RE: Very Strange Query Access Plan

From: Mercadante, Thomas F (LABOR) <Thomas.Mercadante_at_labor.state.ny.us>
Date: Tue, 2 Oct 2007 14:29:17 -0400
Message-ID: <ABB9D76E187C5146AB5683F5A07336FFE09019@EXCNYSM0A1AJ.nysemail.nyenet>

All,  

Thanks to Alvaro Jose Fernandez & Ric Van Dyke, this is solved. The DENSITY and CLUSTER FACTOR values in the user_tab_columns for my database table had bad values. These values are calculated by the DBMS_STATS package. I manually set these to a much lower figure and my problem went away.  

I'm still trying to determine what my next steps are. One definite step is to stop gathering stats for awhile!  

Thanks  

Tom  

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From: Koppelaars, Toon [mailto:T.Koppelaars_at_centraal.boekhuis.nl] Sent: Tuesday, October 02, 2007 1:59 PM
To: Mercadante, Thomas F (LABOR); oracle-l_at_freelists.org Subject: RE: Very Strange Query Access Plan  

Can you provide us with a (couple of) example(s) of these queries?

	-----Oorspronkelijk bericht-----
	Van: oracle-l-bounce_at_freelists.org

[mailto:oracle-l-bounce_at_freelists.org]Namens Mercadante, Thomas F (LABOR)

	Verzonden: dinsdag 2 oktober 2007 17:12
	Aan: oracle-l_at_freelists.org
	Onderwerp: Very Strange Query Access Plan

	All,

	 

	Running on 9.2.0.7 on Aix.

	 

	I have a database table with 18 million rows in it.  There is an

SSN column in the table. Only 625,000 rows have an SSN populated. I also have an index on this column. Statistics on both the table and index are gathered nightly (using dbms_stats with the estimated and default sample options).          

        Yesterday, queries against this table used the index. Today, they do not. There was no large data load overnight. We add about 10,000 records per day. This behavior has happened before where the index gets ignored for a day and then used the next day.

        I really need to use an index here. Queries via ssn are executed all day long and take 10 minutes to complete. CPU is pegged at 99%.         

        What am I missing? Maybe histograms? Haven't used them before, so any suggestions would be helpful.         

        Thanks         

        Tom

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Received on Tue Oct 02 2007 - 13:29:17 CDT