Horton

Re: race condition when writing pg_control

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Nathan Bossart <nathandbossart@gmail.com>, Melanie Plageman <melanieplageman@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, Michael Paquier <michael@paquier.xyz>, Fujii Masao <masao.fujii@oss.nttdata.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2024-05-16T19:01:31Z
Lists: pgsql-hackers 
Andres Freund <andres@anarazel.de> writes:
> On 2024-05-16 14:50:50 -0400, Tom Lane wrote:
>> The intention was certainly always that it be atomic.  If it isn't
>> we have got *big* trouble.

> We unfortunately do *know* that on several systems e.g. basebackup can read a
> partially written control file, while the control file is being
> updated.

Yeah, but can't we just retry that if we get a bad checksum?

What had better be atomic is the write to disk.  Systems that can't
manage POSIX semantics for concurrent reads and writes are annoying,
but not fatal ...

			regards, tom lane

Commits

  1. Fix locking bugs that could corrupt pg_control.