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https://issues.apache.org/jira/browse/LUCENE-584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12515395
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Mark Harwood commented on LUCENE-584:
-------------------------------------
Hi Paul,
Not sure if I'm missing something but I think this patch may not work for
scenarios other than the simple option of a single filter being used on a
search.
A Matcher does not have the same utility as a BitSet because using a BitSet you
can:
1) iterate across it using multiple threads.
2) Clone it.
3) Merge it quickly with other bitsets using Boolean logic .
4) Use it more than once.
I think these differences become important in the following scenarios :
In CachingWrapperFilter I don't think you can cache Matchers instead of bitsets
- because Matchers don't have features 1 and 4
BooleanFilter and ChainedFilter in contrib don't work with Matchers because
there is no support for 3)
Is there something obvious I've missed?
Cheers
Mark
> 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,
> Matcher-core20070725.patch, Matcher-default20070725.patch,
> Matcher-ground20070725.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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