Vector database fundamentals (SOLVED)
Vector databases power every RAG system, yet most candidates can't explain ANN algorithms or hybrid search. This fundamental question appears in 80% of AI engineering loops. Master dense vs sparse retrieval and when hybrid search wins.

TL;DR — Quick Answer
Vector DBs store embeddings and perform approximate nearest neighbor (ANN) search. Dense retrieval captures semantics; sparse (BM25) captures keywords — hybrid approaches often win.
The Interview Question
Explain how vector databases work. Compare dense vs sparse retrieval approaches.
Deep Explanation
Vector DBs index high-dimensional embeddings using HNSW, IVF, or PQ algorithms for fast similarity search. Key considerations: embedding model choice, index rebuild strategy, metadata filtering, and recall/latency trade-offs.
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