improvement according to Michael

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/patterns.scala

@@ -119,6 +119,11 @@ object HashFilteredJoin extends Logging with PredicateHelper {
     case FilteredOperation(predicates, join @ Join(left, right, Inner, condition)) =>
       logger.debug(s"Considering hash inner join on: ${predicates ++ condition}")
       splitPredicates(predicates ++ condition, join)
+    // All predicates can be evaluated for left semi join (those that are in the WHERE
+    // clause can only from left table, so they can all be pushed down.)
+    case FilteredOperation(predicates, join @ Join(left, right, LeftSemi, condition)) =>
+      logger.debug(s"Considering hash left semi join on: ${predicates ++ condition}")
+      splitPredicates(predicates ++ condition, join)
     case join @ Join(left, right, joinType, condition) =>
       logger.debug(s"Considering hash join on: $condition")
       splitPredicates(condition.toSeq, join)

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

@@ -30,11 +30,11 @@ private[sql] abstract class SparkStrategies extends QueryPlanner[SparkPlan] {
 
   object LeftSemiJoin extends Strategy with PredicateHelper {
     def apply(plan: LogicalPlan): Seq[SparkPlan] = plan match {
-      // Find leftsemi joins where at least some predicates can be evaluated by matching hash keys
-      // using the HashFilteredJoin pattern.
+      // Find left semi joins where at least some predicates can be evaluated by matching hash
+      // keys using the HashFilteredJoin pattern.
       case HashFilteredJoin(LeftSemi, leftKeys, rightKeys, condition, left, right) =>
         val semiJoin = execution.LeftSemiJoinHash(
-          leftKeys, rightKeys, BuildRight, planLater(left), planLater(right))
+          leftKeys, rightKeys, planLater(left), planLater(right))
         condition.map(Filter(_, semiJoin)).getOrElse(semiJoin) :: Nil
       // no predicate can be evaluated by matching hash keys
       case logical.Join(left, right, LeftSemi, condition) =>

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

@@ -142,29 +142,23 @@ case class HashJoin(
 
 /**
  * :: DeveloperApi ::
+ * Build the right table's join keys into a HashSet, and iteratively go through the left
+ * table, to find the if join keys are in the Hash set.
  */
 @DeveloperApi
 case class LeftSemiJoinHash(
-                     leftKeys: Seq[Expression],
-                     rightKeys: Seq[Expression],
-                     buildSide: BuildSide,
-                     left: SparkPlan,
-                     right: SparkPlan) extends BinaryNode {
+    leftKeys: Seq[Expression],
+    rightKeys: Seq[Expression],
+    left: SparkPlan,
+    right: SparkPlan) extends BinaryNode {
 
   override def outputPartitioning: Partitioning = left.outputPartitioning
 
   override def requiredChildDistribution =
     ClusteredDistribution(leftKeys) :: ClusteredDistribution(rightKeys) :: Nil
 
-  val (buildPlan, streamedPlan) = buildSide match {
-    case BuildLeft => (left, right)
-    case BuildRight => (right, left)
-  }
-
-  val (buildKeys, streamedKeys) = buildSide match {
-    case BuildLeft => (leftKeys, rightKeys)
-    case BuildRight => (rightKeys, leftKeys)
-  }
+  val (buildPlan, streamedPlan) = (right, left)
+  val (buildKeys, streamedKeys) = (rightKeys, leftKeys)
 
   def output = left.output
 
@@ -175,24 +169,18 @@ case class LeftSemiJoinHash(
   def execute() = {
 
     buildPlan.execute().zipPartitions(streamedPlan.execute()) { (buildIter, streamIter) =>
-    // TODO: Use Spark's HashMap implementation.
-      val hashTable = new java.util.HashMap[Row, ArrayBuffer[Row]]()
+      val hashTable = new java.util.HashSet[Row]()
       var currentRow: Row = null
 
-      // Create a mapping of buildKeys -> rows
+      // Create a Hash set of buildKeys
       while (buildIter.hasNext) {
         currentRow = buildIter.next()
         val rowKey = buildSideKeyGenerator(currentRow)
         if(!rowKey.anyNull) {
-          val existingMatchList = hashTable.get(rowKey)
-          val matchList = if (existingMatchList == null) {
-            val newMatchList = new ArrayBuffer[Row]()
-            hashTable.put(rowKey, newMatchList)
-            newMatchList
-          } else {
-            existingMatchList
+          val keyExists = hashTable.contains(rowKey)
+          if (!keyExists) {
+            hashTable.add(rowKey)
           }
-          matchList += currentRow.copy()
         }
       }
 
@@ -220,7 +208,7 @@ case class LeftSemiJoinHash(
           while (!currentHashMatched && streamIter.hasNext) {
             currentStreamedRow = streamIter.next()
             if (!joinKeys(currentStreamedRow).anyNull) {
-              currentHashMatched = true
+              currentHashMatched = hashTable.contains(joinKeys.currentValue)
             }
           }
           currentHashMatched
@@ -232,6 +220,8 @@ case class LeftSemiJoinHash(
 
 /**
  * :: DeveloperApi ::
+ * Using BroadcastNestedLoopJoin to calculate left semi join result when there's no join keys
+ * for hash join.
  */
 @DeveloperApi
 case class LeftSemiJoinBNL(
@@ -261,26 +251,23 @@ case class LeftSemiJoinBNL(
   def execute() = {
     val broadcastedRelation = sc.broadcast(broadcast.execute().map(_.copy()).collect().toIndexedSeq)
 
-    val streamedPlusMatches = streamed.execute().mapPartitions { streamedIter =>
+    streamed.execute().mapPartitions { streamedIter =>
       val joinedRow = new JoinedRow
 
       streamedIter.filter(streamedRow => {
         var i = 0
         var matched = false
 
         while (i < broadcastedRelation.value.size && !matched) {
-          // TODO: One bitset per partition instead of per row.
           val broadcastedRow = broadcastedRelation.value(i)
           if (boundCondition(joinedRow(streamedRow, broadcastedRow))) {
             matched = true
           }
           i += 1
         }
         matched
-      }).map(streamedRow => (streamedRow, null))
+      })
     }
-
-    streamedPlusMatches.map(_._1)
   }
 }