Hello Nick,
Thanks for bringing this KIP! Just a few thoughts:
1) I agree with Sagar that, we'd probably think about two routes to
rephrase / restructure the proposal:
* we can propose a couple of new APIs, and just list "more
convenient recursion" as one of its benefits. Then we'd need to be careful
and consider all possible use scenarios, e.g. what if "other" is not a
sourced stream, e.g.:
stream2 = stream1.mapValues(...)
stream3 = stream2.mapValues(...)
stream3.to(stream2)
Would that be allowed? If yes what's the implementation semantics of this
code.
* OR, we propose sth just for more convenient recursion, but then we would
need to consider having a more restrictive expressiveness in the new DSL,
e.g. we'd need to enforce that "other" is a source stream, and that "other"
is one of the ancestor of "this", programmatically. Or we can think about a
totally different set of new DSL e.g. (I'm just making it up on top of my
head for illustration, not really advocating it :P):
stream1 = stream2.mapValues(...);
stream1 = recursive(stream1.join(table));
2) Just a nit comment, it seems in your example, the topic name should be:
```
nodes
.map((node, parent) -> { KeyValue(parent, 1L) })
.to("node-updates")
updates
.join(parents, (count, parent) -> { KeyValue(parent, count) }) // the
root node has no parent, so recursion halts at the root
.to("node-updates")
```
Right?
On Sun, Aug 7, 2022 at 7:52 PM Sagar <sagarmeansoc...@gmail.com> wrote:
> Hey Nick,
>
> Since we are adding a new method to the public interface, we should
> probably decide the necessity of doing so, more so when you say that it's
> an alternative to something already existing. My suggestion would be to
> still modify the KIP around the new API, highlight how it's an alternative
> to something already existing and why we should add the new API. You have
> already explained streaming recursion, so that's one added benefit we get
> as part of the new API. So, try to expand a little bit around those points.
> Graph traversal should be fine as an example. You could make it slightly
> more clear.
>
> Let me know if it makes sense.
>
> Thank you for your work on this!
>
> Thanks!
> Sagar.
>
>
> On Fri, Aug 5, 2022 at 8:43 PM Nick Telford <nick.telf...@gmail.com>
> wrote:
>
> > Hi Sagar,
> >
> > Thanks for reading through my proposal.
> >
> > While the 2 new methods were originally intended for the recursive
> > use-case, they could also be used as an alternative means of wiring two
> > different KStreams together. The main reason I didn't document this in
> the
> > KIP is that using the API for this doesn't bring anything new to the
> table:
> > it's just an alternative form of something that already exists. If you
> > believe it would be helpful, I can document this in more detail. I can
> > re-orient the KIP around the new methods themselves, but I felt there was
> > more value in the KIP emphasizing the new functionality and algorithms
> that
> > they enable.
> >
> > What additional context would you like to see in the KIP? Some more
> > examples of recursive algorithms that would benefit? A more concrete
> > example than generic graph traversal? Something else?
> >
> > Regards,
> >
> > Nick Telford
> >
> > On Fri, 5 Aug 2022 at 11:02, Sagar <sagarmeansoc...@gmail.com> wrote:
> >
> > > Hey Nick,
> > >
> > > Thanks for the KIP. This seems like a great addition. However, just
> > > wondering if the 2 new methods that you plan to add are meant only for
> > > streaming recursion? I would imagine they could be repurposed for other
> > use
> > > cases as well? If yes, then probably the KIP should revolve around the
> > > addition of adding these methods which would btw also support streaming
> > > recursion. IMHO adding 2 new methods just for streaming recursion seems
> > > slightly odd to me.
> > >
> > > Also, pardon my ignorance here, but I don't have much insight into
> > > streaming recursion. You can add some more context to it.
> > >
> > > Thanks!
> > > Sagar.
> > >
> > >
> > >
> > >
> > > On Tue, Jul 26, 2022 at 8:46 PM Nick Telford <nick.telf...@gmail.com>
> > > wrote:
> > >
> > > > Hi everyone,
> > > >
> > > > URL:
> > > >
> > > >
> > >
> >
> https://cwiki.apache.org/confluence/display/KAFKA/KIP-857%3A+Streaming+recursion+in+Kafka+Streams
> > > >
> > > > Here's a KIP for extending the Streams DSL API to support "streaming
> > > > recursion". See the Motivation section for details on what I mean by
> > > this,
> > > > along with an example of recursively counting nodes in a graph.
> > > >
> > > > I haven't included changes for the PAPI, mostly because I don't use
> it,
> > > so
> > > > I'm not as familiar with the idioms there. If you can think of a good
> > > > analogue for a new PAPI method, I'm happy to include it in the KIP.
> > > >
> > > > Regards,
> > > >
> > > > Nick Telford
> > > >
> > >
> >
>
--
-- Guozhang
