MySQL Manual
4 Database Administration
4.5.3 FLUSH Syntax
FLUSH [LOCAL | NO_WRITE_TO_BINLOG] flush_option [,flush_option] ...
You should use the FLUSH command if you want to clear some of the
internal caches MySQL uses. To execute FLUSH, you must have
the RELOAD privilege.
flush_option can be any of the following:
| Option | Description |
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 ... is blocked. When more than
max_connect_errors errors occur in a row for a given host while
connection to the MySQL server, MySQL assumes
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 '...' is blocked Error. You can start mysqld with
-O 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 you have specified an update log file or a binary log file without
an extension, the extension number of the log file will be incremented
by one relative to the previous file. If you have used an extension in
the file name, MySQL will close and reopen the update log file.
See section 4.9.3 The Update Log. This is the same thing as sending the SIGHUP
signal to the mysqld server.
|
PRIVILEGES | Reloads the privileges from the grant tables in
the mysql database.
|
QUERY CACHE | Defragment the query cache to better utilise its
memory. This command will not remove any queries from the cache, unlike
RESET QUERY CACHE.
|
TABLES | Closes all open tables and force all tables in use to be closed. This also flushes the query cache. |
[TABLE | TABLES] tbl_name [,tbl_name...] | Flushes only the given tables. |
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, like Veritas, that can take snapshots in time.
|
STATUS | Resets most status variables to zero. This is something one should only use when debugging a query. |
USER_RESOURCES | Resets all user resources to zero. This will enable blocked users to login again. See section 4.3.6 Limiting user resources. |
Strictly before MySQL 4.1.1, FLUSH commands are not written
to the binary log. Since MySQL 4.1.1 they are written to the binary
log unless the optional NO_WRITE_TO_BINLOG keyword
(or its alias LOCAL) was used, or
unless the command contained one of these arguments: LOGS,
MASTER, SLAVE, TABLES WITH READ LOCK, because any
of these arguments may cause problems if replicated to a slave.
You can also access some of the commands shown above with the mysqladmin
utility, using the flush-hosts, flush-logs, flush-privileges,
flush-status or flush-tables commands.
Take also a look at the RESET command used with replication.
See section 4.5.4 RESET Syntax.
