The suffix of the lock file when no subdir is used

   #define CHANGEABLE   (MDB_NOSYNC|MDB_NOMETASYNC|MDB_MAPASYNC|MDB_NOMEMINIT)
       Only a subset of the Environment Flags flags can be changed at runtime. Changing other
       flags requires closing the environment and re-opening it with the new flags.

   #define CHANGELESS
       Value:

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

   #define MDB_NOSPILL   0x8000
       Do not spill pages to disk if txn is getting full, may fail instead

   #define WITH_CURSOR_TRACKING(mn, act)
       Value:

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

Typedef Documentation

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

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

   typedef MDB_ID txnid_t
       A transaction ID. See struct MDB_txn.mt_txnid for details.

   typedef uint16_t indx_t
       Used for offsets within a single page. Since memory pages are typically 4 or 8KB in size,
       12-13 bits, this is plenty.

Function Documentation

   static int mdb_page_alloc (MDB_cursor * mc, int num, MDB_page ** mp) [static]
       Allocate page numbers and memory for writing. Maintain me_pglast, me_pghead and
       mt_next_pgno.

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

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

       Returns:
           0 on success, non-zero on failure.

   static int mdb_page_new (MDB_cursor * mc, uint32_t flags, int num, MDB_page ** mp) [static]
       Allocate and initialize new pages for a database.

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

       Returns:
           0 on success, non-zero on failure.

   static int mdb_page_touch (MDB_cursor * mc) [static]
       Touch a page: make it dirty and re-insert into tree with updated pgno.

       Parameters:
           mc cursor pointing to the page to be touched

       Returns:
           0 on success, non-zero on failure.

   static void mdb_txn_end (MDB_txn * txn, unsigned mode) [static]
       End a transaction, except successful commit of a nested transaction. May be called twice
       for readonly txns: First reset it, then abort.

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

   static int mdb_page_get (MDB_txn * txn, pgno_t pgno, MDB_page ** ret, int * lvl) [static]
       Find the address of the page corresponding to a given page number.

       Parameters:
           txn the transaction for this access.
           pgno the page number for the page to retrieve.
           ret address of a pointer where the page's address will be stored.
           lvl dirty_list inheritance level of found page. 1=current txn, 0=mapped page.

       Returns:
           0 on success, non-zero on failure.

   static int mdb_page_search_root (MDB_cursor * mc, MDB_val * key, int flags) [static]
       Finish mdb_page_search() / mdb_page_search_lowest(). The cursor is at the root page, set
       up the rest of it.

   static int mdb_page_search (MDB_cursor * mc, MDB_val * key, int flags) [static]
       Search for the page a given key should be in. Push it and its parent pages on the cursor
       stack.

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

       Returns:
           0 on success, non-zero on failure.

   static int mdb_page_merge (MDB_cursor * csrc, MDB_cursor * cdst) [static]
       Merge one page into another. The nodes from the page pointed to by csrc will be copied to
       the page pointed to by cdst and then the csrc page will be freed.

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

       Returns:
           0 on success, non-zero on failure.

   static int mdb_page_split (MDB_cursor * mc, MDB_val * newkey, MDB_val * newdata, pgno_t
       newpgno, unsigned int nflags) [static]
       Split a page and insert a new node.

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

       Returns:
           0 on success, non-zero on failure.

   static int ESECT mdb_env_read_header (MDB_env * env, MDB_meta * meta) [static]
       Read the environment parameters of a DB environment before mapping it into memory.

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

       Returns:
           0 on success, non-zero on failure.

   static MDB_meta * mdb_env_pick_meta (const MDB_env * env) [static]
       Check both meta pages to see which one is newer.

       Parameters:
           env the environment handle

       Returns:
           newest MDB_meta.

   static int mdb_env_write_meta (MDB_txn * txn) [static]
       Update the environment info to commit a transaction.

       Parameters:
           txn the transaction that's being committed

       Returns:
           0 on success, non-zero on failure.

   static void ESECT mdb_env_close0 (MDB_env * env, int excl) [static]
       Destroy resources from mdb_env_open(), clear our readers & DBIs

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

   static int mdb_node_add (MDB_cursor * mc, indx_t indx, MDB_val * key, MDB_val * data, pgno_t
       pgno, unsigned int flags) [static]
       Add a node to the page pointed to by the cursor.

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

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

           · ENOMEM - failed to allocate overflow pages for the node.
           · MDB_PAGE_FULL - there is insufficient room in the page. This error should never
             happen since all callers already calculate the page's free space before calling this
             function.
   static void mdb_node_del (MDB_cursor * mc, int ksize) [static]
       Delete the specified node from a page.
       Parameters:
           mc Cursor pointing to the node to delete.
           ksize The size of a node. Only used if the page is part of a MDB_DUPFIXED database.
   static void mdb_node_shrink (MDB_page * mp, indx_t indx) [static]
       Compact the main page after deleting a node on a subpage.
       Parameters:
           mp The main page to operate on.
           indx The index of the subpage on the main page.
   static int mdb_node_move (MDB_cursor * csrc, MDB_cursor * cdst, int fromleft) [static]
       Move a node from csrc to cdst.
   static int mdb_node_read (MDB_txn * txn, MDB_node * leaf, MDB_val * data) [static]
       Return the data associated with a given node.
       Parameters:
           txn The transaction for this operation.
           leaf The node being read.
           data Updated to point to the node's data.
       Returns:
           0 on success, non-zero on failure.
   static size_t mdb_leaf_size (MDB_env * env, MDB_val * key, MDB_val * data) [static]
       Calculate the size of a leaf node. The size depends on the environment's page size; if a
       data item is too large it will be put onto an overflow page and the node size will only
       include the key and not the data. Sizes are always rounded up to an even number of bytes,
       to guarantee 2-byte alignment of the MDB_node headers.
       Parameters:
           env The environment handle.
           key The key for the node.
           data The data for the node.
       Returns:
           The number of bytes needed to store the node.
   static size_t mdb_branch_size (MDB_env * env, MDB_val * key) [static]
       Calculate the size of a branch node. The size should depend on the environment's page size
       but since we currently don't support spilling large keys onto overflow pages, it's simply
       the size of the MDB_node header plus the size of the key. Sizes are always rounded up to
       an even number of bytes, to guarantee 2-byte alignment of the MDB_node headers.
       Parameters:
           env The environment handle.
           key The key for the node.
       Returns:
           The number of bytes needed to store the node.
   static int mdb_rebalance (MDB_cursor * mc) [static]
       Rebalance the tree after a delete operation.
       Parameters:
           mc Cursor pointing to the page where rebalancing should begin.
       Returns:
           0 on success, non-zero on failure.
   static int mdb_update_key (MDB_cursor * mc, MDB_val * key) [static]
       Replace the key for a branch node with a new key.
       Parameters:
           mc Cursor pointing to the node to operate on.
           key The new key to use.
       Returns:
           0 on success, non-zero on failure.
   static void mdb_cursor_pop (MDB_cursor * mc) [static]
       Pop a page off the top of the cursor's stack.
   static int mdb_cursor_push (MDB_cursor * mc, MDB_page * mp) [static]
       Push a page onto the top of the cursor's stack.
   static int mdb_cursor_del0 (MDB_cursor * mc) [static]
       Complete a delete operation started by mdb_cursor_del().
   static int mdb_cursor_sibling (MDB_cursor * mc, int move_right) [static]
       Find a sibling for a page. Replaces the page at the top of the cursor's stack with the
       specified sibling, if one exists.
       Parameters:
           mc The cursor for this operation.
           move_right Non-zero if the right sibling is requested, otherwise the left sibling.
       Returns:
           0 on success, non-zero on failure.
   static int mdb_cursor_next (MDB_cursor * mc, MDB_val * key, MDB_val * data, MDB_cursor_op op)
       [static]
       Move the cursor to the next data item.
   static int mdb_cursor_prev (MDB_cursor * mc, MDB_val * key, MDB_val * data, MDB_cursor_op op)
       [static]
       Move the cursor to the previous data item.
   static int mdb_cursor_set (MDB_cursor * mc, MDB_val * key, MDB_val * data, MDB_cursor_op op,
       int * exactp) [static]
       Set the cursor on a specific data item.
   static int mdb_cursor_first (MDB_cursor * mc, MDB_val * key, MDB_val * data) [static]
       Move the cursor to the first item in the database.
   static int mdb_cursor_last (MDB_cursor * mc, MDB_val * key, MDB_val * data) [static]
       Move the cursor to the last item in the database.
   static void mdb_cursor_init (MDB_cursor * mc, MDB_txn * txn, MDB_dbi dbi, MDB_xcursor * mx)
       [static]
       Initialize a cursor for a given transaction and database.
   static void mdb_xcursor_init0 (MDB_cursor * mc) [static]
       Initial setup of a sorted-dups cursor. Sorted duplicates are implemented as a sub-database
       for the given key. The duplicate data items are actually keys of the sub-database.
       Operations on the duplicate data items are performed using a sub-cursor initialized when
       the sub-database is first accessed. This function does the preliminary setup of the sub-
       cursor, filling in the fields that depend only on the parent DB.
       Parameters:
           mc The main cursor whose sorted-dups cursor is to be initialized.
   static void mdb_xcursor_init1 (MDB_cursor * mc, MDB_node * node) [static]
       Final setup of a sorted-dups cursor. Sets up the fields that depend on the data from the
       main cursor.
       Parameters:
           mc The main cursor whose sorted-dups cursor is to be initialized.
           node The data containing the MDB_db record for the sorted-dup database.
   static void mdb_xcursor_init2 (MDB_cursor * mc, MDB_xcursor * src_mx, 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:
           mc The main cursor whose sorted-dups cursor is to be fixed up.
           src_mx The xcursor of an up-to-date cursor.
           new_dupdata True if converting from a non-F_DUPDATA item.
   static int mdb_drop0 (MDB_cursor * mc, int subs) [static]
       Add all the DB's pages to the free list.
       Parameters:
           mc Cursor on the DB to free.
           subs non-Zero to check for sub-DBs in this DB.
       Returns:
           0 on success, non-zero on failure.
   static void mdb_default_cmp (MDB_txn * txn, MDB_dbi dbi) [static]
       Set the default comparison functions for a database. Called immediately after a database
       is opened to set the defaults. The user can then override them with mdb_set_compare() or
       mdb_set_dupsort().
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
           dbi A database handle returned by mdb_dbi_open()
   static int ESECT mdb_reader_check0 (MDB_env * env, int rlocked, int * dead) [static]
       As mdb_reader_check(). rlocked = <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:
           err The error code
       Return values:
           error message The description of the error
   int mdb_cmp (MDB_txn * txn, MDB_dbi dbi, const MDB_val * a, const MDB_val * b)
       Compare two data items according to a particular database. This returns a comparison as if
       the two data items were keys in the specified database.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
           dbi A database handle returned by mdb_dbi_open()
           a The first item to compare
           b The second item to compare
       Returns:
           < 0 if a < b, 0 if a == b, > 0 if a > b
   int mdb_dcmp (MDB_txn * txn, MDB_dbi dbi, const MDB_val * a, const MDB_val * b)
       Compare two data items according to a particular database. This returns a comparison as if
       the two items were data items of the specified database. The database must have the
       MDB_DUPSORT flag.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
           dbi A database handle returned by mdb_dbi_open()
           a The first item to compare
           b The second item to compare
       Returns:
           < 0 if a < b, 0 if a == b, > 0 if a > b
   static MDB_page* mdb_page_malloc (MDB_txn * txn, unsigned num) [static]
       Allocate memory for a page. Re-use old malloc'd pages first for singletons, otherwise just
       malloc.
   static void mdb_page_free (MDB_env * env, MDB_page * mp) [static]
       Free a single page. Saves single pages to a list, for future reuse. (This is not used for
       multi-page overflow pages.)
   static void mdb_dpage_free (MDB_env * env, MDB_page * dp) [static]
       Free a dirty page
   static void mdb_dlist_free (MDB_txn * txn) [static]
       Return all dirty pages to dpage list
   static int mdb_page_loose (MDB_cursor * mc, MDB_page * mp) [static]
       Loosen or free a single page. Saves single pages to a list for future reuse in this same
       txn. It has been pulled from the freeDB and already resides on the dirty list, but has
       been deleted. Use these pages first before pulling again from the freeDB.
       If the page wasn't dirtied in this txn, just add it to this txn's free list.
   static int mdb_pages_xkeep (MDB_cursor * mc, unsigned pflags, int all) [static]
       Set or clear P_KEEP in dirty, non-overflow, non-sub pages watched by txn.
       Parameters:
           mc A cursor handle for the current operation.
           pflags Flags of the pages to update: P_DIRTY to set P_KEEP, P_DIRTY|P_KEEP to clear
           it.
           all No shortcuts. Needed except after a full mdb_page_flush().
       Returns:
           0 on success, non-zero on failure.
   static int mdb_page_flush (MDB_txn * txn, int keep) [static]
       Flush (some) dirty pages to the map, after clearing their dirty flag.
       Parameters:
           txn the transaction that's being committed
           keep number of initial pages in dirty_list to keep dirty.
       Returns:
           0 on success, non-zero on failure.
   static int mdb_page_spill (MDB_cursor * m0, MDB_val * key, MDB_val * data) [static]
       Spill pages from the dirty list back to disk. This is intended to prevent running into
       MDB_TXN_FULL situations, but note that they may still occur in a few cases: 1) our
       estimate of the txn size could be too small. Currently this seems unlikely, except with a
       large number of MDB_MULTIPLE items. 2) child txns may run out of space if their parents
       dirtied a lot of pages and never spilled them. TODO: we probably should do a preemptive
       spill during mdb_txn_begin() of a child txn, if the parent's dirty_room is below a given
       threshold.
       Otherwise, if not using nested txns, it is expected that apps will not run into
       MDB_TXN_FULL any more. The pages are flushed to disk the same way as for a txn commit,
       e.g. their P_DIRTY flag is cleared. If the txn never references them again, they can be
       left alone. If the txn only reads them, they can be used without any fuss. If the txn
       writes them again, they can be dirtied immediately without going thru all of the work of
       mdb_page_touch(). Such references are handled by mdb_page_unspill().
       Also note, we never spill DB root pages, nor pages of active cursors, because we'll need
       these back again soon anyway. And in nested txns, we can't spill a page in a child txn if
       it was already spilled in a parent txn. That would alter the parent txns' data even though
       the child hasn't committed yet, and we'd have no way to undo it if the child aborted.
       Parameters:
           m0 cursor A cursor handle identifying the transaction and database for which we are
           checking space.
           key For a put operation, the key being stored.
           data For a put operation, the data being stored.
       Returns:
           0 on success, non-zero on failure.
   static txnid_t mdb_find_oldest (MDB_txn * txn) [static]
       Find oldest txnid still referenced. Expects txn->mt_txnid > 0.
   static void mdb_page_dirty (MDB_txn * txn, MDB_page * mp) [static]
       Add a page to the txn's dirty list
   static void mdb_page_copy (MDB_page * dst, MDB_page * src, unsigned int psize) [static]
       Copy the used portions of a non-overflow page.
       Parameters:
           dst page to copy into
           src page to copy from
           psize size of a page
   static int mdb_page_unspill (MDB_txn * txn, MDB_page * mp, MDB_page ** ret) [static]
       Pull a page off the txn's spill list, if present. If a page being referenced was spilled
       to disk in this txn, bring it back and make it dirty/writable again.
       Parameters:
           txn the transaction handle.
           mp the page being referenced. It must not be dirty.
           ret the writable page, if any. ret is unchanged if mp wasn't spilled.
   int mdb_env_sync (MDB_env * env, int force)
       Flush the data buffers to disk. Data is always written to disk when mdb_txn_commit() is
       called, but the operating system may keep it buffered. LMDB always flushes the OS buffers
       upon commit as well, unless the environment was opened with MDB_NOSYNC or in part
       MDB_NOMETASYNC. This call is not valid if the environment was opened with MDB_RDONLY.
       Parameters:
           env An environment handle returned by mdb_env_create()
           force If non-zero, force a synchronous flush. Otherwise if the environment has the
           MDB_NOSYNC flag set the flushes will be omitted, and with MDB_MAPASYNC they will be
           asynchronous.
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EACCES - the environment is read-only.
           · EINVAL - an invalid parameter was specified.
           · EIO - an error occurred during synchronization.
   static int mdb_cursor_shadow (MDB_txn * src, MDB_txn * dst) [static]
       Back up parent txn's cursors, then grab the originals for tracking
   static void mdb_cursors_close (MDB_txn * txn, unsigned merge) [static]
       Close this write txn's cursors, give parent txn's cursors back to parent.
       Parameters:
           txn the transaction handle.
           merge true to keep changes to parent cursors, false to revert.
       Returns:
           0 on success, non-zero on failure.
   static int mdb_reader_pid (MDB_env * env, enum Pidlock_op op, MDB_PID_T pid) [static]
       Set or check a pid lock. Set returns 0 on success. Check returns 0 if the process is
       certainly dead, nonzero if it may be alive (the lock exists or an error happened so we do
       not know).
       On Windows Pidset is a no-op, we merely check for the existence of the process with the
       given pid. On POSIX we use a single byte lock on the lockfile, set at an offset equal to
       the pid.
   static int mdb_txn_renew0 (MDB_txn * txn) [static]
       Common code for mdb_txn_begin() and mdb_txn_renew().
       Parameters:
           txn the transaction handle to initialize
       Returns:
           0 on success, non-zero on failure.
   int mdb_txn_renew (MDB_txn * txn)
       Renew a read-only transaction. This acquires a new reader lock for a transaction handle
       that had been released by mdb_txn_reset(). It must be called before a reset transaction
       may be used again.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · MDB_PANIC - a fatal error occurred earlier and the environment must be shut down.
           · EINVAL - an invalid parameter was specified.
   int mdb_txn_begin (MDB_env * env, MDB_txn * parent, unsigned int flags, MDB_txn ** txn)
       Create a transaction for use with the environment. The transaction handle may be discarded
       using mdb_txn_abort() or mdb_txn_commit().
       Note:
           A transaction and its cursors must only be used by a single thread, and a thread may
           only have a single transaction at a time. If MDB_NOTLS is in use, this does not apply
           to read-only transactions.
           Cursors may not span transactions.
       Parameters:
           env An environment handle returned by mdb_env_create()
           parent If this parameter is non-NULL, the new transaction will be a nested
           transaction, with the transaction indicated by parent as its parent. Transactions may
           be nested to any level. A parent transaction and its cursors may not issue any other
           operations than mdb_txn_commit and mdb_txn_abort while it has active child
           transactions.
           flags Special options for this transaction. This parameter must be set to 0 or by
           bitwise OR'ing together one or more of the values described here.

           · MDB_RDONLY This transaction will not perform any write operations.
           txn Address where the new MDB_txn handle will be stored
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · MDB_PANIC - a fatal error occurred earlier and the environment must be shut down.
           · MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's mapsize and this
             environment's map must be resized as well. See mdb_env_set_mapsize().
           · MDB_READERS_FULL - a read-only transaction was requested and the reader lock table
             is full. See mdb_env_set_maxreaders().
           · ENOMEM - out of memory.
   MDB_env* mdb_txn_env (MDB_txn * txn)
       Returns the transaction's MDB_env.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
   size_t mdb_txn_id (MDB_txn * txn)
       Return the transaction's ID. This returns the identifier associated with this transaction.
       For a read-only transaction, this corresponds to the snapshot being read; concurrent
       readers will frequently have the same transaction ID.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
       Returns:
           A transaction ID, valid if input is an active transaction.
   static void mdb_dbis_update (MDB_txn * txn, int keep) [static]
       Export or close DBI handles opened in this txn.
   void mdb_txn_reset (MDB_txn * txn)
       Reset a read-only transaction. Abort the transaction like mdb_txn_abort(), but keep the
       transaction handle. mdb_txn_renew() may reuse the handle. This saves allocation overhead
       if the process will start a new read-only transaction soon, and also locking overhead if
       MDB_NOTLS is in use. The reader table lock is released, but the table slot stays tied to
       its thread or MDB_txn. Use mdb_txn_abort() to discard a reset handle, and to free its lock
       table slot if MDB_NOTLS is in use. Cursors opened within the transaction must not be used
       again after this call, except with mdb_cursor_renew(). Reader locks generally don't
       interfere with writers, but they keep old versions of database pages allocated. Thus they
       prevent the old pages from being reused when writers commit new data, and so under heavy
       load the database size may grow much more rapidly than otherwise.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
   void mdb_txn_abort (MDB_txn * txn)
       Abandon all the operations of the transaction instead of saving them. The transaction
       handle is freed. It and its cursors must not be used again after this call, except with
       mdb_cursor_renew().
       Note:
           Earlier documentation incorrectly said all cursors would be freed. Only write-
           transactions free cursors.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
   static int mdb_freelist_save (MDB_txn * txn) [static]
       Save the freelist as of this transaction to the freeDB. This changes the freelist. Keep
       trying until it stabilizes.
   int mdb_txn_commit (MDB_txn * txn)
       Commit all the operations of a transaction into the database. The transaction handle is
       freed. It and its cursors must not be used again after this call, except with
       mdb_cursor_renew().
       Note:
           Earlier documentation incorrectly said all cursors would be freed. Only write-
           transactions free cursors.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - an invalid parameter was specified.
           · ENOSPC - no more disk space.
           · EIO - a low-level I/O error occurred while writing.
           · ENOMEM - out of memory.
   static void ESECT mdb_env_init_meta0 (MDB_env * env, MDB_meta * meta) [static]
       Fill in most of the zeroed MDB_meta for an empty database environment
   static int ESECT mdb_env_init_meta (MDB_env * env, MDB_meta * meta) [static]
       Write the environment parameters of a freshly created DB environment.
       Parameters:
           env the environment handle
           meta the MDB_meta to write
       Returns:
           0 on success, non-zero on failure.
   int ESECT mdb_env_create (MDB_env ** env)
       Create an LMDB environment handle. This function allocates memory for a MDB_env structure.
       To release the allocated memory and discard the handle, call mdb_env_close(). Before the
       handle may be used, it must be opened using mdb_env_open(). Various other options may also
       need to be set before opening the handle, e.g. mdb_env_set_mapsize(),
       mdb_env_set_maxreaders(), mdb_env_set_maxdbs(), depending on usage requirements.
       Parameters:
           env The address where the new handle will be stored
       Returns:
           A non-zero error value on failure and 0 on success.
   int ESECT mdb_env_set_mapsize (MDB_env * env, size_t size)
       Set the size of the memory map to use for this environment. The size should be a multiple
       of the OS page size. The default is 10485760 bytes. The size of the memory map is also the
       maximum size of the database. The value should be chosen as large as possible, to
       accommodate future growth of the database. This function should be called after
       mdb_env_create() and before mdb_env_open(). It may be called at later times if no
       transactions are active in this process. Note that the library does not check for this
       condition, the caller must ensure it explicitly.
       The new size takes effect immediately for the current process but will not be persisted to
       any others until a write transaction has been committed by the current process. Also, only
       mapsize increases are persisted into the environment.
       If the mapsize is increased by another process, and data has grown beyond the range of the
       current mapsize, mdb_txn_begin() will return MDB_MAP_RESIZED. This function may be called
       with a size of zero to adopt the new size.
       Any attempt to set a size smaller than the space already consumed by the environment will
       be silently changed to the current size of the used space.
       Parameters:
           env An environment handle returned by mdb_env_create()
           size The size in bytes
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - an invalid parameter was specified, or the environment has an active write
             transaction.
   int ESECT mdb_env_set_maxdbs (MDB_env * env, MDB_dbi dbs)
       Set the maximum number of named databases for the environment. This function is only
       needed if multiple databases will be used in the environment. Simpler applications that
       use the environment as a single unnamed database can ignore this option. This function may
       only be called after mdb_env_create() and before mdb_env_open().
       Currently a moderate number of slots are cheap but a huge number gets expensive: 7-120
       words per transaction, and every mdb_dbi_open() does a linear search of the opened slots.
       Parameters:
           env An environment handle returned by mdb_env_create()
           dbs The maximum number of databases
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - an invalid parameter was specified, or the environment is already open.
   int ESECT mdb_env_set_maxreaders (MDB_env * env, unsigned int readers)
       Set the maximum number of threads/reader slots for the environment. This defines the
       number of slots in the lock table that is used to track readers in the the environment.
       The default is 126. Starting a read-only transaction normally ties a lock table slot to
       the current thread until the environment closes or the thread exits. If MDB_NOTLS is in
       use, mdb_txn_begin() instead ties the slot to the MDB_txn object until it or the MDB_env
       object is destroyed. This function may only be called after mdb_env_create() and before
       mdb_env_open().
       Parameters:
           env An environment handle returned by mdb_env_create()
           readers The maximum number of reader lock table slots
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - an invalid parameter was specified, or the environment is already open.
   int ESECT mdb_env_get_maxreaders (MDB_env * env, unsigned int * readers)
       Get the maximum number of threads/reader slots for the environment.
       Parameters:
           env An environment handle returned by mdb_env_create()
           readers Address of an integer to store the number of readers
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - an invalid parameter was specified.
   static int ESECT mdb_env_open2 (MDB_env * env) [static]
       Further setup required for opening an LMDB environment
   static void mdb_env_reader_dest (void * ptr) [static]
       Release a reader thread's slot in the reader lock table. This function is called
       automatically when a thread exits.
       Parameters:
           ptr This points to the slot in the reader lock table.
   static int ESECT mdb_env_share_locks (MDB_env * env, int * excl) [static]
       Downgrade the exclusive lock on the region back to shared
   static int ESECT mdb_env_excl_lock (MDB_env * env, int * excl) [static]
       Try to get exclusive lock, otherwise shared. Maintain *excl = -1: no/unknown lock, 0:
       shared, 1: exclusive.
   static int ESECT mdb_env_setup_locks (MDB_env * env, char * lpath, int mode, int * excl)
       [static]
       Open and/or initialize the lock region for the environment.
       Parameters:
           env The LMDB environment.
           lpath The pathname of the file used for the lock region.
           mode The Unix permissions for the file, if we create it.
           excl In -1, out lock type: -1 none, 0 shared, 1 exclusive
       Returns:
           0 on success, non-zero on failure.
   int ESECT mdb_env_open (MDB_env * env, const char * path, unsigned int flags, mdb_mode_t mode)
       Open an environment handle. If this function fails, mdb_env_close() must be called to
       discard the MDB_env handle.
       Parameters:
           env An environment handle returned by mdb_env_create()
           path The directory in which the database files reside. This directory must already
           exist and be writable.
           flags Special options for this environment. This parameter must be set to 0 or by
           bitwise OR'ing together one or more of the values described here. Flags set by
           mdb_env_set_flags() are also used.

           · MDB_FIXEDMAP use a fixed address for the mmap region. This flag must be specified
             when creating the environment, and is stored persistently in the environment. If
             successful, the memory map will always reside at the same virtual address and
             pointers used to reference data items in the database will be constant across
             multiple invocations. This option may not always work, depending on how the
             operating system has allocated memory to shared libraries and other uses. The
             feature is highly experimental.
           · MDB_NOSUBDIR By default, LMDB creates its environment in a directory whose pathname
             is given in path, and creates its data and lock files under that directory. With
             this option, path is used as-is for the database main data file. The database lock
             file is the path with '-lock' appended.
           · MDB_RDONLY Open the environment in read-only mode. No write operations will be
             allowed. LMDB will still modify the lock file - except on read-only filesystems,
             where LMDB does not use locks.
           · MDB_WRITEMAP Use a writeable memory map unless MDB_RDONLY is set. This is faster and
             uses fewer mallocs, but loses protection from application bugs like wild pointer
             writes and other bad updates into the database. Incompatible with nested
             transactions. Do not mix processes with and without MDB_WRITEMAP on the same
             environment. This can defeat durability (mdb_env_sync etc).
           · MDB_NOMETASYNC Flush system buffers to disk only once per transaction, omit the
             metadata flush. Defer that until the system flushes files to disk, or next non-
             MDB_RDONLY commit or mdb_env_sync(). This optimization maintains database integrity,
             but a system crash may undo the last committed transaction. I.e. it preserves the
             ACI (atomicity, consistency, isolation) but not D (durability) database property.
             This flag may be changed at any time using mdb_env_set_flags().
           · MDB_NOSYNC Don't flush system buffers to disk when committing a transaction. This
             optimization means a system crash can corrupt the database or lose the last
             transactions if buffers are not yet flushed to disk. The risk is governed by how
             often the system flushes dirty buffers to disk and how often mdb_env_sync() is
             called. However, if the filesystem preserves write order and the MDB_WRITEMAP flag
             is not used, transactions exhibit ACI (atomicity, consistency, isolation) properties
             and only lose D (durability). I.e. database integrity is maintained, but a system
             crash may undo the final transactions. Note that (MDB_NOSYNC | MDB_WRITEMAP) leaves
             the system with no hint for when to write transactions to disk, unless
             mdb_env_sync() is called. (MDB_MAPASYNC | MDB_WRITEMAP) may be preferable. This flag
             may be changed at any time using mdb_env_set_flags().
           · MDB_MAPASYNC When using MDB_WRITEMAP, use asynchronous flushes to disk. As with
             MDB_NOSYNC, a system crash can then corrupt the database or lose the last
             transactions. Calling mdb_env_sync() ensures on-disk database integrity until next
             commit. This flag may be changed at any time using mdb_env_set_flags().
           · MDB_NOTLS Don't use Thread-Local Storage. Tie reader locktable slots to MDB_txn
             objects instead of to threads. I.e. mdb_txn_reset() keeps the slot reseved for the
             MDB_txn object. A thread may use parallel read-only transactions. A read-only
             transaction may span threads if the user synchronizes its use. Applications that
             multiplex many user threads over individual OS threads need this option. Such an
             application must also serialize the write transactions in an OS thread, since LMDB's
             write locking is unaware of the user threads.
           · MDB_NOLOCK Don't do any locking. If concurrent access is anticipated, the caller
             must manage all concurrency itself. For proper operation the caller must enforce
             single-writer semantics, and must ensure that no readers are using old transactions
             while a writer is active. The simplest approach is to use an exclusive lock so that
             no readers may be active at all when a writer begins.
           · MDB_NORDAHEAD Turn off readahead. Most operating systems perform readahead on read
             requests by default. This option turns it off if the OS supports it. Turning it off
             may help random read performance when the DB is larger than RAM and system RAM is
             full. The option is not implemented on Windows.
           · MDB_NOMEMINIT Don't initialize malloc'd memory before writing to unused spaces in
             the data file. By default, memory for pages written to the data file is obtained
             using malloc. While these pages may be reused in subsequent transactions, freshly
             malloc'd pages will be initialized to zeroes before use. This avoids persisting
             leftover data from other code (that used the heap and subsequently freed the memory)
             into the data file. Note that many other system libraries may allocate and free
             memory from the heap for arbitrary uses. E.g., stdio may use the heap for file I/O
             buffers. This initialization step has a modest performance cost so some applications
             may want to disable it using this flag. This option can be a problem for
             applications which handle sensitive data like passwords, and it makes memory
             checkers like Valgrind noisy. This flag is not needed with MDB_WRITEMAP, which
             writes directly to the mmap instead of using malloc for pages. The initialization is
             also skipped if MDB_RESERVE is used; the caller is expected to overwrite all of the
             memory that was reserved in that case. This flag may be changed at any time using
             mdb_env_set_flags().
           mode The UNIX permissions to set on created files and semaphores. This parameter is
           ignored on Windows.
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · MDB_VERSION_MISMATCH - the version of the LMDB library doesn't match the version
             that created the database environment.
           · MDB_INVALID - the environment file headers are corrupted.
           · ENOENT - the directory specified by the path parameter doesn't exist.
           · EACCES - the user didn't have permission to access the environment files.
           · EAGAIN - the environment was locked by another process.
   void ESECT mdb_env_close (MDB_env * env)
       Close the environment and release the memory map. Only a single thread may call this
       function. All transactions, databases, and cursors must already be closed before calling
       this function. Attempts to use any such handles after calling this function will cause a
       SIGSEGV. The environment handle will be freed and must not be used again after this call.
       Parameters:
           env An environment handle returned by mdb_env_create()
   static int mdb_cmp_long (const MDB_val * a, const MDB_val * b) [static]
       Compare two items pointing at aligned size_t's
   static int mdb_cmp_int (const MDB_val * a, const MDB_val * b) [static]
       Compare two items pointing at aligned unsigned int's.
       This is also set as MDB_INTEGERDUP|MDB_DUPFIXED's MDB_dbx.md_dcmp, but mdb_cmp_clong() is
       called instead if the data type is size_t.
   static int mdb_cmp_cint (const MDB_val * a, const MDB_val * b) [static]
       Compare two items pointing at unsigned ints of unknown alignment. Nodes and keys are
       guaranteed to be 2-byte aligned.
   static int mdb_cmp_memn (const MDB_val * a, const MDB_val * b) [static]
       Compare two items lexically
   static int mdb_cmp_memnr (const MDB_val * a, const MDB_val * b) [static]
       Compare two items in reverse byte order
   static int mdb_page_search_lowest (MDB_cursor * mc) [static]
       Search for the lowest key under the current branch page. This just bypasses a NUMKEYS
       check in the current page before calling mdb_page_search_root(), because the callers are
       all in situations where the current page is known to be underfilled.
   int mdb_get (MDB_txn * txn, MDB_dbi dbi, MDB_val * key, MDB_val * data)
       Get items from a database. This function retrieves key/data pairs from the database. The
       address and length of the data associated with the specified key are returned in the
       structure to which data refers. If the database supports duplicate keys (MDB_DUPSORT) then
       the first data item for the key will be returned. Retrieval of other items requires the
       use of mdb_cursor_get().
       Note:
           The memory pointed to by the returned values is owned by the database. The caller need
           not dispose of the memory, and may not modify it in any way. For values returned in a
           read-only transaction any modification attempts will cause a SIGSEGV.
           Values returned from the database are valid only until a subsequent update operation,
           or the end of the transaction.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
           dbi A database handle returned by mdb_dbi_open()
           key The key to search for in the database
           data The data corresponding to the key
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · MDB_NOTFOUND - the key was not in the database.
           · EINVAL - an invalid parameter was specified.
   int mdb_cursor_get (MDB_cursor * cursor, MDB_val * key, MDB_val * data, MDB_cursor_op op)
       Retrieve by cursor. This function retrieves key/data pairs from the database. The address
       and length of the key are returned in the object to which key refers (except for the case
       of the MDB_SET option, in which the key object is unchanged), and the address and length
       of the data are returned in the object to which data refers. See mdb_get() for
       restrictions on using the output values.
       Parameters:
           cursor A cursor handle returned by mdb_cursor_open()
           key The key for a retrieved item
           data The data of a retrieved item
           op A cursor operation MDB_cursor_op
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · MDB_NOTFOUND - no matching key found.
           · EINVAL - an invalid parameter was specified.
   static int mdb_cursor_touch (MDB_cursor * mc) [static]
       Touch all the pages in the cursor stack. Set mc_top. Makes sure all the pages are
       writable, before attempting a write operation.
       Parameters:
           mc The cursor to operate on.
   int mdb_cursor_put (MDB_cursor * cursor, MDB_val * key, MDB_val * data, unsigned int flags)
       Store by cursor. This function stores key/data pairs into the database. The cursor is
       positioned at the new item, or on failure usually near it.
       Note:
           Earlier documentation incorrectly said errors would leave the state of the cursor
           unchanged.
       Parameters:
           cursor A cursor handle returned by mdb_cursor_open()
           key The key operated on.
           data The data operated on.
           flags Options for this operation. This parameter must be set to 0 or one of the values
           described here.

           · MDB_CURRENT - replace the item at the current cursor position. The key parameter
             must still be provided, and must match it. If using sorted duplicates (MDB_DUPSORT)
             the data item must still sort into the same place. This is intended to be used when
             the new data is the same size as the old. Otherwise it will simply perform a delete
             of the old record followed by an insert.
           · MDB_NODUPDATA - enter the new key/data pair only if it does not already appear in
             the database. This flag may only be specified if the database was opened with
             MDB_DUPSORT. The function will return MDB_KEYEXIST if the key/data pair already
             appears in the database.
           · MDB_NOOVERWRITE - enter the new key/data pair only if the key does not already
             appear in the database. The function will return MDB_KEYEXIST if the key already
             appears in the database, even if the database supports duplicates (MDB_DUPSORT).
           · MDB_RESERVE - reserve space for data of the given size, but don't copy the given
             data. Instead, return a pointer to the reserved space, which the caller can fill in
             later. 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:
           cursor A cursor handle returned by mdb_cursor_open()
           flags Options for this operation. This parameter must be set to 0 or one of the values
           described here.

           · MDB_NODUPDATA - delete all of the data items for the current key. This flag may only
             be specified if the database was opened with MDB_DUPSORT.
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EACCES - an attempt was made to write in a read-only transaction.
           · EINVAL - an invalid parameter was specified.
   int mdb_cursor_open (MDB_txn * txn, MDB_dbi dbi, MDB_cursor ** cursor)
       Create a cursor handle. A cursor is associated with a specific transaction and database. A
       cursor cannot be used when its database handle is closed. Nor when its transaction has
       ended, except with mdb_cursor_renew(). It can be discarded with mdb_cursor_close(). A
       cursor in a write-transaction can be closed before its transaction ends, and will
       otherwise be closed when its transaction ends. A cursor in a read-only transaction must be
       closed explicitly, before or after its transaction ends. It can be reused with
       mdb_cursor_renew() before finally closing it.
       Note:
           Earlier documentation said that cursors in every transaction were closed when the
           transaction committed or aborted.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
           dbi A database handle returned by mdb_dbi_open()
           cursor Address where the new MDB_cursor handle will be stored
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - an invalid parameter was specified.
   int mdb_cursor_renew (MDB_txn * txn, MDB_cursor * cursor)
       Renew a cursor handle. A cursor is associated with a specific transaction and database.
       Cursors that are only used in read-only transactions may be re-used, to avoid unnecessary
       malloc/free overhead. The cursor may be associated with a new read-only transaction, and
       referencing the same database handle as it was created with. This may be done whether the
       previous transaction is live or dead.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
           cursor A cursor handle returned by mdb_cursor_open()
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - an invalid parameter was specified.
   int mdb_cursor_count (MDB_cursor * cursor, size_t * countp)
       Return count of duplicates for current key. This call is only valid on databases that
       support sorted duplicate data items MDB_DUPSORT.
       Parameters:
           cursor A cursor handle returned by mdb_cursor_open()
           countp Address where the count will be stored
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - cursor is not initialized, or an invalid parameter was specified.
   void mdb_cursor_close (MDB_cursor * cursor)
       Close a cursor handle. The cursor handle will be freed and must not be used again after
       this call. Its transaction must still be live if it is a write-transaction.
       Parameters:
           cursor A cursor handle returned by mdb_cursor_open()
   MDB_txn* mdb_cursor_txn (MDB_cursor * cursor)
       Return the cursor's transaction handle.
       Parameters:
           cursor A cursor handle returned by mdb_cursor_open()
   MDB_dbi mdb_cursor_dbi (MDB_cursor * cursor)
       Return the cursor's database handle.
       Parameters:
           cursor A cursor handle returned by mdb_cursor_open()
   static void mdb_cursor_copy (const MDB_cursor * csrc, MDB_cursor * cdst) [static]
       Copy the contents of a cursor.
       Parameters:
           csrc The cursor to copy from.
           cdst The cursor to copy to.
   int mdb_del (MDB_txn * txn, MDB_dbi dbi, MDB_val * key, MDB_val * data)
       Delete items from a database. This function removes key/data pairs from the database. If
       the database does not support sorted duplicate data items (MDB_DUPSORT) the data parameter
       is ignored. If the database supports sorted duplicates and the data parameter is NULL, all
       of the duplicate data items for the key will be deleted. Otherwise, if the data parameter
       is non-NULL only the matching data item will be deleted. This function will return
       MDB_NOTFOUND if the specified key/data pair is not in the database.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
           dbi A database handle returned by mdb_dbi_open()
           key The key to delete from the database
           data The data to delete
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EACCES - an attempt was made to write in a read-only transaction.
           · EINVAL - an invalid parameter was specified.
   int mdb_put (MDB_txn * txn, MDB_dbi dbi, MDB_val * key, MDB_val * data, unsigned int flags)
       Store items into a database. This function stores key/data pairs in the database. The
       default behavior is to enter the new key/data pair, replacing any previously existing key
       if duplicates are disallowed, or adding a duplicate data item if duplicates are allowed
       (MDB_DUPSORT).
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
           dbi A database handle returned by mdb_dbi_open()
           key The key to store in the database
           data The data to store
           flags Special options for this operation. This parameter must be set to 0 or by
           bitwise OR'ing together one or more of the values described here.

           · MDB_NODUPDATA - enter the new key/data pair only if it does not already appear in
             the database. This flag may only be specified if the database was opened with
             MDB_DUPSORT. The function will return MDB_KEYEXIST if the key/data pair already
             appears in the database.
           · MDB_NOOVERWRITE - enter the new key/data pair only if the key does not already
             appear in the database. The function will return MDB_KEYEXIST if the key already
             appears in the database, even if the database supports duplicates (MDB_DUPSORT). The
             data parameter will be set to point to the existing item.
           · MDB_RESERVE - reserve space for data of the given size, but don't copy the given
             data. Instead, return a pointer to the reserved space, which the caller can fill in
             later - before the next update operation or the transaction ends. This saves an
             extra memcpy if the data is being generated later. LMDB does nothing else with this
             memory, the caller is expected to modify all of the space requested. This flag must
             not be specified if the database was opened with MDB_DUPSORT.
           · MDB_APPEND - append the given key/data pair to the end of the database. This option
             allows fast bulk loading when keys are already known to be in the correct order.
             Loading unsorted keys with this flag will cause a MDB_KEYEXIST error.
           · MDB_APPENDDUP - as above, but for sorted dup data.
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · MDB_MAP_FULL - the database is full, see mdb_env_set_mapsize().
           · MDB_TXN_FULL - the transaction has too many dirty pages.
           · EACCES - an attempt was made to write in a read-only transaction.
           · EINVAL - an invalid parameter was specified.
   static THREAD_RET ESECT CALL_CONV mdb_env_copythr (void * arg) [static]
       Dedicated writer thread for compacting copy.
   static int ESECT mdb_env_cthr_toggle (mdb_copy * my, int 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:
           env An environment handle returned by mdb_env_create(). It must have already been
           opened successfully.
           path The directory in which the copy will reside. This directory must already exist
           and be writable but must otherwise be empty.
           flags Special options for this operation. This parameter must be set to 0 or by
           bitwise OR'ing together one or more of the values described here.

           · MDB_CP_COMPACT - Perform compaction while copying: omit free pages and sequentially
             renumber all pages in output. This option consumes more CPU and runs more slowly
             than the default.
       Returns:
           A non-zero error value on failure and 0 on success.
   int ESECT mdb_env_copy (MDB_env * env, const char * path)
       Copy an LMDB environment to the specified path. This function may be used to make a backup
       of an existing environment. No lockfile is created, since it gets recreated at need.
       Note:
           This call can trigger significant file size growth if run in parallel with write
           transactions, because it employs a read-only transaction. See long-lived transactions
           under Caveats.
       Parameters:
           env An environment handle returned by mdb_env_create(). It must have already been
           opened successfully.
           path The directory in which the copy will reside. This directory must already exist
           and be writable but must otherwise be empty.
       Returns:
           A non-zero error value on failure and 0 on success.
   int ESECT mdb_env_set_flags (MDB_env * env, unsigned int flags, int onoff)
       Set environment flags. This may be used to set some flags in addition to those from
       mdb_env_open(), or to unset these flags. If several threads change the flags at the same
       time, the result is undefined.
       Parameters:
           env An environment handle returned by mdb_env_create()
           flags The flags to change, bitwise OR'ed together
           onoff A non-zero value sets the flags, zero clears them.
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - an invalid parameter was specified.
   int ESECT mdb_env_get_flags (MDB_env * env, unsigned int * flags)
       Get environment flags.
       Parameters:
           env An environment handle returned by mdb_env_create()
           flags The address of an integer to store the flags
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - an invalid parameter was specified.
   int ESECT mdb_env_set_userctx (MDB_env * env, void * ctx)
       Set application information associated with the MDB_env.
       Parameters:
           env An environment handle returned by mdb_env_create()
           ctx An arbitrary pointer for whatever the application needs.
       Returns:
           A non-zero error value on failure and 0 on success.
   void* ESECT mdb_env_get_userctx (MDB_env * env)
       Get the application information associated with the MDB_env.
       Parameters:
           env An environment handle returned by mdb_env_create()
       Returns:
           The pointer set by mdb_env_set_userctx().
   int ESECT mdb_env_set_assert (MDB_env * env, MDB_assert_func * func)
       Set or reset the assert() callback of the environment. Disabled if liblmdb is buillt with
       NDEBUG.
       Note:
           This hack should become obsolete as lmdb's error handling matures.
       Parameters:
           env An environment handle returned by mdb_env_create().
           func An MDB_assert_func function, or 0.
       Returns:
           A non-zero error value on failure and 0 on success.
   int ESECT mdb_env_get_path (MDB_env * env, const char ** path)
       Return the path that was used in mdb_env_open().
       Parameters:
           env An environment handle returned by mdb_env_create()
           path Address of a string pointer to contain the path. This is the actual string in the
           environment, not a copy. It should not be altered in any way.
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - an invalid parameter was specified.
   int ESECT mdb_env_get_fd (MDB_env * env, mdb_filehandle_t * fd)
       Return the filedescriptor for the given environment.
       Parameters:
           env An environment handle returned by mdb_env_create()
           fd Address of a mdb_filehandle_t to contain the descriptor.
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - an invalid parameter was specified.
   static int ESECT mdb_stat0 (MDB_env * env, MDB_db * db, MDB_stat * arg) [static]
       Common code for mdb_stat() and mdb_env_stat().
       Parameters:
           env the environment to operate in.
           db the MDB_db record containing the stats to return.
           arg the address of an MDB_stat structure to receive the stats.
       Returns:
           0, this function always succeeds.
   int ESECT mdb_env_stat (MDB_env * env, MDB_stat * stat)
       Return statistics about the LMDB environment.
       Parameters:
           env An environment handle returned by mdb_env_create()
           stat The address of an MDB_stat structure where the statistics will be copied
   int ESECT mdb_env_info (MDB_env * env, MDB_envinfo * stat)
       Return information about the LMDB environment.
       Parameters:
           env An environment handle returned by mdb_env_create()
           stat The address of an MDB_envinfo structure where the information will be copied
   int mdb_dbi_open (MDB_txn * txn, const char * name, unsigned int flags, MDB_dbi * dbi)
       Open a database in the environment. A database handle denotes the name and parameters of a
       database, independently of whether such a database exists. The database handle may be
       discarded by calling mdb_dbi_close(). The old database handle is returned if the database
       was already open. The handle may only be closed once.
       The database handle will be private to the current transaction until the transaction is
       successfully committed. If the transaction is aborted the handle will be closed
       automatically. After a successful commit the handle will reside in the shared environment,
       and may be used by other transactions.
       This function must not be called from multiple concurrent transactions in the same
       process. A transaction that uses this function must finish (either commit or abort) before
       any other transaction in the process may use this function.
       To use named databases (with name != NULL), mdb_env_set_maxdbs() must be called before
       opening the environment. Database names are keys in the unnamed database, and may be read
       but not written.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
           name The name of the database to open. If only a single database is needed in the
           environment, this value may be NULL.
           flags Special options for this database. This parameter must be set to 0 or by bitwise
           OR'ing together one or more of the values described here.

           · MDB_REVERSEKEY Keys are strings to be compared in reverse order, from the end of the
             strings to the beginning. By default, Keys are treated as strings and compared from
             beginning to end.
           · MDB_DUPSORT Duplicate keys may be used in the database. (Or, from another
             perspective, keys may have multiple data items, stored in sorted order.) By default
             keys must be unique and may have only a single data item.
           · MDB_INTEGERKEY Keys are binary integers in native byte order, either unsigned int or
             size_t, and will be sorted as such. The keys must all be of the same size.
           · MDB_DUPFIXED This flag may only be used in combination with MDB_DUPSORT. This option
             tells the library that the data items for this database are all the same size, which
             allows further optimizations in storage and retrieval. When all data items are the
             same size, the MDB_GET_MULTIPLE 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.
           dbi Address where the new MDB_dbi handle will be stored
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · MDB_NOTFOUND - the specified database doesn't exist in the environment and
             MDB_CREATE was not specified.
           · MDB_DBS_FULL - too many databases have been opened. See mdb_env_set_maxdbs().
   int ESECT mdb_stat (MDB_txn * txn, MDB_dbi dbi, MDB_stat * stat)
       Retrieve statistics for a database.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
           dbi A database handle returned by mdb_dbi_open()
           stat The address of an MDB_stat structure where the statistics will be copied
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - an invalid parameter was specified.
   void mdb_dbi_close (MDB_env * env, MDB_dbi dbi)
       Close a database handle. Normally unnecessary. Use with care: This call is not mutex
       protected. Handles should only be closed by a single thread, and only if no other threads
       are going to reference the database handle or one of its cursors any further. Do not close
       a handle if an existing transaction has modified its database. Doing so can cause
       misbehavior from database corruption to errors like MDB_BAD_VALSIZE (since the DB name is
       gone).
       Closing a database handle is not necessary, but lets mdb_dbi_open() reuse the handle
       value. Usually it's better to set a bigger mdb_env_set_maxdbs(), unless that value would
       be large.
       Parameters:
           env An environment handle returned by mdb_env_create()
           dbi A database handle returned by mdb_dbi_open()
   int mdb_dbi_flags (MDB_txn * txn, MDB_dbi dbi, unsigned int * flags)
       Retrieve the DB flags for a database handle.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
           dbi A database handle returned by mdb_dbi_open()
           flags Address where the flags will be returned.
       Returns:
           A non-zero error value on failure and 0 on success.
   int mdb_drop (MDB_txn * txn, MDB_dbi dbi, int del)
       Empty or delete+close a database. See mdb_dbi_close() for restrictions about closing the
       DB handle.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
           dbi A database handle returned by mdb_dbi_open()
           del 0 to empty the DB, 1 to delete it from the environment and close the DB handle.
       Returns:
           A non-zero error value on failure and 0 on success.
   int mdb_set_compare (MDB_txn * txn, MDB_dbi dbi, MDB_cmp_func * cmp)
       Set a custom key comparison function for a database. The comparison function is called
       whenever it is necessary to compare a key specified by the application with a key
       currently stored in the database. If no comparison function is specified, and no special
       key flags were specified with mdb_dbi_open(), the keys are compared lexically, with
       shorter keys collating before longer keys.
       Warning:
           This function must be called before any data access functions are used, otherwise data
           corruption may occur. The same comparison function must be used by every program
           accessing the database, every time the database is used.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
           dbi A database handle returned by mdb_dbi_open()
           cmp A MDB_cmp_func function
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - an invalid parameter was specified.
   int mdb_set_dupsort (MDB_txn * txn, MDB_dbi dbi, MDB_cmp_func * cmp)
       Set a custom data comparison function for a MDB_DUPSORT database. This comparison function
       is called whenever it is necessary to compare a data item specified by the application
       with a data item currently stored in the database. This function only takes effect if the
       database was opened with the MDB_DUPSORT flag. If no comparison function is specified, and
       no special key flags were specified with mdb_dbi_open(), the data items are compared
       lexically, with shorter items collating before longer items.
       Warning:
           This function must be called before any data access functions are used, otherwise data
           corruption may occur. The same comparison function must be used by every program
           accessing the database, every time the database is used.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
           dbi A database handle returned by mdb_dbi_open()
           cmp A MDB_cmp_func function
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - an invalid parameter was specified.
   int mdb_set_relfunc (MDB_txn * txn, MDB_dbi dbi, MDB_rel_func * rel)
       Set a relocation function for a MDB_FIXEDMAP database.
       Todo
           The relocation function is called whenever it is necessary to move the data of an item
           to a different position in the database (e.g. through tree balancing operations,
           shifts as a result of adds or deletes, etc.). It is intended to allow
           address/position-dependent data items to be stored in a database in an environment
           opened with the MDB_FIXEDMAP option. Currently the relocation feature is unimplemented
           and setting this function has no effect.
           Parameters:
               txn A transaction handle returned by mdb_txn_begin()
               dbi A database handle returned by mdb_dbi_open()
               rel A MDB_rel_func function
           Returns:
               A non-zero error value on failure and 0 on success. Some possible errors are:
       · EINVAL - an invalid parameter was specified.
   int mdb_set_relctx (MDB_txn * txn, MDB_dbi dbi, void * ctx)
       Set a context pointer for a MDB_FIXEDMAP database's relocation function. See
       mdb_set_relfunc and MDB_rel_func for more details.
       Parameters:
           txn A transaction handle returned by mdb_txn_begin()
           dbi A database handle returned by mdb_dbi_open()
           ctx An arbitrary pointer for whatever the application needs. It will be passed to the
           callback function set by mdb_set_relfunc as its relctx parameter whenever the callback
           is invoked.
       Returns:
           A non-zero error value on failure and 0 on success. Some possible errors are:

           · EINVAL - an invalid parameter was specified.
   int ESECT mdb_env_get_maxkeysize (MDB_env * env)
       Get the maximum size of keys and MDB_DUPSORT data we can write. Depends on the compile-
       time constant MDB_MAXKEYSIZE. Default 511. See MDB_val.
       Parameters:
           env An environment handle returned by mdb_env_create()
       Returns:
           The maximum size of a key we can write
   int ESECT mdb_reader_list (MDB_env * env, MDB_msg_func * func, void * ctx)
       Dump the entries in the reader lock table.
       Parameters:
           env An environment handle returned by mdb_env_create()
           func A MDB_msg_func function
           ctx Anything the message function needs
       Returns:
           < 0 on failure, >= 0 on success.
   static int ESECT mdb_pid_insert (MDB_PID_T * ids, MDB_PID_T pid) [static]
       Insert pid into list if not already present. return -1 if already present.
   int ESECT mdb_reader_check (MDB_env * env, int * dead)
       Check for stale entries in the reader lock table.
       Parameters:
           env An environment handle returned by mdb_env_create()
           dead Number of stale slots that were cleared
       Returns:
           0 on success, non-zero on failure.

Variable Documentation

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

Author

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