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From: Robert Treat <rob@xzilla.net>
Date: Mon, 16 Mar 2026 11:49:36 -0400
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Subject: Re: Adding REPACK [concurrently]
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>,
 Antonin Houska <ah@cybertec.at>,
	Mihail Nikalayeu <mihailnikalayeu@gmail.com>,
 Pg Hackers <pgsql-hackers@lists.postgresql.org>
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On Mon, Mar 16, 2026 at 11:11=E2=80=AFAM Alvaro Herrera <alvherre@alvh.no-i=
p.org> wrote:
> On 2026-Mar-16, Matthias van de Meent wrote:
>

> > However, we don't live in that world, so I am opposed to allowing
> > table owners without REPLICATION to take any/all replication slots.
>
> I think requiring REPACK users to have the REPLICATION priv is rather
> user unfriendly.  Some potential REPACK users might not have any other
> use for replication at all.
>

For many users, I feel like repack concurrently making use of
replication machinery is an implementation detail that some will find
quite surprising (pg_repack doesn't use it), so I'd agree requiring
REPLICATION priv is both unfriendly and a bit counter intuitive,
especially if you need to run repack concurrently on a stand alone
server.

That said, I think Matthias is right that we can't allow "repackers"
to block "replicators"...

> > Note that most of my argument hinges on the impact on other, unrelated
> > databases/tables/sessions. Replication slots have a hard cap defined
> > at startup, and effective_wal_level increases the WAL generated by
> > practically all backends.
>
> I'd rather have a new GUC to declare a bunch of additional slots that
> are reserved exclusively for repack, set its default to something like
> 3, and call it a day.  If all repack slots are in use, you don't get to
> run repack, period.
>
> A slot costs nothing if unused, and we really don't want to make the
> interaction with regular replication more complicated than it is today.
>

I'm never excited about adding GUCs, but at first thought this seems
like a decent work-around; most people are unlikely to run multiple
repack concurrently's, but they can if needed. (I think the most
likely use case is on clusters using the "database per customer"
pattern, but if we have the guc, people will have a means to deal with
it).

Robert Treat
https://xzilla.net