Re: Handle infinite recursion in logical replication setup

On Mon, Mar 7, 2022 at 9:26 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Wed, Feb 23, 2022 at 11:59 AM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> > Here there are two problems for the user: a) incremental
> > synchronization of table sending both local data and replicated data
> > by walsender b) Table synchronization of table using copy command
> > sending both local data and replicated data
> >
> > For the first problem "Incremental synchronization of table by
> > Walsender" can be solved by:
> > Currently the locally generated data does not have replication origin
> > associated and the data that has originated from another instance will
> > have a replication origin associated. We could use this information to
> > differentiate locally generated data and replicated data and send only
> > the locally generated data. This "only_local" could be provided as an
> > option while subscription is created:
> > ex: CREATE SUBSCRIPTION sub1 CONNECTION 'dbname =postgres port=5433'
> > PUBLICATION pub1 with (only_local = on);
>
> I haven't yet gone through the patch, but I have a question about the
> idea. Suppose I want to set up a logical replication like,
> node1->node2->node3->node1. So how would I create the subscriber at
> node1? only_local=on or off?. I mean on node1, I want the changes
> from node3 which are generated on node3 or which are replicated from
> node2 but I do not want changes that are replicated from node1 itself?
> So if I set only_local=on then node1 will not get the changes
> replicated from node2, is that right? and If I set only_local=off then
> it will create the infinite loop again? So how are we protecting
> against this case?
>

In the above topology if you want local changes from both node3 and
node2 then I think the way to get that would be you have to create two
subscriptions on node1. The first one points to node2 (with
only_local=off) and the second one points to node3 (with only_local
=off). Will that address your case or am I missing something?

--
With Regards,
Amit Kapila.