Re: Why CBO doesn't choose the low cost plan

  • From: "eagle fan" <eagle.f@xxxxxxxxx>
  • To: "Jared Still" <jkstill@xxxxxxxxx>, oracle-l@xxxxxxxxxxxxx
  • Date: Thu, 20 Jul 2006 13:20:25 +0800


I create a empty table with the same table/index structure in & test environments and exp/imp the table/index statistics into test

The 9i test database still chose the bad index, but *8i test database chose
the right plan.*

Even when I set the *ANONYMOUS_CE_IDX index's *statistics to very big value,
it still chose the bad one.

I agree that this maybe a bug.

On 7/19/06, Jared Still <jkstill@xxxxxxxxx> wrote:

On 7/19/06, eagle fan <eagle.f@xxxxxxxxx> wrote:

> hi:
> My oracle version is 9205 and optimizer_features_enable is set to 9.2.0.
> We have a query choose a bad plan.
> ...
> What do you think?

I think it's a bug.

Check MetaLink.

A possible candidate is *Bug 4112254 - CBO may not choose best index for
single table access with unpeeked bind/function*

I just searched MetaLink on CBO Bug

You should probably check there.

Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist

-- Eagle Fan

Oracle DBA

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