Date: Wed, 10 Nov 2021 09:09:03 -0300
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
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
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On 2021-Nov-09, Tom Lane wrote:

> 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 = off" to the
> test's postmaster configuration.

Ooh, of course.

> Also, I think we want
> 
> -ok($initfile != $endfile, "$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 ...

Argh!

Thanks for taking care of these issues.

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
"La conclusión que podemos sacar de esos estudios es que
no podemos sacar ninguna conclusión de ellos" (Tanenbaum)