Message-ID: <2df82550-d2e0-47bc-804e-d7cf363f0db0@iki.fi>
Date: Wed, 26 Nov 2025 17:50:25 +0200
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Subject: Re: POC: make mxidoff 64 bits
To: Maxim Orlov <orlovmg@gmail.com>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>,
 Alexander Korotkov <aekorotkov@gmail.com>, wenhui qiu
 <qiuwenhuifx@gmail.com>,
 Postgres hackers <pgsql-hackers@lists.postgresql.org>,
 Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
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From: Heikki Linnakangas <hlinnaka@iki.fi>
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On 26/11/2025 17:23, Maxim Orlov wrote:
> On Tue, 25 Nov 2025 at 13:07, Heikki Linnakangas <hlinnaka@iki.fi 
> <mailto:hlinnaka@iki.fi>> wrote:
>> GetOldMultiXactIdSingleMember() currently asserts that the offset is
>> never zero, but it should try to do something sensible in that case
>> instead of just failing.
> 
> Correct me if I'm wrong, but we added the assertion that offsets are
> never 0, based on the idea that case #2 will never take place during an
> update. If this isn't the case, this assertion could be removed.
> The rest of the function appears to work correctly.
> 
> I even think that, as an experiment, we could randomly reset some of the
> offsets to zero and nothing would happen, except that some data would
> be lost.

+1

> The most sensible thing we can do is give the user a warning, right?
> Something like, "During the update, we encountered some weird offset
> that shouldn't have been there, but there's nothing we can do about it,
> just take note."

Yep, makes sense.

- Heikki