Message-ID: <41cc55f13edfc22ab393fa27b54ca6b7fed32ee9.camel@cybertec.at>
Subject: Re: When UPDATE a row in a table with BEFORE ROW UPDATE trigger,
 the XMAX of new tuple is set to current XID
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Charles Qi <qyqgpower@gmail.com>
Cc: Adrian Klaver <adrian.klaver@aklaver.com>, 
	pgsql-general@lists.postgresql.org
Date: Wed, 13 Aug 2025 07:14:48 +0200
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On Mon, 2025-08-11 at 11:34 +0800, Charles Qi wrote:
> The trigger function in example is doing nothing but return new, the
> row is actually locked by the trigger itself (trigger.c >
> ExecBRUpdateTriggers > GetTupleForTrigger)
>
> You mentioned a very important behavior:
> > A multixact is only necessary
> > if a subtransaction needs to take a stronger lock on the row than what
> > was there before.
>
> We are doing two no key updates in example, and should not need a
> stronger lock on the same row.

Still, you could explicitly lock the row in the trigger function with
a high enough lock level to avoid a multixact being created later on.

Yours,
Laurenz Albe