Hi Kostas and Rong，
Thank you for your reply.
As both of you ask for more info about my use case, I now reply in
unison.
My case is used for counting the number of successful login and failures
within one hour， keyBy other login related attributes （e.g. ip, device,
login type ...）. According to the count result of the previous hour, to
judge whether the next login is compliant.
We have a high requirement for the flink compute time, to reduce the
impact on user login. From receiving source to sinking results into
database, only about 10ms time is acceptable. Base on this, we expect the
compute result as accurate as possible. The best case without error is the
latest sink time after 1-hour compute exactly the same as the user login
time which need judge compliance. Is that means the smaller the step size of
slide window, the more accurate the results? But Now it seems that the
smaller step size of slide window，the longer time need to compute. Because
once a element arrives, it will be processed in every window （number of
windows = window size/step size）serially through one thread.
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