Slowing Little Quickens More: Improving DCTCP for Massive Concurrent Flows

Abstract

DCTCP is a potential TCP replacement to satisfy the requirements of data center network. It receives wide concerns in both academic and industrial circles. However, DCTCP could only support tens of concurrent flows well and suffers timeouts and throughput collapse facing numerous concurrent flows. This is far from the requirement of data center network. Data centers employing partition/aggregation pattern usually involve hundreds of concurrent flows. In this paper, after tracing DCTCP's dynamic behavior through experiments, we explored two roots for DCTCP's failure under the high fan-in traffic pattern: (1) The regulation mechanism of sending window is ineffective when cwnd is decreased to the minimum size, (2) The bursts induced by synchronized flows with small cwnd cause fatal packet loss leading to severe timeouts. We enhance DCTCP to support massive concurrent flows by regulating the sending time interval and desynchronizing the sending time in particular conditions. The new protocol called DCTCP+ outperforms DCTCP when the number of concurrent flows increases to several hundreds. DCTCP+ can normally work to effectively support the short concurrent query responses in the benchmark from real production clusters, and keep the same good performance with the mixture of background traffic.