[jira] [Commented] (BEAM-1589) Add OnWindowExpiration method to Stateful DoFn

["Aljoscha Krettek (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/BEAM-1589?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15894162#comment-15894162 ] 

Aljoscha Krettek commented on BEAM-1589:
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This will probably take the form of a {{@OnWindowExpiration}} annotation. I'm guessing from some of his earlier comments elsewhere that [~kenn] already has an opinion about how this could be done, right?

> 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
>
> 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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