DES_KEY_FILE

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

HOSTS

Empties the host cache. You should flush the host cache if some of your hosts change IP address or if the error message Host 'host_name' is blocked occurs. (See Section C.5.2.6, “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 cache enables further connection attempts from the host. The default value of max_connect_errors is 10. To avoid this error message, start the server with max_connect_errors set to a large value.

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.

Prior to MySQL 5.1.51, if you flush the logs using FLUSH LOGS and mysqld is writing the error log to a file (for example, if it was started with the --log-error option), log file renaming may occur, as described in Section 5.2.2, “The Error Log”.

MASTER

Deletes all binary logs, resets the binary log index file and creates a new binary log. FLUSH MASTER is deprecated in favor of RESET MASTER. FLUSH MASTER is still accepted in MySQL 5.1 for backward compatibility, but is removed in MySQL 5.6. See Section 13.4.1.2, “RESET MASTER Syntax”.

PRIVILEGES

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

The server caches information in memory as a result of GRANT, CREATE USER, CREATE SERVER, and INSTALL PLUGIN statements. This memory is not released by the corresponding REVOKE, DROP USER, DROP SERVER, and UNINSTALL PLUGIN statements, so for a server that executes many instances of the statements that cause caching, there will be an increase in memory use. This cached memory can be freed with FLUSH PRIVILEGES.

QUERY CACHE

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

SLAVE

Resets all replication slave parameters, including relay log files and replication position in the master's binary logs. FLUSH SLAVE is deprecated in favor of RESET SLAVE. FLUSH SLAVE is still accepted in MySQL 5.1 for backward compatibility, but is removed in MySQL 5.6. See Section 13.4.2.5, “RESET SLAVE Syntax”.

STATUS

This option adds the current thread's session status variable values to the global values and resets the session values to zero. Some global variables may be reset to zero as well. It also resets the counters for key caches (default and named) to zero and sets Max_used_connections to the current number of open connections. This is something you should use only when debugging a query. See Section 1.7, “How to Report Bugs or Problems”.

TABLES

FLUSH TABLES flushes tables, and, depending on the variant used, acquires locks. The permitted syntax is discussed later in this section.

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 6.3.4, “Setting Account Resource Limits”.

FLUSH TABLES

Closes all open tables, forces all tables in use to be closed, and flushes the query cache. FLUSH TABLES also removes all query results from the query cache, like the RESET QUERY CACHE statement.

FLUSH TABLES tbl_name [, tbl_name] ...

With a list of one or more comma-separated table names, this statement is like FLUSH TABLES with no names except that the server flushes only the named tables. No error occurs if a named table does not exist.

FLUSH TABLES WITH READ LOCK

Closes all open tables and locks all tables for all databases with a global read lock. This is a very convenient way to get backups if you have a file system such as Veritas or ZFS that can take snapshots in time. Use UNLOCK TABLES to release the lock.

FLUSH TABLES WITH READ LOCK acquires a global read lock and not table locks, so it is not subject to the same behavior as LOCK TABLES and UNLOCK TABLES with respect to table locking and implicit commits:

FLUSH TABLES WITH READ LOCK does not prevent the server from inserting rows into the log tables (see Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”).