Horton

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

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Justin Pryzby <pryzby@telsasoft.com>, Robert Haas <robertmhaas@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-03-31T17:11:14Z
Lists: pgsql-hackers 
Hi,

On 2022-03-31 09:58:18 -0700, Peter Geoghegan wrote:
> On Thu, Mar 31, 2022 at 9:37 AM Andres Freund <andres@anarazel.de> wrote:
> > The only place that appears to access rd_rel->relfrozenxid outside of DDL is
> > heap_abort_speculative().
> 
> I wonder how necessary that really is. Even if the XID is before
> relfrozenxid, does that in itself really make it "in the future"?
> Obviously it's often necessary to make the assumption that allowing
> wraparound amounts to allowing XIDs "from the future" to exist, which
> is dangerous. But why here? Won't pruning by VACUUM eventually correct
> the issue anyway?

I don't think we should weaken defenses against xids from before relfrozenxid
in vacuum / amcheck / .... If anything we should strengthen them.

Isn't it also just plainly required for correctness? We'd not necessarily
trigger a vacuum in time to remove the xid before approaching wraparound if we
put in an xid before relfrozenxid? That happening in prune_xid is obviously
les bad than on actual data, but still.


ISTM we should just use our own xid. Yes, it might delay cleanup a bit
longer. But unless there's already crud on the page (with prune_xid already
set, the abort of the speculative insertion isn't likely to make the
difference?

Greetings,

Andres Freund

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