A self-tuning, self-protecting, self-healing session state management layer

Abstract

Management of semi-persistent state, such as user-session state, is one factor that complicates failure management in clustered three-tier Internet applications (Jacobs, 2003). We observe that the specific properties of user-session state can be exploited to design a lightweight state storage layer that offers many of the same ease-of-management and ease-of recovery properties as stateless components such as Web servers. We describe SSM, a self-tuning, self-protecting, and self-healing session state management layer that provides a storage and retrieval mechanism for semi-persistent, serial-access user session state. SSM is fast, scalable, fault-tolerant, and recovers instantly from individual node failures. Any SSM node may be rebooted at any time and there is no special recovery code, so the performance cost of "eager" recovery is near zero, simplifying recovery policy management when SSM is integrated into a larger system.