A scalable membership service for group communications in WANs

Group Communication System (GCS) is an important building block for reliable, fault-tolerant distributed applications. Due to highly variable and unpredictable latency in WANs, GCS needs to cope with frequent membership changes. It results in diminishing the scalability of GCS. In this paper we propose a new scheme that improves the scalability of group membership service for WANs by exploiting dedicated membership servers configured into multiple layers and reaching global agreement on the view through layered servers. It improves the scalability of a process group of N member processes from O(N/sup 2/) to O(N/sup 3/) with three layers, where N is the number of processes in the group. Computer simulation verifies that the proposed scheme requires much smaller number of message exchanges for reaching an agreement on a next view and does that much quicker. In addition, the proposed scheme prevents applications from being blocked until reaching the final view agreement if the applications permit temporary inconsistency.