cryptoe commented on code in PR #13205: URL: https://github.com/apache/druid/pull/13205#discussion_r1026393929
########## extensions-core/multi-stage-query/src/main/java/org/apache/druid/msq/exec/WorkerSketchFetcher.java: ########## @@ -0,0 +1,335 @@ +/* + * 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.druid.msq.exec; + +import com.google.common.util.concurrent.ListenableFuture; +import org.apache.druid.frame.key.ClusterBy; +import org.apache.druid.frame.key.ClusterByPartition; +import org.apache.druid.frame.key.ClusterByPartitions; +import org.apache.druid.java.util.common.Either; +import org.apache.druid.java.util.common.ISE; +import org.apache.druid.java.util.common.logger.Logger; +import org.apache.druid.msq.kernel.StageDefinition; +import org.apache.druid.msq.statistics.ClusterByStatisticsCollector; +import org.apache.druid.msq.statistics.ClusterByStatisticsSnapshot; +import org.apache.druid.msq.statistics.CompleteKeyStatisticsInformation; + +import java.util.ArrayList; +import java.util.HashSet; +import java.util.Iterator; +import java.util.List; +import java.util.Map; +import java.util.Set; +import java.util.concurrent.CompletableFuture; +import java.util.concurrent.ExecutorService; +import java.util.concurrent.Executors; +import java.util.stream.IntStream; + +/** + * Queues up fetching sketches from workers and progressively generates partitions boundaries. + */ +public class WorkerSketchFetcher +{ + private static final Logger log = new Logger(WorkerSketchFetcher.class); + private static final int DEFAULT_THREAD_COUNT = 4; + // If the combined size of worker sketches is more than this threshold, SEQUENTIAL merging mode is used. + static final long BYTES_THRESHOLD = 1_000_000_000L; + // If there are more workers than this threshold, SEQUENTIAL merging mode is used. + static final long WORKER_THRESHOLD = 100; + + private final ClusterStatisticsMergeMode clusterStatisticsMergeMode; + private final int statisticsMaxRetainedBytes; + private final WorkerClient workerClient; + private final ExecutorService executorService; + + public WorkerSketchFetcher(WorkerClient workerClient, ClusterStatisticsMergeMode clusterStatisticsMergeMode, int statisticsMaxRetainedBytes) + { + this.workerClient = workerClient; + this.clusterStatisticsMergeMode = clusterStatisticsMergeMode; + this.executorService = Executors.newFixedThreadPool(DEFAULT_THREAD_COUNT); + this.statisticsMaxRetainedBytes = statisticsMaxRetainedBytes; + } + + /** + * Submits a request to fetch and generate partitions for the given worker statistics and returns a future for it. It + * decides based on the statistics if it should fetch sketches one by one or together. + */ + public CompletableFuture<Either<Long, ClusterByPartitions>> submitFetcherTask( + CompleteKeyStatisticsInformation completeKeyStatisticsInformation, + List<String> workerTaskIds, + StageDefinition stageDefinition + ) + { + ClusterBy clusterBy = stageDefinition.getClusterBy(); + + switch (clusterStatisticsMergeMode) { + case SEQUENTIAL: + return sequentialTimeChunkMerging(completeKeyStatisticsInformation, stageDefinition, workerTaskIds); + case PARALLEL: + return inMemoryFullSketchMerging(stageDefinition, workerTaskIds); + case AUTO: + if (clusterBy.getBucketByCount() == 0) { + log.debug("Query [%s] AUTO mode: chose PARALLEL mode to merge key statistics", stageDefinition.getId().getQueryId()); + // If there is no time clustering, there is no scope for sequential merge + return inMemoryFullSketchMerging(stageDefinition, workerTaskIds); + } else if (stageDefinition.getMaxWorkerCount() > WORKER_THRESHOLD || completeKeyStatisticsInformation.getBytesRetained() > BYTES_THRESHOLD) { + log.debug("Query [%s] AUTO mode: chose SEQUENTIAL mode to merge key statistics", stageDefinition.getId().getQueryId()); + return sequentialTimeChunkMerging(completeKeyStatisticsInformation, stageDefinition, workerTaskIds); + } + log.debug("Query [%s] AUTO mode: chose PARALLEL mode to merge key statistics", stageDefinition.getId().getQueryId()); + return inMemoryFullSketchMerging(stageDefinition, workerTaskIds); + default: + throw new IllegalStateException("No fetching strategy found for mode: " + clusterStatisticsMergeMode); + } + } + + /** + * Fetches the full {@link ClusterByStatisticsCollector} from all workers and generates partition boundaries from them. + * This is faster than fetching them timechunk by timechunk but the collector will be downsampled till it can fit + * on the controller, resulting in less accurate partition boundries. + */ + CompletableFuture<Either<Long, ClusterByPartitions>> inMemoryFullSketchMerging( + StageDefinition stageDefinition, + List<String> workerTaskIds + ) + { + CompletableFuture<Either<Long, ClusterByPartitions>> partitionFuture = new CompletableFuture<>(); + + // Create a new key statistics collector to merge worker sketches into + final ClusterByStatisticsCollector mergedStatisticsCollector = + stageDefinition.createResultKeyStatisticsCollector(statisticsMaxRetainedBytes); + final int workerCount = workerTaskIds.size(); + // Guarded by synchronized mergedStatisticsCollector + final Set<Integer> finishedWorkers = new HashSet<>(); + + // Submit a task for each worker to fetch statistics + IntStream.range(0, workerCount).forEach(workerNo -> { + executorService.submit(() -> { + ListenableFuture<ClusterByStatisticsSnapshot> snapshotFuture = + workerClient.fetchClusterByStatisticsSnapshot( + workerTaskIds.get(workerNo), + stageDefinition.getId().getQueryId(), + stageDefinition.getStageNumber() + ); + partitionFuture.whenComplete((result, exception) -> { + if (exception != null || (result != null && result.isError())) { + snapshotFuture.cancel(true); + } + }); + + try { + ClusterByStatisticsSnapshot clusterByStatisticsSnapshot = snapshotFuture.get(); + if (clusterByStatisticsSnapshot == null) { + throw new ISE("Worker %s returned null sketch, this should never happen", workerNo); + } + synchronized (mergedStatisticsCollector) { + mergedStatisticsCollector.addAll(clusterByStatisticsSnapshot); + finishedWorkers.add(workerNo); + + if (finishedWorkers.size() == workerCount) { + log.debug("Query [%s] Received all statistics, generating partitions", stageDefinition.getId().getQueryId()); + partitionFuture.complete(stageDefinition.generatePartitionsForShuffle(mergedStatisticsCollector)); + } + } + } + catch (Exception e) { + partitionFuture.completeExceptionally(e); + mergedStatisticsCollector.clear(); Review Comment: This line should be in the synchronized block. -- This is an automated message from the Apache Git Service. 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