Re: find replication slots that "belong" to a publication

On 4/7/25 13:32, Willy-Bas Loos wrote:
> Hi Laurenz,
>
> Thanks for answering!
> I find it very strange, because the publication is needed to make a
> subscription, which makes the slot.

From here:

https://www.postgresql.org/docs/current/logical-replication-subscription.html

"A subscription defines the connection to another database and set of
publications (one or more) to which it wants to subscribe."

and here:

"PUBLICATION publication_name [, ...]

Names of the publications on the publisher to subscribe to.
"

Finding the subscriptions for a given publication and deleting those
slots may break the subscription on the receiving side if it is looking
for data from more then one publication.

> Thanks for looking into it and helping me understand.
>
> Cheers!
> Willy-Bas Loos
>
>
> On Mon, Apr 7, 2025 at 3:31 PM Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at
> <mailto:laurenz(dot)albe(at)cybertec(dot)at>> wrote:
>
> On Mon, 2025-04-07 at 12:16 +0200, Willy-Bas Loos wrote:
> > My question is not so much about "can i drop a certain
> replication slot",
> > more about "does this publication still have any replication slots?".
> > Or, if you will: "what's the publication for this replication slot?".
> >
> > I've double checked the views that you suggested, and I found
> that I can relate
> > the WAL sender processes to replication slots through
> pg_replication_slots.active_pid .
> > I've also looked into replication origins.
> >
> > But I can't find a link to the publication. And that's what I
> need to know.
>
> I don't think that there is a connection between a publication and a
> replication slot.  That connection is only made when a subscriber
> connects
> and runs the START_REPLICATION command [1] and specifies the "pgoutput"
> plugin with the "publication_names" option [2].
>
> I don't think you can see that information reflected in a system view
> on the primary.  You'd have to query "pg_subscription" on the standby.
>
> Yours,
> Laurenz Albe
>
>
>  [1]:
> https://www.postgresql.org/docs/current/protocol-replication.html#PROTOCOL-REPLICATION-START-REPLICATION-SLOT-LOGICAL <https://www.postgresql.org/docs/current/protocol-replication.html#PROTOCOL-REPLICATION-START-REPLICATION-SLOT-LOGICAL>
>  [2]:
> https://www.postgresql.org/docs/current/protocol-logical-replication.html#PROTOCOL-LOGICAL-REPLICATION-PARAMS <https://www.postgresql.org/docs/current/protocol-logical-replication.html#PROTOCOL-LOGICAL-REPLICATION-PARAMS>
>
>
>
> --
> Willy-Bas Loos

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com