From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
cc: Andres Freund <andres@anarazel.de>, Andrew Dunstan <andrew@dunslane.net>,
        "Bossart,
    Nathan" <bossartn@amazon.com>,
        Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
        "masao.fujii@oss.nttdata.com" <masao.fujii@oss.nttdata.com>,
        "pgsql-hackers@lists.postgresql.org"
 <pgsql-hackers@lists.postgresql.org>,
        "mengjuan.cmj@alibaba-inc.com" <mengjuan.cmj@alibaba-inc.com>,
        "Jakub.Wartak@tomtom.com" <Jakub.Wartak@tomtom.com>,
        Ryo Matsumura <matsumura.ryo@fujitsu.com>
Subject: Re: prevent immature WAL streaming
In-reply-to: <1669191.1635881881@sss.pgh.pa.us>
References: <202110132209.uyw4ubpc2ztc@alvherre.pgsql>
 <1669191.1635881881@sss.pgh.pa.us>
Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Tue, 02 Nov 2021 15:38:01 -0400"
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Date: Tue, 09 Nov 2021 18:08:07 -0500
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 <https://www.postgresql.org/message-id/1372189.1636499287%40sss.pgh.pa.us>
Precedence: bulk

I wrote:
> Seems like this hasn't fixed the problem: skink still fails on
> this test occasionally.
> #   Failed test '000000010000000000000002 differs from 00000001000000000=
0000002'
> #   at t/026_overwrite_contrecord.pl line 61.

This is still happening off and on, which makes it look like a
timing-sensitive problem.  Confirming that, I can make it fail
every time by adding a long sleep just ahead of where
026_overwrite_contrecord.pl captures $initfile.  On reflection
I think the problem is obvious: if autovacuum does anything
concurrently with the test's startup portion, it will cause the
carefully-established WAL insertion point to move into the
next segment.  I propose to add "autovacuum =3D off" to the
test's postmaster configuration.

Also, I think we want

-ok($initfile !=3D $endfile, "$initfile differs from $endfile");
+ok($initfile ne $endfile, "$initfile differs from $endfile");

The existing coding works as long as all characters of these
WAL segment names happen to be decimal digits, but ...

			regards, tom lane