mayya-sharipova commented on code in PR #11781:
URL: https://github.com/apache/lucene/pull/11781#discussion_r974364724
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lucene/core/src/test/org/apache/lucene/util/hnsw/TestHnswGraph.java:
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@@ -555,6 +556,78 @@ public void testDiversity() throws IOException {
assertLevel0Neighbors(builder.hnsw, 5, 1, 4);
}
+ public void testDiversityFallback() throws IOException {
+ vectorEncoding = randomVectorEncoding();
+ similarityFunction = VectorSimilarityFunction.EUCLIDEAN;
+ // Some test cases can't be exercised in two dimensions;
+ // in particular if a new neighbor displaces an existing neighbor
+ // by being closer to the target, yet none of the existing neighbors is
closer to the new vector
+ // than to the target -- ie they all remain diverse, so we simply drop the
farthest one.
+ float[][] values = {
+ {0, 0, 0},
+ {0, 1, 0},
+ {0, 0, 2},
+ {1, 0, 0},
+ {0, 0.4f, 0}
+ };
+ MockVectorValues vectors = new MockVectorValues(values);
+ // First add nodes until everybody gets a full neighbor list
+ HnswGraphBuilder<?> builder =
+ HnswGraphBuilder.create(
+ vectors, vectorEncoding, similarityFunction, 1, 10,
random().nextInt());
+ // node 0 is added by the builder constructor
+ // builder.addGraphNode(vectors.vectorValue(0));
+ RandomAccessVectorValues vectorsCopy = vectors.copy();
+ builder.addGraphNode(1, vectorsCopy);
+ builder.addGraphNode(2, vectorsCopy);
+ assertLevel0Neighbors(builder.hnsw, 0, 1, 2);
+ // 2 is closer to 0 than 1, so it is excluded as non-diverse
+ assertLevel0Neighbors(builder.hnsw, 1, 0);
+ // 1 is closer to 0 than 2, so it is excluded as non-diverse
+ assertLevel0Neighbors(builder.hnsw, 2, 0);
+
+ builder.addGraphNode(3, vectorsCopy);
+ // this is one case we are testing; 2 has been displaced by 3
Review Comment:
nice test!
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