Tolerating client and communication failures in distributed groupware systems

If a groupware system is to be effectively used, especially over a wide area network such as the Internet, where the quality of networking and computing resources are unpredictable, it should allow clients to tolerate client, link, and server failures. In particular, clients should be able to join groups and transfer groups´ current state in the presence of most client and link failures. In order to reduce usage overhead, disconnected clients should also be able to rejoin groups without having to restart from scratch. Furthermore, lock management and group membership should tolerate transient failures in the system. We introduce the notion of stateful group communication, which frees clients of administrative management of shared application state and allows fault tolerant group join, state transfer, and rejoin. Stateful group communication is incorporated in Corona, a general purpose, group communication service provider. In order to allow groups to tolerate transient failures, Corona also provides locks with grace period and group membership notification services that are based on client connection status. We present and discuss Corona´s fault tolerant services