oracle auditing

Hello Everyone,

       I have a simple task to capture ddl changes in our production db's done by users as part of internal audit report.

       Currently our production db's are on Oracle 10.2.0.4 RAC with 2 nodes on RHEL 5 Linux 64 bit servers.

       The Oracle auditing is not enabled on the databases.

       How can I capture the ddl changes in production db's by enabling Oracle Auditing.

       The report should look something like this:

login_name	Server	Instance	schema	object	statement	action_desc
Scott	Server_node1	prod1	HR	update_salary	ALTER PROCEDURE HR.update_salary	ALTER PROC

       After going through the documentation, I am concerned about the performance overhead due to auditing on prod db's.