Research

Managing data center networks with low loss requires understanding traffic dynamics at short (millisecond) time-scales, especially the burstiness of traffic, and to what extent bursts contend for switch buffer resources. Yet, monitoring traffic over such intervals is a challenge at scale.

We make two contributions. First, we present Millisampler, a lightweight traffic characterization tool deployed across all Meta hosts. Millisampler takes a host-centric perspective to data collection, which is scalable and allows for correlating traffic patterns with transport layer statistics. Further, simultaneous collection of Millisampler data across servers in a rack enables analysis of how synchronized traffic interacts in rack buffers. In particular, we study contention, which occurs when multiple bursts arrive simultaneously at the dynamically shared rack buffer.

Second, we present a data-center-scale analysis of contention, including a unique joint analysis of burstiness, contention, and loss. Our results show (i) contention characteristics vary widely across and within a region and is influenced by service placement; (ii) contention varies significantly over short time-scales; (iii) bursts are likely to encounter some contention; and (iv) higher contention need not lead to more loss, and the interplay with workload and burst properties matters. We discuss implications for data center design including service placement, buffer sharing algorithms and congestion control.