Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/8844#discussion_r40027112
--- Diff:
core/src/test/scala/org/apache/spark/scheduler/CustomShuffledRDD.scala ---
@@ -0,0 +1,111 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.scheduler
+
+import java.util.Arrays
+
+import org.apache.spark._
+import org.apache.spark.rdd.RDD
+
+/**
+ * A Partitioner that might group together one or more partitions from the
parent.
+ *
+ * @param parent a parent partitioner
+ * @param partitionStartIndices indices of partitions in parent that
should create new partitions
+ * in child (this should be an array of increasing partition IDs). For
example, if we have a
+ * parent with 5 partitions, and partitionStartIndices is [0, 2, 4], we
get three output
+ * partitions, corresponding to partition ranges [0, 1], [2, 3] and [4]
of the parent partitioner.
+ */
+class CoalescedPartitioner(val parent: Partitioner, val
partitionStartIndices: Array[Int])
+ extends Partitioner {
+
+ @transient private lazy val parentPartitionMapping: Array[Int] = {
+ val n = parent.numPartitions
+ val result = new Array[Int](n)
+ for (i <- 0 until partitionStartIndices.length) {
+ val start = partitionStartIndices(i)
+ val end = if (i < partitionStartIndices.length - 1)
partitionStartIndices(i + 1) else n
+ for (j <- start until end) {
+ result(j) = i
+ }
+ }
+ result
+ }
+
+ override def numPartitions: Int = partitionStartIndices.size
+
+ override def getPartition(key: Any): Int = {
+ parentPartitionMapping(parent.getPartition(key))
+ }
+
+ override def equals(other: Any): Boolean = other match {
+ case c: CoalescedPartitioner =>
+ c.parent == parent && Arrays.equals(c.partitionStartIndices,
partitionStartIndices)
+ case _ =>
+ false
+ }
+}
+
+private[spark] class CustomShuffledRDDPartition(
+ val index: Int, val startIndexInParent: Int, val endIndexInParent: Int)
+ extends Partition {
+
+ override def hashCode(): Int = index
+}
+
+/**
+ * A special ShuffledRDD that supports a ShuffleDependency object from
outside and launching reduce
+ * tasks that read multiple map output partitions.
+ */
+class CustomShuffledRDD[K, V, C](
--- End diff --
Same comment here: should this be `private[spark]`
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