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https://issues.apache.org/jira/browse/MAPREDUCE-1700?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tom White updated MAPREDUCE-1700:
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Attachment: MAPREDUCE-1700.patch
Thanks for the comments Alejandro.
bq. What I would add is the capability of blacklisting packages.
I think that is a good idea. Servlet containers do this - e.g. system classes
in Jetty are always loaded from the parent
(http://docs.codehaus.org/display/JETTY/Classloading). Rather than failing the
job if the class is a system class and is found in the job classpath (as you
suggested) I think it would be acceptable to log a warning but load from the
system classpath. I expect the default blacklist would be
{{java.,javax.,org.apache.commons.logging.,org.apache.log4j.,org.apache.hadoop.}}.
bq. 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.
Other YARN apps might benefit from this work, so perhaps we should add the
classloader to YARN (not Common, since HDFS shouldn't need it), and the
MR-specific parts would stay in MR, of course.
bq. we should see how to enable the classloader on the client side as well as
it may be required (to use different JARs) for the submission code. May be as
another JIRA.
I think this is a slightly different problem, since users generally have more
control over the JVM they submit from than the JVM the task runs in. So, yes,
another JIRA would be appropriate.
bq. Also, don't recall now if it is there or not, we may want o have a job
config property to disable it in case some app runs into funny issues with it.
Agreed. It's off by default in the current patch.
> 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, 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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