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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-3179) Combiner is not injected if Reduce or GroupReduce input is explicitly partitioned
Date Mon, 21 Mar 2016 21:57:25 GMT

    [ https://issues.apache.org/jira/browse/FLINK-3179?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15205236#comment-15205236

ASF GitHub Bot commented on FLINK-3179:

Github user fhueske commented on a diff in the pull request:

    --- Diff: flink-optimizer/src/main/java/org/apache/flink/optimizer/operators/ReduceProperties.java
    @@ -61,6 +65,9 @@ public SingleInputPlanNode instantiate(Channel in, SingleInputNode node)
     		if (in.getShipStrategy() == ShipStrategyType.FORWARD ||
     				(node.getBroadcastConnections() != null && !node.getBroadcastConnections().isEmpty()))
    +			if(in.getSource().getOptimizerNode() instanceof PartitionNode) {
    +				LOG.warn("Consider adding an explicit CombinerFunction with groupCombine in front
of the partition operator");
    --- End diff --
    Can you extend the error message as follows?
    > Cannot automatically inject combiner for ReduceFunction. Please add an explicit combiner
with combineGroup() in front of the partition operator. 

> Combiner is not injected if Reduce or GroupReduce input is explicitly partitioned
> ---------------------------------------------------------------------------------
>                 Key: FLINK-3179
>                 URL: https://issues.apache.org/jira/browse/FLINK-3179
>             Project: Flink
>          Issue Type: Bug
>          Components: Optimizer
>    Affects Versions: 0.10.1
>            Reporter: Fabian Hueske
>            Assignee: ramkrishna.s.vasudevan
>            Priority: Critical
>             Fix For: 1.0.0, 0.10.2
> The optimizer does not inject a combiner if the input of a Reducer or GroupReducer is
explicitly partitioned as in the following example
> {code}
> DataSet<Tuple2<String,Integer>> words = ...
> DataSet<Tuple2<String,Integer>> counts = words
>   .partitionByHash(0)
>   .groupBy(0)
>   .sum(1);
> {code}
> Explicit partitioning can be useful to enforce partitioning on a subset of keys or to
use a different partitioning method (custom or range partitioning).
> This issue should be fixed by changing the {{instantiate()}} methods of the {{ReduceProperties}}
and {{GroupReduceWithCombineProperties}} classes such that a combine is injected in front
of a {{PartitionPlanNode}} if it is the input of a Reduce or GroupReduce operator. This should
only happen, if the Reducer is the only successor of the Partition operator.

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