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In-Reply-To: <3132441.1740153303@sss.pgh.pa.us>
From: Amit Langote <amitlangote09@gmail.com>
Date: Sat, 22 Feb 2025 11:13:24 +0900
Message-ID: <CA+HiwqHEy7OLWG1-FZ8XfCzjuLQR_mytu9aYxbtPrs_0NeDYkg@mail.gmail.com>
Subject: Re: generic plans and "initial" pruning
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Tomas Vondra <tomas@vondra.me>, Robert Haas <robertmhaas@gmail.com>, 
	Alvaro Herrera <alvherre@alvh.no-ip.org>, Andres Freund <andres@anarazel.de>, 
	Daniel Gustafsson <daniel@yesql.se>, David Rowley <dgrowleyml@gmail.com>, 
	PostgreSQL Hackers <pgsql-hackers@postgresql.org>, Thom Brown <thom@linux.com>
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On Sat, Feb 22, 2025 at 12:55=E2=80=AFAM Tom Lane <tgl@sss.pgh.pa.us> wrote=
:
> Amit Langote <amitlangote09@gmail.com> writes:
> > The short of it is that the cached-plan-inval test in the
> > delay_execution suite can never be made to work under
> > CLOBBER_CACHE_ALWAYS. The test assumes that locks on partitions for a
> > reused generic plan are not taken until InitPlan(). However, under
> > CLOBBER_CACHE_ALWAYS, generic plans are never reused, so the test's
> > assumption never holds.
>
> Ugh.
>
> > I see two possible ways to address this:
>
> > 1. Find a way to disable the cached-plan-inval test in
> > CLOBBER_CACHE_ALWAYS builds. However, I haven't found any other test
> > that does this.
>
> > 2. Remove the test altogether, though that might be too drastic.
>
> Well, you could force matters with "set debug_discard_caches =3D 0"
> within the test, but I think that's just a band-aid that would
> not make the test fully stable.  The point of CLOBBER_CACHE_ALWAYS
> is to model random arrival of cache flush events, which is *always*
> a possibility due to background activity (autovacuum for instance).
>
> We do have a couple of other regression tests that rely on
> "set debug_discard_caches =3D 0", and I've not seen many buildfarm
> failures tracing to that, but I don't trust it a whole lot.
>
> How badly do you want to keep this test case?  It seems fairly
> rickety to me, even without this particular concern.

Hmm, yeah, I have to admit that even if we address this specific
issue, the risk of this test failing again outweighs the likelihood of
it catching a real breakage in the deferred lock mechanism.

I'll remove the test for now.

--=20
Thanks, Amit Langote