Uber (25M Rides/day, H3 Driver Index, Batch Matching, Exactly-Once Dispatch)
Design Uber for 25 million rides a day. A measured H3 driver index in Redis, batch matching that beats nearest-driver, a location path that never moves a driver backwards, dispatch that never promises one driver to two riders, exactly-once payments, surge with legal caps, what happens when each part goes down, regions, capacity and cost.