The IVF-PQ Compression Trick

Staff ML Engineer interview at Google, and the interviewer asks:

“Your RAG system hits 99% recall on HNSW in the demo. Now it’s 200M vectors and your RAM bill just triggered a budget review. Do you keep HNSW? Why or why not?”

Don’t say: “HNSW is faster and more accurate, so we keep it and add more RAM.”