Better never than late

TLDR

Large‑scale datacenter web applications are soft real‑time systems where network flows must finish by deadlines to contribute to throughput and revenue, yet current transport protocols such as TCP are deadline‑agnostic and prioritize fairness, which can degrade performance. The paper designs and implements D3, a deadline‑aware control protocol tailored to datacenter environments to address TCP’s deficiencies. D3 applies explicit rate control to allocate bandwidth according to flow deadlines. Evaluation on a 19‑node datacenter testbed shows that D3 outperforms TCP in short‑flow latency and burst tolerance, and when deadline information is used it can double the network’s peak load capacity.

Abstract

The soft real-time nature of large scale web applications in today's datacenters, combined with their distributed workflow, leads to deadlines being associated with the datacenter application traffic. A network flow is useful, and contributes to application throughput and operator revenue if, and only if, it completes within its deadline. Today's transport pro- tocols (TCP included), given their Internet origins, are agnostic to such flow deadlines. Instead, they strive to share network resources fairly. We show that this can hurt application performance. Motivated by these observations, and other (previously known) deficiencies of TCP in the datacenter environment, this paper presents the design and implementation of D3, a deadline-aware control protocol that is customized for the datacenter environment. D3 uses explicit rate control to apportion bandwidth according to flow deadlines. Evaluation from a 19-node, two-tier datacenter testbed shows that D3, even without any deadline information, easily outper- forms TCP in terms of short flow latency and burst tolerance. Further, by utilizing deadline information, D3 effectively doubles the peak load that the datacenter network cansupport.