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Posted to mapreduce-dev@hadoop.apache.org by "Jason Lowe (JIRA)" <ji...@apache.org> on 2013/05/06 20:34:16 UTC

[jira] [Created] (MAPREDUCE-5211) Reducer intermediate files can collide during merge

Jason Lowe created MAPREDUCE-5211:
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             Summary: Reducer intermediate files can collide during merge
                 Key: MAPREDUCE-5211
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5211
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: mrv2
    Affects Versions: 0.23.7, 2.0.3-alpha
            Reporter: Jason Lowe
            Assignee: Jason Lowe
            Priority: Critical


The OnDiskMerger.merge method constructs an output path that is not unique to a reduce attempt, and as a result can result in a file collision with other reducers from the same app that are running on the same node.  In addition the name of the output file is based on MapOutput.toString which may not be unique in light of multi-pass merges on disk since the mapId will be null and the basename ends up as "MapOutput(null, DISK)"

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