Stas Levin created BEAM-2859:
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Summary: Processing time based timers are not properly fired in
case the watermark stays put
Key: BEAM-2859
URL: https://issues.apache.org/jira/browse/BEAM-2859
Project: Beam
Issue Type: Bug
Components: runner-spark
Affects Versions: 2.1.0
Reporter: Stas Levin
Assignee: Amit Sela
{{AfterProcessingTime}} based timers are not fired when the input watermark
does not advance, preventing from buffered element to be emitted.
The reason seems to be that {{SparkTimerInternals#getTimersReadyToProcess()}}
determines what triggers are ready to be processed by using the following
condition:
{code:java}
timer.getTimestamp().isBefore(inputWatermark)
{code}
However, if the timer domain is {{TimeDomain.PROCESSING_TIME}} the position of
the input watermark should *NOT* have effect.
In addition, {{SparkTimerInternals#getTimersReadyToProcess()}} deletes timers
once they are deemed eligible for processing (but will not necessarily fire).
This may not be the correct behavior for timers in general and for timers in
the {{TimeDomain.PROCESSING_TIME}} in particular, since they should remain
scheduled until the corresponding window expires and all state is cleared.
For instance, consider a timer that is found eligible for processing is thus
deleted, then it just so happens to be that its {{shouldFire()}} returns
{{false}} and it needs to be re-run next time around, but won't since it's been
deleted.
It may be better to avoid removing timers in
{{SparkTimerInternals#getTimersReadyToProcess()}} and leave timer management up
to {{ReduceFnRunner#clearAllState()}} which has more context to determine
whether it's time for a given timer to deleted.
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