A Nonblocking Approach for Reaching an Agreement on Request Total Orders

In distributed systems that use active replication to achieve robustness, it is important to efficiently enforce consistency among replicas. The nonblocking mode helps to speed up system execution. Unfortunately, this benefit comes at the expense of introducing decision conflicts when the replicas form a single logical token ring and client requests are processed in sequence following the ring. In order to reach an agreement regarding request total orders, this paper proposes a forward-confirmation (FC) approach to identify and solve decision conflicts when up to k successive replicas fail simultaneously. The FC approach can obtain consistent decisions among replicas. An implementation of the FC approach, namely, the queueing method, is proposed. Test results show that our protocol in the nonblocking mode outperforms the Totem protocol regarding delays and failure recovery.