From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Alexander Lakhin <exclusion@gmail.com>, pgsql-bugs@lists.postgresql.org,
        Richard Guo <guofenglinux@gmail.com>,
        Andres Freund <andres@anarazel.de>, Peter Geoghegan <pg@bowt.ie>
Subject: Re: BUG #17798: Incorrect memory access occurs when using BEFORE ROW
 UPDATE trigger
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Thu, 11 Jan 2024 09:34:56 -0500"
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Date: Thu, 11 Jan 2024 16:43:16 -0500
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Robert Haas <robertmhaas@gmail.com> writes:
> On Wed, Jan 10, 2024 at 10:00=E2=80=AFPM Alexander Lakhin <exclusion@gma=
il.com> wrote:
>> I was discouraged by that vast distance and implicit buffer usage too, =
but
>> I found no other feasible way to fix it. On the other hand, 75e03eabe a=
nd
>> Andres's words upthread made me believe that it's an acceptable solutio=
n.

> I agree that it's potentially acceptable. I just wonder if Tom or
> someone else is going to want to propose a bigger change to avoid some
> of this messiness. I don't know what that would look like, though.

I'm still feeling itchy about it.  Maybe the problem could be fixed
better if we didn't re-use slots with such abandon in this code,
but I don't have a concrete proposal.  Also, that'd likely be a
nontrivial rewrite bringing its own possibilities of adding bugs.

Some concrete thoughts:

* Maybe better to Assert(newslot =3D=3D epqslot_clean) instead of
what you did here?  Not sure.

* Why is the ExecMaterializeSlot step needed if we don't have
an epqslot_candidate?

			regards, tom lane