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: Andres Freund <andres@anarazel.de>
Cc: Robert Haas <robertmhaas@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-02-20T04:28:21Z
Lists: pgsql-hackers 
On Sat, Feb 19, 2022 at 8:21 PM Andres Freund <andres@anarazel.de> wrote:
> Why does anything need to happen to it from vacuum's POV?  It'll not be a problem for freezing etc. Until it's deleted vacuum doesn't need to care.
>
> Probably worth a WARNING, and amcheck definitely needs to detect it, but otherwise I think it's fine to just continue.

Maybe that's true, but it's just really weird to imagine not having an
LP_REDIRECT that points to the LIVE item here, without throwing an
error. Seems kind of iffy, to say the least.

> >I guess it doesn't actually matter if we leave an aborted DEAD tuple
> >behind, that we could have pruned away, but didn't. The important
> >thing is to be consistent at the level of the page.
>
> That's not ok, because it opens up dangers of being interpreted differently after wraparound etc.
>
> But I don't see any cases where it would happen with the new pruning logic in your patch and sharing the HTSV status array?

Right. Fundamentally, there isn't any reason why it should matter that
VACUUM reached the heap page just before (rather than concurrent with
or just after) some xact that inserted or updated on the page aborts.
Just as long as we have a consistent idea about what's going on at the
level of the whole page (or maybe the level of each HOT chain, but the
whole page level seems simpler to me).

-- 
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