The role of inhibition in asynchronous consistent-cut protocols

We present results regarding consistent-cut protocols. Consistent-cut protocols are based on finding a consistent global state in an underlying distributed computation; they are used for a variety of applications such as checkpointing and deadlock detection. We formally define what it means for a protocol to be non-inhibitory, which intuitively means that it does not prevent any actions from occurring in an underlying computation. We prove that there is no non-inhibitory consistent-cut protocol for non-FIFO asynchronous systems. We also give a lower bound on communication for non-inhibitory consistent-cut protocols for FIFO systems of one message per bidirectional channel (up to 1/2(n2 — n)). We present two protocols, one non-inhibitory requiring up to two messages between each pair of neighboring nodes in a network and the other inhibitory and requiring only 3(n–1) messages total. In most networks these results illustrate a tradeoff between the amount of necessary communication and the willingness to inhibit actions of the underlying system. Additionally, our inhibitory protocol also works for non-FIFO systems, thus illustrating that the inhibitory condition is exactly what is required to develop consistent-cut protocols for non-FIFO systems which satisfy our model.