Mark - Stupid question. Is is possible one of the tables was dropped and recreated so it no longer has statistics? In my experience, the behavior you are experiencing is more likely due to missing statistics than stale statistics. Dennis Williams On 5/26/05, Mladen Gogala <mgogala@xxxxxxxxxxxxxxxxxxxx> wrote: > Teehan, Mark wrote: >=20 > >Is there any way to tell if the optimizer has suddenly decided that it d= oesnt like the contents of sys.aux_stat$ any more? > > > > > > > Optimizer is not a PHB. Do 10053 or do "select * from > table(DBMS_XPLAN.DISPLAY)" or do @?/rdbms/admin/utlxplp and you'll > have a line which contains string "CPU costing" which can be in 3 > states: On, Off or "Intel Inside". If your optimizer tells you that > the CPU costing is on, then it uses the system statistics. >=20 > -- > Mladen Gogala > Oracle DBA >=20 > -- > //www.freelists.org/webpage/oracle-l > -- //www.freelists.org/webpage/oracle-l