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https://issues.apache.org/jira/browse/BEAM-1314?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15949513#comment-15949513
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Kenneth Knowles commented on BEAM-1314:
---------------------------------------
I think this feature request might make sense, but the description seems a bit
wrong. a DoFn instance that uses state and/or timers can be used for multiple
keys, just not concurrently.
> DoFn per-key lifecycle (Setup/Teardown)
> ---------------------------------------
>
> Key: BEAM-1314
> URL: https://issues.apache.org/jira/browse/BEAM-1314
> Project: Beam
> Issue Type: Improvement
> Components: beam-model
> Reporter: Eugene Kirpichov
>
> DoFn's that use state and timers are implicitly per-key. Setup/Teardown
> methods are usually used to establish expensive resources - long-standing
> connections and such.
> For per-key DoFn's, we'd often want to use these per-key, so it'd be good to
> have ability in the model to ask that there be 1 instance of the DoFn per
> key, reused between e.g. different timer or trigger firings for this key, but
> not used for other keys.
> E.g. this would be particularly useful for Splittable DoFn - for its ability
> to reuse expensive resources between checkpoints.
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