Github user fhueske commented on a diff in the pull request: https://github.com/apache/flink/pull/1553#discussion_r53152668 --- Diff: flink-optimizer/src/main/java/org/apache/flink/optimizer/operators/GroupReduceWithCombineProperties.java --- @@ -87,19 +92,39 @@ public DriverStrategy getStrategy() { return DriverStrategy.SORTED_GROUP_REDUCE; } - @Override public SingleInputPlanNode instantiate(Channel in, SingleInputNode node) { if (in.getShipStrategy() == ShipStrategyType.FORWARD) { // adjust a sort (changes grouping, so it must be for this driver to combining sort - if (in.getLocalStrategy() == LocalStrategy.SORT) { - if (!in.getLocalStrategyKeys().isValidUnorderedPrefix(this.keys)) { - throw new RuntimeException("Bug: Inconsistent sort for group strategy."); + if(in.getSource().getOptimizerNode() instanceof PartitionNode) { + // Inject a combiner before the partition node + Channel toCombiner = new Channel(in.getSource()); + toCombiner.setShipStrategy(ShipStrategyType.FORWARD, DataExchangeMode.PIPELINED); + GroupReduceNode combinerNode = ((GroupReduceNode) node).getCombinerUtilityNode(); + combinerNode.setParallelism(in.getSource().getParallelism()); + if(toCombiner.getSource().getInputs().iterator().hasNext()) { + Channel source = toCombiner.getSource().getInputs().iterator().next(); + // A combiner plan node is created with the map as the input + SingleInputPlanNode combiner = new SingleInputPlanNode(combinerNode, "Combine("+node.getOperator() --- End diff -- We should use a new channel here instead of the existing `source` channel. In the other branch, the new channel is called `toCombiner`.
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