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From: Thomas Munro <thomas.munro@gmail.com>
Date: Wed, 23 Nov 2022 23:03:45 +1300
Message-ID: 
 <CA+hUKGL9w0VhZ=ceMDjXgCXy1BC5VzjwXc-HetSxfNzvBLge3A@mail.gmail.com>
Subject: Re: odd buildfarm failure - "pg_ctl: control file appears to be
 corrupt"
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@postgresql.org
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On Wed, Nov 23, 2022 at 2:42 PM Andres Freund <andres@anarazel.de> wrote:
> The failure has to be happening in wait_for_postmaster_promote(), because the
> standby2 is actually successfully promoted.

I assume this is ext4.  Presumably anything that reads the
controlfile, like pg_ctl, pg_checksums, pg_resetwal,
pg_control_system(), ... by reading without interlocking against
writes could see garbage.  I have lost track of the versions and the
thread, but I worked out at some point by experimentation that this
only started relatively recently for concurrent read() and write(),
but always happened with concurrent pread() and pwrite().  The control
file uses the non-p variants which didn't mash old/new data like
grated cheese under concurrency due to some implementation detail, but
now does.