Apache Flink; Determine Window Boundary Timestamps

Question

In Apache Flink, when processing the result of an aggregation, I need to know the timestamp (process time) of the start of a tumbling window. Is there a way to get this timestamp? Are window boundaries or is the watermark exposed tot he AggregationFunction?

Answer 1

Along with your AggregateFunction, you have the option to specify a WindowFunction.

According to the documentation you can do the following:

stream.
.keyBy()
.window()
.aggregate(new AverageAggregate(), new WindowFunctionTest());


public static class WindowFunctionTest implements WindowFunction<..., ..., 
    Tuple, TimeWindow> {
    public void apply(Tuple key, TimeWindow window, Iterable<...> input, 
    Collector<...> out) {
        long windowStartTime = window.getStart();
    }