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From "Mike Sokolov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-3234) Provide limit on phrase analysis in FastVectorHighlighter
Date Thu, 23 Jun 2011 23:02:47 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-3234?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13054162#comment-13054162
] 

Mike Sokolov commented on LUCENE-3234:
--------------------------------------

I did go back and look at the original case that made me worried; in that case the "bad" document
is 650K, and the matched term occurs 23000 times in it.  The search still finishes in 24 sec
or so on my desktop, which isn't too bad I guess, considering.

After looking at that and measuring the change in the test case in the patch as the number
of terms increase, I don't think there actually is an n^2 - just linear, but the growth is
still enough that the patch has value. The test case in the patch is closely targeted at the
method which takes all the time when you have large numbers of matching terms in a single
document.

> 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
>            Reporter: Mike Sokolov
>         Attachments: 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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