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https://issues.apache.org/jira/browse/BEAM-1956?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15966906#comment-15966906
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Vikas Kedigehalli commented on BEAM-1956:
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cc [~lcwik] [~robertwb] [[email protected]]
> Flatten operation should respect input type hints.
> --------------------------------------------------
>
> Key: BEAM-1956
> URL: https://issues.apache.org/jira/browse/BEAM-1956
> Project: Beam
> Issue Type: Bug
> Components: sdk-py
> Reporter: Vikas Kedigehalli
> Assignee: Vikas Kedigehalli
> Fix For: First stable release
>
>
> Input type hints are currently not respected by the Flatten operation and
> instead `Any` type is chosen as a fallback. This could lead to using a pickle
> coder even if there was a custom coder type hint provided for input
> PCollections.
> Also, this could lead to undesirable results, particularly, when a Flatten
> operation is followed by a GroupByKey operation which requires the key coder
> to be deterministic. Even if the user provides deterministic coder type hints
> to their PCollections, defaulting to Any would result in using the pickle
> coder (non-deterministic). As a result of this, CoGroupByKey is broken in
> such scenarios where input PCollection coder is deterministic for the type
> while pickle coder is not.
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