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help / color / mirror / Atom feedFrom: Peter Geoghegan <[email protected]>
To: Robert Haas <[email protected]>
Cc: Greg Stark <[email protected]>
Cc: vignesh C <[email protected]>
Cc: Ibrar Ahmed <[email protected]>
Cc: David G. Johnston <[email protected]>
Cc: [email protected] <[email protected]>
Cc: Simon Riggs <[email protected]>
Cc: Ron Mayer <[email protected]>
Cc: Euler Taveira de Oliveira <[email protected]>
Cc: Tom Lane <[email protected]>
Subject: Re: explain analyze rows=%.0f
Date: Thu, 7 Jul 2022 13:45:19 -0700
Message-ID: <CAH2-Wz=PFiqsDsFqeOpxg+SrQ3F0wxZURxTp+vcHh+LCE+yb7A@mail.gmail.com> (raw)
In-Reply-To: <CA+TgmoZv8DvmeQHQAX+rkn68id2N+DoUhFZB36d-_w1tyAeqeA@mail.gmail.com>
References: <[email protected]>
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On Thu, Jul 7, 2022 at 1:21 PM Robert Haas <[email protected]> wrote:
> Nested Loop (actual time=TIME FOR THIS AND ALL CHILDREN rows=THE REAL
> ROW COUNT loops=1)
> -> Seq Scan on something (actual time=THE TIME IT REALLY TOOK rows=THE
> REAL ROW COUNT loops=1)
> -> Index Scan using someidx on somethingelse (actual time=NOT REALLY
> HOW LONG IT TOOK rows=NOT REALLY HOW MANY ROWS WE GOT loops=HUGE
> NUMBER)
>
> If I'm looking at this plan and trying to find out what's gone wrong,
> I want to know how much time got spent in the nested loop, how much
> time got spent in the Seq Scan, and how much time got spent in the
> Index Scan. It's easy to figure out how much time got spent in the Seq
> Scan, but to find out how much time got spent in the Index Scan, I
> have to multiply the time by the loop count.
I agree that this general state of affairs is very confusing, and
seems like something that we should still improve. Just because it's a
very old way of presenting the information doesn't mean that it's the
best one, or even a particularly good one. Plus you could probably
make some kind of concession in the direction of maintaining
compatibility with the current approach if you had to. Right?
--
Peter Geoghegan
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Subject: Re: explain analyze rows=%.0f
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