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From "Paul Elschot (JIRA)" <>
Subject [jira] Commented: (LUCENE-1187) Things to be done now that Filter is independent from BitSet
Date Sun, 25 May 2008 18:57:55 GMT


Paul Elschot commented on LUCENE-1187:

While considering DefaultDocIdSet as a class, I thought that perhaps a better way would be
to add a method to class Filter that takes the usual DocIdSet and provides the DocIdSet that
should be used for caching, for example in CachingWrapperFilter. Sth like this:
public class Filter {
  ... the abstract bits() deprecated method ... ;

  public DocIdSet getDocIdSet(IndexReader reader) {
    // unchanged implementation for now. to become abstract later.

  public DocIdSet getDocIdSetForCache(IndexReader reader) {
    // Use a default implementation here that provides a tradeoff for caching,
    // fairly compact when possible, but still fast.
    // For the moment this could be close to the code of the finalResult() method
    // mentioned above:
    DocIdSet result = getDocIdSet(reader);
    if (!(result instanceof SortedVIntList)) 
                and (result.cardinality() < (reader.maxDoc() / 9))) {
      return  new SortedVIntList(result);
    return result;
(One minor problem with this is that DocIdSet does not have a cardinality() method
and that SortedVIntList does not have a constructor for a DocIdSet.)

The question is: how about adding such a getDocIdSetForCache() method to Filter?
Or is there a better place for this functionality, for example in CachingWrapperFilter?

> Things to be done now that Filter is independent from BitSet
> ------------------------------------------------------------
>                 Key: LUCENE-1187
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: contrib/*, Search
>            Reporter: Paul Elschot
>            Assignee: Michael Busch
>            Priority: Minor
>             Fix For: 2.4
>         Attachments: BooleanFilter20080325.patch, ChainedFilterAndCachingFilterTest.patch,
Contrib20080325.patch, Contrib20080326.patch, Contrib20080427.patch, javadocsZero2Match.patch,
lucene-1187.patch, lucene-1187.patch, OpenBitSetDISI-20080322.patch
> (Aside: where is the documentation on how to mark up text in jira comments?)
> The following things are left over after LUCENE-584 :
> For Lucene 3.0  Filter.bits() will have to be removed.
> There is a CHECKME in IndexSearcher about using ConjunctionScorer to have the boolean
behaviour of a Filter.
> I have not looked into Filter caching yet, but I suppose there will be some room for
improvement there.
> Iirc the current core has moved to use OpenBitSetFilter and that is probably what is
being cached.
> In some cases it might be better to cache a SortedVIntList instead.
> Boolean logic on DocIdSetIterator is already available for Scorers (that inherit from
DocIdSetIterator) in the search package. This is currently implemented by ConjunctionScorer,
> ReqOptSumScorer and ReqExclScorer.
> Boolean logic on BitSets is available in contrib/misc and contrib/queries
> DisjunctionSumScorer calls score() on its subscorers before the score value actually
> This could be a reason to introduce a DisjunctionDocIdSetIterator, perhaps as a superclass
of DisjunctionSumScorer.
> To fully implement non scoring queries a TermDocIdSetIterator will be needed, perhaps
as a superclass of TermScorer.
> The javadocs in using matching vs non-zero score:
> I'll investigate this soon, and provide a patch when necessary.
> An early version of the patches of LUCENE-584 contained a class Matcher,
> that differs from the current DocIdSet in that Matcher has an explain() method.
> It remains to be seen whether such a Matcher could be useful between
> DocIdSet and Scorer.
> The semantics of scorer.skipTo(scorer.doc()) was discussed briefly.
> This was also discussed at another issue recently, so perhaps it is wortwhile to open
a separate issue for this.
> Skipping on a SortedVIntList is done using linear search, this could be improved by adding
multilevel skiplist info much like in the Lucene index for documents containing a term.
> One comment by me of 3 Dec 2008:
> A few complete (test) classes are deprecated, it might be good to add the target release
for removal there.

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