A goal is scored at minute 78. Within two seconds, thirty million phones — across continents, on 3G, on Wi-Fi, on the subway — must show the new score before the user feels it as late. The reads are the product. The writes are sparse (a goal happens, not 60 times a second), but the fanout factor is the design pressure: one publish must reach tens of millions of subscribers, and the on-field event rate spikes from 0 to ~5 events/second the instant something happens.

This is not the URL-shortener shape. The hot path is not a key-value lookup against a cache; it is sustaining a 30M-concurrent persistent-connection fleet, holding per-match subscriber lists in memory at the right shard, and absorbing reconnect storms when a PoP flaps. The single most important design decision is "where does the per-match fanout live" — and the answer (per-match actor sharded by hash(matchId), with a tree-relay topology activated for hot matches) determines the rest of the architecture.