On Thu, May 14, 2020 at 8:33 AM Wim Bertels <wim.bertels@xxxxxxx> wrote:
>
>
> The replication slot connection could use any role that has been
> configured to allow replication. So there is no way to know which
> role is actually using a slot without it actually being connected.
> You can look and see which roles have replication privileges by
> checking the output of \du in psql, but there is nothing tying any
> roles to any specific slots.
i assume that a replication slot can only be used by 1 subscriber,
and subscribers can migrate; just to be clear the conneinfo is only
kept on the subscriber and used on the publisher, but not stored on the
publisher (unless active)
so if a replication slot is inactive, you can't contact for example the
user that (implicitely) created the replication slot, to see if it is
still needed for example.
background: i'm trying out an atypical? setup with many students
subscribing to a single publication server, thus with subscribers that
are not always online. As the number of slots might quickly grow:)
>
--
mvg,
Wim Bertels
--
Swerve me? The path to my fixed purpose is laid with iron rails,
whereon my soul is grooved to run. Over unsounded gorges, through
the rifled hearts of mountains, under torrents' beds, unerringly I rush!
-- Captain Ahab, "Moby Dick"
While running CREATE SUBSCRIPTION on the subscriber side does conveniently make a slot for you back on the primary, it's also possible to manually create logical replication slots directly on the primary. So a replication slot could potentially be made directly on the publication side and have no awareness of what role may eventually connect.
If you're going to have multiple subscribers connecting to a single publication, you're going to have to have different slots for each of those subscribers anyway. Otherwise one subscriber could cause another one to miss data. Honestly, the logical replication system really isn't meant to have subscribers be offline for any extended period of time, especially if the publisher is continuing to write. I would question the design of this that is allowing the subscribers to be offline. You may want to rethink this design a bit.
