Oracle Database Discussions

Hi everyone,

We are testing a J2EE application which relies on 11gR2 database. Actually, because this is a development phase of the project, there happens lots of errors (specifically, 500, as the program runs on a web server) which might be related to db. So, I thought, how could I audit (actually monitor) all of the ORA errors on a database (or on a specific schema, table, etc.) , generated either by a wrong query or anything else?
I've looked inside alert log and trace logs (actually dug out $ORACLE_BASE/diag/rdbms folder!) but I couldn't find any. Does that mean it has not generated any errors or it just shows special internal errors? (like No Listener, etc.).
Should I look for them somewhere else?

Thx!