Re: Re-read subscription state after lock in AlterSubscription

On Fri, Jul 3, 2026 at 9:49 AM Bertrand Drouvot
<bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
>
> Hi Kuroda-san,
>
> On Fri, Jul 03, 2026 at 03:13:08AM +0000, Hayato Kuroda (Fujitsu) wrote:
> > Dear Bertrand,
> >
> > > Yeah, but I think they would produce "tuple concurrently updated" error (due to
> > > CatalogTupleUpdate) so that invalid information could not be used.
> >
> > I confirmed with PG14 that tuple concurrently updated ERROR can be raised when
> > ALTER SUBSCRIPTION DISABLE happens concurrently:
> >
> > ```
> > postgres=# ALTER SUBSCRIPTION sub DISABLE ;
> > ERROR: tuple concurrently updated
> > ```
>
> Yeah, reproducible by using a breakpoint just before acquiring the lock for example.
>
> > It might be harmless but I think the correct ERROR should be reported: the patch
> > should be backpatched. Thought?
>
> I'm not sure about the back patch part as it would only improve error messages
> in a rare race condition (and there is no risk of invalid data being used).

Patch LGTM. IMHO we can backpatch this as it is a small change and
also fixes the bug, without this fix a non-superuser executing ALTER
SUBSCRIPTION could bypass the password_required=false restriction if a
concurrent transaction
updated that flag. However, we could argue that this is a corner case
and can be skipped but given the patch's simplicity, I recommend
backpatching.

--
Regards,
Dilip Kumar
Google