Feedback-ID: ia2694551:Fastmail
Date: Thu, 12 Sep 2024 15:14:08 +0200
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Pavel Borisov <pashkin.elfe@gmail.com>
Cc: Maxim Orlov <orlovmg@gmail.com>, 
	Alexander Korotkov <aekorotkov@gmail.com>, wenhui qiu <qiuwenhuifx@gmail.com>, 
	Heikki Linnakangas <hlinnaka@iki.fi>, Postgres hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: POC: make mxidoff 64 bits
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On 2024-Sep-12, Pavel Borisov wrote:

> Hi, Maxim!
> 
> Previously we accessed offsets in shared MultiXactState without locks as
> 32-bit read is always atomic. But I'm not sure it's so when offset become
> 64-bit.
> E.g. GetNewMultiXactId():
> 
> nextOffset = MultiXactState->nextOffset;
> is outside lock.

Good though.  But fortunately I think it's not a problem.  The one you
say is with MultiXactGetLock held in shared mode -- and that works OK,
as the assignment (in line 1263 at the bottom of the same routine) is
done with exclusive lock held.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/