Adaptive plausible clocks

Abstract

Having small-sized logical clocks with high causal-ordering accuracy is useful, especially where (i) the precision of the knowledge of the causal dependencies among events implies savings in time overhead and (ii) the cost of transmitting full vector clock timestamps - that precisely characterise the causal relation - is high. Plausible clocks can be used as timestamps to order events in a distributed system in a way that is consistent with the causal order as long as the events are causally dependent. We introduce the nonuniformly mapped R-entries vector (NUREV) clocks, a general class of plausible clocks that allow accuracy adaptation and we analyse the ways that these clocks may relate causally independent event pairs. Our analysis resulted in a set of conclusions and the formulation of new, adaptive plausible clocks algorithms, with improved accuracy, even when the number of clock entries is very small, which is important in peer-to-peer communication systems.