zhijiang created FLINK-13798:
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Summary: Refactor the process of checking stream status while emitting watermark in source
Key: FLINK-13798
URL:
https://issues.apache.org/jira/browse/FLINK-13798 Project: Flink
Issue Type: Sub-task
Components: Runtime / Task
Reporter: zhijiang
Assignee: zhijiang
As we know, the watermark could be emitted to downstream only when the stream status is active. For the downstream task we already have the component of StatusWatermarkValve in StreamInputProcessor to handle this logic. But for the source task the current implementation of this logic seems a bit tricky. There are two scenarios for the source case:
* Emit watermark via source context: In the specific WatermarkContext, it would toggle the stream status as active before collecting/emitting records/watermarks. Then in the implementation of RecordWriterOutput, it would check the status always active before really emitting watermark.
* TimestampsAndPeriodicWatermarksOperator: The watermark is triggered by timer in interval time. When it happens, it would call output stack to emit watermark. Then the RecordWriterOutput could take the role of checking status before really emitting watermark.
So we can see that the checking status logic in RecordWriterOutput only works for above second scenario, and this logic seems redundant for the first scenario because WatermarkContext always toggle active status before emitting. Even worse, the logic is RecordWriterOutput would bring cycle dependency with StreamStatusMaintainer, which is a blocker for the following work of integrating source processing on runtime side.
The solution is that we could migrate the checking logic from RecordWriterOutput to TimestampsAndPeriodicWatermarksOperator. And we could also remove the toggle active logic in existing WatermarkContext.
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