* corrupt the database. Of course if your application code is known to
* be bug-free (...) then this is not an issue.
*
+ * If this is your first time using a transactional embedded key/value
+ * store, you may find the \ref starting page to be helpful.
+ *
* @section caveats_sec Caveats
* Troubleshooting the lock file, plus semaphores on BSD systems:
*
* stale locks can block further operation.
*
* Fix: Check for stale readers periodically, using the
- * #mdb_reader_check function or the \ref mdb_stat_1 "mdb_stat" tool. Or just
- * make all programs using the database close it; the lockfile
- * is always reset on first open of the environment.
+ * #mdb_reader_check function or the \ref mdb_stat_1 "mdb_stat" tool.
+ * Stale writers will be cleared automatically on some systems:
+ * - Windows - automatic
+ * - Linux, systems using POSIX mutexes with Robust option - automatic
+ * - not on BSD, systems using POSIX semaphores.
+ * Otherwise just make all programs using the database close it;
+ * the lockfile is always reset on first open of the environment.
*
* - On BSD systems or others configured with MDB_USE_POSIX_SEM,
* startup can fail due to semaphores owned by another userid.
* access to locks and lock file. Exceptions: On read-only filesystems
* or with the #MDB_NOLOCK flag described under #mdb_env_open().
*
+ * - An LMDB configuration will often reserve considerable \b unused
+ * memory address space and maybe file size for future growth.
+ * This does not use actual memory or disk space, but users may need
+ * to understand the difference so they won't be scared off.
+ *
* - By default, in versions before 0.9.10, unused portions of the data
* file might receive garbage data from memory freed by other code.
* (This does not happen when using the #MDB_WRITEMAP flag.) As of
* transactions. Each transaction belongs to one thread. See below.
* The #MDB_NOTLS flag changes this for read-only transactions.
*
- * - Use an MDB_env* in the process which opened it, without fork()ing.
+ * - Use an MDB_env* in the process which opened it, not after fork().
*
* - Do not have open an LMDB database twice in the same process at
* the same time. Not even from a plain open() call - close()ing it
- * breaks flock() advisory locking.
+ * breaks fcntl() advisory locking. (It is OK to reopen it after
+ * fork() - exec*(), since the lockfile has FD_CLOEXEC set.)
*
* - Avoid long-lived transactions. Read transactions prevent
* reuse of pages freed by newer write transactions, thus the
* for stale readers is performed or the lockfile is reset,
* since the process may not remove it from the lockfile.
*
+ * This does not apply to write transactions if the system clears
+ * stale writers, see above.
+ *
* - If you do that anyway, do a periodic check for stale readers. Or
* close the environment once in a while, so the lockfile can get reset.
*
*
* @author Howard Chu, Symas Corporation.
*
- * @copyright Copyright 2011-2014 Howard Chu, Symas Corp. All rights reserved.
+ * @copyright Copyright 2011-2017 Howard Chu, Symas Corp. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted only as authorized by the OpenLDAP
/** Library minor version */
#define MDB_VERSION_MINOR 9
/** Library patch version */
-#define MDB_VERSION_PATCH 14
+#define MDB_VERSION_PATCH 22
/** Combine args a,b,c into a single integer for easy version comparisons */
#define MDB_VERINT(a,b,c) (((a) << 24) | ((b) << 16) | (c))
MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
/** The release date of this library version */
-#define MDB_VERSION_DATE "September 15, 2014"
+#define MDB_VERSION_DATE "March 21, 2018"
/** A stringifier for the version info */
#define MDB_VERSTR(a,b,c,d) "LMDB " #a "." #b "." #c ": (" d ")"
#define MDB_REVERSEKEY 0x02
/** use sorted duplicates */
#define MDB_DUPSORT 0x04
- /** numeric keys in native byte order.
+ /** numeric keys in native byte order: either unsigned int or size_t.
* The keys must all be of the same size. */
#define MDB_INTEGERKEY 0x08
/** with #MDB_DUPSORT, sorted dup items have fixed size */
#define MDB_DUPFIXED 0x10
- /** with #MDB_DUPSORT, dups are numeric in native byte order */
+ /** with #MDB_DUPSORT, dups are #MDB_INTEGERKEY-style integers */
#define MDB_INTEGERDUP 0x20
/** with #MDB_DUPSORT, use reverse string dups */
#define MDB_REVERSEDUP 0x40
MDB_PREV_NODUP, /**< Position at last data item of previous key */
MDB_SET, /**< Position at specified key */
MDB_SET_KEY, /**< Position at specified key, return key + data */
- MDB_SET_RANGE /**< Position at first key greater than or equal to specified key. */
+ MDB_SET_RANGE, /**< Position at first key greater than or equal to specified key. */
+ MDB_PREV_MULTIPLE /**< Position at previous page and return key and up to
+ a page of duplicate data items. Only for #MDB_DUPFIXED */
} MDB_cursor_op;
/** @defgroup errors Return Codes
#define MDB_PAGE_NOTFOUND (-30797)
/** Located page was wrong type */
#define MDB_CORRUPTED (-30796)
- /** Update of meta page failed, probably I/O error */
+ /** Update of meta page failed or environment had fatal error */
#define MDB_PANIC (-30795)
/** Environment version mismatch */
#define MDB_VERSION_MISMATCH (-30794)
#define MDB_PAGE_FULL (-30786)
/** Database contents grew beyond environment mapsize */
#define MDB_MAP_RESIZED (-30785)
- /** MDB_INCOMPATIBLE: Operation and DB incompatible, or DB flags changed */
+ /** Operation and DB incompatible, or DB type changed. This can mean:
+ * <ul>
+ * <li>The operation expects an #MDB_DUPSORT / #MDB_DUPFIXED database.
+ * <li>Opening a named DB when the unnamed DB has #MDB_DUPSORT / #MDB_INTEGERKEY.
+ * <li>Accessing a data record as a database, or vice versa.
+ * <li>The database was dropped and recreated with different flags.
+ * </ul>
+ */
#define MDB_INCOMPATIBLE (-30784)
/** Invalid reuse of reader locktable slot */
#define MDB_BAD_RSLOT (-30783)
- /** Transaction cannot recover - it must be aborted */
+ /** Transaction must abort, has a child, or is invalid */
#define MDB_BAD_TXN (-30782)
/** Unsupported size of key/DB name/data, or wrong DUPFIXED size */
#define MDB_BAD_VALSIZE (-30781)
* allowed. LMDB will still modify the lock file - except on read-only
* filesystems, where LMDB does not use locks.
* <li>#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
+ * Use a writeable memory map unless MDB_RDONLY is set. This uses
+ * fewer mallocs but loses protection from application bugs
* like wild pointer writes and other bad updates into the database.
+ * This may be slightly faster for DBs that fit entirely in RAM, but
+ * is slower for DBs larger than RAM.
* Incompatible with nested transactions.
- * Processes with and without MDB_WRITEMAP on the same environment do
- * not cooperate well.
+ * Do not mix processes with and without MDB_WRITEMAP on the same
+ * environment. This can defeat durability (#mdb_env_sync etc).
* <li>#MDB_NOMETASYNC
* Flush system buffers to disk only once per transaction, omit the
* metadata flush. Defer that until the system flushes files to disk,
* reserved in that case.
* This flag may be changed at any time using #mdb_env_set_flags().
* </ul>
- * @param[in] mode The UNIX permissions to set on created files. This parameter
- * is ignored on Windows.
+ * @param[in] mode The UNIX permissions to set on created files and semaphores.
+ * This parameter is ignored on Windows.
* @return A non-zero error value on failure and 0 on success. Some possible
* errors are:
* <ul>
* <li>#MDB_CP_COMPACT - Perform compaction while copying: omit free
* pages and sequentially renumber all pages in output. This option
* consumes more CPU and runs more slowly than the default.
+ * Currently it fails if the environment has suffered a page leak.
* </ul>
* @return A non-zero error value on failure and 0 on success.
*/
* Data is always written to disk when #mdb_txn_commit() is called,
* but the operating system may keep it buffered. LMDB always flushes
* the OS buffers upon commit as well, unless the environment was
- * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC.
+ * opened with #MDB_NOSYNC or in part #MDB_NOMETASYNC. This call is
+ * not valid if the environment was opened with #MDB_RDONLY.
* @param[in] env An environment handle returned by #mdb_env_create()
* @param[in] force If non-zero, force a synchronous flush. Otherwise
* if the environment has the #MDB_NOSYNC flag set the flushes
* @return A non-zero error value on failure and 0 on success. Some possible
* errors are:
* <ul>
+ * <li>EACCES - the environment is read-only.
* <li>EINVAL - an invalid parameter was specified.
* <li>EIO - an error occurred during synchronization.
* </ul>
int mdb_env_get_path(MDB_env *env, const char **path);
/** @brief Return the filedescriptor for the given environment.
+ *
+ * This function may be called after fork(), so the descriptor can be
+ * closed before exec*(). Other LMDB file descriptors have FD_CLOEXEC.
+ * (Until LMDB 0.9.18, only the lockfile had that.)
*
* @param[in] env An environment handle returned by #mdb_env_create()
* @param[out] fd Address of a mdb_filehandle_t to contain the descriptor.
*/
MDB_env *mdb_txn_env(MDB_txn *txn);
+ /** @brief Return the transaction's ID.
+ *
+ * This returns the identifier associated with this transaction. For a
+ * read-only transaction, this corresponds to the snapshot being read;
+ * concurrent readers will frequently have the same transaction ID.
+ *
+ * @param[in] txn A transaction handle returned by #mdb_txn_begin()
+ * @return A transaction ID, valid if input is an active transaction.
+ */
+size_t mdb_txn_id(MDB_txn *txn);
+
/** @brief Commit all the operations of a transaction into the database.
*
* The transaction handle is freed. It and its cursors must not be used
* The database handle may be discarded by calling #mdb_dbi_close().
* The old database handle is returned if the database was already open.
* The handle may only be closed once.
+ *
* The database handle will be private to the current transaction until
* the transaction is successfully committed. If the transaction is
* aborted the handle will be closed automatically.
- * After a successful commit the
- * handle will reside in the shared environment, and may be used
- * by other transactions. This function must not be called from
- * multiple concurrent transactions. A transaction that uses this function
- * must finish (either commit or abort) before any other transaction may
- * use this function.
+ * After a successful commit the handle will reside in the shared
+ * environment, and may be used by other transactions.
+ *
+ * This function must not be called from multiple concurrent
+ * transactions in the same process. A transaction that uses
+ * this function must finish (either commit or abort) before
+ * any other transaction in the process may use this function.
*
* To use named databases (with name != NULL), #mdb_env_set_maxdbs()
- * must be called before opening the environment. Database names
- * are kept as keys in the unnamed database.
+ * must be called before opening the environment. Database names are
+ * keys in the unnamed database, and may be read but not written.
+ *
* @param[in] txn A transaction handle returned by #mdb_txn_begin()
* @param[in] name The name of the database to open. If only a single
* database is needed in the environment, this value may be NULL.
* keys may have multiple data items, stored in sorted order.) By default
* keys must be unique and may have only a single data item.
* <li>#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).
+ * Keys are binary integers in native byte order, either unsigned int
+ * or size_t, and will be sorted as such.
+ * The keys must all be of the same size.
* <li>#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.
+ * all data items are the same size, the #MDB_GET_MULTIPLE, #MDB_NEXT_MULTIPLE
+ * and #MDB_PREV_MULTIPLE cursor operations may be used to retrieve multiple
+ * items at once.
* <li>#MDB_INTEGERDUP
- * This option specifies that duplicate data items are also integers, and
- * should be sorted as such.
+ * This option specifies that duplicate data items are binary integers,
+ * similar to #MDB_INTEGERKEY keys.
* <li>#MDB_REVERSEDUP
* This option specifies that duplicate data items should be compared as
* strings in reverse order.
* the next update operation or the transaction ends. This saves
* an extra memcpy if the data is being generated later.
* LMDB does nothing else with this memory, the caller is expected
- * to modify all of the space requested.
+ * to modify all of the space requested. This flag must not be
+ * specified if the database was opened with #MDB_DUPSORT.
* <li>#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.
+ * database. This option allows fast bulk loading when keys are
+ * already known to be in the correct order. Loading unsorted keys
+ * with this flag will cause a #MDB_KEYEXIST error.
* <li>#MDB_APPENDDUP - as above, but for sorted dup data.
* </ul>
* @return A non-zero error value on failure and 0 on success. Some possible
* the database supports duplicates (#MDB_DUPSORT).
* <li>#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.
+ * reserved space, which the caller can fill in later - before
+ * the next update operation or the transaction ends. This saves
+ * an extra memcpy if the data is being generated later. This flag
+ * must not be specified if the database was opened with #MDB_DUPSORT.
* <li>#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.
+ * a #MDB_KEYEXIST error.
* <li>#MDB_APPENDDUP - as above, but for sorted dup data.
* <li>#MDB_MULTIPLE - store multiple contiguous data elements in a
* single request. This flag may only be specified if the database
* <ul>
* <li>#MDB_MAP_FULL - the database is full, see #mdb_env_set_mapsize().
* <li>#MDB_TXN_FULL - the transaction has too many dirty pages.
- * <li>EACCES - an attempt was made to modify a read-only database.
+ * <li>EACCES - an attempt was made to write in a read-only transaction.
* <li>EINVAL - an invalid parameter was specified.
* </ul>
*/
* @return A non-zero error value on failure and 0 on success. Some possible
* errors are:
* <ul>
- * <li>EACCES - an attempt was made to modify a read-only database.
+ * <li>EACCES - an attempt was made to write in a read-only transaction.
* <li>EINVAL - an invalid parameter was specified.
* </ul>
*/
projects / openldap / blobdiff