[jira] Commented: (LUCENE-584) Decouple Filter from BitSet

["Paul Elschot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12557595#action_12557595 ] 

Paul Elschot commented on LUCENE-584:
-------------------------------------

On the take3 patch of 10 Jan 2008:

SortedVIntList extends DocIdSet: nice, thanks.

PrefixGenerator is used but not defined in the patch, so it will not compile.

Nevertheless, with all tests passing, I think this is a good way to
make Filter independent of BitSet.


Minor concerns:

There is neither a BitSetFilter nor an OpenBitSetFilter in the patch.
These might be useful for existing code currently implementing Filter
to overcome the deprecation of Filter.bits().
With the current core moving to OpenBitSet, it might also use an
explicit OpenBitSetFilter.

Some javadoc changes did not make it into the take3 patch, I'll check these later.

FilteredQuery.explain(): When a document does not pass the Filter
I think it would be better not to use setValue(0.0f) on the resulting
Explanation. However, this may be necessary for backward compatibility.


For the future:

About adding a Filter as a clause to BooleanScorer, and adding
DocSetIdIterator as a "Scorer" to ConjunctionScorer:
This is the reason for the CHECKME in IndexSearcher for using
ConjunctionScorer when a filter is given.
A ConjunctionScorer that accepts a DocIdSetIterator could also be used in
FilteredQuery.

> 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, lucene-584-take2.patch, lucene-584-take3-part1.patch, lucene-584-take3-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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