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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (LUCENE-3254) BitVector.isSparse is sometimes wrong
Date Tue, 28 Jun 2011 13:51:17 GMT

     [ https://issues.apache.org/jira/browse/LUCENE-3254?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Michael McCandless updated LUCENE-3254:
---------------------------------------

    Attachment: LUCENE-3254.patch

Patch, fixing those two issues, and also 1) marking BV as
@lucene.internal, 2) removing BV.subset (we don't use it), 3) adding a
back-compat version header to the BV file (I need this for
LUCENE-3246), and other small changes.


> BitVector.isSparse is sometimes wrong
> -------------------------------------
>
>                 Key: LUCENE-3254
>                 URL: https://issues.apache.org/jira/browse/LUCENE-3254
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: core/other
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>             Fix For: 3.4, 4.0
>
>         Attachments: LUCENE-3254.patch
>
>
> In working on LUCENE-3246, I found a few problems with
> BitVector.isSparse:
>   * Its math can overflow int, such that if there are enough deleted
>     docs and maxDoc() is largish, isSparse may incorrectly return true
>   * It over-estimates the size of the sparse file, since when
>     estimating number of bytes for the vInt dgaps it uses bits.length
>     instead of bits.length divided by number of set bits (ie, the
>     "average" gap between set bits)
> This is relatively harmless (just affects performance / size of .del
> file on disk, not correctness).

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