[GitHub] [lucene] kaivalnp commented on a diff in pull request #932: LUCENE-10559: Add Prefilter Option to KnnGraphTester

[GitBox <gi...@apache.org>]

kaivalnp commented on code in PR #932:
URL: https://github.com/apache/lucene/pull/932#discussion_r887637829


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lucene/core/src/java/org/apache/lucene/search/KnnVectorQuery.java:
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@@ -225,6 +225,11 @@ public BitSetIterator getIterator(int contextOrd) {
       return new BitSetIterator(bitSets[contextOrd], cost[contextOrd]);
     }
 
+    public void setBitSet(BitSet bitSet, int cost) {
+      bitSets[ord] = bitSet;

Review Comment:
   > So .. this relies on the fact that `BitSetCollector.doSetNextReader` will have been called prior to this, setting the appropriate `ord`. This is very clever, but it relies heavily on knowledge of internal implementation details that aren't really part of the published API, and this will tie us to this BitSetCollector implementation. I wonder if we could create a new KnnVectorQuery constructor that would accept a Function<Integer, BitSetIterator>, rather than a Query, that would be responsible for returning a BitSetIterator for a given ord?
   
   This is interesting and would solve many problems of wrapping the BitSet in a Query (and associated BulkScorer). Given this function, we could add a new constructor to BitSetCollector (to instantiate the internal BitSets from these BitSetIterators instead), and no indexSearcher.search would be required thereafter
   
   My concern is that it creates different search paths and constructors for this function, which will only be used from our test and might complicate the class (Though this addition would be helpful if we want to delegate the task of populating the filtered docs into BitSets outside of KnnVectorQuery)



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