A simple quorum reconfiguration for open distributed environments

Synchronizations adopting quorum consensus are the well-known solutions of some fundamental issues in the study of distributed mutual exclusion and replica control problems. Mechanisms to reconfigure quorum structure in open distributed environments are necessary since the membership changes of such systems (i.e., the joining and leaving members) may decrease quorum availability. Many algorithms have been proposed to this problem, however, they mostly change the quorum system totally thus any operation cannot be performed while system in the reconfiguration process. This paper presents a simple quorum reconfiguration algorithm in open distributed computing systems that can evolve their behavior based on membership changes in the environment. The algorithm is easy to use since it simply implements the two quorum operations called join-replace and join-cross. The join-replace operation is used when a set of nodes have leaved from the system while some others are joining, and the join-cross is defined and used if there is only a set of joining nodes enter the system. The great advantages of the algorithm are the ability to complete any operation before a new quorum structure is fully constructed during reconfiguration thus system does not enter the halt state with a wait-avoidance characteristic, and it directly adopts quorum consensus in the static environments without any change to the protocol. Moreover, an extra mapping procedure is unnecessary to be given since the algorithm only works in the logical space.