Re: Time delayed LR (WAS Re: logical replication restrictions)

At Thu, 9 Feb 2023 13:48:52 +0530, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote in
> On Thu, Feb 9, 2023 at 10:45 AM Kyotaro Horiguchi
> <horikyota(dot)ntt(at)gmail(dot)com> wrote:
> >
> > At Wed, 8 Feb 2023 09:03:03 +0000, "Hayato Kuroda (Fujitsu)" <kuroda(dot)hayato(at)fujitsu(dot)com> wrote in
> > > Thank you for reviewing! PSA new version.
> >
> > + if (statusinterval_ms > 0 && diffms > statusinterval_ms)
> >
> > The next expected feedback time is measured from the last status
> > report. Thus, it seems to me this may suppress feedbacks from being
> > sent for an unexpectedly long time especially when min_apply_delay is
> > shorter than wal_r_s_interval.
> >
>
> I think the minimum time before we send any feedback during the wait
> is wal_r_s_interval. Now, I think if there is no transaction for a
> long time before we get a new transaction, there should be keep-alive
> messages in between which would allow us to send feedback at regular
> intervals (wal_receiver_status_interval). So, I think we should be

Right.

> able to send feedback in less than 2 * wal_receiver_status_interval
> unless wal_sender/receiver timeout is very large and there is a very
> low volume of transactions. Now, we can try to send the feedback

We have suffered this kind of feedback silence many times. Thus I
don't want to rely on luck here. I had in mind of exposing last_send
itself or providing interval-calclation function to the logic.

> before we start waiting or maybe after every
> wal_receiver_status_interval / 2 but I think that will lead to more
> spurious feedback messages than we get the benefit from them.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center