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https://issues.apache.org/jira/browse/MAPREDUCE-1938?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12972686#action_12972686
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Alejandro Abdelnur commented on MAPREDUCE-1938:
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A lot of testing goes into Hadoop before doing a release. All this testing is
done using a well defined set of libraries and sometimes a particular version
is used because of a bug fix or because the absence of a bug.
By allowing users to override the libraries used by Hadoop (in the tasks) we
are throwing overboard all the testing/certification done as part of a release
as now pieces of the cluster (the tasks) will run with who-knows-what version
of the different libraries.
IMO, this feature will be the nightmare of the team in charge of
operations/support of the Hadoop cluster.
If we introduce this feature, we should have a switch at cluster config level
that turns it off so admins can switch it off. And by default it should be off.
> 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
> Assignee: Krishna Ramachandran
> Priority: Blocker
> Fix For: 0.22.0
>
> Attachments: mapred-1938-1, mapred-1938-2.patch, mapred-1938-3.patch,
> 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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