From: Tom Lane <tgl@sss.pgh.pa.us>
To: James Coleman <jtc331@gmail.com>
cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>,
        Michael Paquier <michael@paquier.xyz>,
        Rafia Sabih <rafia.pghackers@gmail.com>, Peter Geoghegan <pg@bowt.ie>,
        Simon Riggs <simon@2ndquadrant.com>,
        Shaun Thomas <shaun.thomas@2ndquadrant.com>,
        Dmitry Dolgov <9erthalion6@gmail.com>,
        Alexander Korotkov <a.korotkov@postgrespro.ru>,
        PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>,
        Alvaro Herrera <alvherre@2ndquadrant.com>
Subject: Re: [PATCH] Incremental sort (was: PoC: Partial sort)
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Comments: In-reply-to James Coleman <jtc331@gmail.com>
	message dated "Fri, 13 Mar 2020 13:16:44 -0400"
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Date: Fri, 13 Mar 2020 13:36:44 -0400
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James Coleman <jtc331@gmail.com> writes:
> On Tue, Mar 10, 2020 at 10:44 PM Tomas Vondra
> <tomas.vondra@2ndquadrant.com> wrote:
>> 1) I see a bunch of failures in the regression test, due to minor
>> differences in the explain output. All the differences are about minor
>> changes in memory usage, like this:
>> =

>> -               "Sort Space Used": 30,                             +
>> +               "Sort Space Used": 29,                             +
>> =

>> I'm not sure if it happens on my machine only, but maybe the test is no=
t
>> entirely stable.

> make check passes on multiple machines for me; what arch/distro are you =
using?

I think there's exactly zero chance of such output being stable across
different platforms, particularly 32-vs-64-bit.  You'll need to either
drop that test or find some way to mask the variability.

> Is there a better way to test these? I would prefer these code paths
> have test coverage, but the standard SQL tests don't leave a good way
> to handle stuff like this.

In some places we use plpgsql code to filter the EXPLAIN output.

			regards, tom lane