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From M Singh <mans2si...@yahoo.com>
Subject Re: Apache Flink - Question about TriggerResult.FIRE
Date Fri, 17 Nov 2017 18:36:43 GMT
Also, Stefan - You mentioned 
"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."
I am assuming the first case is FIRE and second case is FIRE_AND_PURGE - I was thinking that
in the first case (FIRE), there would be elements from previous window since we did not purge
and the second case it would have only new elements since it was purged.  Am I missing something
?  
Once again, if there are any examples it would greatly help me in understanding the semantics/usage
scenarios.
Mans 

    On Friday, November 17, 2017 10:33 AM, M Singh <mans2singh@yahoo.com> wrote:
 

 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. 
Mans 

    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.
Best,Aljoscha

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>:
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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