State machine replication (SMR) is a replication technique that ensures fault tolerance by duplicating a service. Geo-replicated SMR is an enhanced version of SMR that distributes replicas in separate geographical locations, making the service more robust against large-scale disasters. Several geo-replicated SMR protocols have been proposed in the literature, each tailored to specific requirements; for example, protocols designed to reduce latency by either sacrificing a part of their fault tolerance or limiting the content of responses to clients. However, this diversity complicates the decision-making process for selecting the best protocol for a particular service. In this study, we introduce a latency estimation model for these SMR protocols based on the communication patterns of the protocols and perform simulations for various cases. Based on the simulation results and an experimental evaluation, we present five selection guidelines for geo-replicated SMR protocols based on their log management policy, distances between replicas, number of replicas, frequency of slow paths, and client distribution. These selection guidelines enable determining the best geo-replicated SMR protocol for each situation.

翻译：状态机复制（SMR）是一种通过复制服务来确保容错的复制技术。地理复制的SMR是SMR的增强版本，它将副本分布在不同的地理位置，使服务能够更好地抵御大规模灾难。文献中已提出了几种地理复制的SMR协议，每种协议都针对特定需求进行了优化；例如，有些协议旨在通过牺牲部分容错能力或限制对客户端的响应内容来降低延迟。然而，这种多样性使得为特定服务选择最佳协议的决策过程变得复杂。在本研究中，我们基于这些SMR协议的通信模式，引入了一种延迟估计模型，并对各种情况进行了模拟。基于模拟结果和实验评估，我们提出了基于日志管理策略、副本间距离、副本数量、慢路径频率和客户端分布的五项地理复制SMR协议选择指南。这些选择指南有助于为每种情况确定最佳的地理复制SMR协议。