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https://issues.apache.org/jira/browse/MAPREDUCE-1938?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12888536#action_12888536
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Owen O'Malley commented on MAPREDUCE-1938:
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This patch basically puts the user in charge of their job. They can leave the
safety switch set in which case they get the current behavior. But if they turn
off the safety, their classes go ahead of the ones installed on the cluster.
That means that they can break things, but all they can break is their own
tasks.
After we do the split of core from library, you still need this switch. There
will always be the possibility of needing to patch something in the core,
because even MapTask has bugs. *smile* After splitting them apart, we can put
the library code at the very end
safety on: core, user, library
safety off: user, core, library
This patch is just about providing the safety switch.
> Ability for having user's classes take precedence over the system classes for
> tasks' classpath
> ----------------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-1938
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1938
> Project: Hadoop Map/Reduce
> Issue Type: New Feature
> Components: job submission, task, tasktracker
> Reporter: Devaraj Das
> Fix For: 0.22.0
>
> Attachments: mr-1938-bp20.1.patch, mr-1938-bp20.patch
>
>
> It would be nice to have the ability in MapReduce to allow users to specify
> for their jobs alternate implementations of classes that are already defined
> in the MapReduce libraries. For example, an alternate implementation for
> CombineFileInputFormat.
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