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>
Subject: Re: Inaccurate Explain Cost
Date: Wed, 26 Sep 2012 22:21:40 +0200
Message-ID: <20120926202140.GB10681@depesz.com> (raw)
In-Reply-To: <ED7ED14D0D304B2FB38B191F3C160A22@ticketevolution.com>
References: <ED7ED14D0D304B2FB38B191F3C160A22@ticketevolution.com>
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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To: pgsql-performance@postgresql.org
Cc: depesz@depesz.com, rsosinski@ticketevolution.com, spike@ticketevolution.com
Subject: Re: Inaccurate Explain Cost
In-Reply-To: <20120926202140.GB10681@depesz.com>
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