Fabian Hueske created FLINK-6969:
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             Summary: Add support for deferred computation for group window 
aggregates
                 Key: FLINK-6969
                 URL: https://issues.apache.org/jira/browse/FLINK-6969
             Project: Flink
          Issue Type: New Feature
          Components: Table API & SQL
            Reporter: Fabian Hueske


Deferred computation is a strategy to deal with late arriving data and avoid 
updates of previous results. Instead of computing a result as soon as it is 
possible (i.e., when a corresponding watermark was received), deferred 
computation adds a configurable amount of slack time in which late data is 
accepted before the result is compute. For example, instead of computing a 
tumbling window of 1 hour at each full hour, we can add a deferred computation 
interval of 15 minute to compute the result quarter past each full hour.

This approach adds latency but can reduce the number of update esp. in use 
cases where the user cannot influence the generation of watermarks. It is also 
useful if the data is emitted to a system that cannot update result (files or 
Kafka). The deferred computation interval should be configured via the 
{{QueryConfig}}.



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