Horton

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

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Andres Freund <andres@anarazel.de>, Masahiko Sawada <sawada.mshk@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-03-23T20:53:13Z
Lists: pgsql-hackers 
On Wed, Mar 23, 2022 at 4:49 PM Peter Geoghegan <pg@bowt.ie> wrote:
> On Wed, Mar 23, 2022 at 1:41 PM Robert Haas <robertmhaas@gmail.com> wrote:
> > It seems to me that if DISABLE_PAGE_SKIPPING doesn't completely
> > disable skipping pages, we have a problem.
>
> It depends on how you define skipping. DISABLE_PAGE_SKIPPING was
> created at a time when a broader definition of skipping made a lot
> more sense.
>
> > The option isn't named CARE_ABOUT_VISIBILITY_MAP. It's named
> > DISABLE_PAGE_SKIPPING.
>
> VACUUM(DISABLE_PAGE_SKIPPING, VERBOSE) will still consistently show
> that 100% of all of the pages from rel_pages are scanned. A page that
> is "skipped" by lazy_scan_noprune isn't pruned, and won't have any of
> its tuples frozen. But every other aspect of processing the page
> happens in just the same way as it would in the cleanup
> lock/lazy_scan_prune path.

I see what you mean about it depending on how you define "skipping".
But I think that DISABLE_PAGE_SKIPPING is intended as a sort of
emergency safeguard when you really, really don't want to leave
anything out. And therefore I favor defining it to mean that we don't
skip any work at all.

-- 
Robert Haas
EDB: http://www.enterprisedb.com

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