This paper proposes a novel algorithm for taking checkpoints and rolling back the processes for recovery in asynchronous distributed systems. The algorithm has the following properties: (1) multiple processes can simultaneously initiate the checkpointing; (2) no additional message is transmitted for taking checkpoints; (3) a set of local checkpoints taken by multiple processes denotes a consistent global state; (4) multiple processes can initiate simultaneously the rollback recovery; (5) the minimum number of processes are rolled back; and (6) each process is rolled back asynchronously. The number of messages for rolling back the processes is O(l) where l is the number of channels. Therefore, the system is kept highly available by the algorithm presented.

In distributed systems, a group of processes are cooperated to execute an application program. A group is established among multiple processes and only processes in the group communicate with each other. This type of group communication is named intra-group communication. The communication system has to support the reliable intra-group communication in the presence of the process fault. In order to tolerate the process fault, each process in the group is replicated into a collection of multiple replicas named a cluster. In this paper, we would like to propose a new intra-group communication protocol which supports the causally ordered delivery of messages for the processes within the group. In addition, the protocol supports the reliable delivery of messages in the presence of the Byzantine faults of the processes.