Github user yhuai commented on a diff in the pull request: https://github.com/apache/spark/pull/5208#discussion_r28200168 --- Diff: sql/core/src/main/scala/org/apache/spark/sql/execution/joins/SortMergeJoin.scala --- @@ -0,0 +1,163 @@ +/* + * 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.joins + +import org.apache.spark.annotation.DeveloperApi +import org.apache.spark.rdd.RDD +import org.apache.spark.sql.Row +import org.apache.spark.sql.catalyst.expressions._ +import org.apache.spark.sql.catalyst.plans._ +import org.apache.spark.sql.catalyst.plans.physical._ +import org.apache.spark.sql.execution.{BinaryNode, SparkPlan} +import org.apache.spark.util.collection.CompactBuffer + +/** + * :: DeveloperApi :: + * Performs an sort merge join of two child relations. + */ +@DeveloperApi +case class SortMergeJoin( + leftKeys: Seq[Expression], + rightKeys: Seq[Expression], + left: SparkPlan, + right: SparkPlan) extends BinaryNode { + + override def output: Seq[Attribute] = left.output ++ right.output + + override def outputPartitioning: Partitioning = left.outputPartitioning + + override def requiredChildDistribution: Seq[Distribution] = + ClusteredDistribution(leftKeys) :: ClusteredDistribution(rightKeys) :: Nil + + private val orders: Seq[SortOrder] = leftKeys.zipWithIndex.map { + case(expr, index) => SortOrder(BoundReference(index, expr.dataType, expr.nullable), Ascending) + } + private val ordering: RowOrdering = new RowOrdering(orders, left.output) + + private def requiredOrders(keys: Seq[Expression], side: SparkPlan): Seq[SortOrder] = keys.map { + k => SortOrder(BindReferences.bindReference(k, side.output, allowFailures = false), Ascending) + } + + override def outputOrdering: Seq[SortOrder] = requiredOrders(leftKeys, left) + + override def requiredInPartitionOrdering: Seq[Seq[SortOrder]] = + requiredOrders(leftKeys, left) :: requiredOrders(rightKeys, right) :: Nil + + @transient protected lazy val leftKeyGenerator = newProjection(leftKeys, left.output) + @transient protected lazy val rightKeyGenerator = newProjection(rightKeys, right.output) + + override def execute(): RDD[Row] = { + val leftResults = left.execute().map(_.copy()) + val rightResults = right.execute().map(_.copy()) + + leftResults.zipPartitions(rightResults) { (leftIter, rightIter) => + new Iterator[Row] { + // Mutable per row objects. + private[this] val joinRow = new JoinedRow5 + private[this] var leftElement: Row = _ + private[this] var rightElement: Row = _ + private[this] var leftKey: Row = _ + private[this] var rightKey: Row = _ + private[this] var rightMatches: CompactBuffer[Row] = _ + private[this] var rightPosition: Int = -1 + private[this] var stop: Boolean = false + private[this] var matchKey: Row = _ + + override final def hasNext: Boolean = nextMatchingPair() + + override final def next(): Row = { + if (hasNext) { + val joinedRow = joinRow(leftElement, rightMatches(rightPosition)) + rightPosition += 1 + if (rightPosition >= rightMatches.size) { + rightPosition = 0 + fetchLeft() + if (leftElement == null || ordering.compare(leftKey, matchKey) != 0) { + stop = false + rightMatches = null + } + } + joinedRow + } else { + // according to Scala doc, this is undefined + null + } + } + + private def fetchLeft() = { + if (leftIter.hasNext) { + leftElement = leftIter.next() + leftKey = leftKeyGenerator(leftElement) + } else { + leftElement = null + } + } + + private def fetchRight() = { + if (rightIter.hasNext) { + rightElement = rightIter.next() + rightKey = rightKeyGenerator(rightElement) + } else { + rightElement = null + } + } + + private def initialize() = { + fetchLeft() + fetchRight() + } + // initialize iterator + initialize() + + /** + * Searches the left/right iterator for the next rows that matches. + * + * @return true if the search is successful, and false if the left/right iterator runs out + * of tuples. + */ + private def nextMatchingPair(): Boolean = { --- End diff -- I think we need more comments to explain what this function does.
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