Github user fhueske commented on the pull request:
https://github.com/apache/flink/pull/1553#issuecomment-198364412
Hi @ramkrish86, I thought about this PR and came to the conclusion that we
should not continue. The optimizer's design does not allow to modify operators
in or inject operators into enumerated subplans. This might cause invalid
execution plans and in worst case wrong results without somebody noticing it.
I would simply log a WARN message that a combiner was not added if the
optimizer identifies a Partition operator in front of a Reduce or combinable
GroupReduce operator and give a hint that an explicit CombinerFunction can be
added with groupCombine in front of the partition operator.
Sorry again @ramkrish86 that I lead you into a dead end with this PR.
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