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From fhueske <...@git.apache.org>
Subject [GitHub] flink pull request: FLINK-3179 Combiner is not injected if Reduce ...
Date Mon, 01 Feb 2016 14:38:14 GMT
Github user fhueske commented on the pull request:

    https://github.com/apache/flink/pull/1553#issuecomment-177997324
  
    The `GroupReduceWithCombineProperties.instanciate()` method checks the shipping strategy
of the input channel. In case of the `WordCount` example *without* explicit hash combiner,
the shipping strategy is `PARTITION_HASH` and the `else` branch will inject a combiner. If
you add an explicit partition operator, the input shipping strategy of the Reduce operator
is `FORWARD` and the `if` branch is executed and does not add a combiner.
    
    Hence the logic has to into the `if` branch and not into the `else` branch. Or even better
add an additional condition to the `if` case `!(in.getSource().getOptimizerNode() instanceof
PartitionNode)` and add an `if else` branch to handle the special case of the explicit partition
operator.


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