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https://issues.apache.org/jira/browse/LUCENE-2843?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12976724#action_12976724
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Robert Muir commented on LUCENE-2843:
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I like this idea, it would be interesting to see what other type of policies we
can come up with.
Just curious, how would the 'let FST decide' work? Do we have some quick way to
know that
selecting term X versus term Y would reduce the number of states/transitions?
Isn't the resulting
FST size also dependent upon the output value (terms dict file pointer)? And if
we optimize
this locally (X versus Y) does it tend to hold globally?
> 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
>
>
> 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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