Hybrid Search Implementation Details (ANSWERED)
BM25 + vector fusion, RRF, weighted scores, rerankers, and same-chunk alignment pitfalls.
TL;DR — Quick Answer
Run dense ANN and sparse BM25 (or SPLADE) in parallel, then fuse with Reciprocal Rank Fusion (RRF) or calibrated weighted scores, often followed by a cross-encoder reranker on top 50–100. Align chunk IDs so both legs reference identical documents, and tune fusion on labeled queries — hybrid beats either alone on most enterprise search tasks.
The Interview Question
How do you implement hybrid search combining dense vectors and sparse keyword retrieval?
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Hybrid SearchBM25RRFRerankingElasticsearchWeaviateVespa