RE: What are the implications of running dbms_stats and analyze compute?

 The default analyze command does not build histograms. Were you using histograms in the prior version? If not change SIZE 200 to SIZE 1. This would eliminate changes in plans due to histograms from the equation.

There were at least a dozen hidden parameters that affect the CBO which had their default value changed from off to on with version 9. One of them might be causing you a problem depending on the type of SQL statements involved.

I suggest you look for and attempt to tune the affected SQL. If you see a pattern in the types of SQL statements affects you can contact support as your site might be a candidate for switching a specific underbar parameter back off.

HTH -- Mark D Powell --

-----Original Message-----

From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Ana Choto Sent: Tuesday, August 09, 2005 11:24 AM
To: oracle-l_at_freelists.org
Subject: What are the implications of running dbms_stats and analyze compute?

We have migrated our datawarehouse to 9.2.0.6 from 8.1.7.4. Since the upgrade we experienced some performance degradation. We run a daily job to analyze the datawarehouse schemas using dbms_stats. But, queries that ran in seconds were taking hours to run. So, the developers started reanalyzing the tables with 'analyze compute', which resulted on the queries running at the same level they were on 8i.

The only thing, is that now, some tables have been analyzed with dbms_stats and others with 'analyze compute'. Is there a problem by doing this?

Oracle support asked me to run the dbms_stats job with the 'exec DBMS_STATS.GATHER_TABLE_STATS(OWNNAME => <'owner'>, TABNAME => <'table_name'> , CASCADE => TRUE, method_opt => 'FOR ALL COLUMNS SIZE 200');' command. But this didn't help, so the developers just reanalyze the tables with 'analyze compute' command.

Thanks

Ana E. Choto
American University
e-Operations - Information Technology
Phone (202) 885-2275
Fax (202) 885-2224

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http://www.freelists.org/webpage/oracle-l Received on Tue Aug 09 2005 - 10:50:13 CDT