Re: Unexpected behavior after OOM errors

Michael Paquier <michael@paquier.xyz>

From: Michael Paquier <michael@paquier.xyz>
To: Matthias van de Meent <boekewurm+postgres@gmail.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, Alexander Lakhin <exclusion@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2026-06-18T23:29:03Z
Lists: pgsql-hackers
On Thu, Jun 18, 2026 at 05:27:57PM +0200, Matthias van de Meent wrote:
> By moving StandbyAcquireAccessExclusiveLock's LockAcquire ahead of
> when it links the lock to the transaction, the local data structure
> doesn't know to clean up the lock until after it's acquired, so
> failure in that process won't make error cleanup try to clean up the
> lock.

Yep, reordering these two actions would take care of the list
inconsistency where the startup process goes down following the ERROR
promoted to a FATAL.

I have been fingering the idea of backpatching this fix for a few
minutes, actually, but discarded the idea at the end.  It does not
require a random pattern to cause the failure, being actionable
through a combination of GUCs as Alexander has proved.  Still, the
only consequence is an extra LOG entry telling that the lock is not
being tracked for non-assert builds.  Confusing, OK, but not really
critical.

Comments?
--
Michael

Commits

  1. Make type cache initialization more resilient on re-entry after OOM

  2. Make StandbyAcquireAccessExclusiveLock() more resilent with OOMs

  3. Make GetSnapshotData() more resilient on out-of-memory errors