Re: RE: query slow in 9i, but not slow in 8i
- From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Tue, 02 Mar 2004 07:44:52 -0700
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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