ElMem: Towards an Elastic Memcached System

Memory caches, such as Memcached, are a critical component of online applications as they help maintain low latencies by alleviating the load at the database. However, memory caches are expensive, both in terms of power and operating costs. It is thus important to dynamically scale such caches in response to workload variations. Unfortunately, stateful systems, such as Memcached, are not elastic in nature. The performance loss that follows a scaling action can severely impact latencies and lead to SLO violations. This paper proposes ElMem, an elastic Memcached system that mitigates post-scaling performance loss by proactively migration hot data between nodes. The key enabler of our work is an efficient algorithm, FuseCache, that migrates the optimal amount of hot data to minimize performance loss. Our experimental results on OpenStack, across several workload traces, show that ElMem elastically scales Memcached while reducing the postscaling performance degradation by about 90%.