I incorporated the changes. The proposed interface of ProcessWindowFunction
is now this:
public abstract class ProcessWindowFunction <IN, OUT, KEY, W extends
Window> implements Function {
public abstract void process(KEY key, Iterable<IN> elements, Context
ctx) throws Exception;
public abstract class Context {
public abstract W window();
public abstract void output(OUT value);
}
}
I'm proposing to not expose Collector anymore because it has the close()
method that should not be called by users. Having the output() call
directly on the context should work just as well.
Also, I marked the "adding a firing reason" and "adding firing counter" as
future work that are only examples of stuff that can be implemented on top
of the new interface. Initially, this will provide exactly the same
features as the old API but be extensible. I did this to not make the scope
of this proposal to big because Radu also suggested more changes and each
of them should be covered in a separate design doc or FLIP.
@Radu: On the different buffer types. I think this would be very tricky.
Right now, people should also not rely on the fact that elements are
"FIFO". Some state backends might keep the elements in a different order
and when you have merging windows/session windows the order of the elements
will also not be preserved.
Cheers,
Aljoscha
On Wed, 13 Jul 2016 at 18:40 Radu Tudoran <radu.tudo...@huawei.com> wrote:
> Hi,
>
> If it is to extend the Context to pass more information between the stages
> of processing a window (triggering -> process -> eviction), why not adding
> also a "EvictionInfo"? I think this might actually help with the issues
> discussed in the tread related to the eviction policy. I could imagine
> using this parameter to pass the conditions, from the processing stage to
> the evictor, about what events to be eliminated.
>
>
>
>
> public abstract class Context {
>
> public abstract EvictionInfo evictionInfo();
>
> ...
>
>
> public abstract KEY key();
>
> public abstract W window();
>
> public abstract int id();
>
> public abstract FiringInfo firingInfo();
>
> public abstract Iterable<IN> elements();
>
> public abstract void output(OUT value);
>
> }
>
>
> Also on a slightly unrelated issue - how hard it would be to introduce
> different types of buffers for the windows. Currently the existing one is
> behaving (when under processing) similar with a FIFO queue (in the sense
> that you need to start from beginning, from the oldest element). How about
> enabling for example also LIFO behavior (start iterating through the list
> from the most recent element). As in the source queues or stacks are not
> actually used, perhaps we can just pass policies to the iterator - or have
> custom itrators
>
>
>
>
>
>
> Dr. Radu Tudoran
> Research Engineer - Big Data Expert
> IT R&D Division
>
>
> HUAWEI TECHNOLOGIES Duesseldorf GmbH
> European Research Center
> Riesstrasse 25, 80992 München
>
> E-mail: radu.tudo...@huawei.com
> Mobile: +49 15209084330
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>
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> -----Original Message-----
> From: Aljoscha Krettek [mailto:aljos...@apache.org]
> Sent: Wednesday, July 13, 2016 2:24 PM
> To: dev@flink.apache.org
> Subject: Re: [DISCUSS] FLIP-2 Extending Window Function Metadata
>
> Sure, I also thought about this but went for the "extreme" initially. If
> no-one objects I'll update the doc in a bit.
>
> On Wed, 13 Jul 2016 at 14:17 Stephan Ewen <se...@apache.org> wrote:
>
> > Thanks for opening this.
> >
> > I see the need for having an extensible context object for window
> > function invocations, but i think hiding every parameter in the
> > context is a bit unnatural.
> >
> > How about having a function "apply(Key, Values, WindowContext,
> Collector)"
> > ?
> > It should be possible to write the straightforward use cases without
> > accessing the context object.
> >
> >
> >
> > On Wed, Jul 13, 2016 at 1:56 PM, Aljoscha Krettek
> > <aljos...@apache.org>
> > wrote:
> >
> > > Hi,
> > > this is a proposal to introduce a new interface for the window
> > > function
> > to
> > > make it more extensible for the future where we might want to
> > > provide additional information about why a window fired to the user
> function:
> > >
> > >
> > >
> > https://cwiki.apache.org/confluence/display/FLINK/FLIP-2+Extending+Win
> > dow+Function+Metadata
> > >
> > > I'd appreciate your thoughts!
> > >
> > > Cheers,
> > > Aljoscha
> > >
> >
>
