[jira] [Created] (FLINK-8384) Session Window Assigner with Dynamic Gaps

["Dyana Rose (JIRA)" <ji...@apache.org>]

Dyana Rose created FLINK-8384:
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             Summary: Session Window Assigner with Dynamic Gaps
                 Key: FLINK-8384
                 URL: https://issues.apache.org/jira/browse/FLINK-8384
             Project: Flink
          Issue Type: Improvement
          Components: Streaming
            Reporter: Dyana Rose
            Priority: Minor


*Reason for Improvement*

Currently both Session Window assigners only allow a static inactivity gap. 
Given the following scenario, this is too restrictive:

* Given a stream of IoT events from many device types
* Assume each device type could have a different inactivity gap
* Assume each device type gap could change while sessions are in flight

By allowing dynamic inactivity gaps, the correct gap can be determined in the [assignWindows function|https://github.com/apache/flink/blob/master/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/windowing/assigners/EventTimeSessionWindows.java#L59] by passing the element currently under consideration, the timestamp, and the context to a user defined function. This eliminates the need to create unwieldy work arounds if you only have static gaps.

Dynamic Session Window gaps should be available for both Event Time and Processing Time streams.



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