Real-time leaderboard

Rank millions of players by score in real time: update a player's score when a match ends, fetch the global top 100, and show any player their exact rank and neighbours. SQL `COUNT(*)` rank queries collapse at scale; augmented skip lists (Redis sorted sets) turn both updates and rank lookups into O(log N) memory operations.

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Duration 45:00

Requirements checklist

Record a match score (increment or max-score update) for a user on a current tournament or daily/monthly board.Fetch the top K players (e.g., top 100) with their scores and ranks.Fetch any player's own global rank and the k players immediately above and below them.Score updates visible in rankings within ~100 ms; read p99 under ~50 ms.Support 25M DAU on a single global board without full-table scans.Durable score history so an in-memory node failure can be rebuilt without losing player points.

Clarifying questions

How many active players are on a single leaderboard, and what is the peak score update rate?
Are scores cumulative (incremented per match) or high-water-mark (best single run)?
How should ties be broken — earlier timestamp wins?
Do we need exact global rank for a player ranked #18,000,000, or is exact rank only needed for the top tier?

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requirements

Suggested time: about 6 minutes. Distinguishes global exact rank from friend leaderboards and approximate percentile tiers.

Notes for requirements