Design a Leaderboard

Design a Leaderboard

Step 1 of 11

players10 M

Ten million players, thousands of score changes a second, and a board that must never be sorted at read time.

The Idea

Show the top hundred and a player's own rank while scores keep changing. Assume ten million players and thousands of score updates a second, so nothing may be re-sorted at read time.

Real-World Example

A scoreboard on a wall. Moving one name up is a single slide; what you avoid is recounting everybody's position from the register every time somebody scores.

The Tradeoff

A score-ordered set makes the top hundred a range read and every update a logarithmic move, all in memory, with the durable copy written behind it. Exact rank deep in the list is the part to watch: a set that keeps per-node counts answers it with another logarithmic walk, but a database index without them has to count everyone above, and a board split across shards has to ask every shard. Counting players per score bucket answers it closely enough for a fraction of the work.

Your turn

Put the steps in the right order.

1. 1Serve the top hundred as a range read from the front of the set↑↓
2. 2Apply the score change to the in-memory ranked set↑↓
3. 3Answer a deep rank from per-bucket counts rather than a full scan↑↓
4. 4Persist the new score asynchronously to the durable store↑↓

Check order

Mini quiz

1 / 3

Reading the top hundred is a range read because:

• AThe scores are cached
• BThere are few players
• CRanks are recomputed hourly
• DThe set is already kept in score order