cloud-fan commented on code in PR #49955: URL: https://github.com/apache/spark/pull/49955#discussion_r1980967440
########## sql/core/src/main/scala/org/apache/spark/sql/execution/RecursiveCTEExecution.scala: ########## @@ -0,0 +1,229 @@ +/* + * 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 scala.collection.mutable + +import org.apache.spark.SparkException +import org.apache.spark.rdd.{EmptyRDD, RDD} +import org.apache.spark.sql.catalyst.InternalRow +import org.apache.spark.sql.catalyst.expressions.{Alias, Attribute, Literal} +import org.apache.spark.sql.catalyst.plans.QueryPlan +import org.apache.spark.sql.catalyst.plans.logical.{Filter, LocalLimit, LogicalPlan, Project, Union, UnionLoopRef} +import org.apache.spark.sql.classic.Dataset +import org.apache.spark.sql.execution.metric.SQLMetrics +import org.apache.spark.sql.internal.SQLConf + + +/** + * The physical node for recursion. Currently only UNION ALL case is supported. + * For the details about the execution, look at the comment above doExecute function. + * + * A simple recursive query: + * {{{ + * WITH RECURSIVE t(n) AS ( + * SELECT 1 + * UNION ALL + * SELECT n+1 FROM t WHERE n < 5) + * SELECT * FROM t; + * }}} + * Corresponding logical plan for the recursive query above: + * {{{ + * WithCTE + * :- CTERelationDef 0, false + * : +- SubqueryAlias t + * : +- Project [1#0 AS n#3] + * : +- UnionLoop 0 + * : :- Project [1 AS 1#0] + * : : +- OneRowRelation + * : +- Project [(n#1 + 1) AS (n + 1)#2] + * : +- Filter (n#1 < 5) + * : +- SubqueryAlias t + * : +- Project [1#0 AS n#1] + * : +- UnionLoopRef 0, [1#0], false + * +- Project [n#3] + * +- SubqueryAlias t + * +- CTERelationRef 0, true, [n#3], false, false + * }}} + * + * @param loopId This is id of the CTERelationDef containing the recursive query. Its value is + * first passed down to UnionLoop when creating it, and then to UnionLoopExec in + * SparkStrategies. + * @param anchor The logical plan of the initial element of the loop. + * @param recursion The logical plan that describes the recursion with an [[UnionLoopRef]] node. + * CTERelationRef, which is marked as recursive, gets substituted with + * [[UnionLoopRef]] in ResolveWithCTE. + * Both anchor and recursion are marked with @transient annotation, so that they + * are not serialized. + * @param output The output attributes of this loop. + * @param limit If defined, the total number of rows output by this operator will be bounded by + * limit. + * Its value is pushed down to UnionLoop in Optimizer in case Limit node is present + * in the logical plan and then transferred to UnionLoopExec in SparkStrategies. + * Note here: limit can be applied in the main query calling the recursive CTE, and not + * inside the recursive term of recursive CTE. + */ +case class UnionLoopExec( + loopId: Long, + @transient anchor: LogicalPlan, + @transient recursion: LogicalPlan, + override val output: Seq[Attribute], + localLimit: Option[Int] = None, + globalLimit: Option[Int] = None) extends LeafExecNode { + + override def innerChildren: Seq[QueryPlan[_]] = Seq(anchor, recursion) + + private val numPartitions: Int = conf.defaultNumShufflePartitions + + override lazy val metrics = Map( + "numOutputRows" -> SQLMetrics.createMetric(sparkContext, "number of output rows"), + "numRecursiveLoops" -> SQLMetrics.createMetric(sparkContext, "number of recursive loops")) + + private val simpleRecursion = { + recursion match { + case Project(_, Filter(_, Project(_, UnionLoopRef(_, _, _)))) => + true + case Filter(_, Project(_, UnionLoopRef(_, _, _))) => + true + case Project(_, Filter(_, UnionLoopRef(_, _, _))) => + true + case Project(_, UnionLoopRef(_, _, _)) => + true + case _ => + false + } + } + /** + * This function executes the plan (optionally with appended limit node) and caches the result, + * with the caching mode specified in config. + */ + private def executeAndCacheAndCount( + plan: LogicalPlan, currentLimit: Int) = { + // In case limit is defined, we create a (local) limit node above the plan and execute + // the newly created plan. + val planOrLimitedPlan = if (globalLimit.isDefined || localLimit.isDefined) { + LocalLimit(Literal(currentLimit), plan) + } else { + plan + } + val df = Dataset.ofRows(session, planOrLimitedPlan) + val newDF = { + if (!simpleRecursion) { + df.repartition(numPartitions) + } else { + df + } + } + val count = newDF.count() + (newDF, count) + } + + /** + * In the first iteration, anchor term is executed. + * Then, in each following iteration, the UnionLoopRef node is substituted with the plan from the + * previous iteration, and such plan is executed. + * After every iteration, the dataframe is repartitioned. + * The recursion stops when the generated dataframe is empty, or either the limit or + * the specified maximum depth from the config is reached. + */ + override protected def doExecute(): RDD[InternalRow] = { + val executionId = sparkContext.getLocalProperty(SQLExecution.EXECUTION_ID_KEY) + val numOutputRows = longMetric("numOutputRows") + val numRecursiveLoops = longMetric("numRecursiveLoops") + val levelLimit = conf.getConf(SQLConf.CTE_RECURSION_LEVEL_LIMIT) + + // currentLimit is initialized from the limit argument, and in each step it is decreased by + // the number of rows generated in that step. + // If limit is not passed down, currentLimit is set to be zero and won't be considered in the + // condition of while loop down (limit.isEmpty will be true). + var globalLimitNum = globalLimit.getOrElse(0) Review Comment: I think -1 is better to indicate no limit, as `0` can also be a legal limit. -- This is an automated message from the Apache Git Service. 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