[SPARK-32820][SQL] Remove redundant shuffle exchanges inserted by EnsureRequirements

sql/core/src/main/scala/org/apache/spark/sql/execution/QueryExecution.scala

@@ -37,7 +37,7 @@ import org.apache.spark.sql.catalyst.util.truncatedString
 import org.apache.spark.sql.execution.adaptive.{AdaptiveExecutionContext, InsertAdaptiveSparkPlan}
 import org.apache.spark.sql.execution.bucketing.{CoalesceBucketsInJoin, DisableUnnecessaryBucketedScan}
 import org.apache.spark.sql.execution.dynamicpruning.PlanDynamicPruningFilters
-import org.apache.spark.sql.execution.exchange.{EnsureRequirements, ReuseExchange}
+import org.apache.spark.sql.execution.exchange.{EnsureRequirements, PruneShuffle, ReuseExchange}
 import org.apache.spark.sql.execution.streaming.{IncrementalExecution, OffsetSeqMetadata}
 import org.apache.spark.sql.internal.SQLConf
 import org.apache.spark.sql.streaming.OutputMode
@@ -344,6 +344,7 @@ object QueryExecution {
       PlanSubqueries,
       RemoveRedundantProjects,
       EnsureRequirements,
+      PruneShuffle(),
       DisableUnnecessaryBucketedScan,
       ApplyColumnarRulesAndInsertTransitions(sparkSession.sessionState.columnarRules),
       CollapseCodegenStages(),

sql/core/src/main/scala/org/apache/spark/sql/execution/exchange/PruneShuffle.scala

@@ -0,0 +1,43 @@
+/*
+ * 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.sql.execution.exchange
+
+import org.apache.spark.sql.catalyst.rules.Rule
+import org.apache.spark.sql.execution.SparkPlan
+
+/**
+ * Removes unnecessary shuffles. A shuffle can be introduced by [[Rule]]s for
+ * [[SparkPlan]]s, such as [[EnsureRequirements]] and then, its immediate child of
+ * another shuffle should be unnecessary.
+ */
+case class PruneShuffle() extends Rule[SparkPlan] {
+
+  override def apply(plan: SparkPlan): SparkPlan = plan.transform {
+    case op @ ShuffleExchangeExec(_, child: ShuffleExchangeExec, _) =>
+      op.withNewChildren(Seq(pruneShuffle(child)))
+    case other => other
+  }
+
+  private def pruneShuffle(plan: SparkPlan): SparkPlan = {
+    plan match {
+      case shuffle: ShuffleExchangeExec =>
+        pruneShuffle(shuffle.child)
+      case other => other
+    }
+  }
+}

sql/core/src/test/scala/org/apache/spark/sql/execution/PlannerSuite.scala

@@ -28,7 +28,7 @@ import org.apache.spark.sql.execution.adaptive.{AdaptiveSparkPlanHelper, Disable
 import org.apache.spark.sql.execution.aggregate.{HashAggregateExec, ObjectHashAggregateExec, SortAggregateExec}
 import org.apache.spark.sql.execution.columnar.{InMemoryRelation, InMemoryTableScanExec}
 import org.apache.spark.sql.execution.exchange.{EnsureRequirements, ReusedExchangeExec, ReuseExchange, ShuffleExchangeExec}
-import org.apache.spark.sql.execution.joins.{BroadcastHashJoinExec, SortMergeJoinExec}
+import org.apache.spark.sql.execution.joins.{BroadcastHashJoinExec, ShuffledJoin, SortMergeJoinExec}
 import org.apache.spark.sql.functions._
 import org.apache.spark.sql.internal.SQLConf
 import org.apache.spark.sql.test.SharedSparkSession
@@ -1001,6 +1001,45 @@ class PlannerSuite extends SharedSparkSession with AdaptiveSparkPlanHelper {
     val numPartitions = range.rdd.getNumPartitions
     assert(numPartitions == 0)
   }
+
+  test("SPARK-32820: Remove redundant shuffle exchange") {
+    withSQLConf(SQLConf.AUTO_BROADCASTJOIN_THRESHOLD.key -> "0") {
+      withSQLConf(SQLConf.SHUFFLE_PARTITIONS.key -> "200") {
+        val ordered = spark.range(1, 100).repartitionByRange(10, $"id".desc).orderBy($"id")
+        val orderedPlan = ordered.queryExecution.executedPlan.collectFirst {
+          case sort: SortExec => sort
+        }.get
+        val exchangeInOrdered = orderedPlan.collectFirst {
+          case shuffle: ShuffleExchangeExec => shuffle
+        }.get
+
+        val partitioning = exchangeInOrdered.outputPartitioning
+        assert(partitioning.numPartitions == 200)
+        assert(partitioning.satisfies(orderedPlan.requiredChildDistribution.head))
+
+        val left = Seq(1, 2, 3).toDF.repartition(10)
+        val right = Seq(1, 2, 3).toDF.repartition(30, $"value")
+        val joined = left.join(right, left("value") + 1 === right("value") + 2)
+        val joinedPlan = joined.queryExecution.executedPlan.collectFirst {
+          case shuffledJoin: ShuffledJoin => shuffledJoin
+        }.get
+        val leftExchangesInJoined = joinedPlan.children(0).collectFirst {
+          case shuffle: ShuffleExchangeExec => shuffle
+        }.get
+        val rightExchangeInJoined = joinedPlan.children(1).collectFirst {
+          case shuffle: ShuffleExchangeExec => shuffle
+        }.get
+
+        val leftPartitioning = leftExchangesInJoined.outputPartitioning
+        assert(leftPartitioning.numPartitions == 200)
+        assert(leftPartitioning.satisfies(joinedPlan.requiredChildDistribution(0)))
+
+        val rightPartitioning = rightExchangeInJoined.outputPartitioning
+        assert(rightPartitioning.numPartitions == 200)
+        assert(rightPartitioning.satisfies(joinedPlan.requiredChildDistribution(1)))
+      }
+    }
+  }
 }
 
 // Used for unit-testing EnsureRequirements