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Using Mysql’s FLUSH Command December 24, 2012

Posted by Tournas Dimitrios in Mysql.

Mysql’s FLUSH statement has several variant forms (options) that clears or reloads various internal caches , flush tables , or acquire locks . Users with reload privileges on a database can use this command to clean up the internal caches on that specific database . Usually , only the root-level user has the proper permissions to issue RELOAD administrative commands (FLUSH) . Common options for the FLUSH command are :

  • PRIVILEGES : Probably the most known option , it simply reloads the grant tables in your MySQL database , enabling the changes to take effect without stopping and restarting MySQL . When you issue a FLUSH PRIVILEGES command , a “Query OK ” response verifies that the new privileges have  taken place .
    mysql> flush privileges ;
  • HOSTS : This option works specifically with the host cache tables . If MySQL server , has reached the maximum number of connections for a particular host , it’s throwing errors , and simply block any additional connection attempts to that host .The “FLUSH HOSTS” command will reset this process and again allow connections to be made .
    mysql> flush hosts ;
  • TABLES : This option , will close all tables currently open or in use and essentially forces all tables in use to be closed by MySQL  . This is a very convenient way to get backups . Read also , How FLUSH TABLES works in MySQL .
    mysql> flush tables ;
  • LOGS : This option closes and reopens all log files , If the size of these files is getting to large (files mysql.log and mysql.err) , and you want to start a new ones , let’s say during a debugging  process . Starting from  clean (empty) log files can help focus on that specific task . The following command will create  new , empty log files .
    mysql> flush logs ;


The manual has more options listed , these four aforementioned options are certainly a must known “tool-set” .



1. Carol - January 7, 2013

good post. thank for sharing.

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