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https://issues.apache.org/jira/browse/MAPREDUCE-1700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13449430#comment-13449430
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Luke Lu commented on MAPREDUCE-1700:
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bq. Without a user doing classloader gymnasitics and fancy packaging
themselves, there is not always a way.
That's an interesting way to say that except for some ways that would always
work, there is not always a way. Using the standard task API to bootstrap an
OSGi container is reasonably straight forward :)
bq. A user cannot simply package a jar up and ask hadoop to execute it and
expose to the user's execution environment only the public Hadoop API.
I do agree that there is a usability issue for certain (and arguably less
common) use cases, where a user wants to use dependencies that conflict with
client framework. However the proposed OSGi approach makes the usability worse
for common cases: You'll always need OSGi bundles, which is a form of "fancy
packaging", to run your jobs.
A more reasonable (and less heavy) solution would not require users to make any
change (including adding metadata to their jars) to their existing code.
> 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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