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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Ehrenreich, Sigrid <Ehrenreich@consist.de>
Cc: David Rowley <dgrowleyml@gmail.com>
Cc: 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
Date: Wed, 28 Oct 2020 12:55:26 -0400
Message-ID: <1345771.1603904126@sss.pgh.pa.us> (raw)
In-Reply-To: <AM0PR02MB5283D15DE7274926B3B212E8AB160@AM0PR02MB5283.eurprd02.prod.outlook.com>
References: <AM6PR02MB5287A0ADD936C1FA80973E72AB190@AM6PR02MB5287.eurprd02.prod.outlook.com>
	<CAApHDvqh4wSDOD+UVZ2xdaymu_-6rvkxjdcTQHOVAT-RTCdzog@mail.gmail.com>
	<807004.1603752841@sss.pgh.pa.us>
	<AM0PR02MB5283D15DE7274926B3B212E8AB160@AM0PR02MB5283.eurprd02.prod.outlook.com>

"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 necessary.
> Could you send me a notification if you managed to program a patch for that?

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=postgresql.git;a=patch;h=ad1c36b0709e47cdb3cc4abd6c939fe64279b6...

			regards, tom lane





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