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From "ASF GitHub Bot (JIRA)" <>
Subject [jira] [Commented] (BEAM-1956) Flatten operation should respect input type hints.
Date Fri, 14 Apr 2017 21:00:42 GMT


ASF GitHub Bot commented on BEAM-1956:

GitHub user vikkyrk opened a pull request:

    [BEAM-1956] Modify types for input PCollections of Flatten transform

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    Modify types for input PCollections of Flatten transform to that of the output PCollection

You can merge this pull request into a Git repository by running:

    $ git pull py_flatten_visitor

Alternatively you can review and apply these changes as the patch at:

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #2543
commit e3ac1f4d3298b2e32463b6b132dda89706a6bc58
Author: Vikas Kedigehalli <>
Date:   2017-04-14T20:53:13Z

    Modifying types for input PCollectios of Flatten transform with that of the output PCollection


> Flatten operation should respect input type hints.
> --------------------------------------------------
>                 Key: BEAM-1956
>                 URL:
>             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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