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From Stefan Richter <s.rich...@data-artisans.com>
Subject Re: Keyed windows with single sink
Date Thu, 22 Jun 2017 14:10:23 GMT
The process function has the signature

void processElement(I value, Context ctx, Collector<O> out) throws Exception
where the context is providing access to the current watermark and you can also register timer
callbacks, when that trigger when a certain watermark is reached. You can simply monitor the
watermark through the context for each incoming window result. Start time is not important,
because you know that you have collected the results for all windows with a smaller end time
than the watermark that you currently see in the context, because this is Flinkā€™s notion
of completeness. This means you can prepare those windows and aggregate results and send them
downstream to the sink.

> Am 22.06.2017 um 15:46 schrieb Ahmad Hassan <ahmad.hassan@gmail.com>:
> Thanks Stefan, But how the Process function will have these watermarks? I have sliding
windows like below
> final DataStream<WindowStats> eventStream = inputStream
> 				.keyBy(TENANT, CATEGORY)
> 				.window(SlidingProcessingTimeWindows.of(Time.minutes(100,Time.minutes(5)))
> 				.fold(new WindowStats(), new ProductAggregationMapper(), new ProductAggregationWindowFunction());
> Window results are coming every 5 minutes after first window output. How the process
function would know that all the windows for a Tenant have finished for a giving start and
end time.
> Thanks for help.
> Cheers,
> On 22 June 2017 at 14:37, Stefan Richter <s.richter@data-artisans.com <mailto:s.richter@data-artisans.com>>
> Hi,
> one possible approach could be that you have a process function before the sink. Process
function is aware of watermarks, so it can collect and buffer window results until it sees
a watermark. This is the signal that all results for windows with an end time smaller than
the watermark are complete. They can then be aggregated and send to the sink.
> Best,
> Stefan
> > Am 22.06.2017 um 15:15 schrieb Ahmad Hassan <ahmad.hassan@gmail.com <mailto:ahmad.hassan@gmail.com>>:
> >
> > Hi All,
> >
> > I am using categoryID as a keyby attribute for creating keyed stream from a product
event stream. Keyed stream then creates time windows for each category. However, when the
window time expires, i want to write the output data of all the products in all all categories
in a single atomic operation collectively. Is there a way to call a single sink function for
all the windows with same start and end time. Or is there a way in flink to know that all
windows with same end time have finished processing their sink function?
> >
> > Currently, each window calls sink function individually.
> >
> > cheers,
> >

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