TinyFlow: Breaking elephants down into mice in data center networks

Current multipath routing solution in data centers relies on ECMP to distribute traffic among all equal-cost paths. It is well known that ECMP suffers from two deficiencies. ECMP does not differentiate between elephant and mice flows, creates head-of-line blocking for mice flows in the egress port buffer, and results in long tail latency. Further it does not fully utilize available bandwidth due to hash collision among elephant flows. We propose TinyFlow, a simple yet effective approach that remedies both problems. TinyFlow changes the traffic characteristics of data center networks to be amenable to ECMP by breaking elephants into mice. In a network with a large number of mice flows only, ECMP naturally balances load and performance is improved. We conduct NS-3 simulations and show that TinyFlow provides 20%-40% speedup in both mean and 99-th percentile FCT for mice, and about 40% throughput improvement for elephants.