Status

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JIRA: here (<- link to https://issues.apache.org/jira/browse/FLINK-XXXX)

Released: <Flink Version>

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Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

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The biggest change includes StreamStatus albeit it's an internal class. We propose to adjust the definition (JavaDoc) to exclude records and rename the class to WatermarkStatus and move it to the watermarkstatus package. Finally, we need to rename emitStreamStatus and processStreamStatus in a few public evolving interfaces (Input, Output). Here, we can add deprecated shortcuts to the top-level interfaces with the old name.

We should also update the definition of StreamStatus#IDLE to make sure that this a) may introduce late records and b) should be user-controlled. With that change, we also remove all code that automatically let's sources go idle without user-specified idleness.

Since sources may offer users the ability to go IDLE beyond the WatermarkStrategy#withIdleness, we propose to also add WatermarkOutput#markActive to quickly go active again without the need to explicitly emit a watermark first. This addition allows to reduce the number of late records when a source knows that records are available until it processed a batch and actually emit a watermark.

Compatibility, Deprecation, and Migration Plan

• User code using Input and Output would work without recompilation. Compiling would yield deprecation warningsAll changes are on internal classes or on public methods that been added only in master. So we can assume that this FLIP causes no visible change.

Test Plan

The change of StreamStatus  reflects the current implementation and is thus already covered by tests. We might need to add additional unit/integration tests if we discover paths where we automatically switch to IDLE (a recent change on 1.14-SNAPSHOT does it).

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