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From: Amit Kapila <[email protected]>
To: Justin Pryzby <[email protected]>
Cc: Peter Geoghegan <[email protected]>
Cc: 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: pgsql-hackers <[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: Fri, 22 Jul 2022 16:17:41 +0530
Message-ID: <CAA4eK1Lmo0FX6Nfr_k3-UX1Hpei1H-xPHL6Wwx7SLUP3s+O1mA@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <CA+TgmoZv8DvmeQHQAX+rkn68id2N+DoUhFZB36d-_w1tyAeqeA@mail.gmail.com>
	<[email protected]>

On Fri, Jul 8, 2022 at 3:50 AM Justin Pryzby <[email protected]> wrote:
>
> On Thu, Jul 07, 2022 at 04:21:37PM -0400, Robert Haas wrote:
> > I mean, what I really want here if I'm honest is to not have the
> > system divide the number of rows by the loop count. And it sort of
> > sounds like maybe that's what you want, too. You want to know whether
> > the loop count is actually zero, not whether it's close to zero when
> > you divide it by some number that might be gigantic.
> ...
> > involves a dozen or two different nested loops, and if we didn't
> > insist on dividing the time by the loop count, it would be MUCH EASIER
> > to figure out whether the time spent in the Index Scan is a
> > significant percentage of the total time or not.
>
> I think the guiding princible for what to do should be to reduce how much is
> needed to explain about how to interpret what explain is showing...
>
> The docs say this:
> | In such cases, the loops value reports the total number of executions of the
> | node, and the actual time and rows values shown are averages per-execution.
> | This is done to make the numbers comparable with the way that the cost
> | estimates are shown.  Multiply by the loops value to get the total time
> | actually spent in the node.
>
> On Thu, Jul 07, 2022 at 01:45:19PM -0700, Peter Geoghegan wrote:
> > Plus you could probably
> > make some kind of concession in the direction of maintaining
> > compatibility with the current approach if you had to. Right?
>
> The minimum would be to show the information in a way that makes it clear that
> it's "new style" output showing a total and not an average, so that a person
> who sees it knows how to interpret it (same for the web "explain tools")
>
> A concession would be to show the current information *plus* total/raw values.
>
> This thread is about how to display the existing values.
>

I feel the discussion has slightly deviated which makes it unclear
whether this patch is required or not?

-- 
With Regards,
Amit Kapila.

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