Aljoscha Krettek created FLINK-3715:
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Summary: 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: Streaming
Reporter: Aljoscha Krettek
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 {{WindowOperato}}. 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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