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From Jamie Grier <ja...@data-artisans.com>
Subject Re: [DISCUSSION] Timely function interface and timer params
Date Sat, 29 Oct 2016 13:37:30 GMT
Hi guys,

Good points, Gyula.  I think it would be much easier on a user if there
could be multiple timers in flight per key.  I prefer the second approach,
though, where a user associates some bit of metadata with the timer and we
pass it back to them in the onTimer() callback, otherwise they are forced
to maintain this state themselves.

It looks to me like somehow exposing the namespaces, even if it's simpler
and just a string, is the way to go.

I'm really excited by this guys!  I think the TimelyFlatMap and
TimelyCoFlatMap are going to get a LOT of use.  This is gonna make a lot of
people happy.


On Fri, Oct 28, 2016 at 1:58 PM, Aljoscha Krettek <aljoscha@apache.org>

> Hi Gyula,
> if you look at the internal API you'll notice that it is pretty much like
> your second proposal. Just for reference, the interface is roughly this:
> public interface InternalTimerService<N> {
>   long currentProcessingTime();
>   long currentWatermark();
>   void registerProcessingTimeTimer(N namespace, long time);
>   void deleteProcessingTimeTimer(N namespace, long time);
>   void registerEventTimeTimer(N namespace, long time);
>   void deleteEventTimeTimer(N namespace, long time);
> }
> that namespace bit can be anything for which you can provide a
> TypeSerializer.
> IMHO, this goes back a bit to the discussion about adding a low level
> operator-like interface that allows pretty much anything a custom operator
> can do but with a defined, stable interface. The internal operator
> interface is somewhat in flux, still, so I wouldn't recommend people to use
> it directly.
> The only thing missing, really, from TimelyFlatMap is access to namespaces
> for state and timers. With that, you could implement even the
> WindowOperator as a TimelyFlatMap since I worked on abstracting everything
> that it uses away behind interfaces that any operator can use. The last
> pice, the generic timer API went in last, of course. :-)
> Cheers,
> Aljoscha
> On Fri, 28 Oct 2016 at 16:55 Gyula Fóra <gyfora@apache.org> wrote:
> > Hello,
> >
> > I was thinking about the methods provided by the timely functions and the
> > timerservice and I am wondering if it makes sense to change them a little
> > so they can cover a wider set of use case. Maybe I missed something
> > completely obvious so please shoot me down in that case :)
> >
> > Currently the user gets a TimerService to register timers that will in
> the
> > future call the onTimer method. It is not completely obvious to me how
> > would I implement a function that needs to trigger two types of callbacks
> > in the future. If I get only one onTimer method I should be able to pass
> in
> > some sort of parameter or flag so I can branch in my onTimer
> > implementation.
> >
> > As parameters are not supported I am left with states that are scoped to
> > the keys which is also pretty useless if I want to trigger different
> timed
> > actions for the same keys.
> >
> > I know this is quite tricky but I see some alternative options:
> >  - The register timer method returns a unique (per key) timer id, so we
> can
> > associate state with this id to fetch info about the timer registered.
> (We
> > could also remove timers with this id and maybe add methods to remove all
> > for the current key)
> >  - Allow the users to pass a custom parameter when registering the
> > callback, and the parameter would be passed to the onTimer method
> >  - Allow users to pass custom callback functions when registering the
> > timers, but this would mean we have to support some sort of context for
> > accessing the state (like the window context before)
> >  - We could go for an annotation based API like in beam but thats
> probably
> > not good to mix in the current ones
> >
> > I personally prefer the first one.
> >
> > What do you think?
> >
> > Regards,
> > Gyula
> >


Jamie Grier
data Artisans, Director of Applications Engineering
@jamiegrier <https://twitter.com/jamiegrier>

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