The Relative Overhead of Piggybacking in Causal Message Logging Protocols

Message logging protocols ensure that crashed processes make the same choices when re-executing nondeterministic events during recovery. Causal message logging protocols achieve this by piggybacking the results of these choices (called determinants) on the ambient message traffic. By doing so, these protocols do not create orphan processes nor introduce blocking in failure-free executions. To survive f failures, they ensure that determinants are stored by at least f +1 processes. Causal logging protocols differ in the kind of information they piggyback to other processes. The more information they send, the better each process is able to estimate global properties of the determinants, which in turn results in fewer needless piggybacking of determinants. This paper attempts to quantify the tradeoff between the cost of sending more information and the benefit of doing so.