title: mysql innodb:innodb_flush_method
body: <p>in the following link</p>
  
  <p><a href="http://dev.mysql.com/doc/refman/5.1/en/innodb-parameters.html#sysvar_innodb_flush_method" rel="noreferrer">http://dev.mysql.com/doc/refman/5.1/en/innodb-parameters.html#sysvar_innodb_flush_method</a></p>
  
  <p>it says:Different values of this variable can have a marked effect on InnoDB performance. For example, on some systems where InnoDB data and log files are located on a SAN, <strong>it has been found that setting innodb_flush_method to O_DIRECT can degrade performance of simple SELECT statements by a factor of three.</strong> </p>
  
  <p>Why O_DIRECT could slow down the select statement? </p>