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Posted to mapreduce-dev@hadoop.apache.org by "Todd Lipcon (JIRA)" <ji...@apache.org> on 2014/04/04 19:50:15 UTC

[jira] [Created] (MAPREDUCE-5821) IFile merge allocates new byte array for every value

Todd Lipcon created MAPREDUCE-5821:
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             Summary: IFile merge allocates new byte array for every value
                 Key: MAPREDUCE-5821
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5821
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: performance, task
    Affects Versions: 2.4.1
            Reporter: Todd Lipcon
            Assignee: Todd Lipcon


I wrote a standalone benchmark of the MapOutputBuffer and found that it did a lot of allocations during the merge phase. After looking at an allocation profile, I found that IFile.Reader.nextRawValue() would always allocate a new byte array for every value, so the allocation rate goes way up during the merge phase of the mapper. I imagine this also affects the reducer input, though I didn't profile that.



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