Demotion-based exclusive caching through demote buffering: design and evaluations over different networks

Multi-level buffer cache architecture has been widely deployed in today's multiple-tier computing environments. However, caches in different levels are inclusive. To make better use of these caches and to achieve the expected performance commensurate to the aggregate cache size, exclusive caching has been proposed. Demotion-based exclusive caching [1] introduces a DEMOTE operation to transfer blocks discarded by a upper level cache to a lower level cache. In this paper, we propose a DEMOTE buffering mechanism over storage networks to reduce the visible costs of DEMOTE operations and provide more flexibility for optimizations. We evaluate the performance of DEMOTE buffering using simulations across both synthetic and real-life workloads on three different networks and protocol layers (TCP/IP on Fast Ethernet, IBNice on InfiniBand, and VAPI on InfiniBand). Our results show that DEMOTE buffering can effectively hide demotion costs. A maximum speedup of 1.4x over the original DEMOTE approach is achieved for some workloads. Speedups in the range of 1.08--1.15x are achieved for two real-life workloads. The vast performance gains results from overlapping demotions and other activities, reduced communication operations and high utilization of the network bandwidth.