Re: Huge optimization costs with 9.2

One of the undocumented init.ora parameters that changed from 8 to 9 is "_UNNEST_SUBQUERY" (from false to true). You could try if that is the culprit. Of course, since it is an undocumented parameter, get the blessing from Oracle support before using it in a production database.

At 10:09 AM 10/1/2003, you wrote:
>Joan, what is the difference in the plans? What specific feature
>made the difference? Are the values of
>optimizer_index_cost_adj and optimizer_index_caching same on both
>versions? How about histograms? What is with
>db_file_multiblock_read_count,sort_area_size and hash_area_size? Is
>everything same as in 8i? May be setting of those parameters can be
>tweaked to your benefit?
>
>On Wed, 2003-10-01 at 11:54, Joan Hsieh wrote:
> > Kirti,
> >
> > I had upgraded a database from 8.1.7.4 to 9.2.0.4. Before the upgrade,
> > performance is good. After upgrade, one query run time from 2 min to 12
> > hours. Of course, I re-analyzed all tables and indexes. The explain plan
> > changed from hash join to nested-loop. All the parameters are same. So I
> > have to put optimized_feature_enable=8.1.7 to make run normal as usual.
> > I hate to disable the new feature, but no choose.

Wolfgang Breitling
Oracle7, 8, 8i, 9i OCP DBA
Centrex Consulting Corporation
http://www.centrexcc.com

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