OK Great!

Thanks a lot for the super ultra fast answer Fabian!

One intuitive follow-up question.

So, keyed state is the most preferable one, as it is easy for the Flink
System to perform the re-distribution in case of change in parallelism, if
we have a scale-up or scale-down. Also, it is useful to use hash partition a
stream to different nodes/processors/PU (Processing Units) in general, by
Keyed State.

Any other reasons for making Keyed State a must?

Last but not least, can you elaborate further on the "when the parallelism
changes" part. I have read this in many topics in this forum, but I cannot
understand its essence. For example, I define the parallelism of each
operator in my Flink Job program based on the number of available PU. Maybe
the essence lies in the fast that the number of PU might change from time to
time, e.g. add more servers to the cluster where Flink runs and without
stopping the Flink Job that runs you may perform the rescaling.

Thanks in advance.


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