LogMemcached an RDMA based continuous cache replication

One of the advantages of cloud computing is its ability to quickly scale out services to meet demand. A common technique to mitigate the increasing load in these services is to deploy a cache. Although it seems natural that the caching layer would also deal with availability and fault tolerance, these issues are nevertheless often ignored, as the cache has only recently begun to be considered a critical system component. A cache may evict items at any moment, and so a failing cache node can simply be treated as if the set of items stored on that node have already been evicted. However, setting up a cache instance is a time-consuming operation that could inadvertently affect the service's operation. This paper addresses this limitation by introducing cache replication at the server side by expanding Memcached (which currently provides availability via client side replication). This paper presents the design and implementation of LogMemcached, a modification of Memcached's internal data structures to include state replication via RDMA to provide an increased system availability, improved failure resilience and enhanced load balancing capabilities without compromising performance and with introducing a very low CPU load, while keeping the main principles of Memcached's Design Philosophy.