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From Aljoscha Krettek <aljos...@apache.org>
Subject Re: Apache Flink - Question about TriggerResult.FIRE
Date Thu, 16 Nov 2017 13:16:46 GMT
Yes, all of this is correct. Sliding windows in fact look like completely separate windows
to the windowing system.


> On 16. Nov 2017, at 10:15, Stefan Richter <s.richter@data-artisans.com> wrote:
> Hi,
> 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.
> Best,
> Stefan
>> Am 13.11.2017 um 20:19 schrieb M Singh <mans2singh@yahoo.com <mailto: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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