From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas@vondra.me>
cc: =?UTF-8?Q?Adrian_M=C3=B6nnich?= <adrian.moennich@cern.ch>,
        Andres Freund <andres@anarazel.de>, pgsql-bugs@lists.postgresql.org,
        Tomas Vondra <tv@fuzzy.cz>, Thomas Munro <thomas.munro@gmail.com>
Subject: Re: BUG #19449: Massive performance degradation for complex query on Postgres 16+ (few seconds -> multiple hours)
In-reply-to: <bbaf15a4-d743-47df-92fe-a1c5e94165ba@vondra.me>
References: <19449-4fac687c06cc7def@postgresql.org> <dihw6lynx3p75sv5fbgqjlsu3kfeagcnm4px2r7mgsvf4w2sf5@53udqm4e5wid> <43225458.20260402160627@cern.ch> <jivwllcuyvd7m4ceydwwpjptmadfe3cfbw47hqnej7yjfkleej@2q33rbrfybm4> <94712944.20260402164957@cern.ch> <2747373b-d188-43b1-8e49-66f9e23e3c24@vondra.me> <e43f543b-fac2-46da-9a4c-951c038ac0bc@vondra.me> <bbaf15a4-d743-47df-92fe-a1c5e94165ba@vondra.me>
Comments: In-reply-to Tomas Vondra <tomas@vondra.me>
	message dated "Fri, 03 Apr 2026 00:34:25 +0200"
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Date: Thu, 02 Apr 2026 18:43:36 -0400
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Tomas Vondra <tomas@vondra.me> writes:
> An interesting question is "What changed in PG16?" causing the query to
> fail, when it worked OK on earlier versions.

"git bisect" could be informative here.  I agree with trying to
minimize the query first, though --- else you may waste time
going down blind alleys, as a result of planner changes changing
the join order without affecting the critical executor behavior.

			regards, tom lane