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Hybrid search with pgvector got worse until I added BM25

The hybrid query most tutorials show, Postgres full-text search fused with pgvector, scored worse on two public benchmarks than vector search alone. With a real BM25 index as the keyword half, the same fusion gave the best result I measured, in under 3 ms a query. Here are the numbers for seven ways to search, and the query shapes that made the fused one 15 times slower until I found them.

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RAG is a search problem wearing a costume

The internal docs assistant answered confidently and was wrong a third of the time. Everyone blamed the model, but the model was fine. Retrieval was returning the right document eleventh out of ten. Fixing it took six weeks of ordinary search engineering, and none of it touched a prompt.

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