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Custom HNSW implementation slower than brute-force search in benchmarks

A developer built and benchmarked a retrieval engine from scratch, comparing a custom Hierarchical Navigable Small World (HNSW) implementation against the Faiss library. Surprisingly, brute-force search methods outperformed HNSW in terms of median latency for queries on datasets of a few thousand documents. The developer attributes this to the overhead of pointer chasing and interpreter costs in Python for HNSW, contrasting it with the efficiency of dense matrix multiplication for brute-force search on smaller datasets. The study also highlighted that the embedding model's computation time was significantly higher than the retrieval step, suggesting it's a more critical bottleneck. AI

IMPACT Highlights that brute-force search can outperform complex indexing methods like HNSW for smaller datasets, and that embedding model computation is a major bottleneck.

RANK_REASON The item details a custom implementation and benchmark of a specific algorithm (HNSW) against an existing library (Faiss), focusing on performance findings. [lever_c_demoted from research: ic=1 ai=1.0]

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AI-generated summary · Google Gemini · from 1 sources. How we write summaries →

Custom HNSW implementation slower than brute-force search in benchmarks

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The item details a custom implementation and benchmark of a specific algorithm (HNSW) against an existing library (Faiss), focusing on performance findings. [lever_c_demoted from research: ic=1 ai=…
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COVERAGE [1]

  1. r/MachineLearning TIER_1 English(EN) · /u/thehuhcoder ·

    HNSW from scratch, benchmarked against FAISS: brute force still wins at 5,183 documents. [P]

    <!-- SC_OFF --><div class="md"><p>I built a retrieval engine with no retrieval libraries in the core — BM25 over a hand-rolled inverted index, HNSW from the Malkov &amp; Yashunin paper, RRF to fuse them — mainly to understand HNSW rather than treat it as a black box inside a vect…