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From "Robert Muir (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2843) Add variable-gap terms index impl.
Date Wed, 02 Feb 2011 15:39:29 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2843?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12989672#comment-12989672
] 

Robert Muir commented on LUCENE-2843:
-------------------------------------

Also, if faceting wants to exploit a codec-specific implementation detail,
its far more interesting to evaluate things like changing VariableGapIndex's 
FST output to be a pair including max(docFreq) for the block it indexes.

Then, faceting that wants to get the top-10 terms by docfreq, would 
instead work an FSTEnum, and only go to disk for the top-10 blocks... this
would actually be a change in complexity order no?


> Add variable-gap terms index impl.
> ----------------------------------
>
>                 Key: LUCENE-2843
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2843
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>             Fix For: 4.0
>
>         Attachments: LUCENE-2843.patch, LUCENE-2843.patch
>
>
> PrefixCodedTermsReader/Writer (used by all "real" core codecs) already
> supports pluggable terms index impls.
> The only impl we have now is FixedGapTermsIndexReader/Writer, which
> picks every Nth (default 32) term and holds it in efficient packed
> int/byte arrays in RAM.  This is already an enormous improvement (RAM
> reduction, init time) over 3.x.
> This patch adds another impl, VariableGapTermsIndexReader/Writer,
> which lets you specify an arbitrary IndexTermSelector to pick which
> terms are indexed, and then uses an FST to hold the indexed terms.
> This is typically even more memory efficient than packed int/byte
> arrays, though, it does not support ord() so it's not quite a fair
> comparison.
> I had to relax the terms index plugin api for
> PrefixCodedTermsReader/Writer to not assume that the terms index impl
> supports ord.
> I also did some cleanup of the FST/FSTEnum APIs and impls, and broke
> out separate seekCeil and seekFloor in FSTEnum.  Eg we need seekFloor
> when the FST is used as a terms index but seekCeil when it's holding
> all terms in the index (ie which SimpleText uses FSTs for).

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