cloud-fan commented on code in PR #32298: URL: https://github.com/apache/spark/pull/32298#discussion_r852157375
########## sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/MergeScalarSubqueries.scala: ########## @@ -0,0 +1,357 @@ +/* + * 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 +import scala.collection.mutable.ListBuffer + +import org.apache.spark.sql.catalyst.expressions._ +import org.apache.spark.sql.catalyst.expressions.aggregate.AggregateExpression +import org.apache.spark.sql.catalyst.plans.logical.{Aggregate, CTERelationDef, CTERelationRef, Filter, Join, LogicalPlan, Project, Subquery, WithCTE} +import org.apache.spark.sql.catalyst.rules.Rule +import org.apache.spark.sql.catalyst.trees.TreePattern.{SCALAR_SUBQUERY, SCALAR_SUBQUERY_REFERENCE, TreePattern} +import org.apache.spark.sql.types.DataType + +/** + * This rule tries to merge multiple non-correlated [[ScalarSubquery]]s to compute multiple scalar + * values once. + * + * The process is the following: + * - While traversing through the plan each [[ScalarSubquery]] plan is tried to merge into the cache + * of already seen subquery plans. If merge is possible then cache is updated with the merged + * subquery plan, if not then the new subquery plan is added to the cache. + * During this first traversal each [[ScalarSubquery]] expression is replaced to a temporal + * [[ScalarSubqueryReference]] reference pointing to its cached version. + * The cache uses a flag to keep track of if a cache entry is a result of merging 2 or more + * plans, or it is a plan that was seen only once. + * Merged plans in the cache get a "Header", that contains the list of attributes form the scalar + * return value of a merged subquery. + * - A second traversal checks if there are merged subqueries in the cache and builds a `WithCTE` + * node from these queries. The `CTERelationDef` nodes contain the merged subquery in the + * following form: + * `Project(Seq(CreateNamedStruct(name1, attribute1, ...) AS mergedValue), mergedSubqueryPlan)` + * and the definitions are flagged that they host a subquery, that can return maximum one row. + * During the second traversal [[ScalarSubqueryReference]] expressions that pont to a merged + * subquery is either transformed to a `GetStructField(ScalarSubquery(CTERelationRef(...)))` + * expression or restored to the original [[ScalarSubquery]]. + * + * Eg. the following query: + * + * SELECT + * (SELECT avg(a) FROM t), + * (SELECT sum(b) FROM t) + * + * is optimized from: + * + * == Optimized Logical Plan == + * Project [scalar-subquery#242 [] AS scalarsubquery()#253, + * scalar-subquery#243 [] AS scalarsubquery()#254L] + * : :- Aggregate [avg(a#244) AS avg(a)#247] + * : : +- Project [a#244] + * : : +- Relation default.t[a#244,b#245] parquet + * : +- Aggregate [sum(a#251) AS sum(a)#250L] + * : +- Project [a#251] + * : +- Relation default.t[a#251,b#252] parquet + * +- OneRowRelation + * + * to: + * + * WithCTE + * :- CTERelationDef 0 + * : +- Project [named_struct(avg(a), avg(a)#247, sum(a), sum(a)#250L) AS mergedValue#260] + * : +- Aggregate [avg(a#244) AS avg(a)#247, sum(a#244) AS sum(a)#250L] + * : +- Project [a#244] + * : +- Relation default.t[a#244,b#245] parquet + * +- Project [scalar-subquery#242 [].avg(a) AS scalarsubquery()#253, + * scalar-subquery#243 [].sum(a) AS scalarsubquery()#254L] + * : :- CTERelationRef 0, true, [mergedValue#260], true + * : +- CTERelationRef 0, true, [mergedValue#260], true + * +- OneRowRelation + */ +object MergeScalarSubqueries extends Rule[LogicalPlan] with PredicateHelper { + def apply(plan: LogicalPlan): LogicalPlan = { + plan match { + case s: Subquery => s.copy(child = extractCommonScalarSubqueries(s.child)) + case _ => extractCommonScalarSubqueries(plan) + } + } + + /** + * An item in the cache of merged scalar subqueries. + * + * @param elements List of member names and attributes that form the struct scalar return value + * of a merged subquery. + * @param plan The plan of a merged scalar subquery. + * @param merged A flag to identify if this item is the result of merging subqueries. + * Please note that `elements.size == 1` doesn't always mean that the plan is not + * merged as there can be subqueries that are different ([[checkIdenticalPlans]] + * is false) due to an extra [[Project]] node in one of them. In that case + * `elements.size` remains 1 after merging, but the merged flag becomes true. + */ + case class Header(elements: Seq[(String, Attribute)], plan: LogicalPlan, merged: Boolean) + + private def extractCommonScalarSubqueries(plan: LogicalPlan) = { + val cache = ListBuffer.empty[Header] + val (newPlan, subqueryCTEs) = removeReferences(insertReferences(plan, cache), cache) + if (subqueryCTEs.nonEmpty) { + WithCTE(newPlan, subqueryCTEs) + } else { + newPlan + } + } + + // First traversal builds up the cache and inserts `ScalarSubqueryReference`s to the plan. + private def insertReferences(plan: LogicalPlan, cache: ListBuffer[Header]): LogicalPlan = { + plan.transformAllExpressionsWithPruning(_.containsAnyPattern(SCALAR_SUBQUERY)) { + case s: ScalarSubquery if !s.isCorrelated && s.deterministic => + val (subqueryIndex, headerIndex) = cacheSubquery(s.plan, cache) + ScalarSubqueryReference(subqueryIndex, headerIndex, s.dataType, s.exprId) + } + } + + // Caching returns the index of the subquery in the cache and the index of scalar member in the + // "Header". + private def cacheSubquery(plan: LogicalPlan, cache: ListBuffer[Header]): (Int, Int) = { + val output = plan.output.head + cache.zipWithIndex.collectFirst(Function.unlift { case (header, subqueryIndex) => + checkIdenticalPlans(plan, header.plan).map { outputMap => + val mappedOutput = mapAttributes(output, outputMap) + val headerIndex = header.elements.indexWhere { + case (_, attribute) => attribute.exprId == mappedOutput.exprId + } + subqueryIndex -> headerIndex + }.orElse(tryMergePlans(plan, header.plan).map { + case (mergedPlan, outputMap) => + val mappedOutput = mapAttributes(output, outputMap) + var headerIndex = header.elements.indexWhere { + case (_, attribute) => attribute.exprId == mappedOutput.exprId + } + val newHeaderElements = if (headerIndex == -1) { + headerIndex = header.elements.size + header.elements :+ (output.name -> mappedOutput) + } else { + header.elements + } + cache(subqueryIndex) = Header(newHeaderElements, mergedPlan, true) + subqueryIndex -> headerIndex + }) + }).getOrElse { + cache += Header(Seq(output.name -> output), plan, false) + cache.length - 1 -> 0 + } + } + + // If 2 plans are identical return the attribute mapping from the new to the cached version. + private def checkIdenticalPlans( + newPlan: LogicalPlan, + cachedPlan: LogicalPlan): Option[AttributeMap[Attribute]] = { + if (newPlan.canonicalized == cachedPlan.canonicalized) { + Some(AttributeMap(newPlan.output.zip(cachedPlan.output))) + } else { + None + } + } + + // Recursively traverse down and try merging 2 plans. If merge is possible then return the merged + // plan with the attribute mapping from the new to the merged version. + // Please note that merging arbitrary plans can be complicated, the current version supports only + // some of the most important nodes. + private def tryMergePlans( + newPlan: LogicalPlan, + cachedPlan: LogicalPlan): Option[(LogicalPlan, AttributeMap[Attribute])] = { + checkIdenticalPlans(newPlan, cachedPlan).map(cachedPlan -> _).orElse( + (newPlan, cachedPlan) match { + case (np: Project, cp: Project) => + tryMergePlans(np.child, cp.child).map { case (mergedChild, outputMap) => + val (mergedProjectList, newOutputMap) = + mergeNamedExpressions(np.projectList, outputMap, cp.projectList) + val mergedPlan = Project(mergedProjectList, mergedChild) + mergedPlan -> newOutputMap + } + case (np, cp: Project) => + tryMergePlans(np, cp.child).map { case (mergedChild, outputMap) => + val (mergedProjectList, newOutputMap) = + mergeNamedExpressions(np.output, outputMap, cp.projectList) + val mergedPlan = Project(mergedProjectList, mergedChild) + mergedPlan -> newOutputMap + } + case (np: Project, cp) => + tryMergePlans(np.child, cp).map { case (mergedChild, outputMap) => + val (mergedProjectList, newOutputMap) = + mergeNamedExpressions(np.projectList, outputMap, cp.output) + val mergedPlan = Project(mergedProjectList, mergedChild) + mergedPlan -> newOutputMap + } + case (np: Aggregate, cp: Aggregate) if supportedAggregateMerge(np, cp) => + tryMergePlans(np.child, cp.child).flatMap { case (mergedChild, outputMap) => + val mappedNewGroupingExpression = + np.groupingExpressions.map(mapAttributes(_, outputMap)) + // Order of grouping expression doesn't matter so we can compare sets + if (ExpressionSet(mappedNewGroupingExpression) == + ExpressionSet(cp.groupingExpressions)) { + val (mergedAggregateExpressions, newOutputMap) = + mergeNamedExpressions(np.aggregateExpressions, outputMap, cp.aggregateExpressions) + val mergedPlan = + Aggregate(cp.groupingExpressions, mergedAggregateExpressions, mergedChild) + Some(mergedPlan -> newOutputMap) + } else { + None + } + } + + case (np: Filter, cp: Filter) => + tryMergePlans(np.child, cp.child).flatMap { case (mergedChild, outputMap) => + val mappedNewCondition = mapAttributes(np.condition, outputMap) + // Comparing the canonicalized form is required to ignore different forms of the same + // expression. + if (mappedNewCondition.canonicalized == cp.condition.canonicalized) { + val mergedPlan = cp.withNewChildren(Seq(mergedChild)) + Some(mergedPlan -> outputMap) + } else { + None + } + } + + case (np: Join, cp: Join) if np.joinType == cp.joinType && np.hint == cp.hint => + tryMergePlans(np.left, cp.left).flatMap { case (mergedLeft, leftOutputMap) => + tryMergePlans(np.right, cp.right).flatMap { case (mergedRight, rightOutputMap) => + val outputMap = leftOutputMap ++ rightOutputMap + val mappedNewCondition = np.condition.map(mapAttributes(_, outputMap)) + // Comparing the canonicalized form is required to ignore different forms of the same + // expression and `AttributeReference.quailifier`s in `cp.condition`. + if (mappedNewCondition.map(_.canonicalized) == cp.condition.map(_.canonicalized)) { + val mergedPlan = cp.withNewChildren(Seq(mergedLeft, mergedRight)) + Some(mergedPlan -> outputMap) + } else { + None + } + } + } + + // Otherwise merging is not possible. + case _ => None + }) + } + + private def createProject(elements: Seq[(String, Attribute)], plan: LogicalPlan): Project = { + Project( + Seq(Alias( + CreateNamedStruct(elements.flatMap { + case (name, attribute) => Seq(Literal(name), attribute) + }), + "mergedValue")()), + plan) + } + + private def mapAttributes[T <: Expression](expr: T, outputMap: AttributeMap[Attribute]) = { + expr.transform { + case a: Attribute => outputMap.getOrElse(a, a) + }.asInstanceOf[T] + } + + // Applies `outputMap` attribute mapping on elements of `newExpressions` and merges them into + // `cachedExpressions`. Returns the merged expressions and the attribute mapping from the new to + // the merged version that can be propagated up during merging nodes. + private def mergeNamedExpressions( + newExpressions: Seq[NamedExpression], + outputMap: AttributeMap[Attribute], + cachedExpressions: Seq[NamedExpression]) = { + val mergedExpressions = ListBuffer[NamedExpression](cachedExpressions: _*) + val newOutputMap = AttributeMap(newExpressions.map { ne => + val mapped = mapAttributes(ne, outputMap) + val withoutAlias = mapped match { + case Alias(child, _) => child + case e => e + } + ne.toAttribute -> mergedExpressions.find { + case Alias(child, _) => child semanticEquals withoutAlias + case e => e semanticEquals withoutAlias + }.getOrElse { + mergedExpressions += mapped + mapped + }.toAttribute + }) + (mergedExpressions.toSeq, newOutputMap) + } + + // Only allow aggregates of the same implementation because merging different implementations + // could cause performance regression. + private def supportedAggregateMerge(newPlan: Aggregate, cachedPlan: Aggregate) = { + val newPlanAggregateExpressions = newPlan.aggregateExpressions.flatMap(_.collect { + case a: AggregateExpression => a + }) + val cachedPlanAggregateExpressions = cachedPlan.aggregateExpressions.flatMap(_.collect { + case a: AggregateExpression => a + }) + val newPlanSupportsHashAggregate = Aggregate.supportsHashAggregate( + newPlanAggregateExpressions.flatMap(_.aggregateFunction.aggBufferAttributes)) + val cachedPlanSupportsHashAggregate = Aggregate.supportsHashAggregate( + cachedPlanAggregateExpressions.flatMap(_.aggregateFunction.aggBufferAttributes)) + newPlanSupportsHashAggregate && cachedPlanSupportsHashAggregate || + !newPlanSupportsHashAggregate && !cachedPlanSupportsHashAggregate && { Review Comment: is it just `newPlanSupportsHashAggregate == cachedPlanSupportsHashAggregate`? -- This is an automated message from the Apache Git Service. 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