Re: Synchronizing slots from primary to standby

On Wed, Dec 13, 2023 at 11:42 AM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> On Wed, Dec 13, 2023 at 10:40 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Mon, Dec 11, 2023 at 5:13 PM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
> > >
> > > On Mon, Dec 11, 2023 at 1:22 PM Drouvot, Bertrand
> > > <bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
> > > >
> > > > > If we agree
> > > > > on that then it would be good to prohibit setting this GUC on standby
> > > > > or at least it should be a no-op even if this GUC should be set on
> > > > > physical standby.
> > > >
> > > > I'd prefer to completely prohibit it on standby (to make it very clear it's not
> > > > working at all) as long as one can enable it without downtime once the standby
> > > > is promoted (which is the case currently).
> > >
> > > And I think slot-sync worker should exit as well on cascading standby. Thoughts?
> > >
> >
> > I think one has set all the valid parameters for the slot-sync worker
> > on standby, we should not exit, rather it should be no-op which means
> > it should not try to sync slots from another standby. One scenario
> > where this may help is when users promote the standby which has
> > already synced slots from the primary. In this case, cascading standby
> > will become non-cascading and should sync slots.
> >
>
> Right, then perhaps we should increase naptime in this no-op case. It
> could be even more then current inactivity naptime which is just
> 10sec. Shall it be say 5min in this case?
>

PFA v47 attached, changes are:

patch 001:
1) Addressed comment in [1]. Thanks Hou-san for this change.

patch 002
2) Slot sync worker will be no-op if it is on cascading standby as
suggested in [2]
3) StartTransaction related optimization as suggested in [3]
4) Few other comments' improvement and code-cleanup.

TODO:
--Few pending comments as I stated in [4] (mainly header inclusion in
tablesync.c, and 'r' to 'n' conversion on promotion)
--The comments given today in [5]

[1]: https://www.postgresql.org/message-id/CABdArM4Cow6aOLjGG9qnp6mhg%2B%2BgjK%3DHDO%3DKSU%3D6%3DyT7hLkknQ%40mail.gmail.com
[2]: https://www.postgresql.org/message-id/CAA4eK1Ki1O65SyA6ijh-Mq4zpzeh644fCmkrZXMJcQXHNrAw0Q%40mail.gmail.com
[3]: https://www.postgresql.org/message-id/CAA4eK1L3DiKL_Wq-VdU%2B9wmjmO5%2Bfrf%3DZHK9Lzq-7zOezPP%2BWg%40mail.gmail.com
[4]: https://www.postgresql.org/message-id/CAJpy0uDcOf5Hvk_CdCCAbfx9SY%2Bog%3D%3D%3DtgiuhWKzkYyqebui9g%40mail.gmail.com
[5]: https://www.postgresql.org/message-id/CAHut%2BPtOc7J_n24HJ6f_dFWTuD3X2ApOByQzZf6jZz%2B0wb-ebQ%40mail.gmail.com

thanks
Shveta