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https://issues.apache.org/jira/browse/SPARK-2774?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14085418#comment-14085418
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Reynold Xin commented on SPARK-2774:
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I assigned to ticket to [~shivaram] and scoped this for 1.2 release.
> Set preferred locations for reduce tasks
> ----------------------------------------
>
> Key: SPARK-2774
> URL: https://issues.apache.org/jira/browse/SPARK-2774
> Project: Spark
> Issue Type: Improvement
> Components: Spark Core
> Reporter: Shivaram Venkataraman
> Assignee: Shivaram Venkataraman
>
> Currently we do not set preferred locations for reduce tasks in Spark. This
> patch proposes setting preferred locations based on the map output sizes and
> locations tracked by the MapOutputTracker. This is useful in two conditions
> 1. When you have a small job in a large cluster it can be useful to co-locate
> map and reduce tasks to avoid going over the network
> 2. If there is a lot of data skew in the map stage outputs, then it is
> beneficial to place the reducer close to the largest output.
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