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From "Uwe Schindler (JIRA)" <>
Subject [jira] [Commented] (LUCENE-4546) SorterTemplate.quicksort incorrect
Date Wed, 07 Nov 2012 16:03:12 GMT


Uwe Schindler commented on LUCENE-4546:

By the way we have a random test (TestArrayUtil) that does exactly the same, but the tested
ArrayUtil handles the pivot value correctly, so it works correct. If you use your failing
example array and sort it with ArrayUtil it passes.
> SorterTemplate.quicksort incorrect
> ----------------------------------
>                 Key: LUCENE-4546
>                 URL:
>             Project: Lucene - Core
>          Issue Type: Bug
>          Components: core/other
>    Affects Versions: 3.6.1, 4.0, 4.1
>            Reporter: Stefan Pohl
>              Labels: patch
>             Fix For: 3.6.1, 4.0, 4.1
>         Attachments:,
> On trying to use the very useful o.a.l.utils.SorterTemplate, I stumbled upon inconsistent
sorting behaviour, of course, only a randomized test caught this;)
> Because SorterTemplate.quicksort is used in several places in the code (directly BytesRefList,
ArrayUtil, BytesRefHash, CollectionUtil and transitively index and search), I'm a bit puzzled
that this either hasn't been caught by another higher-level test or that neither my test nor
my understanding of an insufficiency in the code is valid;)
> If the former holds and given that the same code is released in 3.6 and 4.0, this might
even be a more critical issue requiring a higher priority than 'major'.
> So, can a second pair of eyes please have a timely look at the attached test and patch?
> Basically the current quicksort implementation seems to assume that luckily always the
median is chosen as pivot element by grabbing the mid element, not handling the case where
the initially chosen pivot ends up not in the middle. Hope this and the test helps to understand
the issue.
> Reproducible, currently failing test and a patch attached.

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