| From: | hubert depesz lubaczewski <depesz(at)depesz(dot)com> |
|---|---|
| To: | Robert Sosinski <rsosinski(at)ticketevolution(dot)com> |
| Cc: | pgsql-general(at)postgresql(dot)org, pgsql-performance(at)postgresql(dot)org, Spike Grobstein <spike(at)ticketevolution(dot)com> |
| Subject: | Re: Inaccurate Explain Cost |
| Date: | 2012-09-26 20:21:40 |
| Message-ID: | 20120926202140.GB10681@depesz.com |
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| Thread: | |
| Lists: | pgsql-general pgsql-performance |
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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