Windows emit results at the end of the stream

[Sonex]

Hi everyone,

I am using a simple window computation on a stream with event time. The code
looks like this:

streamData.readTextFile(...)
    .map(...)
    .assignAscendingTimestamps(_.timestamp)
    .keyBy(_.id)
    .timeWindow(Time.seconds(3600),Time.seconds(3600))
    .apply(new MyWindowFunction)
    .map(...)

By monitoring the memory usage and the flink web dashboard, I noticed that
flink applies the window function until the entire stream finishes (thus
storing all aggregations in memory) and then continues to the map
transformation. What I would expect is emission of window results to the map
transformation as soon as results of the window are ready.

Can anyone explain this behavior?



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