persistent database connection?

From my reading a persistent conncetion relates to the database side (in my case oracle), so php opens a connection with oracle, sql is exectued and php closes the connection as far as it is concerned. When another process wants to open a connection to the database the old one gets used. Providing that my assumptions are right, then I have 3 questions: how long does this connection remain active for, what controls this and can the time be extended, and would it be possible to get database errors (or other) if the conection had just timed out and a query was being processed. The error I get is ORA-03113: end of file on communication channel. The error can re-occur persistently for short periods of time and then it could be days before a re-occurance. Oracle documentation details - Cause: An unexpected end of file was processed on the communication channel. This may be an indication that the communications link may have gone down at least temporarily; it may indicate that the server has gone down. Action: You may need to modify your re-transmission count. For more information about troubleshooting this error, refer to the appropriate Oracle operating system specific documentation. Any help would be great. Thanks, Karl. -- Karl Devitt Systems' Group Computer Services Department Dublin City University Tel: +353 1 700 5083 Fax: +353 1 700 5697 email: karl.devitt@dcu.ie