Re: BUG #17257: (auto)vacuum hangs within lazy_scan_prune()

Melanie Plageman <melanieplageman@gmail.com>

From: Melanie Plageman <melanieplageman@gmail.com>

To: Peter Geoghegan <pg@bowt.ie>

Cc: Andres Freund <andres@anarazel.de>, Noah Misch <noah@leadboat.com>, Robert Haas <robertmhaas@gmail.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>, Alexander Lakhin <exclusion@gmail.com>, PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>

Date: 2024-04-26T21:56:36Z

Lists: pgsql-bugs

Commits

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Ensure vacuum removes all visibly dead tuples older than OldestXmin
- 06bf404cd07b 16.4 landed
- 45ce054c02b8 14.13 landed
- dc6354c67017 15.8 landed
Combine freezing and pruning steps in VACUUM
- 6dbb490261a6 17.0 cited
Handle non-chain tuples outside of heap_prune_chain()
- 6f47f6883151 17.0 cited
Fix false reports in pg_visibility
- e85662df44ff 17.0 cited
Remove retry loop in heap_page_prune().
- 1ccc1e05ae8f 17.0 cited
vacuumlazy.c: document vistest and OldestXmin.
- 73f6ec3d3c8d 15.0 cited
Deduplicate choice of horizon for a relation procarray.c.
- d9d8aa9bb9aa 15.0 cited
Remove tupgone special case from vacuumlazy.c.
- 8523492d4e34 14.0 cited
Simplify state managed by VACUUM.
- b4af70cb2103 14.0 cited
Recycle nbtree pages deleted during same VACUUM.
- 9dd963ae2534 14.0 cited
snapshot scalability: Don't compute global horizons while building snapshots.
- dc7420c2c927 14.0 cited
Raise error when affecting tuple moved into different partition.
- f16241bef7cc 11.0 cited

On Fri, Apr 26, 2024 at 5:28 PM Peter Geoghegan <pg@bowt.ie> wrote:
>
> On Fri, Apr 26, 2024 at 4:46 PM Melanie Plageman
> <melanieplageman@gmail.com> wrote:
> > I have a more basic question. How could GlobalVisState->maybe_needed
> > going backwards cause a problem with relfrozenxid? Yes, if
> > maybe_needed goes backwards, we may not remove a tuple whose xmin/xmax
> > are older than VacuumCutoffs->OldestXmin. But, if that tuple's
> > xmin/xmax are older than OldestXmin, then wouldn't we freeze it?
>
> You can't freeze every XID older than OldestXmin.
> heap_prepare_freeze_tuple() isn't prepared for HEAPTUPLE_DEAD tuples,
> and expects that those will be taken care of by the time it is called.

But, the tuple isn't HEAPTUPLE_DEAD -- it's HEAPTUPLE_RECENTLY_DEAD.
It will always be HEAPTUPLE_RECENTLY_DEAD in 17 and in <= 16, if
HeapTupleSatisfiesVacuum() returns HEAPTUPLE_DEAD, we wouldn't call
heap_prepare_freeze_tuple() because of the retry loop.

- Melanie