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From "Robert Joseph Evans (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-4647) We should only unjar jobjar if there is a lib directory in it.
Date Mon, 10 Sep 2012 16:06:07 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4647?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13452105#comment-13452105
] 

Robert Joseph Evans commented on MAPREDUCE-4647:
------------------------------------------------

I think that it is a regression.  It looks like Yarn/MRV2 changed the handling of job.jar
to be through the distributed cache.  Originally we only added the jar to the classpath as
a cache file.  MAPREDUCE-4068 then changed it to be a cache archive so that the classes and
lib directories could be added to the classpath.  So both of those together effectively undid
MAPREDUCE-967.  I am not sure how simple it will be to try and fully implement MAPREUDCE-967
again, because the job.jar is going through the distributed cache and this really is behavior
that seems to be MAPREDUCE specific, unless we want to some how try and make it generic for
everyone on YARN.

That is why I wanted to have the client look at the jar and decided if it should be a cache
file, or a cache archive.  From what I have seen very few jars actually rely on this behavior.
 If you would prefer to make it generic for YARN I can look into that instead.  It should
not be too hard, but it might require a small change to the container launch context.
                
> We should only unjar jobjar if there is a lib directory in it.
> --------------------------------------------------------------
>
>                 Key: MAPREDUCE-4647
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4647
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: mrv2
>    Affects Versions: 0.23.3
>            Reporter: Robert Joseph Evans
>            Assignee: Robert Joseph Evans
>
> For backwards compatibility we recently added made is so we would unjar the job.jar and
add anything to the classpath in the lib directory of that jar.  But this also slows job startup
down a lot if the jar is large.  We should only unjar it if actually doing so would add something
new to the classpath.

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