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https://issues.apache.org/jira/browse/LUCENE-2506?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Uwe Schindler updated LUCENE-2506:
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Fix Version/s: (was: 3.0.2)
> A Stateful Filter That Works Across Index Segments
> --------------------------------------------------
>
> Key: LUCENE-2506
> URL: https://issues.apache.org/jira/browse/LUCENE-2506
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Affects Versions: 3.0.2
> Reporter: Karthick Sankarachary
> Attachments: LUCENE-2506.patch
>
>
> By design, Lucene's Filter abstraction is applied once per segment in the
> index during searching. In particular, the reader provided to its
> #getDocIdSet method does not represent the whole underlying index. In other
> words, if the index has more than one segment the given reader only
> represents a single segment.
> As a result, that definition of the Filter suffers from a limitation in that
> it does not have the ability to permit/prohibit documents in the search
> results based on the terms residing in not just the current segment but also
> the ones that came before it during the search.
> To address this limitation, we introduce here a StatefulFilter which
> specifically builds on the Filter class so as to make it capable of
> remembering terms in segments spanning the whole
> underlying index. To reiterate, the need for making filters stateful stems
> from the fact that some, although not most, filters care about what terms
> they may have come across in prior segments. It does so by keeping track of
> the past terms from prior segments in a cache that is maintained in a
> StatefulTermsEnum instance on a per-thread basis.
> Note that we leave it up to the concrete sub-class of the stateful filter to
> decide what to remember in its state or what not to. In other words, it can
> choose to remember as much or as little from prior segments as it desires. In
> keeping with the TermsEnum interface, which the StatefulTermsEnum class
> builds on, it must let the searcher know what terms to accept and which ones
> to skip over. More often than not, the state of the filter will come in handy
> while implementing that very acceptance logic.
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