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

  • From: Mladen Gogala <mladen@xxxxxxxxxxxxxxx>
  • To: oracle-l@xxxxxxxxxxxxx
  • Date: Tue, 2 Mar 2004 09:51:29 -0500

My personal preference is 'FOR ALL INDEXED COLUMNS', because I don't see
histograms making sense for non-indexed columns.

On 03/02/2004 09:44:52 AM, Wolfgang Breitling wrote:
> 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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