Enhancing replica management services to tolerate group failures

Abstract

In a distributed system, replication of components, such as objects, is a well known way of achieving availability. For increased availability, crashed and disconnected components must be replaced by new components on available spare nodes. In this context, we address the problem of reconfiguring a group after the group as an entity has failed. Such a failure is termed a group failure which, for example, can be the crash of every component in the group or the group being partitioned into minority islands. The solution assumes crash-proof storage, and eventual recovery of crashed nodes and healing of partitions. It guarantees that (i) the number of groups reconfigured after a group failure is never more than one, and (ii) the reconfigured group contains a majority of the components which were members just before the group failed, so that the loss of state information due to group failure is minimal. The protocol is efficient in terms of communication rounds and use of stable store, during both normal operations and reconfiguration after a group failure.