RE: Optimizer change from 8i-9i
- From: "Christian Antognini" <Christian.Antognini@xxxxxxxxxxxx>
- To: <zhuchao@xxxxxxxxx>
- Date: Mon, 9 May 2005 18:13:55 +0200
Hi Zhu
>1. For SQLs using RBO, the plan for the existing SQL won''t change,
>right? As oracle says no change for RBO since oracle 7.3.
Wrong. You could see some differences. (they are lying to us!)
>2. For SQLs using CBO(as some feature will force CBO parsee), when the
>optimizer_feature_enabled=3D3D817, and don't change any =
optimizer_related
>parameters, is it still possible for SQL to choose different plan in
>9i as the old plan in 8i? (Maybe because of different Cost caculation
>in 9i?)
Also in this case you could have different execution plans.=20
IMHO the only way to guarantee a good migration from 8i to 9i is to =
completely reconfigure the CBO and do some extended performance tests. =
(I was called by more than one customer when it was too late!!!!)
HTH
Chris
--
//www.freelists.org/webpage/oracle-l
Other related posts:
