RAG interview question · Most asked
Why use hybrid search in RAG, and how do you combine the results?
Summary
Vector search finds meaning but misses exact identifiers (error codes, product names, flags); keyword search (BM25) finds exact terms but misses paraphrases. Running both and merging rankings with reciprocal rank fusion gets both strengths without normalising incompatible scores.
Longer Answer
RRF scores each document by summing 1/(k + rank) across result lists (k is often 60). Keep identifiers intact in the keyword index, and evaluate by query type.
Key Points
- Vectors miss identifiers; keywords miss paraphrases.
- Run both.
- Reciprocal rank fusion.
- Evaluate per query type.
Deep dive: Embedding Search That Misses Exact Terms
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