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: Thomas Munro <thomas.munro@gmail.com>, Andres Freund <andres@anarazel.de>, Masahiko Sawada <sawada.mshk@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-03-28T03:24:32Z
Lists: pgsql-hackers

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On Thu, Mar 24, 2022 at 2:40 PM Peter Geoghegan <pg@bowt.ie> wrote:
> > > This is absolutely mandatory in the aggressive case, because otherwise
> > > relfrozenxid advancement might be seen as unsafe. My observation is:
> > > Why should we accept the same race in the non-aggressive case? Why not
> > > do essentially the same thing in every VACUUM?
> >
> > Sure, that seems like a good idea. I think I basically agree with the
> > goals of the patch.
>
> Great.

Attached is v12. My current goal is to commit all 3 patches before
feature freeze. Note that this does not include the more complicated
patch including with previous revisions of the patch series (the
page-level freezing work that appeared in versions before v11).

Changes that appear in this new revision, v12:

* Reworking of the commit messages based on feedback from Robert.

* General cleanup of the changes to heapam.c from 0001 (the changes to
heap_prepare_freeze_tuple and related functions).  New and existing
code now fits together a bit better. I also added a couple of new
documenting assertions, to make the flow a bit easier to understand.

* Added new assertions that document
OldestXmin/FreezeLimit/relfrozenxid invariants, right at the point we
update pg_class within vacuumlazy.c.

These assertions would have a decent chance of failing if there were
any bugs in the code.

* Removed patch that made DISABLE_PAGE_SKIPPING not force aggressive
VACUUM, limiting the underlying mechanism to forcing scanning of all
pages in lazy_scan_heap (v11 was the first and last revision that
included this patch).

* Adds a new small patch 0003. This just moves the last piece of
resource allocation that still took place at the top of
lazy_scan_heap() back into its caller, heap_vacuum_rel().

The work in 0003 probably should have happened as part of the patch
that became commit 73f6ec3d -- same idea. It's totally mechanical
stuff. With 0002 and 0003, there is hardly any lazy_scan_heap code
before the main loop that iterates through blocks in rel_pages (and
the code that's still there is obviously related to the loop in a
direct and obvious way). This seems like a big overall improvement in
maintainability.

Didn't see a way to split up 0002, per Robert's suggestion 3 days ago.
As I said at the time, it's possible to split it up, but not in a way
that highlights the underlying issue (since the issue 0002 fixes was
always limited to non-aggressive VACUUMs). The commit message may have
to suffice.

--
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