* 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 most systems:
+ * - Windows - automatic
+ * - BSD, systems using SysV semaphores - automatic
+ * - Linux, systems using POSIX mutexes with Robust option - automatic
+ * 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,
+ * - On BSD systems or others configured with MDB_USE_SYSV_SEM,
* startup can fail due to semaphores owned by another userid.
*
* Fix: Open and close the database as the user which owns the
* The transaction becomes "long-lived" as above until a check
* for stale readers is performed or the lockfile is reset,
* since the process may not remove it from the lockfile.
+ * Except write-transactions on Unix with MDB_ROBUST or on Windows.
*
* - 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.
MDB_VERINT(MDB_VERSION_MAJOR,MDB_VERSION_MINOR,MDB_VERSION_PATCH)
/** The release date of this library version */
-#define MDB_VERSION_DATE "July 8, 2014"
+#define MDB_VERSION_DATE "September 20, 2014"
/** A stringifier for the version info */
#define MDB_VERSTR(a,b,c,d) "LMDB " #a "." #b "." #c ": (" d ")"
#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_CURSOR_FULL (-30787)
/** Page has not enough space - internal error */
#define MDB_PAGE_FULL (-30786)
- /** Environment mapsize was changed by another process */
+ /** Database contents grew beyond environment mapsize */
#define MDB_MAP_RESIZED (-30785)
/** MDB_INCOMPATIBLE: Operation and DB incompatible, or DB flags changed */
#define MDB_INCOMPATIBLE (-30784)
void *me_mapaddr; /**< Address of map, if fixed */
size_t me_mapsize; /**< Size of the data memory map */
size_t me_last_pgno; /**< ID of the last used page */
- size_t me_last_txnid; /**< ID of the last committed transaction */
+ size_t me_last_txnid; /**< ID of the last committed transaction */
unsigned int me_maxreaders; /**< max reader slots in the environment */
unsigned int me_numreaders; /**< max reader slots used in the environment */
} MDB_envinfo;
* 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.
+ * 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,
* 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>
* This may be used to set some flags in addition to those from
* #mdb_env_open(), or to unset these flags. If several threads
* change the flags at the same time, the result is undefined.
+ * Most flags cannot be changed after #mdb_env_open().
* @param[in] env An environment handle returned by #mdb_env_create()
* @param[in] flags The flags to change, bitwise OR'ed together
* @param[in] onoff A non-zero value sets the flags, zero clears them.
* This function should be called after #mdb_env_create() and before #mdb_env_open().
* It may be called at later times if no transactions are active in
* this process. Note that the library does not check for this condition,
- * the caller must ensure it explicitly. The new size takes effect
- * immediately for the current process but will not be persisted to
- * any others until a write transaction has been committed by the
- * current process.
+ * the caller must ensure it explicitly.
*
- * If the mapsize is changed by another process, #mdb_txn_begin() will
+ * The new size takes effect immediately for the current process but
+ * will not be persisted to any others until a write transaction has been
+ * committed by the current process. Also, only mapsize increases are
+ * persisted into the environment.
+ *
+ * If the mapsize is increased by another process, and data has grown
+ * beyond the range of the current mapsize, #mdb_txn_begin() will
* return #MDB_MAP_RESIZED. This function may be called with a size
* of zero to adopt the new size.
*
*/
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
* 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.
+ * 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
* LMDB does nothing else with this memory, the caller is expected
* to modify all of the space requested.
* <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
* <ul>
* <li>#MDB_CURRENT - replace the item at the current cursor position.
* The \b key parameter must still be provided, and must match it.
- * So must \b data if using sorted duplicates (#MDB_DUPSORT).
+ * If using sorted duplicates (#MDB_DUPSORT) the data item must still
+ * sort into the same place. This is intended to be used when the
+ * new data is the same size as the old. Otherwise it will simply
+ * perform a delete of the old record followed by an insert.
* <li>#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
projects / openldap / blobdiff