Thread

Re: Experimental patch for terminating VACUUM freeze blockers

Sami Imseih <samimseih@gmail.com> — 2026-05-13T19:55:00Z

> On Wed, May 13, 2026 at 07:56:43PM +0800, wenhui qiu wrote:
> > I have an experimental patch to explore handling this situation. The patch
> > adds a GUC, vacuum_freeze_terminate_blockers_pid, which allows VACUUM to
> > terminate regular client backends whose transaction horizon blocks VACUUM
> > from advancing its freeze cutoff. The intended targets are
> > idle-in-transaction sessions and long-running active transactions that are
> > holding an old xmin or assigned XID.
>
> Thanks for sharing.  I certainly agree that this area has room for
> improvement in Postgres.

My 2c. Using something like the proposed
vacuum_freeze_terminate_blockers_pid (GUC name is misleading, since
it's a bool )
seems backwards to me. It does not address the root cause, which is
the long-running
transaction, etc and attempts to deal with the symptom rather than the problem.
This also means a poor configuration of this parameter will more
likely lead to a system
silently getting into wraparound, as a DBA may relax a bit on monitoring, maybe.

I do think we need better visibility into what is blocking vacuum, which was
discussed here [1], but ultimately it is up to the DBA to properly monitor
and mitigate workloads that are impacting their vacuum.

[1] https://www.postgresql.org/message-id/flat/CAOzEurSgy-gDtwFmEbj5%2BR9PL0_G3qYB6nnzJtNStyuf87VSVg%40mail.gmail.com

--
Sami Imseih
Amazon Web Services (AWS)