[jira] [Created] (FLINK-5719) Let LatencyMarkers completely bypass operators / chains

[Shang Yuanchun (Jira)]

Tzu-Li (Gordon) Tai created FLINK-5719:
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             Summary: Let LatencyMarkers completely bypass operators / chains
                 Key: FLINK-5719
                 URL: https://issues.apache.org/jira/browse/FLINK-5719
             Project: Flink
          Issue Type: Improvement
          Components: Streaming
            Reporter: Tzu-Li (Gordon) Tai


Currently, {{LatencyMarker}}s are forwarded through operators via the operator interfaces and methods, i.e. {{AbstractStreamOperator#processLatencyMarker()}},  {{Output#emitLatencyMarker()}}, {{OneInputStreamOperator#processLatencyMarker()}} etc.

The main issue with this is that {{LatencyMarker}}s are essentially internal elements, and the implementation on how to handle them should be final. Exposing them through operator interfaces will allow the user to override the implementation, and also makes the user interface for operators over-complicated.

[~aljoscha] suggested to bypass such internal stream elements from the operator to keep the operator interfaces minimal, in FLINK-5017.
We propose a similar approach here for {{LatencyMarker}}s as well. Since the chaining output calls contribute very little to the measured latency and can be ignored, instead of passing it through operator chains, latency markers can simply be passed downstream once tasks receive them.



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