From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
cc: David Christensen <david@endpoint.com>, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #16676: SELECT ... FETCH FIRST ROW WITH TIES FOR UPDATE SKIP
 LOCKED locks rows it doesn't return
In-reply-to: <20201020134114.GA11045@alvherre.pgsql>
References: <20201020134114.GA11045@alvherre.pgsql>
Comments: In-reply-to Alvaro Herrera <alvherre@alvh.no-ip.org>
	message dated "Tue, 20 Oct 2020 10:41:14 -0300"
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Date: Tue, 20 Oct 2020 10:16:56 -0400
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Alvaro Herrera <alvherre@alvh.no-ip.org> writes:
> On 2020-Oct-19, David Christensen wrote:
>> Maybe splitting LockRows into two nodes, one for locking and one for
>> emitting unlocked nodes then interleaving Limit in between? (Or only
>> doing something along these lines for this admittedly narrow use case.)

> I was having a similar idea, but the main reason I don't think it's a
> good fix is that we can't backpatch such a change to pg13.

Um, why not?  I don't have a position yet on whether this is a good way
to fix it; but if we did do it, AFAICS the only thing we'd have to be
careful of in v13 is not renumbering existing NodeTag values.

If your concern is just that EXPLAIN plans will look different, the same
could be said of David's other proposal.

			regards, tom lane