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From "Alejandro Abdelnur (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-1700) User supplied dependencies may conflict with MapReduce system JARs
Date Thu, 04 Oct 2012 07:33:08 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13469203#comment-13469203
] 

Alejandro Abdelnur commented on MAPREDUCE-1700:
-----------------------------------------------

Nice.

What I would add is the capability of blacklisting packages. This is, if a package is blacklisted
and a class under that package hierarchy is found in the job JARs, the job should fail. This
is something avail in webapp classloaders to avoid webapps for bundling things like servlet/jsp
JARs that would break things. In our case we would blacklist common/hdfs/yarn/mapred packages
and log4j (the factory is a singleton and if present in the job JARs will trash the log configuration
of hadoop). I could see other JARs fitting this blacklist, thus I'd suggest that we have a
config property with the list of blacklisted packages.

This is isolating MR jobs from Hadoop JARs. I think we should do the same at YARN level to
isolate YARN JARs from AM JARs. Because of this, the JobClassLoader should be in common and
probably have a different name, like IsolationClassLoader. Also it should receive, in the
constructor, the blacklist.

                
> User supplied dependencies may conflict with MapReduce system JARs
> ------------------------------------------------------------------
>
>                 Key: MAPREDUCE-1700
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1700
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: task
>            Reporter: Tom White
>            Assignee: Tom White
>         Attachments: MAPREDUCE-1700-ccl.patch, MAPREDUCE-1700-ccl.patch, MAPREDUCE-1700.patch,
MAPREDUCE-1700.patch
>
>
> If user code has a dependency on a version of a JAR that is different to the one that
happens to be used by Hadoop, then it may not work correctly. This happened with user code
using a different version of Avro, as reported [here|https://issues.apache.org/jira/browse/AVRO-493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12852081#action_12852081].
> The problem is analogous to the one that application servers have with WAR loading. Using
a specialized classloader in the Child JVM is probably the way to solve this.

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