System designMediumsd-g273

Subject Real time systemsLevel Mid–Senior~40 minCommon in ML systems · Distributed systems · Algorithms & data structures interviewsIndustries Computer games, Technology

Question

Design a real-time global leaderboard for a mobile game with 80M monthly players. After every match a player's score updates, and they want to see (1) the global top 100, (2) their own rank, and (3) a small window of players ranked just above and below them — all updating within ~1 second. Scores change millions of times per minute during peak. Computing an exact rank over 80M rows on every read is far too expensive. How do you maintain ranks and serve these three queries cheaply?

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts — data model, bottlenecks, consistency, failure modes — and name the trade-offs you are making.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.