Horton

Re: New strategies for freezing, advancing relfrozenxid early

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Peter Geoghegan <pg@bowt.ie>
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: 2023-01-26T13:41:06Z
Lists: pgsql-hackers 
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. I can't state with confidence that
the motivating examples wiki page was or was not among the things that
I read. But, you know, when people start running PostgreSQL 16, and
have some problem, they're not going to read the motivating examples
wiki page. They're going to read the documentation. If they can't find
the answer there, they (or some hacker that they contact) will
probably read the code comments and the relevant commit messages.
Those either clearly explain what was changed in a way that somebody
can understand, or they don't. If they don't, *the commits are not
good enough*, regardless of what other information may exist in any
other place.

-- 
Robert Haas
EDB: http://www.enterprisedb.com

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