A common pattern in the architectures of modern interactive web-services is that of large request fan-outs, where even a single end-user request (task) arriving at an application server triggers tens to thousands of data accesses (sub-tasks) to different stateful backend servers. The overall response time of each task is bottlenecked by the completion time of the slowest sub-task, making such workloads highly sensitive to the tail of latency distribution of the backend tier. The large number of decentralized application servers and skewed workload patterns exacerbate the challenge in addressing this problem.