rkhachatryan opened a new pull request, #29270:
URL: https://github.com/apache/flink/pull/29270
A source subtask can announce WatermarkStatus.IDLE downstream and never take
it back while it keeps emitting records. Downstream StatusWatermarkValve then
excludes the channel, stalling the watermark at parallelism 1 and dropping the
records as late at higher parallelism.
Three places on the path from a split's watermark generator to the data
output treat an advancing watermark as the only evidence of activity:
- WatermarkOutputMultiplexer.updateCombinedWatermark() forwards markIdle()
when the combined status is idle but nothing when it is active, so an output
that is active without advancing its watermark produces neither an
emitWatermark nor a markIdle call. Because the split branch of
ProgressiveTimestampsAndWatermarks.IdlenessManager starts out idle and is only
ever cleared by one of those two calls, an active split is then ANDed into IDLE
by the main output's idleness timer .
- WatermarksWithIdleness.onEvent() resets the idleness timer but does not
undo the markIdle() it emitted earlier .
- WatermarkToDataOutput.emitWatermark() gates markActiveInternally() on
the monotonicity check, so a non-advancing watermark is swallowed together with
the activation .
They compound: once all splits fall idle the combined watermark is flushed
to the maximum over all outputs, so a split that resumes behind that maximum
produces no advancing watermark by construction.
Propagate the activity in all three, guarding the multiplexer on the new
CombinedWatermarkStatus.hasOutputs(). That guard is load-bearing:
updateCombinedWatermark() returns early on an empty output list and leaves the
idle flag uncomputed, and a subtask that was never assigned a split has to be
able to stand down via its main-output idleness timer alone.
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