An efficient causal order algorithm for message delivery in distributed system

Though causal order of message delivery simplifies the design and development of distributed applications, the overhead of enforcing it is not negligible. A causal order algorithm which does not send any redundant information is efficient in the sense of communication overhead. The authors characterize and classify redundant information into four categories: information regarding just delivered, already delivered, just replaced, and already replaced messages. They propose an efficient causal order algorithm which prevents propagation of this redundant information. Their algorithm sends less control information needed to ensure causal order than other existing algorithms. Since the algorithm's communication overhead increases relatively slowly as the number of processes increases, it shows good scalability. The potential of the algorithm is shown by simulation.