Re: Huge optimization costs with 9.2

How many more of these "undocumented" but seemingly crucial optimizer parameters has changed from 8i to 9i? I'd think these are a bit more important to know about.

Anyone have a list of these changed parameters? Are they noted in the 9i docs?

boss

>
> We has problems with another undocumented parameter that changed when we
> migrated to 9i in August last year. _B_TREE_BITMAP_PLANS change from false
> to true and caused a number of issues with sub-optimal execution plans.
>
> Another possible trap for the unwary ...
>
> Cheers
>
> Richard
> ----- Original Message -----
> To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com>
> Sent: Thursday, October 02, 2003 2:54 AM
>
>
> > 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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> > INET: breitliw_at_centrexcc.com
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-- 
Author: Todd Boss
  INET: boss_at_i-sphere.com

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