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https://issues.apache.org/jira/browse/MAPREDUCE-1938?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12900388#action_12900388
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Luke Lu commented on MAPREDUCE-1938:
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A couple of questions regarding the patch (filename should probably end with
.patch):
# Are the new property a system/cluster property or a per job property? i.e,
allowing user to to override the behavior (default to system jars first) per
job. Owen's comments seem to imply it's a per job switch, which should be
defined/documented in MRJobConfig (MAPREDUCE-1749)
# Why there are two boolean properties defined in the trunk patch
"mapreduce.user.classpath.first" (defined in TaskRunner) and
"mapreduce.task.classpath.user.precedence" (defined in JobContext)? The latter
seems to have no effect and not tested.
# Why use Vector (in the test code) when there doesn't seem to be need for the
list to be synchronized?
# Why do the test code use hard code paths and string literals when there are
corresponding constants defined?
> 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: mapred-1938-1, 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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