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https://issues.apache.org/jira/browse/BEAM-2447?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Eugene Kirpichov closed BEAM-2447.
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Resolution: Fixed
Fix Version/s: 2.2.0
> Reintroduce DoFn.ProcessContinuation
> ------------------------------------
>
> Key: BEAM-2447
> URL: https://issues.apache.org/jira/browse/BEAM-2447
> Project: Beam
> Issue Type: Bug
> Components: sdk-java-core
> Reporter: Eugene Kirpichov
> Assignee: Eugene Kirpichov
> Fix For: 2.2.0
>
>
> ProcessContinuation.resume() is useful for tailing files - when we reach
> current EOF, we want to voluntarily suspend the process() call rather than
> wait for runner to checkpoint us.
> In BEAM-1903, DoFn.ProcessContinuation was removed because there was
> ambiguity about the semantics of resume() especially w.r.t. the following
> situation described in
> https://docs.google.com/document/d/1BGc8pM1GOvZhwR9SARSVte-20XEoBUxrGJ5gTWXdv3c/edit
> : the runner has taken a checkpoint on the tracker, and then the
> ProcessElement call returns resume() signaling that the work is still not
> done - then there's 2 checkpoints to deal with.
> Instead, the proper way to refine this semantics is:
> - After checkpoint() on a RestrictionTracker, the tracker MUST fail all
> subsequent tryClaim() calls, and MUST succeed in checkDone().
> - After a failed tryClaim() call, the ProcessElement method MUST return stop()
> - So ProcessElement can return resume() only *instead* of doing tryClaim()
> - Then, if the runner has already taken a checkpoint but tracker has returned
> resume(), we do not need to take a new checkpoint - the one already taken
> already accurately describes the remainder of the work.
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