From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Geoghegan <pg@bowt.ie>
cc: Andres Freund <andres@anarazel.de>, David Rowley <dgrowleyml@gmail.com>,
        PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Intermittent buildfarm failures on wrasse
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Comments: In-reply-to Peter Geoghegan <pg@bowt.ie>
	message dated "Wed, 13 Apr 2022 17:17:00 -0700"
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Date: Wed, 13 Apr 2022 20:35:50 -0400
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Peter Geoghegan <pg@bowt.ie> writes:
> On Wed, Apr 13, 2022 at 4:51 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Yeah, we have band-aided around this type of problem repeatedly.
>> Making a fix that's readily accessible from any test script
>> seems like a good idea.

> We might even be able to consistently rely on this new option, given
> *any* problem involving test stability and VACUUM. Having a
> one-size-fits-all solution to these kinds of stability problems would
> be nice -- no more DISABLE_PAGE_SKIPPING bandaids.

My guess is that you'd need both this new wait-for-horizon behavior
*and* DISABLE_PAGE_SKIPPING.  But the two together ought to make
for pretty reproducible behavior.  I noticed while scanning the
commit log that some patches have tried adding a FREEZE option,
which seems more like waving a dead chicken than anything that'd
improve stability.

We'd not necessarily have to embed wait-for-horizon into VACUUM
itself.  It seems like a SQL-accessible function could be written
and then called before any problematic VACUUM.  I like this better
for something we're thinking of jamming in post-feature-freeze;
we'd not be committing to the feature quite as much as if we
added a VACUUM option.

			regards, tom lane