Re: POC: enable logical decoding when wal_level = 'replica' without a server restart - Mailing list pgsql-hackers

On Thu, Jul 17, 2025 at 3:06 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Wed, Jun 18, 2025 at 3:23 PM shveta malik <shveta.malik@gmail.com> wrote:
> >
> > On Wed, Jun 18, 2025 at 2:39 PM Bertrand Drouvot
> > <bertranddrouvot.pg@gmail.com> wrote:
> > >
> > > Hi,
> > >
> > > On Tue, Jun 10, 2025 at 02:00:55PM -0700, Masahiko Sawada wrote:
> > > > > > > > > 0001 patch allows us to create a logical slot without WAL reservation.
> > >
> > > Thanks for the patch and sorry to be late in this conversation.
> > >
> > > The thing that worry me a bit with this is that that could be easy to attempt
> > > to use the slot "by mistake" and then (as a consequence) trigger WAL reservation
> > > by mistake on the primary. I think that this mistake is more likely to happen
> > > with a logical slot as compared to a physical slot.
> > >
> >
> > Yes, agreed. Another concern is the possibility of someone
> > intentionally using it and associating it with a subscription. If the
> > subscription is later dropped, it could also cause the slot to be
> > removed.
> >
>
> IIUC, your main concern here is that the last slot on
> primary/publisher could be dropped unintentionally by the user leading
> to invalidating the logical slots on any physical-standby connected
> with publisher, right?
>
> What if we make DROP SUBSCRIPTION fail if it can lead to removal of
> the last slot on publisher and allow DROP to succeed when the
> subscription's drop_slot_force (a new subscription option) is set?
> Now, users can still be allowed to Drop the subscription, if it
> disassociates the subscription from the slot by using method explained
> in docs [1] (See Notes section).
>

Forgot to specify link. Done now [1].

[1] - https://www.postgresql.org/docs/devel/sql-dropsubscription.html

--
With Regards,
Amit Kapila.