Re: Apache Flink - Question about rolling window function on KeyedStream

Posted by Stefan Richter on
URL: http://deprecated-apache-flink-user-mailing-list-archive.369.s1.nabble.com/Apache-Flink-Question-about-rolling-window-function-on-KeyedStream-tp17494p17529.html

Hi,

I would interpret this as: the reduce produces an output for every new reduce call, emitting the updated value. There is no need for a window because it kicks in on every single invocation.

Best,

Stefan

Am 31.12.2017 um 22:28 schrieb M Singh <[hidden email]>:

Hi:

Apache Flink documentation (https://ci.apache.org/projects/flink/flink-docs-release-1.4/dev/stream/operators/index.html) indicates that a reduce function on a KeyedStream  as follows:

A "rolling" reduce on a keyed data stream. Combines the current element with the last reduced value and emits the new value. 

A reduce function that creates a stream of partial sums:

keyedStream.reduce(new ReduceFunction<Integer>() {
    @Override
    public Integer reduce(Integer value1, Integer value2)
    throws Exception {
        return value1 + value2;
    }
});

The KeyedStream is not windowed, so when does the reduce function kick in to produce the DataStream (ie, is there a default time out, or collection size that triggers it, since we have not defined any window on it).

Thanks

Mans