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Performance Sensitive Replication in Geo-distributed Cloud Datastores

Modern web applications face stringent requirements along many dimensions including latency, scalability, and availability. In response, several geo-distributed cloud data stores have emerged in recent years. Customizing data stores to meet application SLAs is challenging given the scale of applications, and their diverse and dynamic workloads. In this paper, we tackle these challenges in the context of quorum-based systems (e.g. Amazon Dynamo, Cassandra), an important class of cloud storage systems. We present models that optimize percentiles of response time under normal operation and under a data-center (DC) failure. Our models consider factors like the geographic spread of users, DC locations, consistency requirements and inter-DC communication costs. We evaluate our models using real-world traces of three applications: Twitter, Wikipedia and Go Walla on a Cassandra cluster deployed in Amazon EC2. Our results confirm the importance and effectiveness of our models, and highlight the benefits of customizing replication in cloud datastores.