Hi Arnaud,
with version 1.0 the behaviour for window triggering in case of a finite stream was slightly changed. If you use event time, then all unfinished windows are triggered in case that your stream ends. This can be motivated by the fact that the end of a stream is equivalent to no elements will arrive until the maximum time (infinity) has been reached. This knowledge, allows you to emit a Long.MaxValue watermark when an event time stream is finished, which will trigger all lingering windows.
In contrast to event time, you cannot say the same about a finished processing time stream. There we don’t have logical time but the actual processing time we use to reason about windows. When a stream finishes, then we cannot fast forward the processing time to a point where the windows will fire. This can only happen if we keep the operators alive until the wall clock tells us that it’s time to fire the windows. However, there is no such feature implemented yet in Flink.
I hope this helps you to understand the failing test cases.
Cheers,
Till
Hello,
I’ve switched my Flink version from 0.10.1 to 1.0 and I have a regression in some of my unit tests.
To narrow the problem, here is what I’ve figured out:
- I use a simple Streaming application with a source defined as “fromElements("Element 1", "Element 2", "Element 3")
- I use a simple time window function with a 3 second window : timeWindowAll(Time.seconds(3))
- I use an apply() function and counts the total number of elements I get with a global counter
With the previous version, I got all three elements because, not because they are triggered under 3 seconds, but because the source ends
With the 1.0 version, I don’t get any elements, and that’s annoying because as the source ends the application ends even if I sleep 5 seconds after the execute() method.
(If I replace fromElement with fromCollection with a 10000 element list and Time.second(3) with Time.millisecond(1), I get a random number of elements)
Is this behavior wanted ? If yes, how do I get my last elements now ?
Best regards,
Arnaud
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