Provided by: lmdb-doc_0.9.10-1_all 
NAME
MDB Internals -
Modules
ID List Management
Windows 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
Macros
#define MDB_DSYNC O_DSYNC
#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 0x8000
The maximum size of a database page.
#define MDB_MINKEYS 2
#define MDB_MAGIC 0xBEEFC0DE
#define MDB_DATA_VERSION 1
#define MDB_LOCK_VERSION 1
#define MDB_MAXKEYSIZE 511
The maximum size of a key in the database.
#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 DEFAULT_MAPSIZE 1048576
#define PAGEHDRSZ ((unsigned) offsetof(MDB_page, mp_ptrs))
#define METADATA(p) ((void *)((char *)(p) + PAGEHDRSZ))
#define NUMKEYS(p) (((p)->mp_lower - PAGEHDRSZ) >> 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 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]))
#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 CURSOR_STACK 32
#define MDB_COMMIT_PAGES 64
#define MAX_WRITE (0x80000000U >> (sizeof(ssize_t) == 4))
#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_txn_reset0(txn, act) mdb_txn_reset0(txn)
#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
Typedefs
typedef MDB_ID pgno_t
typedef MDB_ID txnid_t
typedef uint16_t indx_t
Enumerations
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 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 int 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_page *mp, indx_t indx, int ksize)
static void mdb_node_shrink (MDB_page *mp, indx_t indx)
static int mdb_node_move (MDB_cursor *csrc, MDB_cursor *cdst)
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, MDB_node *leaf)
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 int mdb_drop0 (MDB_cursor *mc, int subs)
static void mdb_default_cmp (MDB_txn *txn, MDB_dbi dbi)
char * mdb_version (int *major, int *minor, int *patch)
Return the mdb library version information.
char * mdb_strerror (int err)
Return a string describing a given error code.
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_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 void mdb_txn_reset0 (MDB_txn *txn, const char *act)
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.
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 int mdb_env_init_meta (MDB_env *env, MDB_meta *meta)
int mdb_env_create (MDB_env **env)
Create an MDB environment handle.
static int mdb_env_map (MDB_env *env, void *addr, int newsize)
int mdb_env_set_mapsize (MDB_env *env, size_t size)
Set the size of the memory map to use for this environment.
int mdb_env_set_maxdbs (MDB_env *env, MDB_dbi dbs)
Set the maximum number of named databases for the environment.
int mdb_env_set_maxreaders (MDB_env *env, unsigned int readers)
Set the maximum number of threads/reader slots for the environment.
int mdb_env_get_maxreaders (MDB_env *env, unsigned int *readers)
Get the maximum number of threads/reader slots for the environment.
static int mdb_env_open2 (MDB_env *env)
static void mdb_env_reader_dest (void *ptr)
static int mdb_env_share_locks (MDB_env *env, int *excl)
static int mdb_env_excl_lock (MDB_env *env, int *excl)
static int mdb_env_setup_locks (MDB_env *env, char *lpath, int mode, int *excl)
int mdb_env_open (MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode)
Open an environment handle.
int mdb_env_copyfd (MDB_env *env, HANDLE fd)
int mdb_env_copy (MDB_env *env, const char *path)
Copy an MDB environment to the specified path.
void 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.
int mdb_env_set_flags (MDB_env *env, unsigned int flag, int onoff)
Set environment flags.
int mdb_env_get_flags (MDB_env *env, unsigned int *arg)
Get environment flags.
int mdb_env_get_path (MDB_env *env, const char **arg)
Return the path that was used in mdb_env_open().
int mdb_env_get_fd (MDB_env *env, mdb_filehandle_t *arg)
Return the filedescriptor for the given environment.
static int mdb_stat0 (MDB_env *env, MDB_db *db, MDB_stat *arg)
int mdb_env_stat (MDB_env *env, MDB_stat *arg)
Return statistics about the MDB environment.
int mdb_env_info (MDB_env *env, MDB_envinfo *arg)
Return information about the MDB environment.
int mdb_dbi_open (MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi)
Open a database in the environment.
int mdb_stat (MDB_txn *txn, MDB_dbi dbi, MDB_stat *arg)
Retrieve statistics for a database.
void mdb_dbi_close (MDB_env *env, MDB_dbi dbi)
Close a database handle.
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 mdb_env_get_maxkeysize (MDB_env *env)
Get the maximum size of a key for the environment.
int mdb_reader_list (MDB_env *env, MDB_msg_func *func, void *ctx)
Dump the entries in the reader lock table.
static int mdb_pid_insert (MDB_PID_T *ids, MDB_PID_T pid)
int 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
void * 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
void* MDB_page::p_next
for in-memory list of freed structs
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. We guarantee 2-byte alignment for nodes.
Data Fields
unsigned short mn_offset [2]
unsigned short mn_flags
unsigned short mn_ksize
char mn_data [1]
Field Documentation
unsigned short MDB_node::mn_offset[2]
storage for mn_lo and mn_hi
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 [2]
pgno_t mm_last_pg
txnid_t mm_txnid
Field Documentation
uint32_t MDB_meta::mm_magic
Stamp identifying this as an MDB file. It must be set to MDB_MAGIC.
uint32_t MDB_meta::mm_version
Version number of this lock 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[2]
first is free space, 2nd is main db
pgno_t MDB_meta::mm_last_pg
last used page in file
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_IDL mt_spill_pgs
union {
MDB_ID2L dirty_list
MDB_reader * reader
} mt_u
MDB_dbx * mt_dbxs
MDB_db * mt_dbs
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
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_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
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. This number only ever increments; 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
unsigned int me_numreaders
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 [2]
void * me_pbuf
MDB_txn * me_txn
size_t me_mapsize
off_t me_size
pgno_t me_maxpg
MDB_dbx * me_dbxs
uint16_t * me_dbflags
pthread_key_t me_txkey
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
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
unsigned int MDB_env::me_numreaders
max numreaders set by this env
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[2]
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
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
pthread_key_t MDB_env::me_txkey
thread-key for readers
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
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
Macro Definition Documentation
#define MDB_DSYNC O_DSYNC
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. Otherwise compile with the less efficient -DMDB_DSYNC=O_SYNC.
#define MDB_FDATASYNC fdatasync
Function for flushing the data of a file. Define this to fsync if fdatasync() is not
supported.
#define MAX_PAGESIZE 0x8000
The maximum size of a database page. This is 32k, since it 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 MDB 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 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 511
The maximum size of a key in the database. The library rejects bigger keys, and cannot
deal with records with bigger keys stored by a library with bigger max keysize.
We require that keys all fit onto a regular page. This limit could be raised a bit further
if needed; to something just under (page size / MDB_MINKEYS / 3).
Note that data items in an MDB_DUPSORT database are actually keys of a subDB, so they're
also limited to this size.
#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 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 NUMKEYS(p) (((p)->mp_lower - PAGEHDRSZ) >> 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 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]))
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++; *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 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 MDB_SPLIT_REPLACE MDB_APPENDDUP
newkey is not new
#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
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, intnum, 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_tflags, intnum, 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 int mdb_page_get (MDB_txn *txn, pgno_tpgno, 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, intflags) [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, intflags) [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.
static int mdb_page_split (MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata, pgno_tnewpgno,
unsigned intnflags) [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 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 int 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:
meta toggle (0 or 1).
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 mdb_env_close0 (MDB_env *env, intexcl) [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_tindx, MDB_val *key, MDB_val *data, pgno_tpgno,
unsigned intflags) [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_page *mp, indx_tindx, intksize) [static]
Delete the specified node from a page.
Parameters:
mp The page to operate on.
indx The index of 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_tindx) [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) [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 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, MDB_node *leaf) [static]
Complete a delete operation started by mdb_cursor_del().
static int mdb_cursor_sibling (MDB_cursor *mc, intmove_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_opop)
[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_opop)
[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_opop, 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_dbidbi, 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 int mdb_drop0 (MDB_cursor *mc, intsubs) [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_dbidbi) [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()
char* mdb_version (int *major, int *minor, int *patch)
Return the mdb library version information. Return the library version info.
char* mdb_strerror (interr)
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 MDB library error is returned.
See Return Codes for a list of MDB-specific error codes.
Parameters:
err The error code
Return values:
error message The description of the error
int mdb_cmp (MDB_txn *txn, MDB_dbidbi, 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_dbidbi, 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, unsignednum) [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_pages_xkeep (MDB_cursor *mc, unsignedpflags, intall) [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, intkeep) [static]
Flush (some) dirty pages to the map, after clearing their dirty flag.
Parameters:
txn the transaction that's being committed
keep number of initial pages in dirty_list to keep dirty.
Returns:
0 on success, non-zero on failure.
static int mdb_page_spill (MDB_cursor *m0, MDB_val *key, MDB_val *data) [static]
Spill pages from the dirty list back to disk.
This is intended to prevent running into MDB_TXN_FULL situations, but note that they may
still occur in a few cases: 1) our estimate of the txn size could be too small. Currently
this seems unlikely, except with a large number of MDB_MULTIPLE items. 2) child txns may
run out of space if their parents dirtied a lot of pages and never spilled them. TODO: we
probably should do a preemptive spill during mdb_txn_begin() of a child txn, if the
parent's dirty_room is below a given threshold.
Otherwise, if not using nested txns, it is expected that apps will not run into
MDB_TXN_FULL any more. The pages are flushed to disk the same way as for a txn commit,
e.g. their P_DIRTY flag is cleared. If the txn never references them again, they can be
left alone. If the txn only reads them, they can be used without any fuss. If the txn
writes them again, they can be dirtied immediately without going thru all of the work of
mdb_page_touch(). Such references are handled by mdb_page_unspill().
Also note, we never spill DB root pages, nor pages of active cursors, because we'll need
these back again soon anyway. And in nested txns, we can't spill a page in a child txn if
it was already spilled in a parent txn. That would alter the parent txns' data even though
the child hasn't committed yet, and we'd have no way to undo it if the child aborted.
Parameters:
m0 cursor A cursor handle identifying the transaction and database for which we are
checking space.
key For a put operation, the key being stored.
data For a put operation, the data being stored.
Returns:
0 on success, non-zero on failure.
static txnid_t mdb_find_oldest (MDB_txn *txn) [static]
Find oldest txnid still referenced. Expects txn->mt_txnid > 0.
static void mdb_page_dirty (MDB_txn *txn, MDB_page *mp) [static]
Add a page to the txn's dirty list
static void mdb_page_copy (MDB_page *dst, MDB_page *src, unsigned intpsize) [static]
Copy the used portions of a non-overflow page.
Parameters:
dst page to copy into
src page to copy from
psize size of a page
static int mdb_page_unspill (MDB_txn *txn, MDB_page *mp, MDB_page **ret) [static]
Pull a page off the txn's spill list, if present. If a page being referenced was spilled
to disk in this txn, bring it back and make it dirty/writable again.
Parameters:
txn the transaction handle.
mp the page being referenced.
ret the writable page, if any. ret is unchanged if mp wasn't spilled.
int mdb_env_sync (MDB_env *env, intforce)
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. MDB always flushes the OS buffers
upon commit as well, unless the environment was opened with MDB_NOSYNC or in part
MDB_NOMETASYNC.
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:
• 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, unsignedmerge) [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 void mdb_txn_reset0 (MDB_txn *txn, const char *act) [static]
Common code for mdb_txn_reset() and mdb_txn_abort(). May be called twice for readonly
txns: First reset it, then abort.
Parameters:
txn the transaction handle to reset
act why the transaction is being reset
static int mdb_reader_pid (MDB_env *env, enum Pidlock_opop, MDB_PID_Tpid) [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 intflags, 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()
static void mdb_dbis_update (MDB_txn *txn, intkeep) [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 int 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 address of where to store the meta information
Returns:
0 on success, non-zero on failure.
int mdb_env_create (MDB_env **env)
Create an MDB 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 mdb_env_set_mapsize (MDB_env *env, size_tsize)
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.
If the mapsize is changed by another process, 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 mdb_env_set_maxdbs (MDB_env *env, MDB_dbidbs)
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().
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 mdb_env_set_maxreaders (MDB_env *env, unsigned intreaders)
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 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 mdb_env_open2 (MDB_env *env) [static]
Further setup required for opening an MDB 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 mdb_env_share_locks (MDB_env *env, int *excl) [static]
Downgrade the exclusive lock on the region back to shared
static int mdb_env_excl_lock (MDB_env *env, int *excl) [static]
Try to get exlusive lock, otherwise shared. Maintain *excl = -1: no/unknown lock, 0:
shared, 1: exclusive.
static int mdb_env_setup_locks (MDB_env *env, char *lpath, intmode, int *excl) [static]
Open and/or initialize the lock region for the environment.
Parameters:
env The MDB environment.
lpath The pathname of the file used for the lock region.
mode The Unix permissions for the file, if we create it.
excl Resulting file lock type: -1 none, 0 shared, 1 exclusive
excl In -1, out lock type: -1 none, 0 shared, 1 exclusive
Returns:
0 on success, non-zero on failure.
int mdb_env_open (MDB_env *env, const char *path, unsigned intflags, mdb_mode_tmode)
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, MDB 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. MDB will still modify the lock file - except on read-only filesystems,
where MDB 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. Processes with and without MDB_WRITEMAP on the same environment do not
cooperate well.
• 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 MDB'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. 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 MDB 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.
int mdb_env_copy (MDB_env *env, const char *path)
Copy an MDB 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.
void 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
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_dbidbi, 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_opop)
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 intflags)
Store by cursor. This function stores key/data pairs into the database. If the function
fails for any reason, the state of the cursor will be unchanged. If the function succeeds
and an item is inserted into the database, the cursor is always positioned to refer to the
newly inserted item.
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 - overwrite the data of the key/data pair to which the cursor refers
with the specified data item. The key parameter is ignored.
• 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.
• 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 data corruption.
• 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 modify a read-only database.
• EINVAL - an invalid parameter was specified.
int mdb_cursor_del (MDB_cursor *cursor, unsigned intflags)
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 modify a read-only database.
• EINVAL - an invalid parameter was specified.
int mdb_cursor_open (MDB_txn *txn, MDB_dbidbi, 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_dbidbi, 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_dbidbi, MDB_val *key, MDB_val *data, unsigned intflags)
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. MDB does nothing else with this
memory, the caller is expected to modify all of the space requested.
• 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 data corruption.
• 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.
int mdb_env_set_flags (MDB_env *env, unsigned intflags, intonoff)
Set environment flags. This may be used to set some flags in addition to those from
mdb_env_open(), or to unset these flags.
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 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 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 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 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 mdb_env_stat (MDB_env *env, MDB_stat *stat)
Return statistics about the MDB 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 mdb_env_info (MDB_env *env, MDB_envinfo *stat)
Return information about the MDB 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 intflags, 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 must 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. A transaction that
uses this function must finish (either commit or abort) before any other transaction may
use this function.
To use named databases (with name != NULL), mdb_env_set_maxdbs() must be called before
opening the environment.
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. Setting this option
requires all keys to be the same size, typically sizeof(int) or sizeof(size_t).
• 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 also integers,
and should be sorted as such.
• 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 mdb_stat (MDB_txn *txn, MDB_dbidbi, 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_dbidbi)
Close a database handle. 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.
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_dbidbi, 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_dbidbi, intdel)
Empty or delete+close a database.
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_dbidbi, 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_dbidbi, 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_dbidbi, 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_dbidbi, 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 mdb_env_get_maxkeysize (MDB_env *env)
Get the maximum size of a key for the environment. This is 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
int 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 mdb_pid_insert (MDB_PID_T *ids, MDB_PID_Tpid) [static]
Insert pid into list if not already present. return -1 if already present.
int 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",
"MDB_VERSION_MISMATCH: Database environment version mismatch",
"MDB_INVALID: File is not an MDB 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 cannot recover - it must be aborted",
"MDB_BAD_VALSIZE: Too big key/data, key is empty, or wrong DUPFIXED size",
}
Table of descriptions for MDB Return Codes
Author
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