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From "Luke Lu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-1700) User supplied dependencies may conflict with MapReduce system JARs
Date Thu, 06 Sep 2012 21:40:09 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13450074#comment-13450074
] 

Luke Lu commented on MAPREDUCE-1700:
------------------------------------

There is no need to be scared of classloaders, especially for the simple "load only and then
exit" scenarios that we're talking about. Most of the class loader issues stem from long running
containers that need to dynamically load/unload classes. OSGi is an overkill for MR tasks.
To be clear, I'm not anti-OSGi, which I think is perfectly fine for managing server-side plugins.
                
> 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-ccl.patch, 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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