Feedback-ID: i0fe9450f:Fastmail
Date: Tue, 22 Aug 2023 07:55:28 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Andres Freund <andres@anarazel.de>
Cc: Wyatt Alt <wyatt.alt@gmail.com>, pgsql-bugs@lists.postgresql.org
Subject: Re: cache lookup failed dropping public schema with trgm index
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On Mon, Aug 21, 2023 at 03:36:10PM -0700, Andres Freund wrote:
> It also seems to work without even involving a drop schema. Just dropping
> pg_trgm with cascade is sufficient.

FWIW, after a bisect I can see that 911e7020 is the origin of the
failure (`git bisect start b5d69b7 9e1c9f9` based on two merge-bases).

> Now, this isn't a real issue in practice (without such a debugging statement,
> which likely can't work in some cases), but I strongly suspect that it
> indicates a scheduling order issue that's more widespread. Despite, I think,
> correct dependencies, we end up with a topologically inconsistent drop
> order. There aren't any cycles in the directed dependency graph from what I
> can see.

Yeah, guess so.  I was first betting on a missing shared inval here.
Now note that for example, this command works:
psql -v ON_ERROR_STOP=1 -c 'create table foo(t text); create extension pg_trgm; create index on foo using gist(t gist_trgm_ops);create index on foo using gist(t gist_trgm_ops); drop schema public cascade;'
--
Michael

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