Bounding Distance Between Outputs in Distributed Lattice Agreement

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Abstract

This paper studies the lattice agreement problem and proposes a stronger form, $\varepsilon$-bounded lattice agreement, that enforces an additional tightness constraint on the outputs. To formalize the concept, we define a quasi-metric on the structure of the lattice, which captures a natural notion of distance between lattice elements. We consider the bounded lattice agreement problem in both synchronous and asynchronous systems, and provide algorithms that aim to minimize the distance between the output values, while satisfying the requirements of the classic lattice agreement problem. We show strong impossibility results for the asynchronous case, and a heuristic algorithm that achieves improved tightness with high probability, and we test an approximation of this algorithm to show that only a very small number of rounds are necessary.