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: Andres Freund <andres@anarazel.de>, Masahiko Sawada <sawada.mshk@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-03-23T20:49:09Z
Lists: pgsql-hackers 
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.

We'll even still VACUUM the page if it happens to have some existing
LP_DEAD items left behind by opportunistic pruning. We don't need a
cleanup in either lazy_scan_noprune (a share lock is all we need), nor
do we even need one in lazy_vacuum_heap_page (a regular exclusive lock
is all we need).

-- 
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