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From Stephan Ewen <se...@apache.org>
Subject Re: [DISCUSS] FLIP-2 Extending Window Function Metadata
Date Tue, 19 Jul 2016 13:22:13 GMT
I would actually make the output a separate parameter as well. Pretty much
like the old variant, only replacing the "Window" parameter by the context
(which contains everything about the window).
It could also be called "WindowInvocationContext" or so.

The current variant looks too Hadoop to me ;-) Everything done on the
context object, and messy mocking when creating tests.

On Mon, Jul 18, 2016 at 6:42 PM, Radu Tudoran <radu.tudoran@huawei.com>
wrote:

> Hi,
>
> Sorry - I made a mistake - I was thinking of getting access to the
> collection (mist-read :) collector) of events in the window buffer  in
> order to be able to delete/evict some of them which are not necessary the
> last ones.
>
>
> Radu
>
> -----Original Message-----
> From: Aljoscha Krettek [mailto:aljoscha@apache.org]
> Sent: Monday, July 18, 2016 5:54 PM
> To: dev@flink.apache.org
> Subject: Re: [DISCUSS] FLIP-2 Extending Window Function Metadata
>
> What about the collector? This is only used for emitting elements to the
> downstream operation.
>
> On Mon, 18 Jul 2016 at 17:52 Radu Tudoran <radu.tudoran@huawei.com> wrote:
>
> > Hi,
> >
> > I think it looks good and most importantly is that we can extend it in
> > the directions discussed so far.
> >
> > One question though regarding the Collector - are we going to be able
> > to delete random elements from the list if this is not exposed as a
> > collection, at least to the evictor? If not, how are we going to
> > extend in the future to cover this case?
> >
> > Regarding the ordering - I also observed that there are situations
> > where elements do not have a logical order. One example is if you have
> > high rates of the events. Nevertheless, even if now is not the time
> > for this, I think in the future we can imagine having also some data
> > structures that offer some ordering. It can save some computation
> > efforts later in the functions for some use cases.
> >
> >
> > Best regards,
> >
> >
> > -----Original Message-----
> > From: Aljoscha Krettek [mailto:aljoscha@apache.org]
> > Sent: Monday, July 18, 2016 3:45 PM
> > To: dev@flink.apache.org
> > Subject: Re: [DISCUSS] FLIP-2 Extending Window Function Metadata
> >
> > 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.tudoran@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.tudoran@huawei.com
> > > Mobile: +49 15209084330
> > > Telephone: +49 891588344173
> > >
> > > HUAWEI TECHNOLOGIES Duesseldorf GmbH Hansaallee 205, 40549
> > > Düsseldorf, Germany, www.huawei.com Registered
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> > >
> > >
> > > -----Original Message-----
> > > From: Aljoscha Krettek [mailto:aljoscha@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 <sewen@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
> > > > <aljoscha@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
> > > > +W
> > > > in
> > > > dow+Function+Metadata
> > > > >
> > > > > I'd appreciate your thoughts!
> > > > >
> > > > > Cheers,
> > > > > Aljoscha
> > > > >
> > > >
> > >
> >
>

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