Horton

Re: Inaccurate Explain Cost

hubert depesz lubaczewski <depesz@depesz.com>

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From: hubert depesz lubaczewski <depesz@depesz.com>
To: Robert Sosinski <rsosinski@ticketevolution.com>
Cc: pgsql-general@postgresql.org, pgsql-performance@postgresql.org, Spike Grobstein <spike@ticketevolution.com>
Date: 2012-09-26T20:21:40Z
Lists: pgsql-performance, pgsql-general 
On Wed, Sep 26, 2012 at 02:38:09PM -0400, Robert Sosinski wrote:
> The first query shows a cost of 190,169.55 and runs in 199,806.951 ms.
> When I disable nested loop, I get a cost of 2,535,992.34 which runs in
> only 133,447.790 ms.  We have run queries on our database with a cost
> of 200K cost before and they ran less then a few seconds, which makes
> me wonder if the first query plan is inaccurate.  The other issue is
> understanding why a query plan with a much higher cost is taking less
> time to run.

Are you under impression that cost should be somehow related to actual
time?
If yes - that's not true, and afaik never was.
the fact that you got similar time and cost is just a coincidence.

Best regards,

depesz

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