Horton

Re: New strategies for freezing, advancing relfrozenxid early

Jeff Davis <pgsql@j-davis.com>

View thread View on postgr.es
From: Jeff Davis <pgsql@j-davis.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-08-31T06:28:46Z
Lists: pgsql-hackers 
On Tue, 2022-08-30 at 13:45 -0700, Peter Geoghegan wrote:
> It's that I believe
> that it is all but mandatory for me to ameliorate the downside that
> goes with more eager freezing, for example by not doing it at all
> when
> it doesn't seem to make sense. I want to solve the big problem of
> freeze debt, without creating any new problems. And if I should also
> make things in adjacent areas better too, so much the better.

That clarifies your point. It's still a challenge for me to reason
about which of these potential new problems really need to be solved in
v1, though.

> Why stop at a couple of dozens of lines of code? Why not just change
> the default of vacuum_freeze_min_age and
> vacuum_multixact_freeze_min_age to 0?

I don't think that would actually solve the unbounded buildup of
unfrozen pages. It would still be possible for pages to be marked all
visible before being frozen, and then end up being skipped until an
aggressive vacuum is forced, right?

Or did you mean vacuum_freeze_table_age?

Regards,
	Jeff Davis

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