RE: [PoC] pg_upgrade: allow to upgrade publisher node

On Monday, August 21, 2023 11:21 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Sun, Aug 20, 2023 at 6:49 PM Masahiko Sawada
> <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > On Thu, Aug 17, 2023 at 10:31 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> wrote:
> > >
> > > >
> > > > Sorry I was not clear. I meant the logical replication slots that
> > > > are
> > > > *not* used by logical replication, i.e., are created manually and
> > > > used by third party tools that periodically consume decoded
> > > > changes. As we discussed before, these slots will never be able to
> > > > pass that confirmed_flush_lsn check.
> > > >
> > >
> > > I think normally one would have a background process to periodically
> > > consume changes. Won't one can use the walsender infrastructure for
> > > their plugins to consume changes probably by using replication
> > > protocol?
> >
> > Not sure.
> >
>
> I think one can use Streaming Replication Protocol to achieve it [1].
>
> > > Also, I feel it is the plugin author's responsibility to consume
> > > changes or advance slot to the required position before shutdown.
> >
> > How does the plugin author ensure that the slot consumes all WAL
> > records including shutdown_checkpoint before shutdown?
> >
>
> By using "Streaming Replication Protocol" so that walsender can take care of it.
> If not, I think users should drop such slots before the upgrade because anyway,
> they won't be usable after the upgrade.

Yes, I think pglogical is one example which start a bgworker(apply worker) on client to
consume changes which also uses Streaming Replication Protocol IIRC. And
pg_recvlogical is another example which connects to walsender and consume changes.

Best Regards,
Hou zj