Flink IntervalJoin 调用时间戳

Question

From Flink docs: https://nightlies.apache.org/flink/flink-docs-release-1.16/docs/dev/datastream/operators/joining/#interval-join

IntervalJoin will join two streams sharing the same Key and within the lower/upper timestamp boundary, say I have the following streams

packet: [(id=1, ts=20:00:00,...),(id=1,ts=20:00:01,...),(id=3,ts=20:00:02,...),....]
metadata: [(id=1, ts=20:00:03,...),(id=2,ts=20:00:04,...),....]

packetStream
    .keyBy(elem => elem.id)
    .intervalJoin(metadata.keyBy(elem => elem.id))
    .between(Time.seconds(-2), Time.seconds(1))

When will the ProcessFunction be invoked? I understand that it will be invoked twice for id=1 but when? at 20:00:00 and 20:00:01 or only once the window is closed 20:00:03?

Answer 1

The processElement method of the ProcessJoinFunction is called as each pair of elements becomes available for processing.

In the example you've given, it will never be called for id=1 because there's no metadata event within the specified interval of the events at 20:00:00 and 20:00:01.