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Posted to dev@lucene.apache.org by "Michael McCandless (JIRA)" <ji...@apache.org> on 2016/03/11 20:39:39 UTC

[jira] [Updated] (LUCENE-7097) Can we increase the stack depth before Introsorter switches to heapsort?

     [ https://issues.apache.org/jira/browse/LUCENE-7097?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Michael McCandless updated LUCENE-7097:
---------------------------------------
    Attachment: LUCENE-7097.patch

Thanks [~jpountz], that's a good idea, here's a patch using the existing {{MathUtil.log}}.

> Can we increase the stack depth before Introsorter switches to heapsort?
> ------------------------------------------------------------------------
>
>                 Key: LUCENE-7097
>                 URL: https://issues.apache.org/jira/browse/LUCENE-7097
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>             Fix For: trunk, 6.1
>
>         Attachments: LUCENE-7097.patch
>
>
> Introsort is a "safe" quicksort: it uses quicksort but detects when an adversary is at work and cuts over to heapsort at that point.
> The description at https://en.wikipedia.org/wiki/Introsort shows the cutover as 2X log_2(N) but our impl ({{IntroSorter}}) currently uses just log_2.
> So I tested using 2X log_2 instead, and I see a decent (~5.6%, from 98.2 sec to 92.7 sec) speedup in the time for offline sorter to sort when doing the force merge of 6.1 LatLonPoints from the London UK benchmark.
> Is there any reason not to switch?  I know this means 2X the stack required, but since this is log_2 space that seems fine?



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