Github user uce commented on a diff in the pull request: https://github.com/apache/flink/pull/1589#discussion_r51929574 --- Diff: flink-streaming-java/src/main/java/org/apache/flink/streaming/api/datastream/DataStream.java --- @@ -443,6 +443,35 @@ public ExecutionConfig getExecutionConfig() { } /** + * Sets the partitioning of the {@link DataStream} so that the output elements + * are distributed evenly to a subset of instances of the next operation in a round-robin + * fashion. + * + * <p>The subset of downstream operations to which the upstream operation sends + * elements depends on the degree of parallelism of both the upstream and downstream operation. + * For example, if the upstream operation has parallelism 2 and the downstream operation + * has parallelism 4, then one upstream operation would distribute elements to two + * downstream operations while the other upstream operation would distribute to the other + * two downstream operations. If, on the other hand, the downstream operation has parallelism + * 2 while the upstream operation has parallelism 4 then two upstream operations will + * distribute to one downstream operation while the other two upstream operations will + * distribute to the other downstream operations. + * + * <p>In cases where the different parallelisms are not multiples of each other one or several + * downstream operations will have a differing number of inputs from upstream operations. + * + * <p> --- End diff -- Fine with me :) We would have to make sure that the other docs also mention that it only affects the next operation.
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