Horton

Re: Online enabling of checksums

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Magnus Hagander <magnus@hagander.net>, Andrey Borodin <x4mmm@yandex-team.ru>, Heikki Linnakangas <hlinnaka@iki.fi>, Daniel Gustafsson <daniel@yesql.se>, Michael Banck <michael.banck@credativ.de>, Robert Haas <robertmhaas@gmail.com>, Greg Stark <stark@mit.edu>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-04-06T17:46:59Z
Lists: pgsql-hackers 
On 2018-04-06 19:40:59 +0200, Tomas Vondra wrote:
> In any case, I wouldn't call LockBufHdr/UnlockBufHdr a "side channel"
> interlock. It's a pretty direct and intentional interlock, I think.

I mean it's a side-channel as far as DataChecksumsNeedWrite() is
concerned. You're banking on all callers using a barrier implying
operation around it.


> Sure. But what would that be? I can't think of anything. A process that
> modifies a buffer (or any other piece of shared state) without holding
> some sort of lock seems broken by default.

You can quite possibly already *hold* a lock if it's not an exclusive
one.

Greetings,

Andres Freund

Commits

  1. Online enabling and disabling of data checksums

  2. Deactive flapping checksum isolation tests.

  3. Add support for coordinating record typmods among parallel workers.