dongjoon-hyun commented on a change in pull request #23359: [SPARK-26416] [SQL] Refactor `ColumnPruning` from `Optimizer.scala` to `ColumnPruning.scala` URL: https://github.com/apache/spark/pull/23359#discussion_r243457545
########## File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/ColumnPruning.scala ########## @@ -0,0 +1,139 @@ +/* + * 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.AttributeSet +import org.apache.spark.sql.catalyst.plans.LeftExistence +import org.apache.spark.sql.catalyst.plans.logical._ +import org.apache.spark.sql.catalyst.rules.Rule + +/** + * Attempts to eliminate the reading of unneeded columns from the query plan. + * + * Since adding Project before Filter conflicts with PushPredicatesThroughProject, this rule will + * remove the Project p2 in the following pattern: + * + * p1 @ Project(_, Filter(_, p2 @ Project(_, child))) if p2.outputSet.subsetOf(p2.inputSet) + * + * p2 is usually inserted by this rule and useless, p1 could prune the columns anyway. + */ +object ColumnPruning extends Rule[LogicalPlan] { + + def apply(plan: LogicalPlan): LogicalPlan = removeProjectBeforeFilter(plan transform { + // Prunes the unused columns from project list of Project/Aggregate/Expand + case p @ Project(_, p2: Project) if !p2.outputSet.subsetOf(p.references) => + p.copy(child = p2.copy(projectList = p2.projectList.filter(p.references.contains))) + case p @ Project(_, a: Aggregate) if !a.outputSet.subsetOf(p.references) => + p.copy( + child = a.copy(aggregateExpressions = a.aggregateExpressions.filter(p.references.contains))) + case a @ Project(_, e @ Expand(_, _, grandChild)) if !e.outputSet.subsetOf(a.references) => + val newOutput = e.output.filter(a.references.contains(_)) + val newProjects = e.projections.map { proj => + proj.zip(e.output).filter { case (_, a) => + newOutput.contains(a) + }.unzip._1 + } + a.copy(child = Expand(newProjects, newOutput, grandChild)) + + // Prunes the unused columns from child of `DeserializeToObject` + case d @ DeserializeToObject(_, _, child) if !child.outputSet.subsetOf(d.references) => + d.copy(child = prunedChild(child, d.references)) + + // Prunes the unused columns from child of Aggregate/Expand/Generate/ScriptTransformation + case a @ Aggregate(_, _, child) if !child.outputSet.subsetOf(a.references) => + a.copy(child = prunedChild(child, a.references)) + case f @ FlatMapGroupsInPandas(_, _, _, child) if !child.outputSet.subsetOf(f.references) => + f.copy(child = prunedChild(child, f.references)) + case e @ Expand(_, _, child) if !child.outputSet.subsetOf(e.references) => + e.copy(child = prunedChild(child, e.references)) + case s @ ScriptTransformation(_, _, _, child, _) + if !child.outputSet.subsetOf(s.references) => + s.copy(child = prunedChild(child, s.references)) + + // prune unrequired references + case p @ Project(_, g: Generate) if p.references != g.outputSet => + val requiredAttrs = p.references -- g.producedAttributes ++ g.generator.references + val newChild = prunedChild(g.child, requiredAttrs) + val unrequired = g.generator.references -- p.references + val unrequiredIndices = newChild.output.zipWithIndex.filter(t => unrequired.contains(t._1)) + .map(_._2) + p.copy(child = g.copy(child = newChild, unrequiredChildIndex = unrequiredIndices)) + + // Eliminate unneeded attributes from right side of a Left Existence Join. + case j @ Join(_, right, LeftExistence(_), _) => + j.copy(right = prunedChild(right, j.references)) + + // all the columns will be used to compare, so we can't prune them + case p @ Project(_, _: SetOperation) => p + case p @ Project(_, _: Distinct) => p + // Eliminate unneeded attributes from children of Union. + case p @ Project(_, u: Union) => + if (!u.outputSet.subsetOf(p.references)) { + val firstChild = u.children.head + val newOutput = prunedChild(firstChild, p.references).output + // pruning the columns of all children based on the pruned first child. + val newChildren = u.children.map { p => + val selected = p.output.zipWithIndex.filter { case (a, i) => + newOutput.contains(firstChild.output(i)) + }.map(_._1) + Project(selected, p) + } + p.copy(child = u.withNewChildren(newChildren)) + } else { + p + } + + // Prune unnecessary window expressions + case p @ Project(_, w: Window) if !w.windowOutputSet.subsetOf(p.references) => + p.copy(child = w.copy( + windowExpressions = w.windowExpressions.filter(p.references.contains))) + + // Can't prune the columns on LeafNode + case p @ Project(_, _: LeafNode) => p + + // for all other logical plans that inherits the output from it's children + // Project over project is handled by the first case, skip it here. + case p @ Project(_, child) if !child.isInstanceOf[Project] => + val required = child.references ++ p.references + if (!child.inputSet.subsetOf(required)) { + val newChildren = child.children.map(c => prunedChild(c, required)) + p.copy(child = child.withNewChildren(newChildren)) + } else { + p + } + }) + + /** Applies a projection only when the child is producing unnecessary attributes */ + private def prunedChild(c: LogicalPlan, allReferences: AttributeSet) = + if (!c.outputSet.subsetOf(allReferences)) { + Project(c.output.filter(allReferences.contains), c) + } else { + c + } + + /** + * The Project before Filter is not necessary but conflict with PushPredicatesThroughProject, + * so remove it. Since the Projects have been added top-down, we need to remove in bottom-up + * order, otherwise lower Projects can be missed. + */ + private def removeProjectBeforeFilter(plan: LogicalPlan): LogicalPlan = plan transformUp { + case p1 @ Project(_, f @ Filter(_, p2 @ Project(_, child))) + if p2.outputSet.subsetOf(child.outputSet) => Review comment: I can see that this is a clean refactoring and this line is the additional style fix. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on 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]
