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https://issues.apache.org/jira/browse/FLINK-3715?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Konstantin Knauf updated FLINK-3715:
------------------------------------
    Labels:   (was: stale-major)

Removed "stale-critical|major|minor" label in line with 
https://issues.apache.org/jira/browse/FLINK-22429. 

> Move Accumulating/Discarding from Trigger to WindowOperator
> -----------------------------------------------------------
>
>                 Key: FLINK-3715
>                 URL: https://issues.apache.org/jira/browse/FLINK-3715
>             Project: Flink
>          Issue Type: Sub-task
>          Components: API / DataStream
>            Reporter: Aljoscha Krettek
>            Priority: Major
>
> As mentioned in 
> https://docs.google.com/document/d/1Xp-YBf87vLTduYSivgqWVEMjYUmkA-hyb4muX3KRl08/edit#heading=h.pyk1sn8f33q2
>  we should move the decision of whether to {{PURGE}} a window upon firing 
> from the {{Trigger}} to the {{WindowOperator}}. This also requires to add API 
> so that the user can specify whether windows should be purged upon trigger 
> firing (discarding) or kept (accumulating).
> As mentioned in the above doc, the {{Trigger}} can react with 4 results right 
> now: {{CONTINUE}}, {{FIRE}}, {{PURGE}}, {{FIRE_AND_PURGE}}. The behavior of a 
> trigger is not apparent if not looking at the code of the trigger, this has 
> confused a number of users. With the new regime, a {{Trigger}} can just 
> decide whether to {{CONTINUE}} or {{FIRE}}. The setting of 
> accumulating/discarding decides whether to purge the window or keep it.
> This depends on FLINK-3714 where we introduce an "allowed lateness" setting. 
> Having a choice between accumulating and discarding only makes sense with an 
> allowed lateness greater zero. Otherwise no late elements could ever arrive 
> that would go into the kept windows.



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