[jira] [Created] (BEAM-2859) Processing time based timers are not properly fired in case the watermark stays put

["Stas Levin (JIRA)" <ji...@apache.org>]

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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