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From "Luke Lu (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1938) Ability for having user's classes take precedence over the system classes for tasks' classpath
Date Thu, 19 Aug 2010 18:22:21 GMT

    [ 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:
------------------------------------

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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