On the Cost of Prioritized Atomic Multicast Protocols

A prioritized atomic multicast protocol allows an application to tag messages with a priority that expresses their urgency and tries to deliver first those with a higher priority. For instance, such a service can be used in a database replication context, to reduce the transaction abort rate when integrity constraints are used. We present a study of the three most important and well-known classes of atomic multicast protocols in which we evaluate the cost imposed by the prioritization mechanisms, in terms of additional latency overhead, computational cost and memory use. This study reveals that the behavior of the protocols depends on the particular properties of the setting (number of nodes, message sending rates, etc.) and that the extra work done by a prioritized protocol does not introduce any additional latency overhead in most of the evaluated settings. This study is also a performance comparison of these classes of total order protocols and can be used by system designers to choose the proper prioritized protocol for a given deployment.