Hi all, I would like to start a discussion on this feature request (JIRA link). <https://issues.apache.org/jira/browse/FLINK-16039>
Consider the events : [1, event], [2, event] where first element is event timestamp in seconds and second element is event code/name. Also consider that an Event time session window with inactivityGap = 2 seconds is acting on above stream. When the first event arrives, a session window should be created that is [1,1]. When the second event arrives, a new session window should be created that is [2,2]. Since this falls within firstWindowTimestamp+inactivityGap, it should be merged into session window [1,2] and [2,2] should be deleted. *This is my understanding of how session windows are created. Please correct me if wrong.* However, Flink does not follow such a definition of windows semantically. If I call the getEnd() method of the TimeWindow() class, I get back timestamp + inactivityGap. For the above example, after processing the first element, I would get 1 + 2 = 3 seconds as the window "end". The actual window end should be the timestamp 1, which is the last event in the session window. A solution would be to change the "end" definition of all windows, but I suppose this would be breaking and would need some debate. Therefore, I propose an intermediate solution : add a new API method that keeps track of the last element added in the session window. If there is agreement on this, I would like to start drafting a change document and implement this.
