Re: Oracle 7 Cost Base Optimizer

d-mausner_at_nwu.edu (Dave Mausner) wrote:
>
> Recently, yobie_at_well.com (Yobie Benjamin) posted:
> >Has anyone out there experienced inconsistent results between the same query
> >run using cost based optimization and rule based optimization?
>
> you may well perceive different results in a query run in both modes. it is
> not an inconsistency since the presumptions made in each mode are wildly
> different, and depend on how much good info about the environment is available
> to the optimizer.
> --
> Dave Mausner, Senior Consultant, Braun Technology Group, Chicago.
>

        We found many slow queries when we started using the cost based optimizer in 7.0.*. The performance difference was significant for queries that were well tunned for rule based.

        I heard that Oracle is trying to fix most of the cost based optimizier bugs by 7.2. If you look at the README file for each release then one can find the fixes for each release.

        Till then we are using HINTS or if there is too much maintenance then we are setting the optimizer_mode to rule within the session or the whole instance.

Hope this helps.

Anil Sinha          Received on Tue May 16 1995 - 00:00:00 CEST