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https://issues.apache.org/jira/browse/HADOOP-3308?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12592438#action_12592438
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Tsz Wo (Nicholas), SZE commented on HADOOP-3308:
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+1 patch looks good
> Improve QuickSort by excluding values eq the pivot from the partition
> ---------------------------------------------------------------------
>
> Key: HADOOP-3308
> URL: https://issues.apache.org/jira/browse/HADOOP-3308
> Project: Hadoop Core
> Issue Type: Improvement
> Reporter: Chris Douglas
> Assignee: Chris Douglas
> Fix For: 0.18.0
>
> Attachments: 3308-0.patch, 3308-1.patch, 3308-2.patch
>
>
> The current implementation of QuickSort naively partitions on either side of
> the pivot. We can improve this by partitioning on either side of the set of
> values equal to the pivot. This assumes that comparing keys is expensive
> compared to swaps and index comparisons (which it certainly is in MapTask,
> and should be in general).
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