Re: Logical Replication of sequences

On Mon, Jun 10, 2024 at 5:00 PM vignesh C <vignesh21@gmail.com> wrote:
>
> On Mon, 10 Jun 2024 at 12:24, Amul Sul <sulamul@gmail.com> wrote:
> >
> >
> >
> > On Sat, Jun 8, 2024 at 6:43 PM vignesh C <vignesh21@gmail.com> wrote:
> >>
> >> On Wed, 5 Jun 2024 at 14:11, Amit Kapila <amit.kapila16@gmail.com> wrote:
> >> [...]
> >> A new catalog table, pg_subscription_seq, has been introduced for
> >> mapping subscriptions to sequences. Additionally, the sequence LSN
> >> (Log Sequence Number) is stored, facilitating determination of
> >> sequence changes occurring before or after the returned sequence
> >> state.
> >
> >
> > Can't it be done using pg_depend? It seems a bit excessive unless I'm missing
> > something.
>
> We'll require the lsn because the sequence LSN informs the user that
> it has been synchronized up to the LSN in pg_subscription_seq. Since
> we are not supporting incremental sync, the user will be able to
> identify if he should run refresh sequences or not by checking the lsn
> of the pg_subscription_seq and the lsn of the sequence(using
> pg_sequence_state added) in the publisher.

How the user will know from seq's lsn that he needs to run refresh.
lsn indicates page_lsn and thus the sequence might advance on pub
without changing lsn and thus lsn may look the same on subscriber even
though a sequence-refresh is needed. Am I missing something here?

thanks
Shveta