Setting up an audit trail for SQL

Hi,
I’ve been tasked with designing an auditing system for SQL databases. It’s to be implemented at a software level i.e not using triggers, but using Apache Log4j. The technologies we use include JSPs, Java, Tomcat, JBoss and MySQL.

What I’m really looking for is tips on best practice and criteria in terms of deciding how many SQL tables to set up for logging to, how big they should be, and what gets logged (and when) and what doesn’t.

Any help, including links to articles, would be gratefully received.

Fergal.