 <p>I also vote for the second version based on<br> this <a href="http://download.oracle.com/docs/cd/B19306_01/server.102/b14231/undo.htm" rel="nofollow noreferrer">link</a> (which is Oracle 10.2, but I think it still applies to 9.2 as well). </p> <p>It says: "After a transaction is committed, undo data is no longer needed for rollback or transaction recovery purposes. However, for consistent read purposes, long-running queries may require this old undo information for producing older images of data blocks."</p> <p>and</p> <p>"When automatic undo management is enabled, there is always a current undo retention period, which is the minimum amount of time that Oracle Database attempts to retain old undo information before overwriting it."</p>