System Support for Background Replication

Application performance and availability can be improved by aggressive background replication – distributing data across a network to where it is needed before it is requested. However, given the rapid fluctuations of available network bandwidth and changing resource costs due to technology trends, hand tuning applications risks (1) complicating applications, (2) being too aggressive and interfering with other applications, and (3) being too timid and not gaining the benefits of background replication. Our goal is for the operating system to manage network resources in order to provide a simple abstraction of zero-cost background replication. Our system, TCP Nice, provably bounds the interference inflicted by background flows on foreground flows. And our microbenchmarks and case study applications suggest that in practice it interferes little with foreground flows while reaping a large fraction of spare network bandwidth and simplifying application construction and deployment. For example in one microbenchmark, when demand flows consume half of the available bandwidth, Nice flows consume 50%-80% of the remaining bandwidth without increasing demand packets’ average latencies by more than 5%; if the same background flows are transmitted with TCP Reno, they can hurt foreground latencies by up to two orders of magnitude. In our prefetching case study application, aggressive prefetching improves demand performance by a factor of three when Nice manages resources; but the same prefetching hurts demand performance by a factor of six under standard network congestion control.