himanshug commented on a change in pull request #8578: parallel broker merges on fork join pool URL: https://github.com/apache/incubator-druid/pull/8578#discussion_r334646597
########## File path: core/src/main/java/org/apache/druid/java/util/common/guava/ParallelMergeCombiningSequence.java ########## @@ -0,0 +1,1077 @@ +/* + * 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.java.util.common.guava; + +import com.google.common.collect.Lists; +import com.google.common.collect.Ordering; +import org.apache.druid.java.util.common.RE; +import org.apache.druid.java.util.common.logger.Logger; +import org.apache.druid.utils.JvmUtils; + +import javax.annotation.Nullable; +import java.io.IOException; +import java.util.ArrayDeque; +import java.util.ArrayList; +import java.util.Iterator; +import java.util.List; +import java.util.NoSuchElementException; +import java.util.Objects; +import java.util.PriorityQueue; +import java.util.Queue; +import java.util.concurrent.ArrayBlockingQueue; +import java.util.concurrent.BlockingQueue; +import java.util.concurrent.ForkJoinPool; +import java.util.concurrent.RecursiveAction; +import java.util.concurrent.TimeUnit; +import java.util.concurrent.TimeoutException; +import java.util.concurrent.atomic.AtomicReference; +import java.util.function.BinaryOperator; + +/** + * Artisanal, locally-sourced, hand-crafted, gluten and GMO free, bespoke, small-batch parallel merge combinining sequence + */ +public class ParallelMergeCombiningSequence<T> extends YieldingSequenceBase<T> +{ + private static final Logger LOG = new Logger(ParallelMergeCombiningSequence.class); + + private final ForkJoinPool workerPool; + private final List<Sequence<T>> baseSequences; + private final Ordering<T> orderingFn; + private final BinaryOperator<T> combineFn; + private final int queueSize; + private final boolean hasTimeout; + private final long timeoutAtNanos; + private final int queryPriority; // not currently used :( + private final int yieldAfter; + private final int batchSize; + private final int parallelism; + private final CancellationGizmo cancellationGizmo; + + public ParallelMergeCombiningSequence( + ForkJoinPool workerPool, + List<Sequence<T>> baseSequences, + Ordering<T> orderingFn, + BinaryOperator<T> combineFn, + boolean hasTimeout, + long timeoutMillis, + int queryPriority, + int parallelism, + int yieldAfter, + int batchSize + ) + { + this.workerPool = workerPool; + this.baseSequences = baseSequences; + this.orderingFn = orderingFn; + this.combineFn = combineFn; + this.hasTimeout = hasTimeout; + this.timeoutAtNanos = System.nanoTime() + TimeUnit.NANOSECONDS.convert(timeoutMillis, TimeUnit.MILLISECONDS); + this.queryPriority = queryPriority; + this.parallelism = parallelism; + this.yieldAfter = yieldAfter; + this.batchSize = batchSize; + this.queueSize = 4 * (yieldAfter / batchSize); + this.cancellationGizmo = new CancellationGizmo(); + } + + @Override + public <OutType> Yielder<OutType> toYielder(OutType initValue, YieldingAccumulator<OutType, T> accumulator) + { + if (baseSequences.isEmpty()) { + return Sequences.<T>empty().toYielder(initValue, accumulator); + } + + final BlockingQueue<ResultBatch<T>> outputQueue = new ArrayBlockingQueue<>(queueSize); + MergeCombinePartitioningAction<T> finalMergeAction = new MergeCombinePartitioningAction<>( + baseSequences, + orderingFn, + combineFn, + outputQueue, + queueSize, + parallelism, + yieldAfter, + batchSize, + hasTimeout, + timeoutAtNanos, + cancellationGizmo + ); + workerPool.execute(finalMergeAction); + Sequence<T> finalOutSequence = makeOutputSequenceForQueue(outputQueue, hasTimeout, timeoutAtNanos, cancellationGizmo); + return finalOutSequence.toYielder(initValue, accumulator); + } + + /** + * Create an output {@link Sequence} that wraps the output {@link BlockingQueue} of a + * {@link MergeCombinePartitioningAction} + */ + static <T> Sequence<T> makeOutputSequenceForQueue( + BlockingQueue<ResultBatch<T>> queue, + boolean hasTimeout, + long timeoutAtNanos, + CancellationGizmo cancellationGizmo + ) + { + return new BaseSequence<>( + new BaseSequence.IteratorMaker<T, Iterator<T>>() + { + @Override + public Iterator<T> make() + { + return new Iterator<T>() + { + private ResultBatch<T> currentBatch; + + @Override + public boolean hasNext() + { + final long thisTimeoutNanos = timeoutAtNanos - System.nanoTime(); + if (thisTimeoutNanos < 0) { + throw new RE(new TimeoutException("Sequence iterator timed out")); + } + + if (currentBatch != null && !currentBatch.isTerminalResult() && !currentBatch.isDrained()) { + return true; + } + try { + if (currentBatch == null || currentBatch.isDrained()) { + if (hasTimeout) { + currentBatch = queue.poll(thisTimeoutNanos, TimeUnit.NANOSECONDS); + } else { + currentBatch = queue.take(); + } + } + if (currentBatch == null) { + throw new RE(new TimeoutException("Sequence iterator timed out waiting for data")); + } + + if (cancellationGizmo.isCancelled()) { + throw cancellationGizmo.getRuntimeException(); + } + + if (currentBatch.isTerminalResult()) { + return false; + } + return true; + } + catch (InterruptedException e) { + throw new RE(e); + } + } + + @Override + public T next() + { + if (cancellationGizmo.isCancelled()) { + throw cancellationGizmo.getRuntimeException(); + } + + if (currentBatch == null || currentBatch.isDrained() || currentBatch.isTerminalResult()) { + throw new NoSuchElementException(); + } + return currentBatch.next(); + } + }; + } + + @Override + public void cleanup(Iterator<T> iterFromMake) + { + // nothing to cleanup + } + } + ); + } + + /** + * This {@link RecursiveAction} is the initial task of the parallel merge-combine process. Capacity and input sequence + * count permitting, it will partition the input set of {@link Sequence} to do 2 layer parallel merge. + * + * For the first layer, the partitions of input sequences are each wrapped in {@link YielderBatchedResultsCursor}, and + * for each partition a {@link PrepareMergeCombineInputsAction} will be executed to to wait for each of the yielders to + * yield {@link ResultBatch}. After the cursors all have an initial set of results, the + * {@link PrepareMergeCombineInputsAction} will execute a {@link MergeCombineAction} + * to perform the actual work of merging sequences and combining results. The merged and combined output of each + * partition will itself be put into {@link ResultBatch} and pushed to a {@link BlockingQueue} with a + * {@link ForkJoinPool} {@link QueuePusher}. + * + * The second layer will execute a single {@link PrepareMergeCombineInputsAction} to wait for the {@link ResultBatch} + * from each partition to be available in their 'output' {@link BlockingQueue} which each is wrapped in + * {@link BlockingQueueuBatchedResultsCursor}. Like the first layer, after the {@link PrepareMergeCombineInputsAction} + * is complete and some {@link ResultBatch} are ready to merge from each partition, it will execute a + * {@link MergeCombineAction} do a final merge combine of all the parallel computed results, again pushing + * {@link ResultBatch} into a {@link BlockingQueue} with a {@link QueuePusher}. + */ + private static class MergeCombinePartitioningAction<T> extends RecursiveAction + { + private final List<Sequence<T>> sequences; + private final Ordering<T> orderingFn; + private final BinaryOperator<T> combineFn; + private final BlockingQueue<ResultBatch<T>> out; + private final int queueSize; + private final int parallelism; + private final int yieldAfter; + private final int batchSize; + private final boolean hasTimeout; + private final long timeoutAt; + private final CancellationGizmo cancellationGizmo; + + private MergeCombinePartitioningAction( + List<Sequence<T>> sequences, + Ordering<T> orderingFn, + BinaryOperator<T> combineFn, + BlockingQueue<ResultBatch<T>> out, + int queueSize, + int parallelism, + int yieldAfter, + int batchSize, + boolean hasTimeout, + long timeoutAt, + CancellationGizmo cancellationGizmo + ) + { + this.sequences = sequences; + this.combineFn = combineFn; + this.orderingFn = orderingFn; + this.out = out; + this.queueSize = queueSize; + this.parallelism = parallelism; + this.yieldAfter = yieldAfter; + this.batchSize = batchSize; + this.hasTimeout = hasTimeout; + this.timeoutAt = timeoutAt; + this.cancellationGizmo = cancellationGizmo; + } + + @Override + protected void compute() + { + try { + final int parallelTaskCount = computeNumTasks(); + + // if we have a small number of sequences to merge, or computed paralellism is too low, do not run in parallel, + // just serially perform the merge-combine with a single task + if (sequences.size() < 4 || parallelTaskCount < 2) { Review comment: btw , following code ``` final int computedOptimalParallelism = Math.min( (int) Math.floor((double) sequences.size() / 2.0), computedParallelism - 1 ); ``` would always return a value less/equal to 1 for sequences.size() == 3 , that fact could be used to skip something. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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