fix: replenish() hardcodes CosineDistance instead of graph distance#21
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April 11, 2026 12:26
In a binary min-heap, the last array element is not necessarily the maximum. Max() must scan the leaf nodes (indices n/2..n-1) to find the true maximum. PopLast() used Remove(Len()-1) which removed an arbitrary element instead of the worst. This caused incorrect evictions during neighbor selection and search result trimming, degrading graph quality.
…ance replenish() is called after neighbor eviction and node deletion to restore connectivity. It unconditionally used CosineDistance, ignoring the graph's configured distance function. This corrupted the graph topology for any non-Cosine metric. Thread DistanceFunc through replenish() and isolate() so the correct distance function is always used.
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ammario
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Jun 22, 2026
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Correct fix: threads the graph's DistanceFunc through replenish()/isolate() instead of hardcoding CosineDistance. Tests pass.
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Jun 22, 2026
Rewrites layerNode.search() to follow HNSW Algorithm 5 (SEARCH-LAYER): the result set is bounded by efSearch during exploration, termination uses the worst-of-results condition, and only the k closest are returned (with deterministic key tiebreaking). This fixes severely degraded recall: on a 2000-point, 16-dim Euclidean benchmark, recall@1 improves from 0.20 to 1.00 and recall@10 from 0.175 to 0.998. Also clamps efSearch to max(k, efSearch) so Search returns up to k results even when k exceeds the configured EfSearch. Builds on #20 (heap Max/PopLast fix) and #21 (replenish distance fix).
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Summary
replenish()unconditionally calledaddNeighbor(..., CosineDistance)regardless of the graph's configured distance functionDistanceFuncthroughreplenish()andisolate()so the correct function is always usedDepends on #20.
Test plan
TestGraph_DeleteReplenishUsesGraphDistance— builds a Euclidean graph, deletes a node to trigger replenish, verifies search still returns the correct nearest neighborgo test ./...andgo vet ./...pass