Re: Logical Replication of sequences

On Tue, Aug 6, 2024 at 8:49 AM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> On Mon, Aug 5, 2024 at 5:28 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Mon, Aug 5, 2024 at 2:36 PM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> > >
> > > On Fri, 2 Aug 2024 at 14:24, shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
> > > >
> > > > On Thu, Aug 1, 2024 at 9:26 AM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
> > > > >
> > > > > On Mon, Jul 29, 2024 at 4:17 PM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> > > > > >
> > > > > > Thanks for reporting this, these issues are fixed in the attached
> > > > > > v20240730_2 version patch.
> > > > > >
> > > >
> > > > I was reviewing the design of patch003, and I have a query. Do we need
> > > > to even start an apply worker and create replication slot when
> > > > subscription created is for 'sequences only'? IIUC, currently logical
> > > > replication apply worker is the one launching sequence-sync worker
> > > > whenever needed. I think it should be the launcher doing this job and
> > > > thus apply worker may even not be needed for current functionality of
> > > > sequence sync?
> > >
> >
> > But that would lead to maintaining all sequence-sync of each
> > subscription by launcher. Say there are 100 sequences per subscription
> > and some of them from each subscription are failing due to some
> > reasons then the launcher will be responsible for ensuring all the
> > sequences are synced. I think it would be better to handle
> > per-subscription work by the apply worker.
>
> I thought we can give that task to sequence-sync worker. Once sequence
> sync worker is started by launcher, it keeps on syncing until all the
> sequences are synced (even failed ones) and then exits only after all
> are synced; instead of apply worker starting it multiple times for
> failed sequences. Launcher to start sequence sync worker when signaled
> by 'alter-sub refresh seq'.
> But after going through details given by Vignesh in [1], I also see
> the benefits of using apply worker for this task. Since apply worker
> is already looping and doing that for table-sync, we can reuse the
> same code for sequence sync and maintenance will be easy. So looks
> okay if we go with existing apply worker design.
>

Fair enough. However, I was wondering whether apply_worker should exit
after syncing all sequences for a sequence-only subscription or should
it be there for future commands that can refresh the subscription and
add additional tables or sequences?

--
With Regards,
Amit Kapila.