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https://issues.apache.org/jira/browse/FLINK-3179?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15205236#comment-15205236
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ASF GitHub Bot commented on FLINK-3179:
---------------------------------------
Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/1822#discussion_r56904841
--- 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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