Github user aljoscha commented on a diff in the pull request:
https://github.com/apache/flink/pull/1589#discussion_r51929032
--- 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 --
Ah, I just copied it. It's like this in all the data shipping methods. I
think we could also just get rid of this sentence, it does not really add
explanation.
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