Horton

Re: New strategies for freezing, advancing relfrozenxid early

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Jeff Davis <pgsql@j-davis.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>, John Naylor <john.naylor@enterprisedb.com>, Justin Pryzby <pryzby@telsasoft.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2023-01-26T16:35:04Z
Lists: pgsql-hackers 
On Thu, Jan 26, 2023 at 5:41 AM Robert Haas <robertmhaas@gmail.com> wrote:
> On Wed, Jan 25, 2023 at 11:25 PM Peter Geoghegan <pg@bowt.ie> wrote:
> > On Wed, Jan 25, 2023 at 7:41 PM Robert Haas <robertmhaas@gmail.com> wrote:
> > > Both Andres and I have repeatedly expressed concern about how much is
> > > being changed in the behavior of vacuum, and how quickly, and IMHO on
> > > the basis of very limited evidence that the changes are improvements.
> > > The fact that Andres was very quickly able to find cases where the
> > > patch produces large regression is just more evidence of that. It's
> > > also hard to even understand what has been changed, because the
> > > descriptions are so theoretical.
> >
> > Did you actually read the motivating examples Wiki page?
>
> I don't know. I've read a lot of stuff that you've written on this
> topic, which has taken a significant amount of time, and I still don't
> understand a lot of what you're changing, and I don't agree with all
> of the things that I do understand.

You complained about the descriptions being theoretical. But there's
nothing theoretical about the fact that we more or less do *all*
freezing in an eventual aggressive VACUUM in many important cases,
including very simple cases like pgbench_history -- the simplest
possible append-only table case. We'll merrily rewrite the entire
table, all at once, for no good reason at all. Consistently, reliably.
It's so incredibly obvious that this makes zero sense! And yet I don't
think you've ever engaged with such basic points as that one.

-- 
Peter Geoghegan

Commits

  1. Revert "Add eager and lazy freezing strategies to VACUUM."

  2. Add eager and lazy freezing strategies to VACUUM.

  3. Refine the definition of page-level freezing.

  4. Avoid special XID snapshotConflictHorizon values.

  5. Add page-level freezing to VACUUM.

  6. Remove overzealous MultiXact freeze assertion.

  7. Refactor how VACUUM passes around its XID cutoffs.

  8. Deduplicate freeze plans in freeze WAL records.

  9. Set relfrozenxid to oldest extant XID seen by VACUUM.

  10. Only skip pages marked as clean in the visibility map, if the last 32

  11. Add vacuum_freeze_table_age GUC option, to control when VACUUM should