SEDA : An Architecture for Highly Concurrent Server Applications
2005. 7. 29. 18:28
My Ph.D. thesis work at UC Berkeley focused on the development of a robust, high-performance platform for Internet services, called SEDA. 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.
Our current prototype of a SEDA-based services platform is called Sandstorm. Sandstorm is implemented entirely in Java and uses the NBIO package to provide nonblocking I/O support. Support for the JDK 1.4 java.nio package is included as well. Despite using Java, we have achieved performance that rivals (and sometimes exceeds) that of C/C++. We have also implemented a SEDA-based asynchronous SSL and TLS protocol library, called aTLS. All of this software is available for download below.
We have built a number of applications to demonstrate the SEDA framework. Haboob is a a high-performance Web server including support for both static and dynamic pages that outperforms both Apache and Flash (which are implemented in C) on a SPECWeb99-like benchmark. Other applications include a Gnutella packet router and Arashi, a Web-based email service similar to Yahoo! Mail.
The best place to start for more information is the SOSP'01 paper on SEDA and the corresponding talk slides. My Ph.D. thesis has much more information as well. If you have questions, comments, or are interested in collaborations, please feel free to contact me by e-mail (see my home page).
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.
Our current prototype of a SEDA-based services platform is called Sandstorm. Sandstorm is implemented entirely in Java and uses the NBIO package to provide nonblocking I/O support. Support for the JDK 1.4 java.nio package is included as well. Despite using Java, we have achieved performance that rivals (and sometimes exceeds) that of C/C++. We have also implemented a SEDA-based asynchronous SSL and TLS protocol library, called aTLS. All of this software is available for download below.
We have built a number of applications to demonstrate the SEDA framework. Haboob is a a high-performance Web server including support for both static and dynamic pages that outperforms both Apache and Flash (which are implemented in C) on a SPECWeb99-like benchmark. Other applications include a Gnutella packet router and Arashi, a Web-based email service similar to Yahoo! Mail.
The best place to start for more information is the SOSP'01 paper on SEDA and the corresponding talk slides. My Ph.D. thesis has much more information as well. If you have questions, comments, or are interested in collaborations, please feel free to contact me by e-mail (see my home page).
