maropu commented on a change in pull request #23964: [SPARK-26975][SQL] Support nested-column pruning over limit/sample/repartition URL: https://github.com/apache/spark/pull/23964#discussion_r263275860
########## File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/NestedColumnAliasing.scala ########## @@ -0,0 +1,193 @@ +/* + * 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 scala.collection.mutable.ArrayBuffer + +import org.apache.spark.sql.catalyst.expressions._ +import org.apache.spark.sql.catalyst.plans.QueryPlan +import org.apache.spark.sql.catalyst.plans.logical._ +import org.apache.spark.sql.types._ + +/** + * This aims to handle nested column aliasing pattern inside `ColumnPruning` optimizer rule. + * If a project or its child references to nested fields, and not all the fields + * in a nested attribute are used, we can substitute the by alias attributes; then a project + * of the nested fields as aliases on the children of the child will be created. + */ +object NestedColumnAliasing { + + def unapply(plan: LogicalPlan) + : Option[(Map[GetStructField, Alias], Map[ExprId, Seq[Alias]])] = plan match { + case Project(_, child) if canProjectPushThrough(child) => + getAliasSubMap(plan, child) + case _ => None + } + + /** + * Replace nested columns to prune unused nested columns later. + */ + def replaceToAliases( + plan: LogicalPlan, + nestedFieldToAlias: Map[GetStructField, Alias], + attrToAliases: Map[ExprId, Seq[Alias]]): LogicalPlan = plan match { + case Project(projectList, g @ GlobalLimit(_, grandChild: LocalLimit)) => + Project( + getNewProjectList(projectList, nestedFieldToAlias), + g.copy(child = replaceChildrenWithAliases(grandChild, attrToAliases))) + + case Project(projectList, child) => + Project( + getNewProjectList(projectList, nestedFieldToAlias), + replaceChildrenWithAliases(child, attrToAliases)) + } + + /** + * Return a replaced project list. + */ + private def getNewProjectList( + projectList: Seq[NamedExpression], + nestedFieldToAlias: Map[GetStructField, Alias]): Seq[NamedExpression] = { + projectList.map(_.transform { + case f: GetStructField if nestedFieldToAlias.contains(f) => + nestedFieldToAlias(f).toAttribute + }.asInstanceOf[NamedExpression]) + } + + /** + * Return a plan with new childen replaced with aliases. + */ + private def replaceChildrenWithAliases( + plan: LogicalPlan, + attrToAliases: Map[ExprId, Seq[Alias]]): LogicalPlan = { + plan.withNewChildren(plan.children.map { plan => + Project(plan.output.flatMap(a => attrToAliases.getOrElse(a.exprId, Seq(a))), plan) + }) + } + + /** + * Returns true for those operators that project can be pushed through. + */ + private def canProjectPushThrough(plan: LogicalPlan) = plan match { + case _: GlobalLimit => true + case _: LocalLimit => true Review comment: Can you add a test case for a plan having `LocalLimit` w/o `GlobalLimit`? ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected] With regards, Apache Git Services --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
