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From "Robert Muir (Updated) (JIRA)" <>
Subject [jira] [Updated] (LUCENE-3503) DisjunctionSumScorer gives slightly (float iotas) different scores when you .nextDoc vs .advance
Date Mon, 10 Oct 2011 18:14:29 GMT


Robert Muir updated LUCENE-3503:

    Attachment: LUCENE-3503.patch

not a real 'fix' but maybe this solves it for practical purposes?
> DisjunctionSumScorer gives slightly (float iotas) different scores when you .nextDoc
vs .advance
> ------------------------------------------------------------------------------------------------
>                 Key: LUCENE-3503
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Bug
>            Reporter: Michael McCandless
>         Attachments: LUCENE-3503.patch, LUCENE-3503.patch
> Spinoff from LUCENE-1536.
> I dug into why we hit a score diff when using luceneutil to benchmark
> the patch.
> At first I thought it was BS1/BS2 difference, but because of a bug in
> the patch it was still using BS2 (but should be BS1) -- Robert's last
> patch fixes that.
> But it's actually a diff in BS2 itself, whether you next or advance
> through the docs.
> It's because DisjunctionSumScorer, when summing the float scores for a
> given doc that matches multiple sub-scorers, might sum in a different
> order, when you had .nextDoc'd to that doc than when you had .advance'd
> to it.
> This in turn is because the PQ used by that scorer (ScorerDocQueue)
> makes no effort to break ties.  So, when the top N scorers are on the
> same doc, the PQ doesn't care what order they are in.
> Fixing ScorerDocQueue to break ties will likely be a non-trivial perf
> hit, though, so I'm not sure whether we should do anything here...

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