note 8361 added to Persistent Database Connections

Persistant connections can use up resources very quickly on a heavily worked server. The biggest resources they use up are file handles, backends, and memory. There are limits on all three of these on most systems. If you've got 256 Megs of ram, your database is configured for a few hundred backends, and your OS isn't going to run out of file handles, persistant database connects are great. Otherwise they often are the first thing that kills the server. http://www.php.net/manual/features.persistent-connections.php