Horton

Re: New strategies for freezing, advancing relfrozenxid early

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Jeff Davis <pgsql@j-davis.com>, 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: 2023-01-16T05:12:56Z
Lists: pgsql-hackers 
On Mon, Jan 9, 2023 at 7:16 AM Peter Geoghegan <pg@bowt.ie> wrote:
>
> On Tue, Jan 3, 2023 at 12:30 PM Peter Geoghegan <pg@bowt.ie> wrote:
> > Attached is v14.
>
> This has stopped applying due to conflicts with nearby work on VACUUM
> from Tom. So I attached a new revision, v15, just to make CFTester
> green again.
>
> I didn't have time to incorporate any of the feedback from Matthias
> just yet. That will have to wait until v16.
>
I have looked into the patch set, I think 0001 looks good to me about
0002 I have a few questions, 0003 I haven't yet looked at

1.
+    /*
+     * Finally, set tableagefrac for VACUUM.  This can come from either XID or
+     * XMID table age (whichever is greater currently).
+     */
+    XIDFrac = (double) (nextXID - cutoffs->relfrozenxid) /
+        ((double) freeze_table_age + 0.5);

I think '(nextXID - cutoffs->relfrozenxid) / freeze_table_age' should
be the actual fraction right?  What is the point of adding 0.5 to the
divisor?  If there is a logical reason, maybe we can explain in the
comments.

2.
While looking into the logic of 'lazy_scan_strategy', I think the idea
looks very good but the only thing is that
we have kept eager freeze and eager scan completely independent.
Don't you think that if a table is chosen for an eager scan
then we should force the eager freezing as well?

-- 
Regards,
Dilip Kumar
EnterpriseDB: 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