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+~~ Licensed under the Apache License, Version 2.0 (the "License");
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+~~ you may not use this file except in compliance with the License.
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+~~ You may obtain a copy of the License at
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+~~
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+~~ http://www.apache.org/licenses/LICENSE-2.0
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+~~
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+~~ Unless required by applicable law or agreed to in writing, software
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+~~ distributed under the License is distributed on an "AS IS" BASIS,
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+~~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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+~~ See the License for the specific language governing permissions and
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+~~ limitations under the License. See accompanying LICENSE file.
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+
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+ ---
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+ Hadoop Map Reduce Next Generation-${project.version} - Pluggable Shuffle and Pluggable Sort
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+ ---
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+ ---
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+ ${maven.build.timestamp}
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+
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+Hadoop MapReduce Next Generation - Pluggable Shuffle and Pluggable Sort
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+
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+ \[ {{{./index.html}Go Back}} \]
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+
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+* Introduction
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+
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+ The pluggable shuffle and pluggable sort capabilities allow replacing the
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+ built in shuffle and sort logic with alternate implementations. Example use
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+ cases for this are: using a different application protocol other than HTTP
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+ such as RDMA for shuffling data from the Map nodes to the Reducer nodes; or
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+ replacing the sort logic with custom algorithms that enable Hash aggregation
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+ and Limit-N query.
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+
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+ <<IMPORTANT:>> The pluggable shuffle and pluggable sort capabilities are
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+ experimental and unstable. This means the provided APIs may change and break
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+ compatibility in future versions of Hadoop.
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+
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+* Implementing a Custom Shuffle and a Custom Sort
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+
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+ A custom shuffle implementation requires a
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+ <<<org.apache.hadoop.yarn.server.nodemanager.containermanager.AuxServices.AuxiliaryService>>>
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+ implementation class running in the NodeManagers and a
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+ <<<org.apache.hadoop.mapred.ShuffleConsumerPlugin>>> implementation class
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+ running in the Reducer tasks.
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+
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+ The default implementations provided by Hadoop can be used as references:
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+
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+ * <<<org.apache.hadoop.mapred.ShuffleHandler>>>
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+
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+ * <<<org.apache.hadoop.mapreduce.task.reduce.Shuffle>>>
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+
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+ A custom sort implementation requires a <<<org.apache.hadoop.mapred.MapOutputCollector>>>
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+ implementation class running in the Mapper tasks and (optionally, depending
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+ on the sort implementation) a <<<org.apache.hadoop.mapred.ShuffleConsumerPlugin>>>
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+ implementation class running in the Reducer tasks.
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+
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+ The default implementations provided by Hadoop can be used as references:
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+
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+ * <<<org.apache.hadoop.mapred.MapTask$MapOutputBuffer>>>
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+
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+ * <<<org.apache.hadoop.mapreduce.task.reduce.Shuffle>>>
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+
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+* Configuration
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+
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+ Except for the auxiliary service running in the NodeManagers serving the
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+ shuffle (by default the <<<ShuffleHandler>>>), all the pluggable components
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+ run in the job tasks. This means, they can be configured on per job basis.
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+ The auxiliary service servicing the Shuffle must be configured in the
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+ NodeManagers configuration.
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+
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+** Job Configuration Properties (on per job basis):
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+
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+*--------------------------------------+---------------------+-----------------+
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+| <<Property>> | <<Default Value>> | <<Explanation>> |
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+*--------------------------------------+---------------------+-----------------+
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+| <<<mapreduce.job.reduce.shuffle.consumer.plugin.class>>> | <<<org.apache.hadoop.mapreduce.task.reduce.Shuffle>>> | The <<<ShuffleConsumerPlugin>>> implementation to use |
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+*--------------------------------------+---------------------+-----------------+
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+| <<<mapreduce.job.map.output.collector.class>>> | <<<org.apache.hadoop.mapred.MapTask$MapOutputBuffer>>> | The <<<MapOutputCollector>>> implementation to use |
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+*--------------------------------------+---------------------+-----------------+
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+
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+ These properties can also be set in the <<<mapred-site.xml>>> to change the default values for all jobs.
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+
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+** NodeManager Configuration properties, <<<yarn-site.xml>>> in all nodes:
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+
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+*--------------------------------------+---------------------+-----------------+
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+| <<Property>> | <<Default Value>> | <<Explanation>> |
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+*--------------------------------------+---------------------+-----------------+
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+| <<<yarn.nodemanager.aux-services>>> | <<<...,mapreduce.shuffle>>> | The auxiliary service name |
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+*--------------------------------------+---------------------+-----------------+
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+| <<<yarn.nodemanager.aux-services.mapreduce.shuffle.class>>> | <<<org.apache.hadoop.mapred.ShuffleHandler>>> | The auxiliary service class to use |
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+*--------------------------------------+---------------------+-----------------+
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+
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+ <<IMPORTANT:>> If setting an auxiliary service in addition the default
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+ <<<mapreduce.shuffle>>> service, then a new service key should be added to the
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+ <<<yarn.nodemanager.aux-services>>> property, for example <<<mapred.shufflex>>>.
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+ Then the property defining the corresponding class must be
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+ <<<yarn.nodemanager.aux-services.mapreduce.shufflex.class>>>.
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+
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Alejandro Abdelnur