RE: Optimizer change from 8i-9i

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

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