#19529 [Opn->Fbk]: Occational "Commands out of sync" errors

ID: 19529 Updated by: georg@php.net Reported By: sroussey@network54.com -Status: Open +Status: Feedback Bug Type: MySQL related Operating System: Linux 2.4.18 PHP Version: 4.2.3 -Assigned To: +Assigned To: georg New Comment: Currently, neither mysql 4.x or 3.x supports enough functionality for handling some problems when using persistent connections, e.g. restoring session variables to global variables, restoring auto_commit, unsetting user variables etc. The probably error is not MySQL-version dependend. The 4.x clientlib is 100% backwards compatible to MySQL 3.x (> .23). For some more information, it would be useful, if you could send me some sources... assigned to myself. Georg Previous Comments: ------------------------------------------------------------------------ [2002-10-06 12:23:42] erik@gavert.net The problem seems to have disappeared when the ROLLBACK was removed. ------------------------------------------------------------------------ [2002-10-06 11:02:28] valvatne@pvv.org Scratch the above; I was looking at the current CVS version. In 4.2.3 the function is still called _rollback_mysql_transactions and only does the ROLLBACK, nothing more. I just disabled the ROLLBACK as well, so if neither Erik nor myself see any more errors, I think it's safe to assume that's where the problem is. But shouldn't it always be safe to execute a rollback in MySQL, even if transactions aren't in use? ------------------------------------------------------------------------ [2002-10-06 10:14:36] valvatne@pvv.org I agree that the most plausible cause of the problem is in the _restore_connection_defaults function, which is the one responsible for doing the ROLLBACK. That theory would seem to be supported by the fact that the problem disappears when disabling persistent connections (since the function does nothing when the connection isn't persistent). What I don't get is why executing ROLLBACK on a straight-MyISAM database would cause problems. Is that a bug in MySQL? If the ROLLBACK isn't the problem, it would have to be either the SET AUTOCOMMIT=1 or the stuff about unsetting the selected DB. Since my application uses only one DB and no transactions, I'm going to just disable the entire function and recompile. ------------------------------------------------------------------------ [2002-10-06 09:58:10] erik@gavert.net What happens is that the mysql connection that gets the problem is locked up. It won't ever work again. After a while all of our mysql connections showed the problem making the site completely unusable. As of v4.2.3 php does a ROLLBACK each time connection is re-used. ROLLBACKS will give an error if updates have been done on a MyISAM table, I have removed that query now. Will see if that solves it. It looks like all us are running quite many queries per second? I see the problem on a site running 60+ queries per second. ------------------------------------------------------------------------ [2002-10-06 08:13:00] jonva@avidgamers.com Another note: sroussey@network54.com states that the problem seems to only happen at high load, and is intermittent. In my experience, it seems to happen after long periods of running. More specifically, my (production) system will run fine for hours with 30+ queries/second, and then suddenly start having several of the "Commands out of sync" error messages per second. They are still intermittent (ie. they don't appear at every query), but these symptoms seem to indicate a memory leak or other delayed-impact bug as the cause of the problems. ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at http://bugs.php.net/19529 -- Edit this bug report at http://bugs.php.net/?id=19529&edit=1