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Date: Tue, 11 Sep 2012 05:30:08 +1100 (NCT)
From: "Arun C Murthy (JIRA)" <jira@apache.org>
To: mapreduce-issues@hadoop.apache.org
Message-ID: <1804773508.58957.1347301808921.JavaMail.jiratomcat@arcas>
Subject: [jira] [Commented] (MAPREDUCE-199) Locality hints for Reduce
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    [ https://issues.apache.org/jira/browse/MAPREDUCE-199?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13452276#comment-13452276 ] 

Arun C Murthy commented on MAPREDUCE-199:
-----------------------------------------

Harsh - I'm not familiar with the HBase case; can you please add more colour?

bq.  in HBase-land we would benefit by direct control if the reducer can be scheduled directly onto the RegionServer that hosts the sorted area of keys the reducer is going to process, or even fetch.

In this case, won't it be sufficient to schedule maps on the RS? If the data is already sorted, but would you try schedule reduces instead? 

My concern adding apis/config is that it becomes part of the user interface and I'd like to think through it's implications, and whether it's really necessary, before we commit to it. Makes sense?
                
> Locality hints for Reduce
> -------------------------
>
>                 Key: MAPREDUCE-199
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-199
>             Project: Hadoop Map/Reduce
>          Issue Type: New Feature
>          Components: applicationmaster, mrv2
>            Reporter: Benjamin Reed
>            Assignee: Harsh J
>         Attachments: MAPREDUCE-199.patch, MAPREDUCE-199.patch
>
>
> It would be nice if we could add method to OutputFormat that would allow a job to indicate where a reducer for a given partition should should run. This is similar to the getSplits() method on InputFormat. In our application the reducer is using other data in addition to the map outputs during processing and data accesses could be made more efficient if the JobTracker scheduled the reducers to run on specific hosts.

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