[GitHub] [lucene] jtibshirani commented on a diff in pull request #11756: LUCENE-10577: Remove LeafReader#searchNearestVectorsExhaustively

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

jtibshirani commented on code in PR #11756:
URL: https://github.com/apache/lucene/pull/11756#discussion_r965154356


##########
lucene/core/src/java/org/apache/lucene/search/KnnVectorQuery.java:
##########
@@ -175,9 +176,42 @@ private TopDocs approximateSearch(LeafReaderContext context, Bits acceptDocs, in
   }
 
   // We allow this to be overridden so that tests can check what search strategy is used
-  protected TopDocs exactSearch(LeafReaderContext context, DocIdSetIterator acceptDocs)
+  protected TopDocs exactSearch(LeafReaderContext context, DocIdSetIterator acceptIterator)
       throws IOException {
-    return context.reader().searchNearestVectorsExhaustively(field, target, k, acceptDocs);
+    FieldInfo fi = context.reader().getFieldInfos().fieldInfo(field);
+    if (fi == null || fi.getVectorDimension() == 0) {
+      // The field does not exist or does not index vectors
+      return NO_RESULTS;
+    }
+
+    VectorScorer vectorScorer = VectorScorer.create(context, fi, target);
+    HitQueue queue = new HitQueue(k, true);
+    ScoreDoc topDoc = queue.top();
+    int doc;
+    while ((doc = acceptIterator.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
+      boolean advanced = vectorScorer.advanceExact(doc);
+      assert advanced;
+
+      float score = vectorScorer.score();
+      if (score >= topDoc.score) {

Review Comment:
   That seems right, I updated this and pushed a test covering the tie-breaking case. As a note, we don't guarantee we'll always return the lowest matching doc IDs (since approximate HNSW search can't do this efficiently).



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