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https://issues.apache.org/jira/browse/LUCENE-584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12487940
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Hoss Man commented on LUCENE-584:
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I'm a little behind on following this issue, but if i can attempt to sum up the
recent discussion about performance...
"Migrating towards a "Matcher" API *may* allow some types of Queries to be
faster in situations where clients can use a MatchCollector instead of a
HitCollector, but this won't be a silver bullet performance win for all Query
classes -- just those where some of the score calculations is (or can be)
isolated to the score method (as opposed to skipTO or next)"
I think it's important to remember the motivation of this issue wasn't to
improve the speed performance of non-scoring searchers, it was to decouple the
concept of "Filtering" results away from needing to populate a (potentially
large) BitSet when the logic neccessary for Filtering can easily be expressed
in terms of a doc iterator (aka: a Matcher) -- opening up the possibility of
memory performance improvements.
A second benefit that has arisen as the issue evolved, has been the API
generalization of the "Matcher" concept to be a super class of Scorer for
simpler APIs moving forward.
> 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
> Priority: Minor
> Attachments: bench-diff.txt, bench-diff.txt, BitsMatcher.java,
> Filter-20060628.patch, HitCollector-20060628.patch,
> IndexSearcher-20060628.patch, MatchCollector.java, Matcher.java,
> Matcher20070226.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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