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From "Chad Whipkey (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3442) QuickSort may get into unbounded recursion
Date Mon, 02 Jun 2008 21:23:46 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3442?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12601768#action_12601768

Chad Whipkey commented on HADOOP-3442:

Can you try testing my version in your environment to see if you get a performance change?
 I'm thinking that there may be some JIT thing going on that makes the no-recursion version
better.  I did get a significant (like, 20%+ less time), repeatable, performance gain when
using my version.

Introsort still uses insertionSort instead of quicksort for low n.  It uses heapsort when
quicksort has recursed deeply; unlike quicksort, heapsort has guaranteed worst-case performance
of O(n*log(n)), avoiding both the huge recursion (it's not recursion) and the O(n*n) runtime
that such a recursion produces.  But it's generally slower, so introsort uses it only when
quicksort has hit a bad case.


> QuickSort may get into unbounded recursion
> ------------------------------------------
>                 Key: HADOOP-3442
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3442
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>    Affects Versions: 0.17.0
>            Reporter: Runping Qi
>            Assignee: Chris Douglas
>         Attachments: 3442-0.patch, HADOOP-3442.patch

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