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https://issues.apache.org/jira/browse/MAPREDUCE-259?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Allen Wittenauer resolved MAPREDUCE-259.
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Resolution: Duplicate
> 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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