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https://issues.apache.org/jira/browse/FLINK-22587?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dawid Wysakowicz updated FLINK-22587:
-------------------------------------
    Issue Type: Bug  (was: Improvement)

> Support aggregations in batch mode with DataStream API
> ------------------------------------------------------
>
>                 Key: FLINK-22587
>                 URL: https://issues.apache.org/jira/browse/FLINK-22587
>             Project: Flink
>          Issue Type: Bug
>          Components: API / DataStream
>            Reporter: Etienne Chauchot
>            Priority: Major
>
> A pipeline like this *in batch mode* would output no data
> {code:java}
> stream.join(otherStream)
>     .where(<KeySelector>)
>     .equalTo(<KeySelector>)
>     .window(GlobalWindows.create())
>     .apply(<JoinFunction>)
> {code}
> Indeed the default trigger for GlobalWindow is NeverTrigger which never 
> fires. If we set a _EventTimeTrigger_ it will fire with every element as the 
> watermark will be set to +INF (batch mode) and will pass the end of the 
> global window with each new element. A _ProcessingTimeTrigger_ never fires 
> either and all elapsed time or delta based triggers would not be suited for 
> batch.
> Same goes for _reduce()_ instead of join().
> So I guess we miss something for batch support with DataStream.



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