Hierarchical Cache Consistency in a WAN Extended Abstract

This paper explores ways to provide strong consistency for Internet applications scaling to millions of clients. We make four contributions. First, we identify the ways in which specific characteristics of data-access workloads affect the scalability of cache consistency algorithms. Second, we define two primitive mechanisms, split and join for growing and shrinking hierarchies. We show how these primitives can be implemented with a simple mechanism already present in a protocol for strong consistency that we have previously proposed. Third, we describe and evaluate policies for using split and join to address the fault tolerance and performance challenges of hierarchies. Finally, we compare various algorithms for maintaining strong consistency in a range of hierarchy configurations. We evaluate our algorithms using simulations.