[jira] [Commented] (LUCENE-10606) Optimize hit collection of prefilter in KnnVectorQuery for BitSet backed queries

["Kaival Parikh (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-10606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17551976#comment-17551976 ] 

Kaival Parikh commented on LUCENE-10606:
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Instead of collecting hit-by-hit using a LeafCollector, we can break down the search by instantiating a weight, creating scorers, and checking the underlying iterator. If it is backed by a BitSet, we can directly update the reference (as we won't be editing it). Else we can create a new BitSet from the iterator using BitSet.of

This way the collection is optimized (and can be advantageous as LRUQueryCache internally uses a BitSet, so such iterators will be common). Sample [code|https://github.com/apache/lucene/compare/main...kaivalnp:alternate_collection]

> Optimize hit collection of prefilter in KnnVectorQuery for BitSet backed queries
> --------------------------------------------------------------------------------
>
>                 Key: LUCENE-10606
>                 URL: https://issues.apache.org/jira/browse/LUCENE-10606
>             Project: Lucene - Core
>          Issue Type: Improvement
>          Components: core/search
>            Reporter: Kaival Parikh
>            Priority: Minor
>              Labels: performance
>
> While working on this [PR|https://github.com/apache/lucene/pull/932] to add prefilter testing support, we saw that hit collection took a long time for BitSetIterator backed scorers (due to iteration over the entire underlying BitSet, and copying it into an internal one) (Link to [numbers|https://github.com/apache/lucene/pull/932#discussion_r888896850], second table)
> These BitSetIterators can be frequent (as they are used in LRUQueryCache), and bulk collection can be optimized with more knowledge of the underlying iterator



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