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https://issues.apache.org/jira/browse/MAPREDUCE-1700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13448882#comment-13448882
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Luke Lu commented on MAPREDUCE-1700:
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bq. The conflict might require a user jar that is not compatible with one
needed by the framework, either order breaks something
You can always change the client framework and make it work with user code, per
job, with class path ordering. There is currently always a way in both Hadoop 1
and 2 to submit a job with arbitrary dependencies, even though it might not be
pretty (may require change to client framework).
bq. The user might override a system jar and alter functionality in a way that
breaks the framework, or subverts security.
The client framework code can always be changed per job to accommodate new
dependencies. MR security is done at protocol level, i.e. no amount class path
ordering can subvert security.
I agree with Arun that this is a nice to have feature to improve usability.
Advanced users can already achieve whatever that can be achieved (including
running an OSGi container) per job.
> 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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