That one was a phone screen, so no it was not the deepest technical dive ever. But in fairness a 1-hour interview is rarely the deepest technical dive possible. I normally pose some big problem like "design a system that accomplishes X at high scale" and then drill into some area iteratively until we're discussing fairly specific details. At the high level I'm looking for the candidate to recognize tradeoffs between centralized/distributed designs, sanely choose the major components, deal with stateful and stateless components, recognize security tradeoffs, etc. As we drill in we might talk about data partitioning, georeplication, or high availability and implementation tradeoffs there. We might get down to the level of something like handling out-of-order change notifications. Rarely do I drill down to the level of file I/O or memory management strategies.