Horton

Re: New strategies for freezing, advancing relfrozenxid early

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Robert Haas <robertmhaas@gmail.com>, 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: 2023-01-27T09:02:53Z
Lists: pgsql-hackers 
Hi,

On 2023-01-27 00:51:59 -0800, Andres Freund wrote:
> One use-case where the eager strategy is particularly useful is
> [nearly-]append-only tables - and it's also the one workload that's reasonably
> easy to detect using stats. Maybe something like
> (dead_tuples_since_last_vacuum / inserts_since_last_vacuum) < 0.05
> or so.
> 
> That'll definitely leave out loads of workloads where eager freezing would be
> useful - but are there semi-reasonable workloads where it'll hurt badly? I
> don't *think* so.

That 0.05 could be a GUC + relopt combo, which'd allow users to opt in tables
with known usage pattern into always using eager freezing.

Greetings,

Andres Freund

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