Step 1: System Definition

A flash sale system is an e-commerce component designed to handle short-term sales events where a limited inventory of products is sold to a massive number of buyers in a very short time frame. In such events, traffic spikes dramatically (e.g. hundreds of thousands of users hitting the site simultaneously), and the number of purchase requests far exceeds the available items (for example, millions of requests for only thousands of items). The system must rapidly serve many concurrent users, reliably track inventory, and fairly allocate the product items