May 26, 2018

Architecture for Highly Concurrent Server Applications

[ excerpt from developer’s web site with modifications ]

The goal is to build a system capable of supporting massive concurrency on the order of tens of thousands of simultaneous client connections and avoid the pitfalls which arise with traditional thread and event-based approaches.

SEDA is an acronym for staged event-driven architecture, and 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. By performing admission control on each event queue, the service can be well-conditioned to load, preventing resources from being overcommitted when demand exceeds service capacity. SEDA employs dynamic control to automatically tune runtime parameters such as the scheduling parameters of each stage, as well as to manage load, for example, by performing adaptive load shedding. 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.

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