Re: BUG #19500: pgrepack logical decoding plugin can crash assert builds via SQL decoding API

On Thu, Jun 4, 2026 at 2:50 AM Alvaro Herrera <alvherre(at)kurilemu(dot)de> wrote:

> On 2026-Jun-03, Antonin Houska wrote:
>
> > Srinath Reddy Sadipiralla <srinath2133(at)gmail(dot)com> wrote:
> >
> > > Could we reject the pgrepack plugin at slot creation instead, in
> > > pg_create_logical_replication_slot() and the CREATE_REPLICATION_SLOT
> > > command, so misuse gets a clear "reserved for REPACK (CONCURRENTLY)"
> > > error up front, before any decoding? REPACK creates its slot directly
> via
> > > ReplicationSlotCreate(), so it's unaffected, and the begin-callback
> check
> > > with magic guard can stay as the internal safety net.
> > > Happy to be told this isn't worth special-casing :)
> >
> > Another possible approach: restrict the use of the plugin to the REPACK
> > decoding worker.
>
> I don't like either of these approaches, because they are forcing the
> generic facility (either slot creation or logical decoding setup) to
> know something about one specific user of the facility. That is to say,
> the restriction is being added on the wrong side of the abstraction.
> I know my implementation the drawback you (Srinath) mentioned, because
> the abstraction doesn't provide us with a great way to inject an error
> report at the exact spot we need it; but I think it's at the correct
> side of the abstraction.

> (I'm not really sure that there _is_ a great way to throw an error
> report at the right time. That would require every single output plugin
> author to add a function we can call; and every single one of them,
> except REPACK, would do nothing. This seems quite pointless.)
>
> I frankly don't have a problem with letting a transaction spill a few
> GBs to disk only to then report an error that pgrepack is being misused.
> It's just not something that anyone would do for fun.
>

makes sense, we can go with your approach, thanks for
the clarification.

--
Thanks :)
Srinath Reddy Sadipiralla
EDB: https://www.enterprisedb.com/