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From M Singh <mans2si...@yahoo.com>
Subject Re: Apache Flink - Question about TriggerResult.FIRE
Date Fri, 17 Nov 2017 18:33:02 GMT
Thanks Stefan and Aljoscha for your responses.
Stefan - When I mentioned "new window" - I meant the next window being created. 
Eg:  if the event was in w1 based processing time and the trigger returned FIRE - then after
the window function is computed, what happens to the events in that window (w1).  Are they
(elements in w1) propagated to the next processing time window (w2) ?  If not, then what
is the difference between FIRE and FIRE_AND_PURGE and when do we use FIRE vs FIRE_AND PURGE
?  Are there any examples to demonstrated these differences ?
Thanks again for your help. 

    On Thursday, November 16, 2017 5:16 AM, Aljoscha Krettek <aljoscha@apache.org> wrote:

 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:

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.

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