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From "Arun C Murthy (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-1700) User supplied dependencies may conflict with MapReduce system JARs
Date Tue, 04 Sep 2012 18:35:09 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13447911#comment-13447911
] 

Arun C Murthy commented on MAPREDUCE-1700:
------------------------------------------

Tom, I don't understand specific advantages of OSGI or Felix, so please pardon some of my
questions.

However, with MR being an application in YARN (see MAPREDUCE-4421) we can just add user jars
in front of the classpath for the tasks (we already allow it). This isn't the same Map/Reduce
child inherits the TT classpath problem in MR1 (actually even in MR1 you can put child jars
ahead in the classpath for a long while now). Given this, do we need to bring in OSGI or Felix,
what do else do they provide? Thanks.
                
> User supplied dependencies may conflict with MapReduce system JARs
> ------------------------------------------------------------------
>
>                 Key: MAPREDUCE-1700
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1700
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: task
>            Reporter: Tom White
>            Assignee: Tom White
>         Attachments: MAPREDUCE-1700.patch, MAPREDUCE-1700.patch
>
>
> If user code has a dependency on a version of a JAR that is different to the one that
happens to be used by Hadoop, then it may not work correctly. This happened with user code
using a different version of Avro, as reported [here|https://issues.apache.org/jira/browse/AVRO-493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12852081#action_12852081].
> The problem is analogous to the one that application servers have with WAR loading. Using
a specialized classloader in the Child JVM is probably the way to solve this.

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