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https://issues.apache.org/jira/browse/FLINK-2398?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14655038#comment-14655038
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ASF GitHub Bot commented on FLINK-2398:
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Github user gyfora commented on the pull request:
https://github.com/apache/flink/pull/988#issuecomment-127924076
Why isn't rebalance implied when the 2 operators don't have the same
parallelism and partitioning is not defined? If you don't specify the
partitioning (which defaults to forward) means that you don't specifically
care, in this case implied rebalance is the most natural thing.
It's arguable that if the user specifically says forward then we give an
error but otherwise I this this just hurts the developers.
> Decouple StreamGraph Building from the API
> ------------------------------------------
>
> Key: FLINK-2398
> URL: https://issues.apache.org/jira/browse/FLINK-2398
> Project: Flink
> Issue Type: Improvement
> Components: Streaming
> Reporter: Aljoscha Krettek
> Assignee: Aljoscha Krettek
>
> Currently, the building of the StreamGraph is very intertwined with the API
> methods. DataStream knows about the StreamGraph and keeps track of splitting,
> selected names, unions and so on. This leads to the problem that is is very
> hard to understand how the StreamGraph is built because the code that does it
> is all over the place. This also makes it hard to extend/change parts of the
> Streaming system.
> I propose to introduce "Transformations". A transformation hold information
> about one operation: The input streams, types, names, operator and so on. An
> API method creates a transformation instead of fiddling with the StreamGraph
> directly. A new component, the StreamGraphGenerator creates a StreamGraph
> from the tree of transformations that result from program specification using
> the API methods. This would relieve DataStream from knowing about the
> StreamGraph and makes unions, splitting, selection visible transformations
> instead of being scattered across the different API classes as fields.
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