If you have the window and use monitoring what is wrong with getting
histograms on every table? I'm doing all new development with new queries
getting developed everyday. It seems easier just to put histograms on
everything. I have the window to do this overnight and will have it when we
go live?
- Original Message -----
From: "Wolfgang Breitling" <breitliw_at_centrexcc.com>
To: <oracle-l_at_freelists.org>
Sent: Monday, March 01, 2004 5:55 PM
Subject: Re: RE: query slow in 9i, but not slow in 8i
> As I said, if the columns did not have histograms in 8i I would not create
> histograms in 9i.
>
> I do no a-priori create a histogram on a column. ONLY if the analysis of a
> sql performance problem indicates that a histogram is indicated.
>
> In 9i you also can query sys.col_usage$ to find candidates for histograms.
> That is what Oracle does when you request "method_opt => 'for ... columns
> size auto' ".
>
> At 02:51 PM 3/1/2004, you wrote:
> >yeah good idea. how do you determine which columns need histograms? I
have
> >100s of tables in my applications and I do not have time to determine it.
I
> >typically have them run over night.
> >----- Original Message -----
> >From: "Wolfgang Breitling" <breitliw_at_centrexcc.com>
> >To: <oracle-l_at_freelists.org>
> >Sent: Monday, March 01, 2004 2:17 PM
> >Subject: Re: RE: query slow in 9i, but not slow in 8i
> >
> >
> > > I would NOT do that. "method_opt='FOR ALL COLUMNS'" will collect
> >histograms
> > > of (default) size 75 for ALL columns of the table. At best that would
be a
> > > waste of time and resources, but it could easily be rather detrimental
to
> > > access paths. You do NOT want to collect histograms unless it is
> >warranted.
> > >
> > > If the columns did not have histograms in 8i, I would not suddenly
create
> > > any in 9i.
> > >
>
> Wolfgang Breitling
> Oracle7, 8, 8i, 9i OCP DBA
> Centrex Consulting Corporation
> http://www.centrexcc.com
>
>
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Received on Mon Mar 01 2004 - 17:11:47 CST
