as far as DBI is concerned, I'm pretty sure you will be ok, since DBI is a wrapper... if something gets broken, it would be DBD::Oracle. Or some non-portable SQL you may have (but since you are switching from oracle to oracle, I guess the latter shouldn't be an issue). Also, I've heard that Oracle is one of the better supported platforms in the set of DBD's, so if something breaks with oracle 9, it would be fixed quickly... another thing: oracle9 has been stable for quite a while now, so I guess they have all the bugs fixed (if they were any) in DBD::Oracle, but you should take a quick look at the changelog for the latest version of DBD::Oracle to be on the safe side.

hope this helps,