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Coping miss synchronization in hierarchical caching systems with nonlinear TTL functions

Under the weak consistency paradigm, time-to-live (TTL)-based hierarchical caching systems are proposed to support Web content delivery. Within such systems, due to strictly hierarchical caching structure and linear TTL countdown function, a single user request may encounter consecutive cache miss events at cache servers of different levels in the hierarchy. This behavior, referred to as miss synchronization, is the main cause of a sudden increase in user-perceived response time. In this paper, we examine this undesirable behavior to gain a better understanding of its properties and characteristics. To mitigate this problem, we propose a family of nonlinear TTL countdown functions using a novel concept called extended lifetime. Performance analysis indicates that the proposed approach can effectively avoid miss synchronization in hierarchical caching systems. Further, a carefully-designed nonlinear countdown function can reduce cache miss ratio and user response time without any significant increase in outlived objects.