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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