Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/11865#discussion_r60138955
--- Diff: core/src/main/scala/org/apache/spark/rdd/CoalescedRDD.scala ---
@@ -121,6 +121,21 @@ private[spark] class CoalescedRDD[T: ClassTag](
}
/**
+ * A PartitionCoalescer defines how to coalesce the partitions of a given
RDD.
+ */
+trait PartitionCoalescer {
+
+ /**
+ * Coalesce the partitions of the given RDD.
+ *
+ * @param maxPartitions the maximum number of partitions to have after
coalescing
+ * @param parent the parent RDD whose partitions to coalesce
+ * @return a grouping of the parent RDD's partitions
+ */
+ def coalesce(maxPartitions: Int, parent: RDD[_]): Array[PartitionGroup]
--- End diff --
can you document a little bit more the semantics of the return?
i think it's better to say explicitly each element in the returned array
represents one rdd partition post-coalescing.
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