RAG Interview Questions, issue 11, Jul 15, 2026
The Zombie Hub Trap
Senior AI Engineer interview at Meta, and the interviewer asks:
“Your HNSW index takes a delete every few seconds in production. Do you remove the node and repair the graph?”
Don’t say: “Yes, delete the node, rewire its neighbors, keep the graph clean.”
How soft-deleting vectors silently inflates latency and collapses recall, and why tracking your tombstone ratio as a first-class SLO is the only way to survive the inevitable memory spike.
The full answer, with the mechanism and the arithmetic, is for paid subscribers on Substack.