From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
cc: Michael Paquier <michael@paquier.xyz>, pgsql-hackers@lists.postgresql.org
Subject: Re: Odd, intermittent failure in contrib/pageinspect
In-reply-to: <20210118223019.GA2579@alvherre.pgsql>
References: <20210118223019.GA2579@alvherre.pgsql>
Comments: In-reply-to Alvaro Herrera <alvherre@alvh.no-ip.org>
	message dated "Mon, 18 Jan 2021 19:30:19 -0300"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <416194.1611009300.1@sss.pgh.pa.us>
Date: Mon, 18 Jan 2021 17:35:00 -0500
Message-ID: <416195.1611009300@sss.pgh.pa.us>
Precedence: bulk

Alvaro Herrera <alvherre@alvh.no-ip.org> writes:
> On 2021-Jan-18, Tom Lane wrote:
>> Searching the buildfarm logs turned up exactly one previous occurrence,
>> also on whelk [2].  So I'm not sure what to make of it.  Could the
>> immediately preceding VACUUM FREEZE command have silently skipped this
>> page for some reason?  That'd be a bug I should think.

> Hmm, doesn't vacuum skip pages when they are pinned?  I don't think
> VACUUM FREEZE would be treated especially -- only "aggressive"
> wraparound would be an exception, IIRC.

Right.  If that's the explanation, then adding DISABLE_PAGE_SKIPPING
to the test's VACUUM options should fix it.  However, to believe that
theory you have to have some reason to think that some other process
might have the page pinned.  What would that be?  test1 only has one
small tuple in it, so it doesn't seem credible that autovacuum or
autoanalyze would have fired on it.

[ thinks for a bit... ]  Does the checkpointer pin pages it's writing
out?  I guess it'd have to ...

			regards, tom lane