* cause further writes to grow the database quickly, and
* stale locks can block further operation.
*
- * Fix: Terminate all programs using the database, or make
- * them close it. Next database user will reset the lockfile.
+ * Fix: Check for stale readers periodically, using the
+ * #mdb_reader_check function or the mdb_stat tool. Or 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.
* ...when several processes can use a database concurrently:
*
* - Avoid aborting a process with an active transaction.
- * The transaction becomes "long-lived" as above until the lockfile
- * is reset, since the process may not remove it from the lockfile.
+ * 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.
*
- * - If you do that anyway, close the environment once in a while,
- * so the lockfile can get reset.
+ * - 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.
*
* - Do not use MDB databases on remote filesystems, even between
* processes on the same host. This breaks flock() on some OSes,
extern "C" {
#endif
+/** Unix permissions for creating files, or dummy definition for Windows */
#ifdef _MSC_VER
typedef int mdb_mode_t;
#else
typedef mode_t mdb_mode_t;
#endif
+/** An abstraction for a file handle.
+ * On POSIX systems file handles are small integers. On Windows
+ * they're opaque pointers.
+ */
+#ifdef _WIN32
+typedef void *mdb_filehandle_t;
+#else
+typedef int mdb_filehandle_t;
+#endif
+
/** @defgroup mdb MDB API
* @{
* @brief OpenLDAP Lightning Memory-Mapped Database Manager
/** Library minor version */
#define MDB_VERSION_MINOR 9
/** Library patch version */
-#define MDB_VERSION_PATCH 6
+#define MDB_VERSION_PATCH 7
/** 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_MAXKEYSIZE inclusive. This currently defaults to 511. The
* same applies to data sizes in databases with the #MDB_DUPSORT flag.
* Other data items can in theory be from 0 to 0xffffffff bytes long.
+ *
+ * Values returned from the database are valid only until a subsequent
+ * update operation, or the end of the transaction.
*/
typedef struct MDB_val {
size_t mv_size; /**< size of the data item */
#define MDB_APPEND 0x20000
/** Duplicate data is being appended, don't split full pages. */
#define MDB_APPENDDUP 0x40000
-/** Store multiple data items in one call. */
+/** Store multiple data items in one call. Only for #MDB_DUPFIXED. */
#define MDB_MULTIPLE 0x80000
/* @} */
Only for #MDB_DUPSORT */
MDB_NEXT_MULTIPLE, /**< Return all duplicate data items at the next
cursor position. Only for #MDB_DUPFIXED */
- MDB_NEXT_NODUP, /**< Position at first data item of next key.
- Only for #MDB_DUPSORT */
+ MDB_NEXT_NODUP, /**< Position at first data item of next key */
MDB_PREV, /**< Position at previous data item */
MDB_PREV_DUP, /**< Position at previous data item of current key.
Only for #MDB_DUPSORT */
- MDB_PREV_NODUP, /**< Position at last data item of previous key.
- Only for #MDB_DUPSORT */
+ 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. */
#define MDB_PAGE_FULL (-30786)
/** Database contents grew beyond environment mapsize */
#define MDB_MAP_RESIZED (-30785)
- /** Database flags changed or would change */
+ /** MDB_INCOMPATIBLE: Operation and DB incompatible, or DB flags changed */
#define MDB_INCOMPATIBLE (-30784)
/** Invalid reuse of reader locktable slot */
#define MDB_BAD_RSLOT (-30783)
-#define MDB_LAST_ERRCODE MDB_BAD_RSLOT
+ /** Transaction cannot recover - it must be aborted */
+#define MDB_BAD_TXN (-30782)
+ /** Too big key/data, key is empty, or wrong DUPFIXED size */
+#define MDB_BAD_VALSIZE (-30781)
+#define MDB_LAST_ERRCODE MDB_BAD_VALSIZE
/** @} */
/** @brief Statistics for a database in the environment */
/** @brief 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 @ref caveats_sec.
* @param[in] env An environment handle returned by #mdb_env_create(). It
* must have already been opened successfully.
* @param[in] path The directory in which the copy will reside. This
*/
int mdb_env_copy(MDB_env *env, const char *path);
+ /** @brief Copy an MDB environment to the specified file descriptor.
+ *
+ * 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 @ref caveats_sec.
+ * @param[in] env An environment handle returned by #mdb_env_create(). It
+ * must have already been opened successfully.
+ * @param[in] fd The filedescriptor to write the copy to. It must
+ * have already been opened for Write access.
+ * @return A non-zero error value on failure and 0 on success.
+ */
+int mdb_env_copyfd(MDB_env *env, mdb_filehandle_t fd);
+
/** @brief Return statistics about the MDB environment.
*
* @param[in] env An environment handle returned by #mdb_env_create()
*/
int mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs);
+ /** @brief Get the maximum size of a key for the environment.
+ *
+ * @param[in] env An environment handle returned by #mdb_env_create()
+ * @return The maximum size of a key. (#MDB_MAXKEYSIZE)
+ */
+int mdb_env_get_maxkeysize(MDB_env *env);
+
/** @brief 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.
- * @note Cursors may not span transactions; each cursor must be opened and closed
- * within a single transaction.
+ * @note Cursors may not span transactions.
* @param[in] env An environment handle returned by #mdb_env_create()
* @param[in] parent If this parameter is non-NULL, the new transaction
* will be a nested transaction, with the transaction indicated by \b parent
* as its parent. Transactions may be nested to any level. A parent
- * transaction may not issue any other operations besides mdb_txn_begin,
- * mdb_txn_abort, or mdb_txn_commit while it has active child transactions.
+ * transaction and its cursors may not issue any other operations than
+ * mdb_txn_commit and mdb_txn_abort while it has active child transactions.
* @param[in] flags Special options for this transaction. This parameter
* must be set to 0 or by bitwise OR'ing together one or more of the
* values described here.
* errors are:
* <ul>
* <li>#MDB_PANIC - a fatal error occurred earlier and the environment
-- * must be shut down.
+ * must be shut down.
* <li>#MDB_MAP_RESIZED - another process wrote data beyond this MDB_env's
* mapsize and the environment must be shut down.
* <li>#MDB_READERS_FULL - a read-only transaction was requested and
*/
int mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **txn);
+ /** @brief Returns the transaction's #MDB_env
+ *
+ * @param[in] txn A transaction handle returned by #mdb_txn_begin()
+ */
+MDB_env *mdb_txn_env(MDB_txn *txn);
+
/** @brief Commit all the operations of a transaction into the database.
*
- * All cursors opened within the transaction will be closed by this call. The cursors
- * and transaction handle will be freed and must not be used again after this call.
+ * 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.
* @param[in] txn A transaction handle returned by #mdb_txn_begin()
* @return A non-zero error value on failure and 0 on success. Some possible
* errors are:
/** @brief Abandon all the operations of the transaction instead of saving them.
*
- * All cursors opened within the transaction will be closed by this call. The cursors
- * and transaction handle will be freed and must not be used again after this call.
+ * 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.
* @param[in] txn A transaction handle returned by #mdb_txn_begin()
*/
void mdb_txn_abort(MDB_txn *txn);
* 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.
- * All cursors opened within the transaction must be closed before the transaction
- * is reset.
+ * 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
/** @brief 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.
*/
int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *stat);
+ /** @brief Retrieve the DB flags for a database handle.
+ *
+ * @param[in] txn A transaction handle returned by #mdb_txn_begin()
+ * @param[in] dbi A database handle returned by #mdb_dbi_open()
+ * @param[out] flags Address where the flags will be returned.
+ * @return A non-zero error value on failure and 0 on success.
+ */
+int mdb_dbi_flags(MDB_txn *txn, MDB_dbi dbi, unsigned int *flags);
+
/** @brief Close a database handle.
*
* This call is not mutex protected. Handles should only be closed by
*/
void mdb_dbi_close(MDB_env *env, MDB_dbi dbi);
- /** @brief Delete a database and/or free all its pages.
+ /** @brief Empty or delete+close a database.
*
- * If the \b del parameter is 1, the DB handle will be closed
- * and the DB will be deleted.
* @param[in] txn A transaction handle returned by #mdb_txn_begin()
* @param[in] dbi A database handle returned by #mdb_dbi_open()
- * @param[in] del 1 to delete the DB from the environment,
- * 0 to just free its pages.
+ * @param[in] del 0 to empty the DB, 1 to delete it from the
+ * environment and close the DB handle.
* @return A non-zero error value on failure and 0 on success.
*/
int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del);
* 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.
+ * @note Values returned from the database are valid only until a
+ * subsequent update operation, or the end of the transaction.
* @param[in] txn A transaction handle returned by #mdb_txn_begin()
* @param[in] dbi A database handle returned by #mdb_dbi_open()
* @param[in] key The key to search for in the database
* parameter will be set to point to the existing item.
* <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
+ * 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.
* <li>#MDB_APPEND - append the given key/data pair to the end of the
* database. No key comparisons are performed. This option allows
/** @brief Create a cursor handle.
*
* A cursor is associated with a specific transaction and database.
- * It must be closed before its transaction ends.
+ * 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.
* @param[in] txn A transaction handle returned by #mdb_txn_begin()
* @param[in] dbi A database handle returned by #mdb_dbi_open()
* @param[out] cursor Address where the new #MDB_cursor handle will be stored
/** @brief 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.
* @param[in] cursor A cursor handle returned by #mdb_cursor_open()
*/
void mdb_cursor_close(MDB_cursor *cursor);
/** @brief Renew a cursor handle.
*
* A cursor is associated with a specific transaction and database.
- * It must be closed before its transaction ends.
* 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.
* @param[in] txn A transaction handle returned by #mdb_txn_begin()
* @param[in] cursor A cursor handle returned by #mdb_cursor_open()
* @return A non-zero error value on failure and 0 on success. Some possible
* case of the #MDB_SET option, in which the \b key object is unchanged), and
* the address and length of the data are returned in the object to which \b data
* refers.
+ * See #mdb_get() for restrictions on using the output values.
* @param[in] cursor A cursor handle returned by #mdb_cursor_open()
* @param[in,out] key The key for a retrieved item
* @param[in,out] data The data of a retrieved item
* correct order. Loading unsorted keys with this flag will cause
* data corruption.
* <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
+ * was opened with #MDB_DUPFIXED. The \b 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.
* </ul>
* @return A non-zero error value on failure and 0 on success. Some possible
* errors are:
/** @brief Compare two data items according to a particular database.
*
* This returns a comparison as if the two items were data items of
- * a sorted duplicates #MDB_DUPSORT database.
+ * the specified database. The database must have the #MDB_DUPSORT flag.
* @param[in] txn A transaction handle returned by #mdb_txn_begin()
* @param[in] dbi A database handle returned by #mdb_dbi_open()
* @param[in] a The first item to compare
* @return < 0 if a < b, 0 if a == b, > 0 if a > b
*/
int mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b);
+
+ /** @brief A callback function used to print a message from the library.
+ *
+ * @param[in] msg The string to be printed.
+ * @param[in] ctx An arbitrary context pointer for the callback.
+ * @return < 0 on failure, 0 on success.
+ */
+typedef int (MDB_msg_func)(const char *msg, void *ctx);
+
+ /** @brief Dump the entries in the reader lock table.
+ *
+ * @param[in] env An environment handle returned by #mdb_env_create()
+ * @param[in] func A #MDB_msg_func function
+ * @param[in] ctx Anything the message function needs
+ * @return < 0 on failure, 0 on success.
+ */
+int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx);
+
+ /** @brief Check for stale entries in the reader lock table.
+ *
+ * @param[in] env An environment handle returned by #mdb_env_create()
+ * @param[out] dead Number of stale slots that were cleared
+ * @return 0 on success, non-zero on failure.
+ */
+int mdb_reader_check(MDB_env *env, int *dead);
/** @} */
#ifdef __cplusplus
projects / openldap / blobdiff