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https://issues.apache.org/jira/browse/MAPREDUCE-1700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13450030#comment-13450030
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Steve Loughran commented on MAPREDUCE-1700:
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no, we don't want to go anywhere near servlet classloaders, because you end up
in WAR EAR and app server trees. The app server takes priority, except in the
special case of JBoss in the past, which shared classes across webapps
https://community.jboss.org/wiki/JBossClassLoaderHistory
http://docs.jboss.org/jbossweb/2.1.x/class-loader-howto.html
people will hit walls when they try to do things like upgrade the XML parser or
try and add a new URL handler.
I'll look at the patch, but classloaders are a mine of grief. That's the
strength of OSGi: the grief is standardised an someone else has done the grief
mining already
> 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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