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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-5716) Queue-based memory assignment for buffering operators
Date Fri, 06 Oct 2017 03:25:03 GMT

    [ https://issues.apache.org/jira/browse/DRILL-5716?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16194083#comment-16194083
] 

ASF GitHub Bot commented on DRILL-5716:
---------------------------------------

Github user paul-rogers commented on a diff in the pull request:

    https://github.com/apache/drill/pull/928#discussion_r143082265
  
    --- 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 --
    
    Does Drill have a standard? Nested-classes-at-the-top is the rule I've always followed,
though in Drill I also see classes-at-the-bottom and even classes-in-the-middle.


> Queue-based memory assignment for buffering operators
> -----------------------------------------------------
>
>                 Key: DRILL-5716
>                 URL: https://issues.apache.org/jira/browse/DRILL-5716
>             Project: Apache Drill
>          Issue Type: Improvement
>    Affects Versions: 1.11.0
>            Reporter: Paul Rogers
>            Assignee: Paul Rogers
>              Labels: doc-impacting
>             Fix For: 1.12.0
>
>
> Apache Drill already has a queueing feature based on ZK semaphores. We did a bit of testing
to  show that the feature does, in fact work. We propose to enhance the feature with some
light revisions to make work with the "managed" external sort and the newly-added spilling
feature for the hash agg operator. The key requirement is to build on what we have for now;
we may want to tackle a larger project to create a more complete solution later.
> Existing functionality:
> * Two ZK-based queues called the “small” and “large” query queues.
> * A threshold, call it T, given as a query cost, to determine the queue into which a
query will go.
> * Admit levels for the two queues: call them Qs and Ql.
> Basically, when a query comes in:
> * Plan the query as usual.
> * Obtain the final query cost from the planner, call this C.
> * If C<T, the query goes into the small queue, else it goes into the large queue.
> * Suppose the small queue. Ask ZK if the query can run.
> * ZK checks if Qs queries are already running. If so, the query waits, else the query
runs.
> The proposed changes include:
> * Refactor the code to provide a queueing API that supports a variety of queuing mechanisms.
> * Provide three: the null queue (default), an in-process queue (for testing) and the
ZK queues.
> * Modify the query profile web UI to show two new bits of information about queues:
> - The queue to which the query was sent.
> - The total planning cost.
> * Modify the query profile web UI to show two memory assignment numbers:
> - Total memory allocated to the query
> - Memory per sort or hash-add operator
> Then, add to the queue mechanism the ability to do memory assignment:
> * Provide a weight, W: every small query gets 1 unit, every large query gets W units.
> * Use the queue admit levels to determine total units: U = Qs + W * Ql.
> * Obtain total direct memory from the system. M.
> * Subtract a reserve percent R for overhead.
> * Do the math to get the memory per query for each query:
> * For the small queue: (M - R) / U
> * For the large queue: (M - R) / U * W
> * Use this memory amount as the “memory per query” number in the existing sort/hash-agg
memory assignment (instead of the fixed 2 GB.)
> The result will be a nice incremental addition to what we already have, and should make
it a bit easier people to actually use the feature (because they can see the planning numbers
and see the queues used, allowing them to effectively tune the system.)
> The API used for the above features also allow third parties to add on a more robust
admission control feature as needed, perhaps tying into an existing queueing mechanism of
their choice.



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