Last tuple of time window

Question

I have the following situation

stream<Tuple2<String, Integer>
   .keyBy(0)
   .timeWindow(Time.of(10, TimeUnit.SECONDS))
   .sum(1)
   .flatMap(..)
   .sink()

What I am trying to do is calculate a top N for my time window. The top N for each window is stored by the sink.

I can calculate the top N in the flatmap, but I do not know when to send it to the sink for storage. As far as I can see there is no way to know when the window has ended from within the flatmap function.

I know there are alternatives such as an apply function which does both or creating markers in the stream to indicate the end, but I am wondering if there is a more elegant solution.

Answer 1

If you want to calculate the top N for each window over all keys, then you should apply a time window all with the same length in whose apply method you calculate the top N. You could do something like:

final int n = 10;
stream
    .keyBy(0)
    .timeWindow(Time.of(10L, TimeUnit.SECONDS))
    .sum(1)
    .timeWindowAll(Time.of(10L, TimeUnit.SECONDS))
    .apply(new AllWindowFunction<Tuple2<String,Integer>, Tuple2<String, Integer>, TimeWindow>() {
        @Override
        public void apply(TimeWindow window, Iterable<Tuple2<String, Integer>> values, Collector<Tuple2<String, Integer>> out) throws Exception {
            PriorityQueue<Tuple2<String, Integer>> priorityQueue = new PriorityQueue<>(n, new Comparator<Tuple2<String, Integer>>() {
                @Override
                public int compare(Tuple2<String, Integer> o1, Tuple2<String, Integer> o2) {
                    return o1.f1 - o2.f1;
                }
            });

            for (Tuple2<String, Integer> value : values) {
                priorityQueue.offer(value);

                while (priorityQueue.size() > n) {
                    priorityQueue.poll();
                }
            }

            for (Tuple2<String, Integer> stringIntegerTuple2 : priorityQueue) {
                out.collect(stringIntegerTuple2);
            }
        }
    })
    .print();