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: Andres Freund <andres@anarazel.de>
Cc: Peter Geoghegan <pg@bowt.ie>, 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: 2023-01-26T03:41:15Z
Lists: pgsql-hackers 
On Wed, Jan 25, 2023 at 8:49 PM Andres Freund <andres@anarazel.de> wrote:
> The concrete setting of vacuum_freeze_strategy_threshold doesn't matter.
> Table size simply isn't a usable proxy for whether eager freezing is a good
> idea or not.

I strongly agree. I can't imagine how a size-based threshold can make
any sense at all.

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.

I think we're on a very dangerous path here. I want VACUUM to be
better as the next person, but I really don't believe that's the
direction we're headed. I think if we release like this, we're going
to experience more VACUUM pain, not less. And worse still, I don't
think anyone other than Peter and Andres is going to understand why
it's happening.

-- 
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