How to debug window step in flink

[Sachin Mittal]

Hi,

I have a following windowing step in my pipeline:

inputData
    .keyBy(new MyKeySelector())
    .window(
        TumblingEventTimeWindows.of(Time.seconds(60)))
    .reduce(new MyReducer())
    .name("MyReducer");


Same step when I see in Flink UI shows as:

Window(TumblingEventTimeWindows(60000), EventTimeTrigger, MyReducer,
PassThroughWindowFunction) :- Sink: MyData sink +- Filter


So far I don't see any errors in the pipeline.

However when I check the following metrics:
0.MyReducer.numRecordsInPerSecond = 600 / s
0.MyReducer.numRecordsOutPerSecond = 0 / s

It shows that the step is receiving data but it is not outputting anything.
Looks like some problem in the step.

Most obvious thing that I can deduce is that the window step may not be
outputting any record.
Also MyReducer is a pretty simple function and it does not catch any
exception, so if there was a problem in this function it would have been
thrown to the pipeline
and I would have known.

Please let me know how I can debug this better.

Thanks
Sachin