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Subject [GitHub] [spark] maryannxue commented on a change in pull request #25703: [SPARK-29002][SQL] Avoid changing SMJ to BHJ if the build side has a high ratio of empty partitions
Date Fri, 06 Sep 2019 02:21:31 GMT
maryannxue commented on a change in pull request #25703: [SPARK-29002][SQL] Avoid changing
SMJ to BHJ if the build side has a high ratio of empty partitions
URL: https://github.com/apache/spark/pull/25703#discussion_r321553775
 
 

 ##########
 File path: sql/core/src/main/scala/org/apache/spark/sql/execution/adaptive/DemoteBroadcastHashJoin.scala
 ##########
 @@ -0,0 +1,60 @@
+/*
+ * 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.MapOutputStatistics
+import org.apache.spark.sql.catalyst.plans.logical.{HintInfo, Join, LogicalPlan, NO_BROADCAST_HASH}
+import org.apache.spark.sql.catalyst.rules.Rule
+import org.apache.spark.sql.internal.SQLConf
+
+/**
+ * This optimization rule detects a join child that has a high ratio of empty partitions
and
+ * adds a no-broadcast-hash-join hint to avoid it being broadcast.
+ */
+case class DemoteBroadcastHashJoin(conf: SQLConf) extends Rule[LogicalPlan] {
+
+  private def shouldDemote(plan: LogicalPlan): Boolean = plan match {
+    case LogicalQueryStage(_, stage: QueryStageExec)
+      if stage.resultOption.isDefined &&
+        stage.resultOption.get.isInstanceOf[MapOutputStatistics] =>
+      val mapOutputStatistics = stage.resultOption.get.asInstanceOf[MapOutputStatistics]
+      val partitionCnt = mapOutputStatistics.bytesByPartitionId.length
+      val nonZeroCnt = mapOutputStatistics.bytesByPartitionId.count(_ > 0)
+      partitionCnt > 0 && nonZeroCnt > 0 &&
+        (nonZeroCnt * 1.0 / partitionCnt) < conf.nonEmptyPartitionRatioForBroadcastJoin
+    case _ => false
+  }
+
+  def apply(plan: LogicalPlan): LogicalPlan = plan.transformDown {
+    case j @ Join(left, right, _, _, hint) =>
+      var newHint = hint
 
 Review comment:
   You might have misunderstood the logic here. Left and right aren't exclusive here, so it's
not an "if-else" logic. 

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