peter-toth commented on a change in pull request #28885: URL: https://github.com/apache/spark/pull/28885#discussion_r459266941
########## File path: sql/catalyst/src/main/scala/org/apache/spark/sql/util/ReuseMap.scala ########## @@ -0,0 +1,73 @@ +/* + * 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.util + +import scala.collection.mutable.Map +import scala.language.existentials + +import org.apache.spark.sql.catalyst.plans.QueryPlan +import org.apache.spark.sql.types.StructType + +/** + * Map of canonicalized plans that can be used to find reuse possibilities. + * + * To avoid costly canonicalization of a plan: + * - we use its schema first to check if it can be replaced to a reused one at all + * - we insert it into the map of canonicalized plans only when at least 2 have the same schema + */ +class ReuseMap[T <: QueryPlan[_]] { + // scalastyle:off structural.type + private val map = Map[StructType, (T, Map[T2 forSome { type T2 >: T }, T])]() + // scalastyle:on structural.type + + /** + * Find a matching plan with the same canonicalized form in the map or add the new plan to the + * map otherwise. + * + * @param plan the input plan + * @return the matching plan or the input plan + */ + def lookupOrElseAdd(plan: T): T = { + val (firstSameSchemaPlan, sameResultPlans) = map.getOrElseUpdate(plan.schema, plan -> Map()) Review comment: I see your point and I'm fine with reverting this change to the `ArrayBuffer`. To me `Map[StructType, ArrayBuffer[SparkPlan]]` doesn't look intuitive at all exactly because of (a). Plan nodes are immutable case classes which provide consistent `equals()` and `hashcode()` and IMHO in those cases a map is better fit to look up an item. Using the `ArrayBuffer` suggests that something is weird with those nodes but I don't think it is. (We use canonicalized map of plans in `ReuseAdaptiveSubquery` too.) To answer (b) as well, no, they very likely doesn't bring much improvement in a real word use case. The change is mainly due to the above reason. ---------------------------------------------------------------- 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: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For additional commands, e-mail: reviews-h...@spark.apache.org
