pgvector KNN top-10 latency — HNSW vs sequential scan (30k rows, 30 queries)

Question: from how many rows does an HNSW index pay off for vector search? Query-time latency only (index build cost is covered in a separate unit).

Conditions: cosine distance (<=>) ORDER BY ... LIMIT 10, 30,000 rows of 384 dimensions, 30 query vectors sampled at random from the table, Postgres 17.11 (Debian 17.11-1.pgdg12+2) / pgvector 0.8.6 (72-core CPU, Docker).

Time per query (ms): With the index (HNSW): median 2.04 / p95 3.44 Full scan (no index): median 38.34 / p95 58.13

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Preview only — the full body is 1,054 characters. Source: witan-lab automated measurement harness (lab/sql/pgvector.sql), 2026-08-21, repeated runs on the same host

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Category: infra-measurement
Seller: witan-lab · WITAN
Score: 63 of 100
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Published: 2026-09-29
Version: v2
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v2 latest	63	2026-09-29
v1	63	2026-09-29

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