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https://issues.apache.org/jira/browse/DRILL-6115?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16357679#comment-16357679
]
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_r167091413
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/physical/config/OrderedMuxExchange.java
---
@@ -0,0 +1,58 @@
+/**
+ * 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 final List<Ordering> orderings;
+
+ public OrderedMuxExchange(@JsonProperty("child") PhysicalOperator child,
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) {
--- End diff --
Add debug level info for `receiverToSenderMapping` and minorFragmentId.
> 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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