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From: Tom Lane <tgl@sss.pgh.pa.us>
To: James Coleman <jtc331@gmail.com>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Michael Paquier <michael@paquier.xyz>
Cc: Rafia Sabih <rafia.pghackers@gmail.com>
Cc: Peter Geoghegan <pg@bowt.ie>
Cc: Simon Riggs <simon@2ndquadrant.com>
Cc: Shaun Thomas <shaun.thomas@2ndquadrant.com>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>
Cc: Alexander Korotkov <a.korotkov@postgrespro.ru>
Cc: PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Subject: Re: [PATCH] Incremental sort (was: PoC: Partial sort)
Date: Fri, 13 Mar 2020 13:36:44 -0400
Message-ID: <32110.1584121004@sss.pgh.pa.us> (raw)
In-Reply-To: <CAAaqYe-AMOQ9Rr_zcGtNXfAaMj9sT6mGCp_M0tJbQeuLsms-Rw@mail.gmail.com>
References: <20190904191710.gogtnktjbvtg5zq3@development>
	<20190909215538.42hrv6j4z5ztcft4@development>
	<CAAaqYe-L4a2mj=AqguVjdkf65LZ772C-GbKgAj7CQro8rftXBg@mail.gmail.com>
	<20190928230049.k4l2mayun7jomhxy@development>
	<20191129060146.GH2505@paquier.xyz>
	<20191201004716.cenkc33em2lnrrdl@development>
	<20200121142529.wpickvfefp7lok4p@development>
	<CAAaqYe-=w0RaadtaTxfwuVa7GK+8QS7D51YzmfJLX9YZGfqc4A@mail.gmail.com>
	<CAAaqYe_ctGqQsauuYS5StPULkES7=t8vNwvEPyzXQdbjAuZ6vA@mail.gmail.com>
	<CAAaqYe-BV=kuMmwHCnOfdAG_mKjCo=41MeFrdtBjB+iXd6-FJg@mail.gmail.com>
	<20200311024355.5h2v56jpgzvd7yox@development>
	<CAAaqYe-AMOQ9Rr_zcGtNXfAaMj9sT6mGCp_M0tJbQeuLsms-Rw@mail.gmail.com>

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 not
>> 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





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