Feedback-ID: ia2694551:Fastmail
Date: Tue, 31 Mar 2026 20:23:57 +0200
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Srinath Reddy Sadipiralla <srinath2133@gmail.com>
Cc: Mihail Nikalayeu <mihailnikalayeu@gmail.com>,
	Antonin Houska <ah@cybertec.at>,
 Matthias van de Meent <boekewurm+postgres@gmail.com>,
	Pg Hackers <pgsql-hackers@lists.postgresql.org>,
 Robert Treat <rob@xzilla.net>
Subject: Re: Adding REPACK [concurrently]
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On 2026-Mar-31, Srinath Reddy Sadipiralla wrote:

> In this case, there's no circular wait. The deadlock detector never
> fires.  REPACK simply queues behind the SELECT, eventually hits its
> lock_timeout, aborts and cleans up.Initially, I thought this cleanup
> was expected behavior. But after seeing your solution to protect
> REPACK from losing its transient table work, I thought it's "not
> expected".

Yeah.  Keep in mind that REPACK could have been running for many hours
or even days before it reaches the point of acquiring its AEL lock to do
the final swap; and it may well be critical work.  We do not want to
lose it.  So whatever is waiting to obtain a lock on the table, or
already has a lock on the table, has to yield.

> If the goal is to prevent REPACK's work from being wasted, should we
> error out the backend that is making REPACK wait during the final swap
> phase? I am thinking of something conceptually similar to
> ResolveRecoveryConflictWithLock, actively cancelling the conflicting
> session to allow the AEL upgrade to proceed.

Something like that might be appropriate, yeah.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"El miedo atento y previsor es la madre de la seguridad" (E. Burke)