[jira] Updated: (LUCENE-2843) Add variable-gap terms index impl.

["Michael McCandless (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/LUCENE-2843?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Michael McCandless updated LUCENE-2843:
---------------------------------------

    Attachment: LUCENE-2843.patch

Attached patch.

Still some nocommits but I think it's close... though I still need to
get indexDivisor working for var gap.  Note that this patch changes
the index format, even for Standard codec (using fixed gap terms
index).

A few tests fail because they assume Standard codec supports ord...

To properly test the alternatives we now have for the terms index
(including fixed vs variable, and then different index term selectors
fro the variable case), I created a new fun testing codec,
MockRandomCodec.  It randomly pairs up a postings impl with a terms
index impl.  EG it sometimes uses an IndexTermPolicy that randomly
picks index terms.  We may now be able to remove the other Mock*
codecs...


> 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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