Flash sales, black Friday e-commerce drops, and concert ticket releases (Taylor Swift Eras tour, Glastonbury, Supreme drops) represent the most extreme concurrency stress tests in software engineering. Within milliseconds of release, hundreds of thousands of concurrent users and automated bot networks hammer a single endpoint, competing for only a few hundred or thousand inventory seats.
Naive designs that query relational databases with SELECT ... FOR UPDATE collapse instantaneously under database connection exhaustion, lock queues, and transaction deadlocks.
This module deconstructs the architecture of high-concurrency reservation systems: edge virtual waiting rooms, atomic Redis Lua script reservation leases, hot-inventory partition sharding, asynchronous payment webhooks, and distributed reservation release sagas.