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From "Robert Joseph Evans (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-4549) Distributed cache conflicts breaks backwards compatability
Date Mon, 13 Aug 2012 14:30:38 GMT
Robert Joseph Evans created MAPREDUCE-4549:

             Summary: 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, 2.1.0-alpha, 3.0.0, 2.2.0-alpha
            Reporter: Robert Joseph Evans
            Assignee: Robert Joseph Evans
            Priority: Critical

I recently put in MAPREDUCE-4503 which went a bit too far, and broke backwards compatibility
with 1.0 in distribtued cache entries.  This is to change the behavior of the distributed
cache to more closely match that of 1.0.

In 1.0 when adding in a cache archive link the first link would win (be the one that was created),
not the last one as is the current behavior, when there were conflicts then all of the others
were ignored and just did not get a symlink created, and finally no symlink was created for
archives that had did not have a fragment in the URL.  

To simulate this behavior after we parse the cache files and cache archives configuration
we should walk through all conflicting links and pick the first link that has a fragment to
win.  If no link has a fragment then it is just the first link wins.  All other conflicting
links will have a warning an the name of the link will be changed to include a UUID.  If the
same file is both in the distributed cache as a cache file and a cache archive we will throw
an exception, for backwards compatibility.

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