From: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-hackers@lists.postgresql.org
Subject: Possible SSI bug in heap_update
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Date: Sun, 11 Apr 2021 12:54:45 -0400
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While re-reading heap_update() in connection with that PANIC we're
chasing, my attention was drawn to this comment:

    /*
     * Note: beyond this point, use oldtup not otid to refer to old tuple.
     * otid may very well point at newtup->t_self, which we will overwrite
     * with the new tuple's location, so there's great risk of confusion if we
     * use otid anymore.
     */

This seemingly sage advice is being ignored in one place:

	CheckForSerializableConflictIn(relation, otid, BufferGetBlockNumber(buffer));

I wonder whether that's a mistake.  There'd be only a low probability
of our detecting it through testing, I fear.

			regards, tom lane