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https://issues.apache.org/jira/browse/MAPREDUCE-6015?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14081023#comment-14081023
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Sangjin Lee commented on MAPREDUCE-6015:
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I understand the nature of the issue, but it also makes me wonder how effective
the proposed solution would be. There are cases like uberized jobs where the
proposed config probably cannot be used. Even in the case of non-uberized jobs,
the MR app master loads several user classes and those may still need
user.classpath.first for their operation.
Curious, have you used mapreduce.job.classloader? To me that should be a much
more robust solution, including issues in the MR app master (with the fix that
was recently made in MAPREDUCE-5957).
> Make MR ApplicationMaster disable loading user's jars firstly
> --------------------------------------------------------------
>
> Key: MAPREDUCE-6015
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-6015
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: applicationmaster
> Affects Versions: 2.4.1
> Reporter: Bing Jiang
>
> In most cases, we want to use -Dmapreduce.user.classpath.first=true to pick
> user's jars ahead of hadoop system's jars, which can make tasks run based
> upon the customized environment under the circumstance that hadoop system
> default library contains the different version of dependent jars.
> However, using -Dmapreduce.user.classpath.first=true will cause
> ApplicationMaster failure to launch due to conflicting classes.
> In most cases, if users do not customize the ApplicationMaster for MapReduce
> framework, I believe we can treat MRAppMaster different with
> MapTask/ReduceTask at the point of loading user's jar in classloader.
> I believe it can provide a property of
> '-Dmapreduce.am.user.classpath.first=false' to disable the feature of
> loading user's jars firstly.
>
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