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13.5.5.2. FLUSH Syntax

FLUSH [LOCAL | NO_WRITE_TO_BINLOG] flush_option [, flush_option] ...

The FLUSH statement clears or reloads various internal caches used by MySQL. To execute FLUSH, you must have the RELOAD privilege.

The RESET statement is similar to FLUSH. See Section 13.5.5.5, “RESET Syntax”.

flush_option can be any of the following:

  • HOSTS

    Empties the host cache tables. You should flush the host tables if some of your hosts change IP number or if you get the error message Host 'host_name' is blocked. When more than max_connect_errors errors occur successively for a given host while connecting to the MySQL server, MySQL assumes that something is wrong and blocks the host from further connection requests. Flushing the host tables allows the host to attempt to connect again. See Section A.2.5, “Host 'host_name' is blocked. You can start mysqld with --max_connect_errors=999999999 to avoid this error message.

  • DES_KEY_FILE

    Reloads the DES keys from the file that was specified with the --des-key-file option at server startup time.

  • LOGS

    Closes and reopens all log files. If binary logging is enabled, the sequence number of the binary log file is incremented by one relative to the previous file. On Unix, this is the same thing as sending a SIGHUP signal to the mysqld server (except on some Mac OS X 10.3 versions where mysqld ignores SIGHUP and SIGQUIT).

    If the server was started with the --log-error option, FLUSH LOGS causes the error log is renamed with a suffix of -old and mysqld creates a new empty log file. No renaming occurs if the --log-error option was not given.

  • PRIVILEGES

    Reloads the privileges from the grant tables in the mysql database.

  • QUERY CACHE

    Defragment the query cache to better utilize its memory. FLUSH QUERY CACHE does not remove any queries from the cache, unlike RESET QUERY CACHE.

  • STATUS

    Resets most status variables to zero. This is something you should use only when debugging a query. See Section 1.8, “How to Report Bugs or Problems”.

  • {TABLE | TABLES} [tbl_name [, tbl_name] ...]

    When no tables are named, closes all open tables and forces all tables in use to be closed. This also flushes the query cache. With one or more table names, flushes only the given tables. FLUSH TABLES also removes all query results from the query cache, like the RESET QUERY CACHE statement.

  • TABLES WITH READ LOCK

    Closes all open tables and locks all tables for all databases with a read lock until you execute UNLOCK TABLES. This is very convenient way to get backups if you have a filesystem such as Veritas that can take snapshots in time.

  • USER_RESOURCES

    Resets all per-hour user resources to zero. This enables clients that have reached their hourly connection, query, or update limits to resume activity immediately. FLUSH USER_RESOURCES does not apply to the limit on maximum simultaneous connections. See Section 13.5.1.3, “GRANT Syntax”.

FLUSH statements are written to the binary log unless the optional NO_WRITE_TO_BINLOG keyword (or its alias LOCAL) is used. This is done so that FLUSH statements used on a MySQL server acting as a replication master will be replicated by default to the replication slave.

Note: FLUSH LOGS, FLUSH MASTER, FLUSH SLAVE, and FLUSH TABLES WITH READ LOCK are not logged in any case because they would cause problems if replicated to a slave.

You can also access some of these statements with the mysqladmin utility, using the flush-hosts, flush-logs, flush-privileges, flush-status, or flush-tables commands.

Note: It is not possible in MySQL 5.1 to issue FLUSH statements within stored functions or triggers. However, you may use FLUSH in stored procedures, so long as these are not called from stored functions or triggers. See Section I.1, “Restrictions on Stored Routines and Triggers”.

See also Section 13.5.5.5, “RESET Syntax”, for information about how the RESET statement is used with replication.


 
 
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