MAPREDUCE-5184. Document compatibility for MapReduce applications in hadoop-2 vis-a-vis hadoop-1. Contributed by Zhijie Shen.
git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1493570 13f79535-47bb-0310-9956-ffa450edef68
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Arun Murthy
parent
98d97d316c
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7f96128e43
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@ -288,6 +288,9 @@ Release 2.1.0-beta - UNRELEASED
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MAPREDUCE-5192. Allow for alternate resolutions of TaskCompletionEvents.
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(cdouglas via acmurthy)
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MAPREDUCE-5184. Document compatibility for MapReduce applications in
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hadoop-2 vis-a-vis hadoop-1. (Zhijie Shen via acmurthy)
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OPTIMIZATIONS
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MAPREDUCE-4974. Optimising the LineRecordReader initialize() method
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@ -0,0 +1,107 @@
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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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Hadoop Map Reduce Next Generation-${project.version} - Backward Compatibility
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---
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---
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${maven.build.timestamp}
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Apache Hadoop MapReduce - Migrating from Apache Hadoop 1.x to Apache Hadoop 2.x
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\[ {{{../../hadoop-yarn/hadoop-yarn-site/index.html}Go Back}} \]
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* {Introduction}
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This document provides information for users to migrate their Apache Hadoop
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MapReduce applications from Apache Hadoop 1.x to Apache Hadoop 2.x.
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In Apache Hadoop 2.x we have spun off resource management capabilities
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into Apache Hadoop YARN, a general purpose, distributed application management
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framework while Apache Hadoop MapReduce (aka MRv2) remains as a pure
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distributed computation framework.
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In general, the previous MapReduce runtime (aka MRv1) has been reused and
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no major surgery has been conducted on it. Therefore, MRv2 is able to ensure
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satisfactory compatibility with MRv1 applications. However, due to some
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improvements and code refactorings, a few APIs have been rendered
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backward-incompatible.
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The remainder of this page will discuss the scope and the level of backward
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compatibility that we support in Apache Hadoop MapReduce 2.x (MRv2).
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* {Binary Compatibility}
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First, we ensure binary compatibility to the applications that use old
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<<mapred>> APIs. This means that applications which were built against MRv1
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<<mapred>> APIs can run directly on YARN without recompilation, merely by
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pointing them to an Apache Hadoop 2.x cluster via configuration.
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* {Source Compatibility}
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We cannot ensure complete binary compatibility with the applications that use
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<<mapreduce>> APIs, as these APIs have evolved a lot since MRv1. However, we
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ensure source compatibility for <<mapreduce>> APIs that break binary
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compatibility. In other words, users should recompile their applications that
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use <<mapreduce>> APIs against MRv2 jars. One notable binary incompatibility
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break is Counter and CounterGroup.
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* {Not Supported}
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MRAdmin has been removed in MRv2 because because <<<mradmin>>> commands
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no longer exist. They have been replaced by the commands in <<<rmadmin>>>. We
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neither support binary compatibility nor source compatibility for the
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applications that use this class directly.
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* {Tradeoffs between MRv1 Users and Early MRv2 Adopters}
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Unfortunately, maintaining binary compatibility for MRv1 applications may lead
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to binary incompatibility issues for early MRv2 adopters, in particular Hadoop
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0.23 users. For <<mapred>> APIs, we have chosen to be compatible with MRv1
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applications, which have a larger user base. For <<mapreduce>> APIs, if they
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don't significantly break Hadoop 0.23 applications, we still change them to be
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compatible with MRv1 applications. Below is the list of MapReduce APIs which
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are incompatible with Hadoop 0.23.
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*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
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| <<Problematic Function>> | <<Incompatibility Issue>> |
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*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
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| <<<org.apache.hadoop.util.ProgramDriver#drive>>> | Return type changes from <<<void>>> to <<<int>>> |
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*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
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| <<<org.apache.hadoop.mapred.jobcontrol.Job#getMapredJobID>>> | Return type changes from <<<String>>> to <<<JobID>>> |
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*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
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| <<<org.apache.hadoop.mapred.TaskReport#getTaskId>>> | Return type changes from <<<String>>> to <<<TaskID>>> |
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*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
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| <<<org.apache.hadoop.mapred.ClusterStatus#UNINITIALIZED_MEMORY_VALUE>>> | Data type changes from <<<long>>> to <<<int>>> |
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*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
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| <<<org.apache.hadoop.mapreduce.filecache.DistributedCache#getArchiveTimestamps>>> | Return type changes from <<<long[]>>> to <<<String[]>>> |
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*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
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| <<<org.apache.hadoop.mapreduce.filecache.DistributedCache#getFileTimestamps>>> | Return type changes from <<<long[]>>> to <<<String[]>>> |
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*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
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| <<<org.apache.hadoop.mapreduce.Job#failTask>>> | Return type changes from <<<void>>> to <<<boolean>>> |
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*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
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| <<<org.apache.hadoop.mapreduce.Job#killTask>>> | Return type changes from <<<void>>> to <<<boolean>>> |
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*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
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| <<<org.apache.hadoop.mapreduce.Job#getTaskCompletionEvents>>> | Return type changes from <<<o.a.h.mapred.TaskCompletionEvent[]>>> to <<<o.a.h.mapreduce.TaskCompletionEvent[]>>> |
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*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
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* {Malicious}
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For the users who are going to try <<<hadoop-examples-1.x.x.jar>>> on YARN,
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please note that <<<hadoop -jar hadoop-examples-1.x.x.jar>>> will still use
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<<<hadoop-mapreduce-examples-2.x.x.jar>>>, which is installed together with
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other MRv2 jars. By default Hadoop framework jars appear before the users'
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jars in the classpath, such that the classes from the 2.x.x jar will still be
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picked. Users should either remove <<<hadoop-mapreduce-examples-2.x.x.jar>>>
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from the classpath or set <<<HADOOP_USER_CLASSPATH_FIRST=true>>> and
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<<<HADOOP_CLASSPATH=...:hadoop-examples-1.x.x.jar>>> to run their target
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examples jar.
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@ -79,6 +79,7 @@
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</menu>
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<menu name="MapReduce" inherit="top">
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<item name="Compatibilty between Hadoop 1.x and Hadoop 2.x" href="hadoop-mapreduce-client/hadoop-mapreduce-client-core/MapReduce_Compatibility_Hadoop1_Hadoop2.html"/>
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<item name="Encrypted Shuffle" href="hadoop-mapreduce-client/hadoop-mapreduce-client-core/EncryptedShuffle.html"/>
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<item name="Pluggable Shuffle/Sort" href="hadoop-mapreduce-client/hadoop-mapreduce-client-core/PluggableShuffleAndPluggableSort.html"/>
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</menu>
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@ -53,5 +53,6 @@ MapReduce NextGen aka YARN aka MRv2
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* {{{../../hadoop-project-dist/hadoop-common/CLIMiniCluster.html}CLI MiniCluster}}
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* {{{../../hadoop-mapreduce-client/hadoop-mapreduce-client-core/EncryptedShuffle.html}Encrypted Shuffle}}
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* {{{../../hadoop-mapreduce-client/hadoop-mapreduce-client-core/MapReduce_Compatibility_Hadoop1_Hadoop2.html}Backward Compatibility between Apache Hadoop 1.x and 2.x for MapReduce}}
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* {{{../../hadoop-mapreduce-client/hadoop-mapreduce-client-core/EncryptedShuffle.html}Encrypted Shuffle}}
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