Github user nongli commented on a diff in the pull request: https://github.com/apache/spark/pull/9276#discussion_r43473922 --- Diff: sql/core/src/main/scala/org/apache/spark/sql/execution/ExchangeCoordinator.scala --- @@ -0,0 +1,251 @@ +/* + * 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 java.util.{Map => JMap, HashMap => JHashMap} + +import scala.collection.mutable.ArrayBuffer + +import org.apache.spark.sql.catalyst.plans.physical.HashPartitioning +import org.apache.spark.{Logging, SimpleFutureAction, ShuffleDependency, MapOutputStatistics} +import org.apache.spark.rdd.RDD +import org.apache.spark.sql.catalyst.InternalRow + +/** + * A coordinator used to determines how we shuffle data between stages generated by Spark SQL. + * Right now, the work of this coordinator is to determine the number of post-shuffle partitions + * for a stage that needs to fetch shuffle data from one or multiple stages. + * + * A coordinator is constructed with two parameters, `numExchanges` and + * `targetPostShuffleInputSize`. `numExchanges` is used to indicated that how many [[Exchange]]s + * that will be registered to this coordinator. So, when we start to do any actual work, we have + * a way to make sure that we have got expected number of [[Exchange]]s. + * `targetPostShuffleInputSize` is the targeted size of a post-shuffle partition's input data size. + * With this parameter, we can estimate the number of post-shuffle partitions. This parameter + * is configured through `spark.sql.adaptive.shuffle.targetPostShuffleInputSize`. + * + * The workflow of this coordinator is described as follows: + * - Before the execution of a [[SparkPlan]], for an [[Exchange]] operator, + * if an [[ExchangeCoordinator]] is assigned to it, it registers itself to this coordinator. + * This happens in the `doPrepare` method. + * - Once we start to execute a physical plan, an [[Exchange]] registered to this coordinator will + * call `postShuffleRDD` to get its corresponding post-shuffle [[RDD]]. If this coordinator has + * made the decision on how to shuffle data, this [[Exchange]] will immediately get its + * corresponding post-shuffle [[RDD]]. + * - If this coordinator has not made the decision on how to shuffle data, it will ask those + * registered [[Exchange]]s to submit their pre-shuffle stages. Then, based on the the size + * statistics of pre-shuffle partitions, this coordinator will determine the number of + * post-shuffle partitions and pack multiple pre-shuffle partitions with continuous indices + * to a post-shuffle partition whenever necessary. + * - Finally, this coordinator will create post-shuffle [[RDD]]s for all registered [[Exchange]]s. + * So, when an [[Exchange]] calls `postShuffleRDD`, this coordinator can lookup the + * corresponding [[RDD]]. + * + * The strategy used to determine the number of post-shuffle partitions is described as follows. + * To determine the number of post-shuffle partitions, we have a target input size for a + * post-shuffle partition. Once we have size statistics of pre-shuffle partitions from stages + * corresponding to the registered [[Exchange]]s, we will do a pass of those statistics and + * pack pre-shuffle partitions with continuous indices to a single post-shuffle partition until + * the size of a post-shuffle partition is equal or greater than the target size. + * For example, we have two stages with the following pre-shuffle partition size statistics: + * stage 1: [100 MB, 20 MB, 100 MB, 10MB, 30 MB] + * stage 2: [10 MB, 10 MB, 70 MB, 5 MB, 5 MB] + * assuming the target input size is 128 MB, we will have three post-shuffle partitions, + * which are: + * - post-shuffle partition 0: pre-shuffle partition 0 and 1 + * - post-shuffle partition 1: pre-shuffle partition 2 + * - post-shuffle partition 2: pre-shuffle partition 3 and 4 + * + * If `minNumPostShufflePartitions` is defined. This ExchangeCoordinator will try to enforce + * the minimal number of post-shuffle partitions to this number. + */ +private[sql] class ExchangeCoordinator( + numExchanges: Int, + advisoryTargetPostShuffleInputSize: Long, + minNumPostShufflePartitions: Option[Int] = None) + extends Logging { + + // The registered Exchange operators. + private[this] val exchanges = ArrayBuffer[Exchange]() + + // This map that is used to lookup the post-shuffle RDD for an Exchange operator. --- End diff -- Can you comment on thread safety? Multiple threads read from the postShuffleRDDs at the same time right? But this happens after one batch insert?
--- If your project is set up for it, you can reply to this email and have your reply appear on GitHub as well. If your project does not have this feature enabled and wishes so, or if the feature is enabled but not working, please contact infrastructure at infrastruct...@apache.org or file a JIRA ticket with INFRA. --- --------------------------------------------------------------------- To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For additional commands, e-mail: reviews-h...@spark.apache.org