Design a Matchmaking Service for Multiplayer Games

Roblox hosts millions of multiplayer game sessions daily. It is planning to release a matchmaking service for game developers such that users can join a waiting queue, be grouped together by skill level, and join a new gameserver at the same time. A popular game might have 500k concurrent players, hundreds of players joining per second. A user may have skill level e.g. userId : skill (1-100) Design a service to help organize these users into groups of 16 before allocating them a new empty gameserver. A user may only queue for 1 game at a time. You may assume the following ID types exist long GameID long UserID long ServerId And the following table Table UserSkill long GameId long UserId int skill