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From "Michael McCandless (Resolved) (JIRA)" <>
Subject [jira] [Resolved] (LUCENE-2948) Make var gap terms index a partial prefix trie
Date Tue, 20 Mar 2012 15:19:40 GMT


Michael McCandless resolved LUCENE-2948.

    Resolution: Won't Fix

I think BlockTree terms dict accomplished the same thing.
> Make var gap terms index a partial prefix trie
> ----------------------------------------------
>                 Key: LUCENE-2948
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: core/index
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>             Fix For: 4.0
>         Attachments: LUCENE-2948.patch, LUCENE-2948.patch, LUCENE-2948.patch, LUCENE-2948_automaton.patch,
> Var gap stores (in an FST) the indexed terms (every 32nd term, by
> default), minus their non-distinguishing suffixes.
> However, often times the resulting FST is "close" to a prefix trie in
> some portion of the terms space.
> By allowing some nodes of the FST to store all outgoing edges,
> including ones that do not lead to an indexed term, and by recording
> that this node is then "authoritative" as to what terms exist in the
> terms dict from that prefix, we can get some important benefits:
>   * It becomes possible to know that a certain term prefix cannot
>     exist in the terms index, which means we can save a disk seek in
>     some cases (like PK lookup, docFreq, etc.)
>   * We can query for the next possible prefix in the index, allowing
>     some MTQs (eg FuzzyQuery) to save disk seeks.
> Basically, the terms index is able to answer questions that previously
> required seeking/scanning in the terms dict file.

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