Wed, 22 May 2013 09:42:37 +0000 http://bugs.horde.org/ticket/9173 Deadlocks in mysql SessionHandler under heavy loads We use the mysql Sessionhandler of Horde on our installation, and under heavy loads (> 500 users), we start having a lot of deadlocks messages in the logs: Aug 05 09:45:47 HORDE [error] [horde] Error writing session data: Deadlock found when trying to get lock; try restarting transaction [pid 27607 on line 185 of "/htdocs/horde/lib/Horde/SessionHandler/mysql.php"] When this happens, users have to try to login many times before getting access. We added the following statement to the mysql driver and it solved the problem nicely: mysql_query('SET TRANSACTION ISOLATION LEVEL READ COMMITTED;', $this->_db); ref: http://dev.mysql.com/doc/refman/5.0/en/set-transaction.html No more deadlock seen even for > 2000 active users Wed, 11 Aug 2010 20:05:45 +0000 http://bugs.horde.org/ticket/9173#t59610 Transaction isolation is over my head. Fri, 13 Aug 2010 13:04:37 +0000 http://bugs.horde.org/ticket/9173#t59619