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https://issues.apache.org/jira/browse/DRILL-6115?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16361121#comment-16361121
 ] 

ASF GitHub Bot commented on DRILL-6115:
---------------------------------------

Github user vrozov commented on a diff in the pull request:

    https://github.com/apache/drill/pull/1110#discussion_r167616026
  
    --- Diff: 
exec/java-exec/src/main/java/org/apache/drill/exec/physical/config/OrderedMuxExchange.java
 ---
    @@ -0,0 +1,64 @@
    +/**
    + * 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.physical.config;
    +
    +import java.util.List;
    +
    +import org.apache.drill.exec.physical.MinorFragmentEndpoint;
    +import org.apache.drill.exec.physical.base.PhysicalOperator;
    +import org.apache.drill.exec.physical.base.Receiver;
    +import org.apache.drill.common.logical.data.Order.Ordering;
    +import com.fasterxml.jackson.annotation.JsonProperty;
    +import com.fasterxml.jackson.annotation.JsonTypeName;
    +
    +/**
    + * OrderedMuxExchange is a version of MuxExchange where the incoming 
batches are sorted
    + * merge operation is performed to produced a sorted stream as output.
    + */
    +@JsonTypeName("ordered-mux-exchange")
    +public class OrderedMuxExchange extends AbstractMuxExchange {
    +  private static final org.slf4j.Logger logger = 
org.slf4j.LoggerFactory.getLogger(OrderedMuxExchange.class);
    +
    +  private final List<Ordering> orderings;
    +
    +  public OrderedMuxExchange(@JsonProperty("child") PhysicalOperator child, 
@JsonProperty("orderings")List<Ordering> orderings) {
    +    super(child);
    +    this.orderings = orderings;
    +  }
    +
    +  @Override
    +  public Receiver getReceiver(int minorFragmentId) {
    +    createSenderReceiverMapping();
    +
    +    List<MinorFragmentEndpoint> senders = 
receiverToSenderMapping.get(minorFragmentId);
    +    if (senders == null || senders.size() <= 0) {
    +      throw new IllegalStateException(String.format("Failed to find 
senders for receiver [%d]", minorFragmentId));
    +    }
    +
    +    if (logger.isDebugEnabled()) {
    +      logger.debug(String.format("Minor fragment %d, receives data from 
following senders %s", minorFragmentId, senders));
    +    }
    +
    +    return new MergingReceiverPOP(senderMajorFragmentId, senders, 
orderings, false);
    --- End diff --
    
    I don't think that locality plays a role in enabling/disabling spooling. If 
spooling was disabled for a remote receiver, it should be also disabled for a 
local receiver.


> SingleMergeExchange is not scaling up when many minor fragments are allocated 
> for a query.
> ------------------------------------------------------------------------------------------
>
>                 Key: DRILL-6115
>                 URL: https://issues.apache.org/jira/browse/DRILL-6115
>             Project: Apache Drill
>          Issue Type: Improvement
>          Components: Execution - Relational Operators
>    Affects Versions: 1.12.0
>            Reporter: Hanumath Rao Maduri
>            Assignee: Hanumath Rao Maduri
>            Priority: Major
>             Fix For: 1.13.0
>
>         Attachments: Enhancing Drill to multiplex ordered merge exchanges.docx
>
>
> SingleMergeExchange is created when a global order is required in the output. 
> The following query produces the SingleMergeExchange.
> {code:java}
> 0: jdbc:drill:zk=local> explain plan for select L_LINENUMBER from 
> dfs.`/drill/tables/lineitem` order by L_LINENUMBER;
> +------+------+
> | text | json |
> +------+------+
> | 00-00 Screen
> 00-01 Project(L_LINENUMBER=[$0])
> 00-02 SingleMergeExchange(sort0=[0])
> 01-01 SelectionVectorRemover
> 01-02 Sort(sort0=[$0], dir0=[ASC])
> 01-03 HashToRandomExchange(dist0=[[$0]])
> 02-01 Scan(table=[[dfs, /drill/tables/lineitem]], 
> groupscan=[JsonTableGroupScan [ScanSpec=JsonScanSpec 
> [tableName=maprfs:///drill/tables/lineitem, condition=null], 
> columns=[`L_LINENUMBER`], maxwidth=15]])
> {code}
> On a 10 node cluster if the table is huge then DRILL can spawn many minor 
> fragments which are all merged on a single node with one merge receiver. 
> Doing so will create lot of memory pressure on the receiver node and also 
> execution bottleneck. To address this issue, merge receiver should be 
> multiphase merge receiver. 
> Ideally for large cluster one can introduce tree merges so that merging can 
> be done parallel. But as a first step I think it is better to use the 
> existing infrastructure for multiplexing operators to generate an OrderedMux 
> so that all the minor fragments pertaining to one DRILLBIT should be merged 
> and the merged data can be sent across to the receiver operator.
> On a 10 node cluster if each node processes 14 minor fragments.
> Current version of code merges 140 minor fragments
> the proposed version has two level merges 1 - 14 merge in each drillbit which 
> is parallel 
> and 10 minorfragments are merged at the receiver node.



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