The Staged Event-Driven Architecture (SEDA) is a new design for building scalable Internet services. SEDA has three major goals: To support massive concurrency, on the order of tens of thousands of clients per node To exhibit robust performance under wide variations in load and, To simplify the design of complex Internet services. SEDA decomposes a complex, event-driven application into a set of stages connected by queues. This design avoids the high overhead associated with thread-based concurrency models, and decouples event and thread scheduling from application logic. SEDA enables services to be well-conditioned to load, preventing resources from being overcommitted when demand exceeds service capacity. Decomposing services into a set of stages also enables modularity and code reuse, as well as the development of debugging tools for complex event-driven applications.
