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Date: Mon, 2 May 2011 19:00:03 +0000 (UTC)
From: "Dawid Weiss (JIRA)" <jira@apache.org>
To: dev@lucene.apache.org
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Subject: [jira] [Commented] (LUCENE-3054) SorterTemplate.quickSort stack
 overflows on broken comparators that produce only few disticnt values in
 large arrays
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    [ https://issues.apache.org/jira/browse/LUCENE-3054?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13027772#comment-13027772 ] 

Dawid Weiss commented on LUCENE-3054:
-------------------------------------

I'm sure many of you know this, but there is a new implementation of mergesort in java.util.Collections -- it is based on a few clever heuristics (so it is a merge sort, only a finely tuned one) and has been ported/ partially inspired by the sort in Python as far as I recall.

Maybe it'd be sensible to compare against this and see what happens. I know Lucene/Solr would rather have its own implementation so that it doesn't rely on the standard library, but in my benchmarks the implementation in Collections.sort() was hard to beat...

> SorterTemplate.quickSort stack overflows on broken comparators that produce only few disticnt values in large arrays
> --------------------------------------------------------------------------------------------------------------------
>
>                 Key: LUCENE-3054
>                 URL: https://issues.apache.org/jira/browse/LUCENE-3054
>             Project: Lucene - Java
>          Issue Type: Task
>    Affects Versions: 3.1
>            Reporter: Robert Muir
>            Assignee: Uwe Schindler
>            Priority: Critical
>             Fix For: 3.1.1, 3.2, 4.0
>
>         Attachments: LUCENE-3054-stackoverflow.patch, LUCENE-3054.patch, LUCENE-3054.patch, LUCENE-3054.patch, LUCENE-3054.patch, LUCENE-3054.patch, LUCENE-3054.patch
>
>
> Looking at Otis's sort problem on the mailing list, he said:
> {noformat}
> * looked for other places where this call is made - found it in
> MultiPhraseQuery$MultiPhraseWeight and changed that call from
> ArrayUtil.quickSort to ArrayUtil.mergeSort
> * now we no longer see SorterTemplate.quickSort in deep recursion when we do a
> thread dump
> {noformat}
> I thought this was interesting because PostingsAndFreq's comparator
> looks like it needs a tiebreaker.
> I think in our sorts we should add some asserts to try to catch some of these broken comparators.

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