spark LimitPushDownThroughWindow 源码
spark LimitPushDownThroughWindow 代码
文件路径:/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/LimitPushDownThroughWindow.scala
/*
* 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.catalyst.optimizer
import org.apache.spark.sql.catalyst.expressions.{Alias, CurrentRow, DenseRank, IntegerLiteral, NamedExpression, Rank, RowFrame, RowNumber, SpecifiedWindowFrame, UnboundedPreceding, WindowExpression, WindowSpecDefinition}
import org.apache.spark.sql.catalyst.plans.logical.{Limit, LocalLimit, LogicalPlan, Project, Sort, Window}
import org.apache.spark.sql.catalyst.rules.Rule
import org.apache.spark.sql.catalyst.trees.TreePattern.{LIMIT, WINDOW}
/**
* Pushes down [[LocalLimit]] beneath WINDOW. This rule optimizes the following case:
* {{{
* SELECT *, ROW_NUMBER() OVER(ORDER BY a) AS rn FROM Tab1 LIMIT 5 ==>
* SELECT *, ROW_NUMBER() OVER(ORDER BY a) AS rn FROM (SELECT * FROM Tab1 ORDER BY a LIMIT 5) t
* }}}
*/
object LimitPushDownThroughWindow extends Rule[LogicalPlan] {
// The window frame of RankLike and RowNumberLike can only be UNBOUNDED PRECEDING to CURRENT ROW.
private def supportsPushdownThroughWindow(
windowExpressions: Seq[NamedExpression]): Boolean = windowExpressions.forall {
case Alias(WindowExpression(_: Rank | _: DenseRank | _: RowNumber, WindowSpecDefinition(Nil, _,
SpecifiedWindowFrame(RowFrame, UnboundedPreceding, CurrentRow))), _) => true
case _ => false
}
def apply(plan: LogicalPlan): LogicalPlan = plan.transformWithPruning(
_.containsAllPatterns(WINDOW, LIMIT), ruleId) {
// Adding an extra Limit below WINDOW when the partitionSpec of all window functions is empty.
case LocalLimit(limitExpr @ IntegerLiteral(limit),
window @ Window(windowExpressions, Nil, orderSpec, child))
if supportsPushdownThroughWindow(windowExpressions) && child.maxRows.forall(_ > limit) &&
limit < conf.topKSortFallbackThreshold =>
// Sort is needed here because we need global sort.
window.copy(child = Limit(limitExpr, Sort(orderSpec, true, child)))
// There is a Project between LocalLimit and Window if they do not have the same output.
case LocalLimit(limitExpr @ IntegerLiteral(limit), project @ Project(_,
window @ Window(windowExpressions, Nil, orderSpec, child)))
if supportsPushdownThroughWindow(windowExpressions) && child.maxRows.forall(_ > limit) &&
limit < conf.topKSortFallbackThreshold =>
// Sort is needed here because we need global sort.
project.copy(child = window.copy(child = Limit(limitExpr, Sort(orderSpec, true, child))))
}
}
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