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: Andres Freund <andres@anarazel.de>
Cc: Justin Pryzby <pryzby@telsasoft.com>, Jeff Davis <pgsql@j-davis.com>, pgsql-hackers@lists.postgresql.org
Date: 2022-12-06T21:45:09Z
Lists: pgsql-hackers 
On Tue, Dec 6, 2022 at 10:42 AM Andres Freund <andres@anarazel.de> wrote:
> The docs don't build:
> https://cirrus-ci.com/task/5456939761532928
> [20:00:58.203] postgres.sgml:52: element link: validity error : IDREF attribute linkend references an unknown ID "vacuum-for-wraparound"

Thanks for pointing this out. FWIW it is a result of Bruce's recent
addition of the transaction processing chapter to the docs.

My intention is to post v9 later in the week, which will fix the doc
build, and a lot more besides that. If you are planning on doing
another round of review, I'd suggest that you hold off until then. v9
will have structural improvements that will likely make it easier to
understand all the steps leading up to removing aggressive mode
completely. It'll be easier to relate each local step/patch to the
bigger picture for VACUUM.

v9 will also address some of the concerns you raised in your review
that weren't covered by v8, especially about the VM snapshotting
infrastructure. But also your concerns about the transition from lazy
strategies to eager strategies. The "catch up freezing" performed by
the first VACUUM operation run against a table that just exceeded the
GUC-controlled table size threshold will have far more limited impact,
because the burden of freezing will be spread out across multiple
VACUUM operations. The big idea behind the patch series is to relieve
users from having to think about a special type of VACUUM that has to
do much more freezing than other VACUUMs that ran against the same
table in the recent past, of course, so it is important to avoid
accidentally allowing any behavior that looks kind of like the ghost
of aggressive VACUUM.

-- 
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