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Re: Inconsistent performance

From: Joseph Bove <jbove(at)vetstar(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Inconsistent performance
Date: 2003-09-15 22:24:27
Message-ID: 5.1.0.14.2.20030915182422.00a8a2d8@mail.vetstar.com (view raw or flat)
Thread:
Lists: pgsql-performance
Stephan,

Actually, it's inconsistent with the exact same command. I've now 
replicated the problem by doing the following command:

select count (*) from table;

The table in question has 88899 rows.

The response time is anywhere from 1 second to 12 seconds. Different 
response times can occur in the same minute of testing!

Regards,

Joseph



At 02:34 PM 9/15/2003 -0700, you wrote:
>On Mon, 15 Sep 2003, Joseph Bove wrote:
>
> > I am working with a decent sized database on an extremely powerful machine.
> > The specs follow:
> >
> >       OS:                     RedHat Linux 9.0
> >       PG Version              7.3
> >       Memory          1 gig
> >       CPU                     Quad Processor - Unsure of exact CPUs
> >       Hard Drive              80 gigs
> >       Database Size           2 gigs
> >
> >
> > As you can see the server is built for overkill.
> >
> > The problem that I see is as follows.
> >
> > I do a rather simple query: select count (*) from large-table where column
> > = some value;
> >
> > About 80% of the time, the response time is sub-second. However, at 10% of
> > the time, the response time is 5 - 10 seconds.
>
>Is it consistant for various values of "some value"?  If so, it's possible
>that it's switching plans based on the apparent selectivity of the column
>for that value.



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