Measures of importance and symmetry in distributed systems
Mitchell L. Neilsen · 2002
Quorum-based protocols can be formalized in terms of the data structures they use. These data structures, called quorum structures, include quorum sets, coteries, and bicoteries. In this paper, we present measures that can be used to determine the relative importance of each node in a quorum structure. By knowing the relative importance of each node in the system, it is possible to improve the overall system reliability by investing more effort on improving the reliability of important nodes. Secondly, such measures can be used to accurately define symmetry in a distributed system. A quorum structure is symmetrical, if all nodes are equally important. Finally, since several well known protocols are based on composition, we present simple recursive methods to compute the importance of nodes in composite quorum structures.>