Github user aljoscha commented on the pull request:
https://github.com/apache/flink/pull/988#issuecomment-128133833
About rebalance()/forward(). Yes, when the parallelism differs it throws an
exception now. Previously, when a user did not specify a partition strategy,
forward was assumed. This was valid for a change of parallelism, which led to
either the degenerative case of only one downstream instance receiving elements
(1 to n parallelism) or one or several downstream instances receiving skewed
numbers of instances (m to n, where m > n).
I think we can document forward as the default for n -> n parallelism and
rebalance as default for n -> m parallelism and change the behavior.
About the dangling operators, also true. I think before it was more an
implementation artifact because the stream graph was basically being built form
the sources. Now it is built from the sinks. I see that this can be good
behavior and I can adapt the current code if we agree on this.
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