Github user arina-ielchiieva commented on a diff in the pull request: https://github.com/apache/drill/pull/928#discussion_r142723896 --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/work/foreman/rm/DistributedQueryQueue.java --- @@ -0,0 +1,342 @@ +/* + * 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.drill.exec.work.foreman.rm; + +import java.util.concurrent.TimeUnit; + +import javax.xml.bind.annotation.XmlRootElement; + +import org.apache.drill.exec.ExecConstants; +import org.apache.drill.exec.coord.ClusterCoordinator; +import org.apache.drill.exec.coord.DistributedSemaphore; +import org.apache.drill.exec.coord.DistributedSemaphore.DistributedLease; +import org.apache.drill.exec.proto.UserBitShared.QueryId; +import org.apache.drill.exec.proto.helper.QueryIdHelper; +import org.apache.drill.exec.server.DrillbitContext; +import org.apache.drill.exec.server.options.SystemOptionManager; + +/** + * Distributed query queue which uses a Zookeeper distributed semaphore to + * control queuing across the cluster. The distributed queue is actually two + * queues: one for "small" queries, another for "large" queries. Query size is + * determined by the Planner's estimate of query cost. + * <p> + * This queue is configured using system options: + * <dl> + * <dt><tt>exec.queue.enable</tt> + * <dt> + * <dd>Set to true to enable the distributed queue.</dd> + * <dt><tt>exec.queue.large</tt> + * <dt> + * <dd>The maximum number of large queries to admit. Additional + * queries wait in the queue.</dd> + * <dt><tt>exec.queue.small</tt> + * <dt> + * <dd>The maximum number of small queries to admit. Additional + * queries wait in the queue.</dd> + * <dt><tt>exec.queue.threshold</tt> + * <dt> + * <dd>The cost threshold. Queries below this size are small, at + * or above this size are large..</dd> + * <dt><tt>exec.queue.timeout_millis</tt> + * <dt> + * <dd>The maximum time (in milliseconds) a query will wait in the + * queue before failing.</dd> + * </dl> + * <p> + * The above values are refreshed every five seconds. This aids performance + * a bit in systems with very high query arrival rates. + */ + +public class DistributedQueryQueue implements QueryQueue { + private static final org.slf4j.Logger logger = org.slf4j.LoggerFactory.getLogger(DistributedQueryQueue.class); + + private class DistributedQueueLease implements QueueLease { --- End diff -- Frankly saying, I prefer when class content (like variables and methods) are placed at the top of class, and other helper stuff at the bottom, not critical though.
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