Github user massie commented on a diff in the pull request:
https://github.com/apache/spark/pull/7403#discussion_r38468044
--- Diff: core/src/main/scala/org/apache/spark/rdd/PairRDDFunctions.scala
---
@@ -565,12 +603,25 @@ class PairRDDFunctions[K, V](self: RDD[(K, V)])
}
/**
- * Simplified version of combineByKey that hash-partitions the resulting
RDD using the
- * existing partitioner/parallelism level.
+ * This method is here for backward compatibility. It
+ * does not provide combiner classtag information to
+ * the shuffle.
+ *
+ * @see [[combineByKeyWithClassTag]]
*/
def combineByKey[C](createCombiner: V => C, mergeValue: (C, V) => C,
mergeCombiners: (C, C) => C)
- : RDD[(K, C)] = self.withScope {
- combineByKey(createCombiner, mergeValue, mergeCombiners,
defaultPartitioner(self))
+ : RDD[(K, C)] = {
+ combineByKeyWithClassTag(createCombiner, mergeValue,
mergeCombiners)(null)
+ }
+
+ /**
+ * Simplified version of combineByKeyWithClassTag that hash-partitions
the resulting RDD using the
+ * existing partitioner/parallelism level.
+ */
+ def combineByKeyWithClassTag[C](createCombiner: V => C, mergeValue: (C,
V) => C,
--- End diff --
Adding a `ClassTag` to the original `combineByKey` methods, would change
the method signature break compatibility. The `PairRDDFunctions` is not marked
a `@DeveloperApi`, so that break is not allowed.
To work around this, there are now three new methods that exactly mirror
the `combineByKey` methods but have a `*withClassTag` suffix on their name and,
of course, a `ClassTag`. We want developers to use the
`combineByKeyWithClassTag` methods need to be `public` just as the original
`combineByKey` methods are.
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