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From Eric Isling <out.code....@gmail.com>
Subject Multiple trigger events on keyed window
Date Wed, 21 Aug 2019 16:19:51 GMT
Dear list-members,

I have a question regarding window-firing and element accumulation for a
slidindingwindow on a DataStream (Flink 1.8.1-2.12).

My DataStream is derived from a custom SourceFunction, which emits
stirng-sequences of WINDOW size, in a deterministic sequence.
The aim is to crete sliding windows over the keyedstream for processing on
the accumulated strings, based on EventTime.
To assign EventTime and Watermark, I attech an
AssignerWithPeriodicWaterMarks, to the stream.
The sliding window is processed with a custom ProcessWindowFunction.

val seqStream = env.addSource(Seqstream)

val result = seqStream.process(ProcessSeqWindow(target1))

My AssignerWithPeriodicWaterMarks looks like this.
class FASTATimeStampExtractor : AssignerWithPeriodicWatermarks<FASTAstring> {
    var waterMark  = 9999L
    override fun extractTimestamp(element: FASTAstring,
previousElementTimestamp: Long): Long {
        return element.f1

    override fun getCurrentWatermark(): Watermark? {
        waterMark += 1
        return Watermark(waterMark)

In other words, each element emitted by the source should have its own
EvenTime, and the WaterMark should be emitted allowing no further
events for that time.
Stepping through the stream in a debugger, indicates that EventTime /
Watremarks are generated as would expect.

My expectation is that ProcessSeqWindow.run() ought to be called with
a number of elements proportional to the time window (e.g. 10 ms),
over EventTime. However, what I observe is that run() is called
multiple times with single elemnts, and in an arbitrary sequence with
respect to EventTime.

My question is whether this is likely to be caused by multiple
trigger-events on each window, or are there other possible
explainations? How can I debug the cause?



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