I second this. We migrated from 9i to 10g in 2007. Oracle had significantly changed/re-written the CBO. Things that used to fly, crawled. There is definitely a post migration need to stress test your queries, and user adhoc queries if they are allowed. Rodd Holman On Wed, Mar 7, 2012 at 12:33 PM, Dennis Williams < oracledba.williams@xxxxxxxxx> wrote: > David, (resending without quoting prior posts) > Does your applications on 8i use RBO or CBO? Even if it uses CBO, the query > execution plans may differ in 11g. When we migrated some critical apps from > 8i to 10g a few years ago (a direct upgrade) that was the main source of > issues. > > Dennis Williams > > > -- > //www.freelists.org/webpage/oracle-l > > > -- //www.freelists.org/webpage/oracle-l