Re: replication_origin and replication_origin_lsn usage on subscriber

On Tue, Jul 14, 2020 at 2:47 PM Petr Jelinek <petr(at)2ndquadrant(dot)com> wrote:
>
> Hi,
>
> On 14/07/2020 10:29, Amit Kapila wrote:
> > On Tue, Jul 14, 2020 at 12:05 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> >>
> >> On Tue, Jul 14, 2020 at 11:14 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >>>
> >>> On Tue, Jul 14, 2020 at 11:00 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> >>>>
> >>>> On Thu, Jul 9, 2020 at 6:55 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >>>>>
> >>>>> On Thu, Jul 9, 2020 at 6:14 PM Petr Jelinek <petr(at)2ndquadrant(dot)com> wrote:
> >>>>>>
> >>>>>>
> >>>>>> If we were to support the origin forwarding, then strictly speaking we
> >>>>>> need everything only at commit time from correctness perspective,
> >>>>>>
> >>>>>
> >>>>> Okay. Anyway streaming mode is optional, so in such cases, we can keep it 'off'
> >>>>>
> >>>>>> but
> >>>>>> ideally origin_id would be best sent with first message as it can be
> >>>>>> used to filter out changes at decoding stage rather than while we
> >>>>>> process the commit so having it set early improves performance of decoding.
> >>>>>>
> >>>>>
> >>>>> Yeah, makes sense. So, we will just send origin_id (with first
> >>>>> streaming start message) and leave others.
> >>>>
> >>>> So IIUC, currently we are sending the latest origin_id which is set
> >>>> during the commit time. So in our case, while we start streaming we
> >>>> will send the origin_id of the latest change in the current stream
> >>>> right?
> >>>>
> >>>
> >>> It has to be sent only once with the first start message not with
> >>> consecutive start messages.
> >>
> >> Okay, so do you mean to say that with the first start message we send
> >> the origin_id of the latest change?
> >>
> >
> > Yes.
> >
> >> because during the transaction
> >> lifetime, the origin id can be changed.
> >>
> >
> > Yeah, it could be changed but if we have to send again apart from with
> > the first message then it should be sent with each message. So, I
> > think it is better to just send it once during the transaction as we
> > do it now (send with begin message).
> >
> >
>
> I am not sure if I can follow the discussion here very well, but if I
> understand correctly I'd like to clarify two things:
> - origin id does not change mid transaction as you can only have one per xid
>

As shown by Dilip, I don't think currently we have any way to prevent
this from changing during the transaction.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com