Date: Thu, 4 Aug 2022 07:21:10 -0700
From: Noah Misch <noah@leadboat.com>
To: David Steele <david@pgmasters.net>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
	pgsql-hackers@postgresql.org, don@seiler.us
Subject: Re: Race between KeepFileRestoredFromArchive() and restartpoint
Message-ID: <20220804142110.GA3878007@rfd.leadboat.com>
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 <20220804.170640.1425291966829818860.horikyota.ntt@gmail.com>
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On Thu, Aug 04, 2022 at 06:32:38AM -0400, David Steele wrote:
> On 8/4/22 04:06, Kyotaro Horiguchi wrote:
> >At Wed, 3 Aug 2022 23:24:56 -0700, Noah Misch <noah@leadboat.com> wrote in
> >>>>I think in this case a HINT might be sufficient to at least keep people from
> >>>>wasting time tracking down a problem that has already been fixed.
> >>
> >>Here's a patch to add that HINT.  I figure it's better to do this before next
> >>week's minor releases.  In the absence of objections, I'll push this around
> >>2022-08-05 14:00 UTC.
> >
> >+1
> 
> Looks good to me as well.

Thanks for reviewing.

> >>>>However, there is another issue [1] that might argue for a back patch if
> >>>>this patch (as I believe) would fix the issue.
> >>>
> >>>>[1] https://www.postgresql.org/message-id/CAHJZqBDxWfcd53jm0bFttuqpK3jV2YKWx%3D4W7KxNB4zzt%2B%2BqFg%40mail.gmail.com
> >>>
> >>>That makes sense.  Each iteration of the restartpoint recycle loop has a 1/N
> >>>chance of failing.  Recovery adds >N files between restartpoints.  Hence, the
> >>>WAL directory grows without bound.  Is that roughly the theory in mind?
> >>
> >>On further reflection, I don't expect it to happen that way.  Each failure
> >>message is LOG-level, so the remaining recycles still happen.  (The race
> >>condition can yield an ERROR under PreallocXlogFiles(), but recycling is
> >>already done at that point.)
> >
> >I agree to this.
> 
> Hmmm, OK. We certainly have a fairly serious issue here, i.e. pg_wal growing
> without bound. Even if we are not sure what is causing it, how confident are
> we that the patches applied to v15 would fix it?

I'll say 7%; certainly too low to stop investigating.  The next things I'd want
to see are:

- select name, setting, source from pg_settings where setting <> boot_val;
- log_checkpoints log entries, and other log entries having the same PID

If the theory about checkpoint skipping holds, there should be a period where
the volume of WAL replayed greatly exceeds max_wal_size, yet 0-1 restartpoints
begin and 0 restartpoints complete.