Top-K Heavy Hitters — most-viewed items over 1m / 5m / 1h / 1d
10B events/day · 350K/s peak ingest · exact counting until cardinality forces sketches · fast-path error ≤2%, disclosed · day window batch-exact
arrows 0/14cards 12letters A–L
happy-pathside-effectfailure-compnew-infra
▶ BOTE — canonical numbers (every N- chip in the rail links here)▶ Failure playbook (A–L)▶ What breaks first · the four counting approaches · interview framing