Horton

Re: pg14b1 stuck in lazy_scan_prune/heap_page_prune of pg_statistic

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>, Andres Freund <andres@anarazel.de>, Michael Paquier <michael@paquier.xyz>, Justin Pryzby <pryzby@telsasoft.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Masahiko Sawada <sawada.mshk@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>
Date: 2021-06-10T18:14:55Z
Lists: pgsql-hackers 
On 2021-Jun-10, Peter Geoghegan wrote:

> On Thu, Jun 10, 2021 at 10:29 AM Matthias van de Meent
> <boekewurm+postgres@gmail.com> wrote:
> > I see one exit for HEAPTUPLE_DEAD on a potentially recently committed
> > xvac (?), and we might also check against recently committed
> > transactions if xmin == xmax, although apparently that is not
> > implemented right now.

xvac was used by the pre-9.0 VACUUM FULL, so I don't think it's possible
to see a recently committed one.  (I think you'd have to find a table
that was pg_upgraded from 8.4 or older, with leftover tuples from an
aborted VACUUM FULL, and never vacuumed after that.)

A scenario with such a tuple on disk is not impossible [in theory],
but if it does exist, then the VACUUM FULL would not be in the
possibly-visible horizon.

-- 
Álvaro Herrera       Valdivia, Chile
"Linux transformó mi computadora, de una `máquina para hacer cosas',
en un aparato realmente entretenido, sobre el cual cada día aprendo
algo nuevo" (Jaime Salinas)

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.