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From "Harsh J (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-199) Locality hints for Reduce
Date Mon, 10 Sep 2012 15:30:08 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-199?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13452070#comment-13452070

Harsh J commented on MAPREDUCE-199:

bq. I'm not sure I see the value in user-specifying 'hints', the way to get this to work is
to 'figure' where the map-outputs are (the AM knows it) and then try to pick the right hosts/racks.

This is good too, as an auto-optimization of regular MR apps. However, 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.

Seems like we can go for two things:

# Auto-optimize by default, so that all users benefit somehow.
# Provide a way to override the automation via API supplied partition->host mappings, to
allow those who want to control for other odd purposes.

Arun - Would this be good?
> 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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