Re: relfrozenxid may disagree with row XIDs after 1ccc1e05ae

Bowen Shi <zxwsbg12138@gmail.com>

From: Bowen Shi <zxwsbg12138@gmail.com>

To: Melanie Plageman <melanieplageman@gmail.com>

Cc: Noah Misch <noah@leadboat.com>, 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: 2024-05-28T09:03:37Z

Lists: pgsql-bugs

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

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

Hi,

On Thu, May 23, 2024 at 12:57 AM Melanie Plageman <melanieplageman@gmail.com>
wrote:

> One option is to add the logic in fix_hang_15.patch to master as well
> (always remove tuples older than OldestXmin). This addresses your
> concern about gaining confidence in a single solution.
>
> However, I can see how removing more tuples could be concerning. In
> the case that the horizon moves backwards because of a standby
> reconnecting, I think the worst case is that removing that tuple
> causes a recovery conflict on the standby (depending on the value of
> max_standby_streaming_delay et al).
>

I'm confused about this part. The comment above OldestXmin says:
/*
 * OldestXmin is the Xid below which tuples deleted by any xact (that
 * committed) should be considered DEAD, not just RECENTLY_DEAD.
 */
With the fix_hang_15 patch, why is there a risk here when we use Oldestxmin
to judge whether a tuple could be moved?

I think the keypoint is: OldestXmin and VisTest, which one is more accurate
when we judge to remove the tuple.

-- 
Regards
Bowen Shi