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: 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>, Robert Haas <robertmhaas@gmail.com>
Date: 2023-01-26T01:37:17Z
Lists: pgsql-hackers 
On Wed, Jan 25, 2023 at 5:26 PM Andres Freund <andres@anarazel.de> wrote:
> Another bad scenario: Some longrunning / hung transaction caused us to get
> close to the xid wraparound. Problem was resolved, autovacuum runs. Previously
> we wouldn't have frozen the portion of the table that was actively changing,
> now we will. Consequence: We get closer to the "no write" limit / the outage
> lasts longer.

Obviously it isn't difficult to just invent a new rule that gets
applied by lazy_scan_strategy. For example, it would take me less than
5 minutes to write a patch that disables eager freezing when the
failsafe is in effect.

> I don't see an alternative to reverting this for now.

I want to see your test case before acting.

-- 
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