From: Tom Lane <tgl@sss.pgh.pa.us>
To: "Ehrenreich, Sigrid" <Ehrenreich@consist.de>
cc: David Rowley <dgrowleyml@gmail.com>,
        "pgsql-performance@lists.postgresql.org"
 <pgsql-performance@lists.postgresql.org>
Subject: Re: Postgres Optimizer ignores information about foreign key
 relationship, severly misestimating number of returned rows in join
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Comments: In-reply-to "Ehrenreich, Sigrid" <Ehrenreich@consist.de>
	message dated "Tue, 27 Oct 2020 07:50:19 -0000"
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Date: Wed, 28 Oct 2020 12:55:26 -0400
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"Ehrenreich, Sigrid" <Ehrenreich@consist.de> writes:
> A patch would be very much appreciated.
> We are currently running on Version 12, but could upgrade to 13, if nece=
ssary.
> Could you send me a notification if you managed to program a patch for t=
hat?

I've pushed a patch for this to HEAD, but current thinking is that we
will not be back-patching it.  Still, if you're desperate you could
consider running a custom build of v13 with that patch --- a quick
check suggests that it would back-patch easily.  v12 would be a
slightly harder lift (I see one hunk doesn't apply) but probably
not by much.

https://git.postgresql.org/gitweb/?p=3Dpostgresql.git;a=3Dpatch;h=3Dad1c36=
b0709e47cdb3cc4abd6c939fe64279b63f

			regards, tom lane