Caching — Part 4: Interview Q&A (Staff/Principal Level)

maang.io System Design Series

What is this?

Think of this part as sitting across the table from a mentor running mock interviews with you. For each question we'll do three things: figure out what the interviewer is really asking, walk through a strong answer, and call out the senior line — the one sentence that makes you sound like someone who's operated caches, not just read about them.

The big secret: at Staff/Principal level, nobody's impressed that you know what a cache is. They're listening for whether you understand its failure modes (stampede, avalanche, penetration), its consistency reality (eventual, bounded), and how you choose — pattern, policy, engine — for this data. Name the trade-off, pick a default, say why. That's the whole game.