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

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
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
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.

--
With Regards,
Amit Kapila.