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https://issues.apache.org/jira/browse/BEAM-1589?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16338284#comment-16338284
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ASF GitHub Bot commented on BEAM-1589:
--------------------------------------
huygaa11 opened a new pull request #4482: [BEAM-1589] Added
@onWindowExpiration annotation.
URL: https://github.com/apache/beam/pull/4482
Added @onWindowExpiration annotation for annotating a user defined method
(similar to a method annotated with @onTimer), which allows user to do some
work before garbage collection. For example, users can use this annotation to
write a method that extracts a value saved in a state before garbage collection.
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> Add OnWindowExpiration method to Stateful DoFn
> ----------------------------------------------
>
> Key: BEAM-1589
> URL: https://issues.apache.org/jira/browse/BEAM-1589
> Project: Beam
> Issue Type: New Feature
> Components: runner-core, sdk-java-core
> Reporter: Jingsong Lee
> Assignee: Batkhuyag Batsaikhan
> Priority: Major
>
> See BEAM-1517
> This allows the user to do some work before the state's garbage collection.
> It seems kind of annoying, but on the other hand forgetting to set a final
> timer to flush state is probably data loss most of the time.
> FlinkRunner does this work very simply, but other runners, such as
> DirectRunner, need to traverse all the states to do this, and maybe it's a
> little hard.
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