How Bad Are Wrong Suspicions? Towards Adaptive Distributed Protocols

In this paper, we analyze the performance of consensus protocols based on the rotating coordinator paradigm. We consider a simulated production environment, on which processing and communication resources available for the different processes running the protocols are not necessarily the same. Firstly, we show that, in some scenarios, the performance of the consensus protocol is enhanced when there is an increase in the number and duration of the wrong suspicions periods of the failure detection service used. Since it is well known that wrong suspicions may also decrease the performance of the consensus protocol, a new dilemma is posed to the designers of such protocols. We then propose a new approach to address performance issues in the design of crash-detection based distributed protocols for asynchronous systems. We argue that they must be designed to adapt themselves to the variations on the availability of resources. The concept of slowness oracles is proposed to achieve this goal. Finally, we present a slowness oracle that can be used to transform a non-adaptive consensus protocol into an adaptive one. Simulations show that the adaptive protocol outperforms its conventional non-adaptive counterpart in a number of scenarios, having an equivalent performance in the other scenarios.