Feedback-ID: ia2694551:Fastmail
Date: Wed, 1 Apr 2026 13:42:17 +0200
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Antonin Houska <ah@cybertec.at>,
	Mihail Nikalayeu <mihailnikalayeu@gmail.com>,
 Srinath Reddy Sadipiralla <srinath2133@gmail.com>,
	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]
Message-ID: <202604011042.zdevjay65ws7@alvherre.pgsql>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: 
 <CAA4eK1+CNiuphtE=wwExsHD_McmYtGp2XK4qwX146VqRbgXmbA@mail.gmail.com>
Archived-At: 
 <https://www.postgresql.org/message-id/202604011042.zdevjay65ws7%40alvherre.pgsql>
Precedence: bulk

On 2026-Apr-01, Amit Kapila wrote:

> BTW, is the reason to skip REPACK while building a snapshot is that it
> can take a long time to finish?

As I understand the issue, yes, that's precisely the problem: if you
have one REPACK running, then starting a second REPACK (which requires
building a new snapshot) would have to wait until the first REPACK is
over.  In other words, you wouldn't be able to have two repacks running
concurrently.  This sounds like a problematic requirement.  So having
snapbuild ignore REPACK is there to allow the second REPACK to work at
all.  But more generally,  *all* users of snapbuild would be prevented
from starting until REPACK is done; so if you have a very very large
table that takes a long time to repack, then everything would be blocked
behind it until it completes, which sounds extremely unpleasant.

So, if we're unable to get this particular patch in, we would have to
have a big fat warning in the docs, telling people to be careful about
other load if they choose to run concurrent repack -- it could have
serious consequences.  But on the other hand, it's better to *have* the
tool, even if it has problems, than not have it.  Keep in mind that
pg_repack and pg_squeeze also have all these problems/limitations (and
others), and still people use them.

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/