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From "Chris Douglas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-5821) IFile merge allocates new byte array for every value
Date Wed, 09 Apr 2014 00:31:17 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-5821?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13963651#comment-13963651
] 

Chris Douglas commented on MAPREDUCE-5821:
------------------------------------------

Sure, I can take a look later this week if it can wait.

> 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
>         Attachments: after-patch.png, before-patch.png, mapreduce-5821.txt, mapreduce-5821.txt
>
>
> 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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