System Design Article

Design a Stock Exchange

Difficulty: Hard

Design a stock exchange like NASDAQ that matches buy and sell orders for thousands of symbols at sub-100-microsecond latency, handles 200K orders per second per symbol at peak, and produces a deterministic, replayable trade history with regulatory audit guarantees. The interview centerpiece is the matching engine: a deliberately single-threaded, in-memory order book that processes orders sequentially in price-time priority. We design the order book data structures (price-indexed levels with FIFO queues), the gateway path (ultra-low-latency parsing and rate-limit), the event-sourced persistence (every order and trade as an append-only event), and how to scale by sharding per symbol.