cloud-fan commented on a change in pull request #25295: [SPARK-28560][SQL] 
Optimize shuffle reader to local shuffle reader when smj converted to bhj in 
adaptive execution
URL: https://github.com/apache/spark/pull/25295#discussion_r325529240
 
 

 ##########
 File path: 
sql/core/src/main/scala/org/apache/spark/sql/execution/adaptive/OptimizedLocalShuffleReader.scala
 ##########
 @@ -0,0 +1,124 @@
+/*
+ * 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.adaptive
+
+import org.apache.spark.rdd.RDD
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.expressions.Attribute
+import org.apache.spark.sql.catalyst.plans.physical.{Partitioning, 
UnknownPartitioning}
+import org.apache.spark.sql.catalyst.rules.Rule
+import org.apache.spark.sql.execution.{SparkPlan, UnaryExecNode}
+import org.apache.spark.sql.execution.exchange.{EnsureRequirements, 
ShuffleExchangeExec}
+import org.apache.spark.sql.execution.joins.{BroadcastHashJoinExec}
+import org.apache.spark.sql.internal.SQLConf
+
+case class OptimizedLocalShuffleReader(conf: SQLConf) extends Rule[SparkPlan] {
+
+  private def setIsLocalToFalse(shuffleStage: QueryStageExec): QueryStageExec 
= {
+    shuffleStage match {
+      case stage: ShuffleQueryStageExec =>
+        stage.isLocalShuffle = false
+      case ReusedQueryStageExec(_, stage: ShuffleQueryStageExec, _) =>
+        stage.isLocalShuffle = false
+    }
+    shuffleStage
+  }
+
+  private def revertLocalShuffleReader(newPlan: SparkPlan): SparkPlan = {
+    val revertPlan = newPlan.transformUp {
+      case localReader: LocalShuffleReaderExec
+        if (ShuffleQueryStageExec.isShuffleQueryStageExec(localReader.child)) 
=>
+        setIsLocalToFalse(localReader.child)
+    }
+    revertPlan
+  }
+
+  override def apply(plan: SparkPlan): SparkPlan = {
+    // Collect the `BroadcastHashJoinExec` nodes and if isEmpty directly 
return.
+    val bhjs = plan.collect {
+      case bhj: BroadcastHashJoinExec => bhj
+    }
+
+    if (!conf.optimizedLocalShuffleReaderEnabled || bhjs.isEmpty) {
+      return plan
+    }
+
+    // If the streamedPlan is `ShuffleQueryStageExec`, set the value of 
`isLocalShuffle` to true
+    bhjs.map {
+      case bhj: BroadcastHashJoinExec =>
+        bhj.children map {
+          case stage: ShuffleQueryStageExec => stage.isLocalShuffle = true
+          case ReusedQueryStageExec(_, stage: ShuffleQueryStageExec, _) =>
+            stage.isLocalShuffle = true
+          case plan: SparkPlan => plan
+        }
+    }
+
+    // Add the new `LocalShuffleReaderExec` node if the value of 
`isLocalShuffle` is true
+    val newPlan = plan.transformUp {
 
 Review comment:
   Why don't we traverse the tree once?
   ```
   def isShuffleStage(plan: SparkPlan): Boolean = plan match {
     case _: ShuffleQueryStageExec => true
     case ReusedQueryStageExec(_: ShuffleQueryStageExec) => true
     case _ => false
   }
   
   def canUseLocalShuffleReaderLeft(j: BroadcastHashJoinExec): Boolean = {
     j.buildSide = BuildLeft && isShuffleStage(j.left)
   }
   
   def canUseLocalShuffleReaderRight ...
   ...
   plan transformDown {
     case join: BroadcastHashJoinExec if canUseLocalShuffleReaderLeft(join) =>
       val localShuffleReader = ...
       join.copy(left = localShuffleReader)
   
     ...
   }
   ```

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