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From "nemon lou (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-259) Rack-aware Shuffle
Date Sat, 25 May 2013 02:20:20 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13666927#comment-13666927
] 

nemon lou commented on MAPREDUCE-259:
-------------------------------------

MAPREDUCE-2038 is doing the same thing,but is not updated for a long time,too.
                
> Rack-aware Shuffle
> ------------------
>
>                 Key: MAPREDUCE-259
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-259
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>            Reporter: Arun C Murthy
>            Assignee: Arun C Murthy
>
> We could try and experiment with *rack-aware* scheduling of fetches per-reducer. Given
the disparities between in-rack and off-rack bandwidth it could be a improvement to do something
along these lines:
> {noformat}
> if (no. of known map-output locations > than no. of copier threads) {
>   try to schedule 75% of copies off-rack
>   try schedule 25% of copies in-rack
> }
> {noformat}
> This could lead to better utilization of both in-rack & switch b/w...
> Clearly we want to schedule more cross-switch than in-rack since off-rack copies will
take significantly more time; hence the 75-25 split.

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