Horton

Re: relfrozenxid may disagree with row XIDs after 1ccc1e05ae

Melanie Plageman <melanieplageman@gmail.com>

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From: Melanie Plageman <melanieplageman@gmail.com>
To: Noah Misch <noah@leadboat.com>, Bowen Shi <zxwsbg12138@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>, Peter Geoghegan <pg@bowt.ie>, Alexander Lakhin <exclusion@gmail.com>, PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>
Date: 2024-06-21T00:33:59Z
Lists: pgsql-bugs

Commits

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  1. Ensure vacuum removes all visibly dead tuples older than OldestXmin

  2. Combine freezing and pruning steps in VACUUM

  3. Handle non-chain tuples outside of heap_prune_chain()

  4. Fix false reports in pg_visibility

  5. Remove retry loop in heap_page_prune().

  6. vacuumlazy.c: document vistest and OldestXmin.

  7. Deduplicate choice of horizon for a relation procarray.c.

  8. Remove tupgone special case from vacuumlazy.c.

  9. Simplify state managed by VACUUM.

  10. Recycle nbtree pages deleted during same VACUUM.

  11. snapshot scalability: Don't compute global horizons while building snapshots.

  12. Raise error when affecting tuple moved into different partition.

On Thu, Jun 20, 2024 at 11:49 AM Melanie Plageman
<melanieplageman@gmail.com> wrote:
>
> On Tue, Jun 18, 2024 at 6:51 PM Melanie Plageman
> <melanieplageman@gmail.com> wrote:
> >
> > Finally, upthread there is discussion of how we could end up doing a
> > catalog lookup after vacuum_get_cutoffs() and before the tuple
> > visibility check on 16. Assuming this is true, we would want to
> > backport the fix to 16 as well. I could use some help getting a repro
> > (using btree index deletion for example) of the infinite loop on 16.
>
> So, I ended up working on a new repro that works by forcing a round of
> index vacuuming after the standby reconnects and before pruning a dead
> tuple whose xmax is older than OldestXmin.
>
> At the end of the round of index vacuuming, _bt_pendingfsm_finalize()
> calls GetOldestNonRemovableTransactionId(), thereby updating the
> backend's GlobalVisState and moving maybe_needed backwards.
>
> Then vacuum's first pass will continue with pruning and find our later
> inserted and updated tuple HEAPTUPLE_RECENTLY_DEAD when compared to
> maybe_needed but HEAPTUPLE_DEAD when compared to OldestXmin.
>
> I make sure that the standby reconnects between vacuum_get_cutoffs()
> (vacuum_set_xid_limits() on 14/15) and pruning because I have a cursor
> on the page keeping VACUUM FREEZE from getting a cleanup lock.
>
> See the repros for step-by-step explanations of how it works.
>
> With this, I can repro the infinite loop on 14-16.
>
> Backporting 1ccc1e05ae fixes 16 but, with the new repro, 14 and 15
> error out with "cannot freeze committed xmax". I'm going to
> investigate further why this is happening. It definitely makes me
> wonder about the fix.

It turns out it was also erroring out on 16 (i.e. backporting
1ccc1e05ae did not fix anything), but I didn't notice it because the
perl TAP test passed. I also discovered we can hit this error in
master, so I started a thread about that here [1].

- Melanie

[1] https://www.postgresql.org/message-id/CAAKRu_bDD7oq9ZwB2OJqub5BovMG6UjEYsoK2LVttadjEqyRGg%40mail.gmail.com