Re: POC: enable logical decoding when wal_level = 'replica' without a server restart

Hi,

On Wed, Jun 25, 2025 at 09:15:04AM +0530, shveta malik wrote:
> On Wed, Jun 25, 2025 at 9:12 AM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
> >
> > On Tue, Jun 24, 2025 at 2:12 PM Bertrand Drouvot
> > <bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
> > >
> > > Yeah, I think that sounds reasonable and that would avoid users to use
> > > the slot created with immediately_reserve set to false by mistake.
> > >
> >
> > +1.
> > I think we do need to provide 'immediately_reserve' as a new argument
> > now for logical slots creation. If the slot is a special one with a
> > reserved name, it can internally be created with WALs not reserved for
> > our purpose.
> >
>
> One correction here.
> I think we do NOT need to provide 'immediately_reserve' as a new
> argument now for logical slots creation. ...

Agree.

> > > Right...So not sure we need such a GUC. What about always behave with the
> > > automatic behavior?
> > >
> >
> > Does it make sense to provide a GUC which will have the default set to
> > automatic but if the user is not interested or having some issues with
> > new behaviour, he can switch off the GUC, making the new functions
> > no-op as well?
> > In absence of such a GUC, users will have absolutely no way to switch
> > back to old behaviour. Will that be okay?

Since it will be possible to switch back to logical without a restart I do
think that it could make sense to avoid a new GUC. Unless there is a use case
to keep the wal level to logical (outside of the "logical decoding from
standby" context)?

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
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