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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Histograms
Thanks all.
Perhaps to play devil's advocate slightly (as I said, we don't use histograms much here for the reasons given): why not turn this on its head and say gather ALL histograms (so CBO has maximum information) and then remove those that cause trouble? (And since you don't compulsively regather stats of course, it's only a one-off exercise to get the histograms :-)
I guess I was also slightly interested in the detail behind the web site - I think David Kurtz paraphrased it well when he said 'I heard about this from some people, it sounds like a good idea but I haven't tried it for myself'. Has anyone talked about this to the people listed, namely Jeff Maresh, Arup Nanda or Mike Ault, who appear to HAVE actually tried it and seem to think there's something in it; I'm curious as to their thinking.
Thank you
Charlotte
> Like David and Yasin, I am against the "broad brush"
> method and use
> histograms only in specific cases with demonstrated
> benefits.
> I don't have a testcase, but I have a documented
> case at a client where
> they changed their week(end)ly statistics gathreing
> from the default
> "for all columns size 1" to "for all indexed columns
> size skewonly" and
> had the bottom fall out of a batch job that usually
> took 1.5 minutes
> because one frequently executes sql (1000s of times)
> went from .01
> elapsed to around 80 seconds elapsed.
> So be careful whenever you change your statistics
> gathering strategy.
> And that is not limited to histograms.
>
> Charlotte Hammond wrote:
>
> > Hi All,
> >
> > Can I poll the list on their views on the use of
> > histograms? I've previously been quite
> conservative,
> > only gathering them when we've had a specific case
> of
> > bad CBO performance due to skewed data. However I
> was
> > interested in this article mentioning a "broad
> brush"
> > approach to histogram gathering:
> >
> >
>
http://www.dba-oracle.com/oracle_tips_all_columns_histograms.htm
> >
> > Any thoughts to share?
> >
> > Thank you
> > Charlotte
> >
> >
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> --
> Regards
>
> Wolfgang Breitling
> Centrex Consulting Corporation
> www.centrexcc.com
>
-- http://www.freelists.org/webpage/oracle-lReceived on Tue Aug 16 2005 - 09:17:48 CDT
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