Adaptive and dynamic funnel replication in clouds

We consider the problem of strongly consistent replication in a multi data center cloud setting. This environment is characterized by high latency communication between data centers, significant fluctuations in the performance of seemingly identical virtual machines (VMs) and temporary disconnects of data centers from the rest of the cloud. In this paper we introduce the adaptive and dynamic Funnel Replication (FR) protocol that is designed to achieve high throughout and low latency for reads, to accommodate arbitrary latency/throughput tradeoffs for writes, to maximize performance in the face of VM performance variations and to provide high availability for read requests in the presence of network partitions. FR is based on the idea of flexible write dissemination topologies which enables it to achieve, per message, the desired tradeoff between latency and throughput, depending on the message size, the observed network conditions, and the importance of latency as indicated by the client. We demonstrate the benefits of flexible dissemination topologies and show that in a cloud setting with N identical replicas FR can improve the write latency up to a factor of N/2 for N ≥ 2 compared to the notable chain replication (CR) protocol at the expense of a slight decrease in the write throughput. In a setting with potentially high variability in the performance of replicas, e.g., as in Amazon EC2, FR can achieve throughput up to a factor of 16 higher than CR while also improving the latency. FR does this by adopting a topology that consists of concurrent disjoint data replication paths so that load on high throughput paths is adaptively increased while load on congested replicas is reduced.