The Network Effects of Prefetching

Prefetching has been shown to be an e ective technique for reducing user perceived latency in distributed systems. In this paper we show that even when prefetching adds no extra tra c to the network, it can have serious negative performance e ects. Straightforward approaches to prefetching increase the burstiness of individual sources, leading to increased average queue sizes in network switches. However, we also show that applications can avoid the undesirable queueing e ects of prefetching. In fact, we show that applications employing prefetching can signi cantly improve network performance, to a level much better than that obtained without any prefetching at all. This is because prefetching o ers increased opportunities for tra c shaping that are not available in the absence of prefetching. Using a simple transport rate control mechanism, a prefetching application can modify its behavior from a distinctly ON/OFF entity to one whose data transfer rate changes less abruptly, while still delivering all data in advance of the user's actual requests.