CBO Puzzles

From: Oracle-L <orclbabu_at_hotmail.com>
Date: Fri, 10 Oct 2003 13:44:25 -0800
Message-ID: <F001.005D2B93.20031010134425@fatcity.com>

All

We have a 8.0.4 database using choose optimizer. We have a query that access a single table using index.

If we analyze the table and indexes - query takes 8 min to complete

If we analyze table and then delete stats on indexes - query runs in two minutes.

Explain plan is the same in both cases. I did a event 10053 trace but could not find any difference between the choices the CBO makes except when the indexes are not analyzed it thinks the cost is low.

Any ideas why the query would execute faster - with the same explain plan - if the CBO thinks its cost is low ?

PS : We ruled out the effects of caching in the buffer by reversing the order of the tests..

TIA Babu
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Author: Oracle-L
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