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From "Paul Elschot (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-584) Decouple Filter from BitSet
Date Fri, 15 Sep 2006 07:04:24 GMT
    [ http://issues.apache.org/jira/browse/LUCENE-584?page=comments#action_12434901 ] 
            
Paul Elschot commented on LUCENE-584:
-------------------------------------

In the inheritance from Matcher to Scorer there is an asymmetry
in this patch.

Matcher provides a default implementation for Matcher.explain()
but Scorer does not, and this might lead to unexpected surprises
for future Scorers when the current Matcher.explain() is used.
One could add an abstract Scorer.explain() to catch these, or
provide a default implementation for Scorer.explain().

With matcher implementations quite a few other implementation
decisions need to be taken. 
Also any place in the current code where a Scorer is used, but none
of the Scorer.score() methods, is a candidate for a change from
Scorer to Matcher.
This will be mostly the current filtering implementations,
but ConstantScoringQuery is another nice example.

Regards,
Paul Elschot


> Decouple Filter from BitSet
> ---------------------------
>
>                 Key: LUCENE-584
>                 URL: http://issues.apache.org/jira/browse/LUCENE-584
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Search
>    Affects Versions: 2.0.1
>            Reporter: Peter Schäfer
>            Priority: Minor
>         Attachments: BitsMatcher.java, Filter-20060628.patch, HitCollector-20060628.patch,
IndexSearcher-20060628.patch, MatchCollector.java, Matcher.java, Matcher20060830b.patch, Scorer-20060628.patch,
Searchable-20060628.patch, Searcher-20060628.patch, Some Matchers.zip, SortedVIntList.java,
TestSortedVIntList.java
>
>
> {code}
> package org.apache.lucene.search;
> public abstract class Filter implements java.io.Serializable 
> {
>   public abstract AbstractBitSet bits(IndexReader reader) throws IOException;
> }
> public interface AbstractBitSet 
> {
>   public boolean get(int index);
> }
> {code}
> It would be useful if the method =Filter.bits()= returned an abstract interface, instead
of =java.util.BitSet=.
> Use case: there is a very large index, and, depending on the user's privileges, only
a small portion of the index is actually visible.
> Sparsely populated =java.util.BitSet=s are not efficient and waste lots of memory. It
would be desirable to have an alternative BitSet implementation with smaller memory footprint.
> Though it _is_ possibly to derive classes from =java.util.BitSet=, it was obviously not
designed for that purpose.
> That's why I propose to use an interface instead. The default implementation could still
delegate to =java.util.BitSet=.

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