[SPARK-2213][SQL] Sort Merge Join #3173
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| /* | ||
| * 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. | ||
| */ | ||
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| package org.apache.spark.sql.execution.joins | ||
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| import org.apache.spark.annotation.DeveloperApi | ||
| import org.apache.spark.sql.catalyst.expressions._ | ||
| import org.apache.spark.sql.catalyst.plans.physical.{ClusteredOrderedDistribution, Partitioning} | ||
| import org.apache.spark.sql.execution.{BinaryNode, SparkPlan} | ||
| import org.apache.spark.util.collection.CompactBuffer | ||
| /* : Developer Api : | ||
| * Performs sort-merge join of two child relations by first shuffling the data using the join | ||
| * keys. Also, when shuffling the data, sort the data by join keys. | ||
| */ | ||
| @DeveloperApi | ||
| case class MergeJoin( | ||
| leftKeys: Seq[Expression], | ||
| rightKeys: Seq[Expression], | ||
| left: SparkPlan, | ||
| right: SparkPlan | ||
| ) extends BinaryNode { | ||
| // Implementation: the tricky part is handling duplicate join keys. | ||
| // To handle duplicate keys, we use a buffer to store all matching elements | ||
| // in right iterator for a certain join key. The buffer is used for | ||
| // generating join tuples when the join key of the next left element is | ||
| // the same as the current join key. | ||
| // TODO: add outer join support | ||
| override def outputPartitioning: Partitioning = left.outputPartitioning | ||
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| override def output = left.output ++ right.output | ||
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| private val orders = leftKeys.map(s => SortOrder(s, Ascending)) | ||
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| override def requiredChildDistribution = | ||
| ClusteredOrderedDistribution(leftKeys) :: ClusteredOrderedDistribution(rightKeys) :: Nil | ||
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| @transient protected lazy val leftKeyGenerator: Projection = | ||
| newProjection(leftKeys, left.output) | ||
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| @transient protected lazy val rightKeyGenerator: Projection = | ||
| newProjection(rightKeys, right.output) | ||
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| private val ordering = new RowOrdering(orders, left.output) | ||
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| override def execute() = { | ||
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| left.execute().zipPartitions(right.execute()) { (leftIter, rightIter) => | ||
| new Iterator[Row] { | ||
| private[this] val joinRow = new JoinedRow2 | ||
| private[this] var leftElement:Row = _ | ||
| private[this] var rightElement:Row = _ | ||
| private[this] var leftKey:Row = _ | ||
| private[this] var rightKey:Row = _ | ||
| private[this] var buffer:CompactBuffer[Row] = _ | ||
| private[this] var index = -1 | ||
| private[this] var last = false | ||
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| // initialize iterator | ||
| private def initialize() = { | ||
| if (leftIter.hasNext) { | ||
| leftElement = leftIter.next() | ||
| leftKey = leftKeyGenerator(leftElement) | ||
| } else { | ||
| last = true | ||
| } | ||
| if (rightIter.hasNext) { | ||
| rightElement = rightIter.next() | ||
| rightKey = rightKeyGenerator(rightElement) | ||
| } else { | ||
| last = true | ||
| } | ||
| } | ||
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| initialize() | ||
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| override final def hasNext: Boolean = { | ||
| // Two cases that hasNext returns true | ||
| // 1. We are iterating the buffer | ||
| // 2. We can find tuple pairs that have matching join key | ||
| // | ||
| // hasNext is stateless as nextMatchingPair() is called when | ||
| // index == -1 and will set index to 0 when nextMatchingPair() | ||
| // returns true. Muptiple calls to hasNext modifies iterator | ||
| // state at most once. | ||
| if (index != -1) return true | ||
| if (last) return false | ||
| return nextMatchingPair() | ||
| } | ||
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| override final def next(): Row = { | ||
| if (index == -1) { | ||
| // We need this becasue the client of the join iterator may | ||
| // call next() without calling hasNext | ||
| if (!hasNext) return null | ||
| } | ||
| val joinedRow = joinRow(leftElement, buffer(index)) | ||
| index += 1 | ||
| if (index == buffer.size) { | ||
| // finished iterating the buffer, fetch | ||
| // next element from left iterator | ||
| if (leftIter.hasNext) { | ||
| // fetch next element | ||
| val leftElem = leftElement | ||
| val leftK = leftKeyGenerator(leftElem) | ||
| leftElement = leftIter.next() | ||
| leftKey = leftKeyGenerator(leftElement) | ||
| if (ordering.compare(leftKey,leftK) == 0) { | ||
| // need to go over the buffer again | ||
| // as we have the same join key for | ||
| // next left element | ||
| index = 0 | ||
| } else { | ||
| // need to find a matching element from | ||
| // right iterator | ||
| index = -1 | ||
| } | ||
| } else { | ||
| // no next left element, we are done | ||
| index = -1 | ||
| last = true | ||
| } | ||
| } | ||
| joinedRow | ||
| } | ||
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| // find the next pair of left/right tuples that have a | ||
| // matching join key | ||
| private def nextMatchingPair(): Boolean = { | ||
| while (ordering.compare(leftKey, rightKey) != 0) { | ||
| if (ordering.compare(leftKey, rightKey) < 0) { | ||
| if (leftIter.hasNext) { | ||
| leftElement = leftIter.next() | ||
| leftKey = leftKeyGenerator(leftElement) | ||
| } else { | ||
| last = true | ||
| return false | ||
| } | ||
| } else { | ||
| if (rightIter.hasNext) { | ||
| rightElement = rightIter.next() | ||
| rightKey = rightKeyGenerator(rightElement) | ||
| } else { | ||
| last = true | ||
| return false | ||
| } | ||
| } | ||
| } | ||
| // outer == inner | ||
| index = 0 | ||
| buffer = null | ||
| buffer = new CompactBuffer[Row]() | ||
| buffer += rightElement | ||
| val rightElem = rightElement | ||
| val rightK = rightKeyGenerator(rightElem) | ||
| while(rightIter.hasNext) { | ||
| rightElement = rightIter.next() | ||
| rightKey = rightKeyGenerator(rightElement) | ||
| if (ordering.compare(rightKey,rightK) == 0) { | ||
| buffer += rightElement | ||
| } else { | ||
| return true | ||
| } | ||
| } | ||
| true | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } |
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