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https://issues.apache.org/jira/browse/MAPREDUCE-4549?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13565633#comment-13565633
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Robert Joseph Evans commented on MAPREDUCE-4549:
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Do we want it on trunk?
For example if I pass in -libjar a/foo.jar -libjar b/foo.jar in 1.0 everything
will work and both foo.jar files will be on the classpath (I don't know why you
would do this, but it is possible). Under YARN only one of them will even be
shipped in the distributed cache, so there is no way at all for both of them to
be on the classpath.
With this patch it will output a warning message when a conflict occurs so
people can try and fix the issue, but eventually we want to have the upper
parts of the stack fix it, or we need to do what I was looking at doing
initially and try to keep the colliding files separate by adding in support of
sub directories in the distributed cache and using UUIDs.
> Distributed cache conflicts breaks backwards compatability
> ----------------------------------------------------------
>
> Key: MAPREDUCE-4549
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4549
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: mrv2
> Affects Versions: 0.23.3, 2.0.2-alpha
> Reporter: Robert Joseph Evans
> Assignee: Robert Joseph Evans
> Priority: Critical
> Fix For: 2.0.3-alpha, 0.23.5
>
> Attachments: MAPREDUCE-4549-trunk.patch, MR-4549-branch-0.23.txt
>
>
> I recently put in MAPREDUCE-4503 which went a bit too far, and broke
> backwards compatibility with 1.0 in distribtued cache entries. instead of
> changing the behavior of the distributed cache to more closely match 1.0
> behavior I want to just change the exception to a warning message informing
> the users that it will become an error in 2.0
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