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From Stefan Richter <s.rich...@data-artisans.com>
Subject Re: Apache Flink - Question about TriggerResult.FIRE
Date Thu, 16 Nov 2017 09:15:44 GMT

I think the effect is pretty straight forward, the elements in a window are not purged if
the trigger is only FIRE and not FIRE_AND_PURGE. Unfortunately, your question is a bit unclear
about what exactly you mean by „new window“: a truly „new“ window or another triggering
of the previous (non-purged) window? In the first case, it is a new window without the previous
elements, in the second case the window reflects the old contents plus all changes since the
last trigger.

For sliding windows, if I remember correctly, every slide is actually a different window and
elements are just added repeatedly to all windows in which they belong. So window n+1 should
not be affected by whether or not window n purges or not. Maybe Aljoscha (in CC) can confirm
this for us.


> Am 13.11.2017 um 20:19 schrieb M Singh <mans2singh@yahoo.com>:
> Hi Flink Users
> I have a few questions about triggers:
> If a trigger returns TriggerResult.FIRE from say the onProcessingTime method - the window
computation is triggered but elements are kept in the window.  If there a second invocation
of the onProcessingTime method will the elements from the previous window (which were not
purged) a part of the new window computation along with new events added since the last FIRE
event ? 
> Secondly, how does the FIRE option affect the sliding window computation ?
> If there are any other insights/pitfalls while dealing with this, please let me know.
> Thanks
> Mans

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