Design a real-time gaming leaderboard.

Question

Anonymous · Accepted Answer

functional requirement:
- user can view current leaderboard
- after a valid game, user can update their score
- the leaderboard is updated near real-time

non-functional requirement
- low latency (< 200 ms)
- durable, data is recorded correctly
- eventual consistency

core entities
- user/player
- id
- games
- id
- leaderboard
- game_id
- user_id
- scores

API:
- GET /api/v1/games/{game_id}/leaderboards
response:
{
topRank: [
{
- username
- ranking
- point
}
self: {
- username
- ranking
- point
}
]
}

- POST /api/v1/games/{game_id}/scores
{
- timestamp
- score
}

HLD:
----- background process to update leaderboard
| |
client ---> API Gateway ---> leaderboard-service --> DB
|
-----------> Redis

DB tables
- leaderboard
- id
- user_id
- game_id
- aggregated_score
- last_updated_at

- user_score_history
- id
- user_id
- game_id
- score
- created_at
- synced_at (nullable)

when user finishes a valid game, the game will submit user's score to the
leaderboard-service using the POST API,
it will insert the data to user_score_history.
it will continuously append data for however many user/player that plays the
game.

in the background a scheduled process will batch process those
user_score_history data looking it up based on synced_at is NULL,
and ordered them by created_at, process them into a way that is valid for the
aggregated score.
and then this background scheduler will update that leaderboard accordingly.

Design a real-time gaming leaderboard.

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