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https://issues.apache.org/jira/browse/BEAM-1983?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17546501#comment-17546501
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Kenneth Knowles commented on BEAM-1983:
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This issue has been migrated to https://github.com/apache/beam/issues/18366
> SDF should properly support windowed side inputs
> ------------------------------------------------
>
> Key: BEAM-1983
> URL: https://issues.apache.org/jira/browse/BEAM-1983
> Project: Beam
> Issue Type: Bug
> Components: runner-apex, runner-dataflow, runner-direct,
> runner-flink, sdk-java-core
> Reporter: Eugene Kirpichov
> Priority: P3
> Labels: Clarified
>
> Currently there is no test coverage for Splittable DoFn + windowed side
> inputs, especially when not all of the side input windows are ready.
> Moreover, current implementation of SDF in the direct runner is definitely
> wrong: it uses a ParDoEvaluator to run the ProcessFn, and this ParDoEvaluator
> looks at the wrong windows to decide which windows are ready and which are
> not:
> https://github.com/apache/beam/blob/master/runners/direct-java/src/main/java/org/apache/beam/runners/direct/ParDoEvaluator.java#L134
> - the WindowedValue in question is a KeyedWorkItem, and they are always in
> the global window, but the important windows are windows of elements inside
> this KWI's elementsIterable().
> The Flink implementation is also wrong in the same way.
> This JIRA is to:
> 1) add test coverage for this case
> 2) implement proper support in all runners
> I believe the easiest way to do 2) is to:
> - make SplittableParDo, in case the DoFn has side inputs, pre-explode windows
> before feeding them into GroupByKeyIntoKeyedWorkItems , so that the resulting
> KWI's have elements only in a single window
> - tweak runners to look at the proper window, and assert that there's only
> one window, while evaluating ProcessFn, in case the DoFn uses side inputs
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