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https://issues.apache.org/jira/browse/LUCENE-584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12558076#action_12558076
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Paul Elschot commented on LUCENE-584:
-------------------------------------
{quote}
it looks like ChainedFilter could become obsolete if Filter/DocSetIdIterator
gets added as a Clause to the BooleanQuery?
{quote}
The function is indeed the same, but ChainedFilter works directly on BitSets
and BooleanQuery works on input Scorers/DocIdSetIterators and outputs collected
docids (and score values). Working directly on (Open)BitSets is normally
faster, so ChainedFilter can have a good use.
And boolean operations on DocIdSets are not (yet) directly available in Lucene.
The various boolean scorers have the logic, but currently only for Scorers.
That leaves the question on what to do with ChainedFilter here. Any ideas?
The easiest way is to open another issue for it. This will have to be resolved
before Filter.bits() is removed.
> Decouple Filter from BitSet
> ---------------------------
>
> Key: LUCENE-584
> URL: https://issues.apache.org/jira/browse/LUCENE-584
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Affects Versions: 2.0.1
> Reporter: Peter Schäfer
> Assignee: Michael Busch
> Priority: Minor
> Fix For: 2.4
>
> Attachments: bench-diff.txt, bench-diff.txt,
> ContribQueries20080111.patch, lucene-584-take2.patch,
> lucene-584-take3-part1.patch, lucene-584-take3-part2.patch,
> lucene-584-take4-part1.patch, lucene-584-take4-part2.patch, lucene-584.patch,
> Matcher-20070905-2default.patch, Matcher-20070905-3core.patch,
> Matcher-20071122-1ground.patch, Some Matchers.zip
>
>
> {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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