c21 commented on a change in pull request #34702: URL: https://github.com/apache/spark/pull/34702#discussion_r757197263
########## File path: sql/core/src/main/scala/org/apache/spark/sql/execution/ReplaceHashWithSortAgg.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.execution + +import org.apache.spark.sql.catalyst.expressions.SortOrder +import org.apache.spark.sql.catalyst.expressions.aggregate.{Complete, Final, Partial} +import org.apache.spark.sql.catalyst.rules.Rule +import org.apache.spark.sql.execution.aggregate.HashAggregateExec +import org.apache.spark.sql.internal.SQLConf + +/** + * Replace [[HashAggregateExec]] with [[SortAggregateExec]] in the spark plan if: + * + * 1. The plan is a pair of partial and final [[HashAggregateExec]], and the child of partial + * aggregate satisfies the sort order of corresponding [[SortAggregateExec]]. + * or + * 2. The plan is a [[HashAggregateExec]], and the child satisfies the sort order of + * corresponding [[SortAggregateExec]]. + * + * Examples: + * 1. aggregate after join: + * + * HashAggregate(t1.i, SUM, final) + * | SortAggregate(t1.i, SUM, complete) + * HashAggregate(t1.i, SUM, partial) => | + * | SortMergeJoin(t1.i = t2.j) + * SortMergeJoin(t1.i = t2.j) + * + * 2. aggregate after sort: + * + * HashAggregate(t1.i, SUM, partial) SortAggregate(t1.i, SUM, partial) + * | => | + * Sort(t1.i) Sort(t1.i) + * + * [[HashAggregateExec]] can be replaced when its child satisfies the sort order of + * corresponding [[SortAggregateExec]]. [[SortAggregateExec]] is faster in the sense that + * it does not have hashing overhead of [[HashAggregateExec]]. + */ +object ReplaceHashWithSortAgg extends Rule[SparkPlan] { + def apply(plan: SparkPlan): SparkPlan = { + if (!conf.getConf(SQLConf.REPLACE_HASH_WITH_SORT_AGG_ENABLED)) { + plan + } else { + replaceHashAgg(plan) + } + } + + /** + * Replace [[HashAggregateExec]] with [[SortAggregateExec]]. + */ + private def replaceHashAgg(plan: SparkPlan): SparkPlan = { + plan.transformDown { + case hashAgg: HashAggregateExec => + val sortAgg = hashAgg.toSortAggregate + hashAgg.child match { + case partialAgg: HashAggregateExec if isPartialAgg(partialAgg, hashAgg) => + if (SortOrder.orderingSatisfies( + partialAgg.child.outputOrdering, sortAgg.requiredChildOrdering.head)) { + sortAgg.copy( + aggregateExpressions = sortAgg.aggregateExpressions.map(_.copy(mode = Complete)), Review comment: > if there is a shuffle in the middle, we can't optimize? We can, and the rule here also does pattern matching for single `HashAggregate` below. I added a unit test case in `ReplaceHashWithSortAggSuite.scala` to demonstrate replacing partial aggregate - `"replace partial hash aggregate with sort aggregate"`. But I think it would be rare to be able to replace final aggregate (though this rule also covers it), as final aggregate is almostly always immediately after a shuffle, so there's no sort ordering before final aggregate. Spark native shuffle does not guarantee any sort orders, for Cosco (a remote shuffle service we are running in-house), we support sorted shuffle, so final aggregate can also be possible to replace. -- 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. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
