Aljoscha Krettek created FLINK-4994:
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Summary: Don't Clear Trigger State and Merging Window Set When
Purging
Key: FLINK-4994
URL: https://issues.apache.org/jira/browse/FLINK-4994
Project: Flink
Issue Type: Sub-task
Components: Streaming
Reporter: Aljoscha Krettek
Assignee: Aljoscha Krettek
Right now, when a {{Trigger}} returns {{TriggerResult.PURGE}} from any of the
{{on*()}} methods the {{WindowOperator}} will clear all state of that window
(window contents, merging window set) and call {{Trigger.clear()}} so that the
{{Trigger}} can clean up its state/timers.
This is problematic in some cases. For example, with merging windows (session
windows) this means that a late-arriving element will not be put into the
session that was previously built up but will be put into a completely new
session that only contains this one element.
The proposed new behaviour is this:
* Only clean window contents on {{PURGE}}
* Register cleanup timer for any window, don't delete this on {{PURGE}}
* When the cleanup timer fires: clean window state, clean merging window set,
call {{Trigger.clear()}} to allow it to clean state/timers
Together with FLINK-4415 this would give the trigger the power to purge state
and window contents separately.
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