Aljoscha Krettek created FLINK-4415:
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Summary: Enhance Trigger Interface with onFire() and onCleanup()
Key: FLINK-4415
URL: https://issues.apache.org/jira/browse/FLINK-4415
Project: Flink
Issue Type: Sub-task
Components: Streaming
Reporter: Aljoscha Krettek
Currently, when a {{Trigger}} returns {{PURGE}} (or {{FIRE_AND_PURGE}}) the
window state, trigger state and timer state are completely deleted. Some use
cases might only want to have the window contents deleted. In addition,
triggers have no way of reacting to garbage collection, i.e. the time when
allowed lateness expires and we completely clean up everything.
I want to propose to add these two new methods:
{code}
void onFire(...)
boolean onCleanup(...)
{code}
The {{onFire()}} is called when a window fires and we emit data. This gives the
trigger the chance to reset/cleanup state. {{onCleanup()}} gives the trigger
the chance to emit one final result before everything is purged, and also
allows to cleanup data, i.e. it also replaces {{clear()}}. The window operator
will not purge window state and timers anymore but call {{Trigger.onFire()}} to
give it a chance to decide whether to delete state and timers.
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