From: Tom Lane <tgl@sss.pgh.pa.us>
To: Elvis Pranskevichus <elprans@gmail.com>
cc: PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>,
        David Rowley <dgrowleyml@gmail.com>
Subject: Re: BUG #17213: Wrong result from a query involving Merge Semi Join
 and Memoize
In-reply-to: <4374396.LvFx2qVVIh@vulcan.edgedb.net>
References: <17213-988ed34b225a2862@postgresql.org>
 <CAApHDvq-auQ9rK8VzD79X77cY4AOKP0mKp1whYjfNX8xYMEZGw@mail.gmail.com>
 <4374396.LvFx2qVVIh@vulcan.edgedb.net>
Comments: In-reply-to Elvis Pranskevichus <elprans@gmail.com>
	message dated "Mon, 04 Oct 2021 17:36:09 -0700"
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Date: Mon, 04 Oct 2021 21:21:21 -0400
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Elvis Pranskevichus <elprans@gmail.com> writes:
> On Monday, October 4, 2021 5:14:47 PM PDT David Rowley wrote:
>>> It appears a combination of Merge Semi Join and Memoize in
>>> PostgreSQL 14 produces incorrect results on a particular query. 

> It seems like a very particular set of stats is causing the plan there, 
> as running ANALYZE turns the query into a Nested Loop Semi Join.

Surely this plan tree is broken on its face?  The inner side of
a mergejoin has to be able to support mark/restore, and nestloop
doesn't (cf ExecSupportsMarkRestore, as well as assertions in
nodeNestloop).  It looks to me like somebody removed an essential
plan-time check.

			regards, tom lane