Horton

Re: New strategies for freezing, advancing relfrozenxid early

Jeff Davis <pgsql@j-davis.com>

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From: Jeff Davis <pgsql@j-davis.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>, John Naylor <john.naylor@enterprisedb.com>, Andres Freund <andres@anarazel.de>, Justin Pryzby <pryzby@telsasoft.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-12-22T00:30:28Z
Lists: pgsql-hackers 
On Tue, 2022-12-20 at 21:26 -0800, Peter Geoghegan wrote:
> When freeze_required is set to true, that means that lazy_scan_prune
> literally has no choice -- it simply must freeze the page as
> instructed by heap_prepare_freeze_tuple/FreezeMultiXactId. It's not
> just a strong suggestion -- it's crucial that lazy_scan_prune freezes
> the page as instructed.

The confusing thing to me is perhaps just the name -- to me,
"freeze_required" suggests that if it were set to true, it would cause
freezing to happen. But as far as I can tell, it does not cause
freezing to happen, it causes some other things to happen that are
necessary when freezing happens (updating and using the right
trackers).

A minor point, no need to take action here. Perhaps rename the
variable.

I think 0001+0002 are about ready.


-- 
Jeff Davis
PostgreSQL Contributor Team - AWS

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