Author: acmurthy
Date: Sun Jun 16 19:09:48 2013
New Revision: 1493570
URL: http://svn.apache.org/r1493570
Log:
MAPREDUCE-5184. Document compatibility for MapReduce applications in hadoop-2
vis-a-vis hadoop-1. Contributed by Zhijie Shen.
Added:
hadoop/common/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/site/apt/MapReduce_Compatibility_Hadoop1_Hadoop2.apt.vm
Modified:
hadoop/common/trunk/hadoop-mapreduce-project/CHANGES.txt
Modified: hadoop/common/trunk/hadoop-mapreduce-project/CHANGES.txt
URL:
http://svn.apache.org/viewvc/hadoop/common/trunk/hadoop-mapreduce-project/CHANGES.txt?rev=1493570&r1=1493569&r2=1493570&view=diff
==============================================================================
--- hadoop/common/trunk/hadoop-mapreduce-project/CHANGES.txt (original)
+++ hadoop/common/trunk/hadoop-mapreduce-project/CHANGES.txt Sun Jun 16
19:09:48 2013
@@ -288,6 +288,9 @@ Release 2.1.0-beta - UNRELEASED
MAPREDUCE-5192. Allow for alternate resolutions of TaskCompletionEvents.
(cdouglas via acmurthy)
+ MAPREDUCE-5184. Document compatibility for MapReduce applications in
+ hadoop-2 vis-a-vis hadoop-1. (Zhijie Shen via acmurthy)
+
OPTIMIZATIONS
MAPREDUCE-4974. Optimising the LineRecordReader initialize() method
Added:
hadoop/common/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/site/apt/MapReduce_Compatibility_Hadoop1_Hadoop2.apt.vm
URL:
http://svn.apache.org/viewvc/hadoop/common/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/site/apt/MapReduce_Compatibility_Hadoop1_Hadoop2.apt.vm?rev=1493570&view=auto
==============================================================================
---
hadoop/common/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/site/apt/MapReduce_Compatibility_Hadoop1_Hadoop2.apt.vm
(added)
+++
hadoop/common/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/site/apt/MapReduce_Compatibility_Hadoop1_Hadoop2.apt.vm
Sun Jun 16 19:09:48 2013
@@ -0,0 +1,107 @@
+~~ Licensed 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. See accompanying LICENSE file.
+
+ ---
+ Hadoop Map Reduce Next Generation-${project.version} - Backward Compatibility
+ ---
+ ---
+ ${maven.build.timestamp}
+
+Apache Hadoop MapReduce - Migrating from Apache Hadoop 1.x to Apache Hadoop
2.x
+
+ \[ {{{../../hadoop-yarn/hadoop-yarn-site/index.html}Go Back}} \]
+
+* {Introduction}
+
+ This document provides information for users to migrate their Apache Hadoop
+ MapReduce applications from Apache Hadoop 1.x to Apache Hadoop 2.x.
+
+ In Apache Hadoop 2.x we have spun off resource management capabilities
+ into Apache Hadoop YARN, a general purpose, distributed application
management
+ framework while Apache Hadoop MapReduce (aka MRv2) remains as a pure
+ distributed computation framework.
+
+ In general, the previous MapReduce runtime (aka MRv1) has been reused and
+ no major surgery has been conducted on it. Therefore, MRv2 is able to ensure
+ satisfactory compatibility with MRv1 applications. However, due to some
+ improvements and code refactorings, a few APIs have been rendered
+ backward-incompatible.
+
+ The remainder of this page will discuss the scope and the level of backward
+ compatibility that we support in Apache Hadoop MapReduce 2.x (MRv2).
+
+* {Binary Compatibility}
+
+ First, we ensure binary compatibility to the applications that use old
+ <<mapred>> APIs. This means that applications which were built against MRv1
+ <<mapred>> APIs can run directly on YARN without recompilation, merely by
+ pointing them to an Apache Hadoop 2.x cluster via configuration.
+
+* {Source Compatibility}
+
+ We cannot ensure complete binary compatibility with the applications that use
+ <<mapreduce>> APIs, as these APIs have evolved a lot since MRv1. However, we
+ ensure source compatibility for <<mapreduce>> APIs that break binary
+ compatibility. In other words, users should recompile their applications
that
+ use <<mapreduce>> APIs against MRv2 jars. One notable binary incompatibility
+ break is Counter and CounterGroup.
+
+* {Not Supported}
+
+ MRAdmin has been removed in MRv2 because because <<<mradmin>>> commands
+ no longer exist. They have been replaced by the commands in <<<rmadmin>>>. We
+ neither support binary compatibility nor source compatibility for the
+ applications that use this class directly.
+
+* {Tradeoffs between MRv1 Users and Early MRv2 Adopters}
+
+ Unfortunately, maintaining binary compatibility for MRv1 applications may
lead
+ to binary incompatibility issues for early MRv2 adopters, in particular
Hadoop
+ 0.23 users. For <<mapred>> APIs, we have chosen to be compatible with MRv1
+ applications, which have a larger user base. For <<mapreduce>> APIs, if they
+ don't significantly break Hadoop 0.23 applications, we still change them to
be
+ compatible with MRv1 applications. Below is the list of MapReduce APIs which
+ are incompatible with Hadoop 0.23.
+
+*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
+| <<Problematic Function>>
| <<Incompatibility Issue>>
|
+*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
+| <<<org.apache.hadoop.util.ProgramDriver#drive>>>
| Return type changes from <<<void>>> to <<<int>>>
|
+*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
+| <<<org.apache.hadoop.mapred.jobcontrol.Job#getMapredJobID>>>
| Return type changes from <<<String>>> to <<<JobID>>>
|
+*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
+| <<<org.apache.hadoop.mapred.TaskReport#getTaskId>>>
| Return type changes from <<<String>>> to <<<TaskID>>>
|
+*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
+| <<<org.apache.hadoop.mapred.ClusterStatus#UNINITIALIZED_MEMORY_VALUE>>>
| Data type changes from <<<long>>> to <<<int>>>
|
+*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
+|
<<<org.apache.hadoop.mapreduce.filecache.DistributedCache#getArchiveTimestamps>>>
| Return type changes from <<<long[]>>> to <<<String[]>>>
|
+*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
+|
<<<org.apache.hadoop.mapreduce.filecache.DistributedCache#getFileTimestamps>>>
| Return type changes from <<<long[]>>> to <<<String[]>>>
|
+*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
+| <<<org.apache.hadoop.mapreduce.Job#failTask>>>
| Return type changes from <<<void>>> to <<<boolean>>>
|
+*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
+| <<<org.apache.hadoop.mapreduce.Job#killTask>>>
| Return type changes from <<<void>>> to <<<boolean>>>
|
+*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
+| <<<org.apache.hadoop.mapreduce.Job#getTaskCompletionEvents>>>
| Return type changes from <<<o.a.h.mapred.TaskCompletionEvent[]>>> to
<<<o.a.h.mapreduce.TaskCompletionEvent[]>>> |
+*-----------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------+
+
+* {Malicious}
+
+ For the users who are going to try <<<hadoop-examples-1.x.x.jar>>> on YARN,
+ please note that <<<hadoop -jar hadoop-examples-1.x.x.jar>>> will still use
+ <<<hadoop-mapreduce-examples-2.x.x.jar>>>, which is installed together with
+ other MRv2 jars. By default Hadoop framework jars appear before the users'
+ jars in the classpath, such that the classes from the 2.x.x jar will still be
+ picked. Users should either remove <<<hadoop-mapreduce-examples-2.x.x.jar>>>
+ from the classpath or set <<<HADOOP_USER_CLASSPATH_FIRST=true>>> and
+ <<<HADOOP_CLASSPATH=...:hadoop-examples-1.x.x.jar>>> to run their target
+ examples jar.
