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From "David Smiley (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-3234) Provide limit on phrase analysis in FastVectorHighlighter
Date Sun, 25 Sep 2011 06:02:26 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-3234?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13114157#comment-13114157
] 

David Smiley commented on LUCENE-3234:
--------------------------------------

Why is the default unlimited; shouldn't it be the suggested 5000?  I doubt it could be for
backwards compatibility since I can't see how an app might depend on the unlimited behavior.
I think Solr should have good defaults that protect against pathological cases. Other defaults
in Lucene/Solr have such defaults, in general (e.g. hl.maxAnalyzedChars).

> Provide limit on phrase analysis in FastVectorHighlighter
> ---------------------------------------------------------
>
>                 Key: LUCENE-3234
>                 URL: https://issues.apache.org/jira/browse/LUCENE-3234
>             Project: Lucene - Java
>          Issue Type: Improvement
>    Affects Versions: 2.9.4, 3.0.3, 3.1, 3.2, 3.3
>            Reporter: Mike Sokolov
>            Assignee: Koji Sekiguchi
>             Fix For: 3.4, 4.0
>
>         Attachments: LUCENE-3234.patch, LUCENE-3234.patch, LUCENE-3234.patch, LUCENE-3234.patch,
LUCENE-3234.patch
>
>
> With larger documents, FVH can spend a lot of time trying to find the best-scoring snippet
as it examines every possible phrase formed from matching terms in the document.  If one is
willing to accept
> less-than-perfect scoring by limiting the number of phrases that are examined, substantial
speedups are possible.  This is analogous to the Highlighter limit on the number of characters
to analyze.
> The patch includes an artifical test case that shows > 1000x speedup.  In a more normal
test environment, with English documents and random queries, I am seeing speedups of around
3-10x when setting phraseLimit=1, which has the effect of selecting the first possible snippet
in the document.  Most of our sites operate in this way (just show the first snippet), so
this would be a big win for us.
> With phraseLimit = -1, you get the existing FVH behavior. At larger values of phraseLimit,
you may not get substantial speedup in the normal case, but you do get the benefit of protection
against blow-up in pathological cases.

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