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From "Sangjin Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-10893) isolated classloader on the client side
Date Mon, 18 Aug 2014 18:02:30 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-10893?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14100957#comment-14100957
] 

Sangjin Lee commented on HADOOP-10893:
--------------------------------------

On the other hand, mapred-default.xml had a good description on the format of the system classes
value:

{panel}
A comma-separated list of classes that should be loaded from the system classpath, not the
user-supplied JARs, when mapreduce.job.classloader is enabled. Names ending in '.' (period)
are treated as package names, and names starting with a '-' are treated as negative matches.
{panel}

We could move that to the javadoc of ApplicationClassLoader, but that's a little less than
satisfying, as users (not developers) are the ones who need to override this value.

> isolated classloader on the client side
> ---------------------------------------
>
>                 Key: HADOOP-10893
>                 URL: https://issues.apache.org/jira/browse/HADOOP-10893
>             Project: Hadoop Common
>          Issue Type: New Feature
>          Components: util
>    Affects Versions: 2.4.0
>            Reporter: Sangjin Lee
>            Assignee: Sangjin Lee
>         Attachments: HADOOP-10893.patch, HADOOP-10893.patch, HADOOP-10893.patch, HADOOP-10893.patch,
classloader-test.tar.gz
>
>
> We have the job classloader on the mapreduce tasks that run on the cluster. It has a
benefit of being able to isolate class space for user code and avoid version clashes.
> Although it occurs less often, version clashes do occur on the client JVM. It would be
good to introduce an isolated classloader on the client side as well to address this. A natural
point to introduce this may be through RunJar, as that's how most of hadoop jobs are run.



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