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https://issues.apache.org/jira/browse/FLINK-2398?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14660144#comment-14660144
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ASF GitHub Bot commented on FLINK-2398:
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Github user StephanEwen commented on the pull request:
https://github.com/apache/flink/pull/988#issuecomment-128405914
+1 for rebalancing automatically between operators of different DOP. The
batch API does the same. But it should really be "rebalance", not a form of
forward that typically creates skew.
I am somewhat indifferent to the sink-or-no-sink question. The batch API
requires sinks strictly, and it makes total sense there. For streaming, it may
be different.
If we require sinks, we should have a simple function `sink()` or so, which
marks the operation as sink, so we don't force people to implement a
*discarding sink* or so unnecessarily.
> 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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