Horton

Re: BUG: Postgres 14 + vacuum_defer_cleanup_age + FOR UPDATE + UPDATE

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Andres Freund <andres@anarazel.de>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, Andrey Borodin <amborodin86@gmail.com>, Michail Nikolaev <michail.nikolaev@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2023-02-04T19:10:55Z
Lists: pgsql-hackers 
On Sat, Feb 4, 2023 at 2:57 AM Andres Freund <andres@anarazel.de> wrote:
> Is there a good way to make breakage in the page recycling mechanism
> visible with gist? I guess to see corruption, I'd have to halt a scan
> before a page is visited with gdb, then cause the page to be recycled
> prematurely in another session, then unblock the first? Which'd then
> visit that page, thinking it to be in a different part of the tree than
> it actually is?

Yes. This bug is similar to an ancient nbtree bug fixed back in 2012,
by commit d3abbbeb.

> which clearly doesn't seem right.
>
> I just can't quite judge how bad that is.

It's really hard to judge, even if you're an expert. We're talking
about a fairly chaotic scenario. My guess is that there is a very
small chance of a very unpleasant scenario if you have a GiST index
that has regular page deletions, and if you use
vacuum_defer_cleanup_age. It's likely that most GiST indexes never
have any page deletions due to the workload characteristics.

-- 
Peter Geoghegan

Commits

  1. Fix incorrect TAP test ordering

  2. pg_amcheck: Minor test speedups

  3. amcheck: Fix FullTransactionIdFromXidAndCtx() for xids before epoch 0

  4. amcheck: Fix ordering bug in update_cached_xid_range()

  5. Fix corruption due to vacuum_defer_cleanup_age underflowing 64bit xids

  6. Add hardening to catch invalid TIDs in indexes.

  7. Use full 64-bit XID for checking if a deleted GiST page is old enough.

  8. Avoid early reuse of btree pages, causing incorrect query results.