Proactive Incast Congestion Control in a Datacenter Serving Web Applications

Abstract

With the rapid development of web applications in datacenters, network latency becomes more important to user experience. The network latency will be greatly increased by incast congestion, in which a huge number of requests arrive at the front-end server simultaneously. Previous incast problem solutions usually handle the data transmission between the data servers and the front-end server directly, and they are not sufficiently effective in proactively avoiding incast congestion. To further improve the effectiveness, in this paper, we propose a Proactive Incast Congestion Control system (PICC). Since each connection has bandwidth limit, PICC novelly limits the number of data servers concurrently connected to the front-end server to avoid the incast congestion through data placement. Specifically, the front-end server gathers popular data objects (i.e., frequently requested data objects) into as few data servers as possible, but without overloading them. It also re-allocates the data objects that are likely to be concurrently or sequentially requested into the same server. As a result, PICC reduces the number of data servers concurrently connected to the front-end server (which avoids the incast congestion), and also the number of connection establishments (which reduces the network latency). Since the selected data servers tend to have long queues to send out data, to reduce the queuing latency, PICC incorporates a queuing delay reduction algorithm that assigns higher transmission priorities to data objects with smaller sizes and longer queuing times. The experimental results on simulation and a real cluster based on a benchmark show the superior performance of PICC over previous incast congestion problem solutions.