Cheatsheets
The numbers, models, and trade-offs a senior engineer is expected to have on reflex — not definitions, but the figures you reach for mid-design and the note on when each one changes a decision. Glanceable, version-dated, and framed for the interview.
Reviewed August 30, 2026. Every value is an established engineering fact — order-of-magnitude where hardware-dependent.
Order-of-magnitude latencies from L1 cache (~1 ns) to a cross-continent round trip (~150 ms). The point isn't the exact figure — it's the ratios: memory is ~100× faster than SSD, and a network hop dwarfs everything local.
4 min readThe powers of two, time constants, and object sizes that turn “design for 100M users” into concrete QPS, storage, and bandwidth in your head — deliberately order-of-magnitude, not false precision.
5 min readThe read/write patterns (cache-aside, read/write-through, write-back), eviction policies (LRU/LFU/TTL), and the two hard problems — stale reads and the thundering herd — with the mitigations that actually work.
5 min read