Re: Logical Replication of sequences

On Tue, 11 Jun 2024 at 09:41, Amul Sul <sulamul(at)gmail(dot)com> wrote:
>
> On Mon, Jun 10, 2024 at 5:00 PM vignesh C <vignesh21(at)gmail(dot)com> wrote:
>>
>> On Mon, 10 Jun 2024 at 12:24, Amul Sul <sulamul(at)gmail(dot)com> wrote:
>> >
>> >
>> >
>> > On Sat, Jun 8, 2024 at 6:43 PM vignesh C <vignesh21(at)gmail(dot)com> wrote:
>> >>
>> >> On Wed, 5 Jun 2024 at 14:11, Amit Kapila <amit(dot)kapila16(at)gmail(dot)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. Also, this parallels our
>> implementation for pg_subscription_seq and will aid in expanding for
>> a) incremental synchronization and b) utilizing workers for
>> synchronization using sequence states if necessary.
>>
>> How do you track sequence mapping with the publication?
>>
>> In the publisher we use pg_publication_rel and
>> pg_publication_namespace for mapping the sequences with the
>> publication.
>
>
> Thanks for the explanation. I'm wondering what the complexity would be, if we
> wanted to do something similar on the subscriber side, i.e., tracking via
> pg_subscription_rel.

Because we won't utilize sync workers to synchronize the sequence, and
the sequence won't necessitate sync states like init, sync,
finishedcopy, syncdone, ready, etc., initially, I considered keeping
the sequences separate. However, I'm ok with using pg_subscription_rel
as it could potentially help in enhancing incremental synchronization
and parallelizing later on.

Regards,
Vignesh