Re: RE: query slow in 9i, but not slow in 8i

From: Wolfgang Breitling <breitliw_at_centrexcc.com>
Date: Tue, 02 Mar 2004 07:44:52 -0700
Message-Id: <6.0.3.0.2.20040302073804.02976dd0@pop.centrexcc.com>

At 05:51 AM 3/2/2004, you wrote:
>is this on metalink or in the docs anywhere? I never saw it? You would
>think that oracle would warn you about over-using histograms. I guess I
>have to be more careful now.
>
>If I use options=>'GATHER AUTO' does oracle make a decision to use
>histograms? If so, what causes that decision?

If you are using options=>'GATHER AUTO' ( or method_opt=>'... size auto' ) Oracle consults sys.col_usage$ to decide which columns to probe for histograms. If the data for the column is sufficiently skewed - in Oracle's sole discretion - it will build the histogram. So, yes, gather auto is probably your answer. Not mine as I like to have more control over when, what and how statistics are gathered.

Wolfgang Breitling
Oracle7, 8, 8i, 9i OCP DBA
Centrex Consulting Corporation
http://www.centrexcc.com

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Received on Tue Mar 02 2004 - 08:42:23 CST