Horton

Re: Removing more vacuumlazy.c special cases, relfrozenxid optimizations

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, Andres Freund <andres@anarazel.de>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-01-06T23:58:48Z
Lists: pgsql-hackers 
On Thu, Jan 6, 2022 at 2:45 PM Peter Geoghegan <pg@bowt.ie> wrote:
> But the "freeze early" heuristics work a bit like that anyway. We
> won't freeze all the tuples on a whole heap page early if we won't
> otherwise set the heap page to all-visible (not all-frozen) in the VM
> anyway.

I believe that applications tend to update rows according to
predictable patterns. Andy Pavlo made an observation about this at one
point:

https://youtu.be/AD1HW9mLlrg?t=3202

I think that we don't do a good enough job of keeping logically
related tuples (tuples inserted around the same time) together, on the
same original heap page, which motivated a lot of my experiments with
the FSM from last year. Even still, it seems like a good idea for us
to err in the direction of assuming that tuples on the same heap page
are logically related. The tuples should all be frozen together when
possible. And *not* frozen early when the heap page as a whole can't
be frozen (barring cases with one *much* older XID before
FreezeLimit).

-- 
Peter Geoghegan

Commits

  1. Have VACUUM warn on relfrozenxid "in the future".

  2. vacuumlazy.c: Further consolidate resource allocation.

  3. Generalize how VACUUM skips all-frozen pages.

  4. Set relfrozenxid to oldest extant XID seen by VACUUM.

  5. Doc: Add relfrozenxid Tip to XID wraparound section.

  6. vacuumlazy.c: document vistest and OldestXmin.

  7. Increase hash_mem_multiplier default to 2.0.

  8. Consolidate VACUUM xid cutoff logic.

  9. Add VACUUM instrumentation for scanned pages, relfrozenxid.

  10. Simplify lazy_scan_heap's handling of scanned pages.

  11. Try to stabilize reloptions test, again.

  12. Unify VACUUM VERBOSE and autovacuum logging.

  13. Fix possible HOT corruption when RECENTLY_DEAD changes to DEAD while pruning.

  14. pg_resetxlog: add option to set oldest xid & use by pg_upgrade

  15. Teach VACUUM to bypass unnecessary index vacuuming.

  16. Centralize horizon determination for temp tables, fixing bug due to skew.

  17. pg_surgery: Try to stabilize regression tests.

  18. Add "split after new tuple" nbtree optimization.

  19. Fix bugs in vacuum of shared rels, by keeping their relcache entries current.

  20. Avoid useless truncation attempts during VACUUM.

  21. Only skip pages marked as clean in the visibility map, if the last 32

  22. Fix recently-understood problems with handling of XID freezing, particularly