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

On Tue, Feb 28, 2023 at 8:14 AM Kyotaro Horiguchi
<horikyota(dot)ntt(at)gmail(dot)com> wrote:
>
> At Mon, 27 Feb 2023 14:56:19 +0530, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote in
> > The one difference w.r.t recovery_min_apply_delay is that here we will
> > hold locks for the duration of the delay which didn't seem to be a
> > good idea. This will also probably lead to more bloat as we will keep
> > transactions open for a long time. Doing it before DecodePrepare won't
>
> I don't have a concrete picture but could we tell reorder buffer to
> retain a PREPAREd transaction until a COMMIT PREPARED comes?
>

Yeah, we could do that and that is what is the behavior unless the
user enables 2PC via 'two_phase' subscription option. But, I don't see
the need to unnecessarily delay the prepare till the commit if a user
has specified 'two_phase' option. It is quite possible that COMMIT
PREPARED happens at a much later time frame than the amount of delay
the user is expecting.

> If
> delaying non-prepared transactions until COMMIT is adequate, then the
> same thing seems to work for prepared transactions.
>
> > have such problems. This is the reason that we decide to perform a
> > delay at the start of the transaction instead at commit/prepare in the
> > subscriber-side approach.
>
> It seems that there are no technical obstacles to do that on the
> publisher side. The only observable difference would be that
> relatively large prepared transactions may experience noticeable
> additional delays. IMHO I don't think it's a good practice
> protocol-wise to intentionally choke a stream at the receiving end
> when it has not been flow-controlled on the transmitting end.
>

But in this proposal, we are not choking/delaying anything on the receiving end.

--
With Regards,
Amit Kapila.