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https://issues.apache.org/jira/browse/LUCENE-2948?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael McCandless updated LUCENE-2948:
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Attachment: LUCENE-2948.patch
Initial patch. This is a checkpoint of work-in-progress -- all tests pass, but
there are zillions of nocommits to be resolved...
> Make var gap terms index a partial prefix trie
> ----------------------------------------------
>
> Key: LUCENE-2948
> URL: https://issues.apache.org/jira/browse/LUCENE-2948
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Fix For: 4.0
>
> Attachments: LUCENE-2948.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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