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From: Alvaro Herrera <[email protected]>
To: Pavel Borisov <[email protected]>
Cc: Maxim Orlov <[email protected]>
Cc: Alexander Korotkov <[email protected]>
Cc: wenhui qiu <[email protected]>
Cc: Heikki Linnakangas <[email protected]>
Cc: Postgres hackers <[email protected]>
Subject: Re: POC: make mxidoff 64 bits
Date: Thu, 12 Sep 2024 15:14:08 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <CALT9ZEHm138m2rTi6-N_Xcm0ibfbK0b7yysdPHj1v144YUOFQg@mail.gmail.com>

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/

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