Horton

Re: pg14b1 stuck in lazy_scan_prune/heap_page_prune of pg_statistic

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Matthias van de Meent <boekewurm+postgres@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Michael Paquier <michael@paquier.xyz>, Justin Pryzby <pryzby@telsasoft.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Masahiko Sawada <sawada.mshk@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>
Date: 2021-06-10T17:07:36Z
Lists: pgsql-hackers 
On Thu, Jun 10, 2021 at 9:57 AM Matthias van de Meent
<boekewurm+postgres@gmail.com> wrote:
> > By "matches what we expect", I meant "involves a just-aborted
> > transaction". We could defensively verify that the inserting
> > transaction concurrently aborted at the point of retrying/calling
> > heap_page_prune() a second time. If there is no aborted transaction
> > involved (as was the case with this bug), then we can be confident
> > that something is seriously broken.
>
> I believe there are more cases than only the rolled back case, but
> checking for those cases would potentially help, yes.

Why do you believe that there are other cases?

I'm not aware of any case that causes lazy_scan_prune() to retry using
the goto, other than the aborted transaction case I described
(excluding the bug that you diagnosed, which was of course never
supposed to happen). If it really is possible to observe a retry for
any other reason then I'd very much like to know all the details - it
might well signal a distinct bug of the same general variety.

-- 
Peter Geoghegan

Commits

  1. Deduplicate choice of horizon for a relation procarray.c.

  2. Use correct horizon when vacuuming catalog relations.

  3. Truncate line pointer array during VACUUM.

  4. Remove tupgone special case from vacuumlazy.c.

  5. Refactor lazy_scan_heap() loop.

  6. snapshot scalability: Don't compute global horizons while building snapshots.