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Date: Mon, 20 Aug 2012 18:05:38 +1100 (NCT)
From: "Tsuyoshi OZAWA (JIRA)" <jira@apache.org>
To: mapreduce-issues@hadoop.apache.org
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Subject: [jira] [Commented] (MAPREDUCE-4502) Multi-level aggregation with
 combining the result of maps per node/rack
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    [ https://issues.apache.org/jira/browse/MAPREDUCE-4502?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13437688#comment-13437688 ] 

Tsuyoshi OZAWA commented on MAPREDUCE-4502:
-------------------------------------------

I'm working on refactoring ApplicationMaster of MapReduce to come true re-using containers(MAPREDUCE-3902) with Siddharth.
                
> Multi-level aggregation with combining the result of maps per node/rack
> -----------------------------------------------------------------------
>
>                 Key: MAPREDUCE-4502
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4502
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: applicationmaster, mrv2
>            Reporter: Tsuyoshi OZAWA
>
> The shuffle costs is expensive in Hadoop in spite of the existence of combiner, because the scope of combining is limited within only one MapTask. To solve this problem, it's a good way to aggregate the result of maps per node/rack by launch combiner.
> This JIRA is to implement the multi-level aggregation infrastructure, including combining per container(MAPREDUCE-3902 is related), coordinating containers by application master without breaking fault tolerance of jobs.

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