Can unstructured P2P protocols survive flash crowds?

Abstract

Today's Internet periodically suffers from hot spots, a.k.a., flash crowds. A hot spot is typically triggered by an unanticipated news event that triggers an unanticipated surge of users that request data objects from a particular site, temporarily overwhelming the site's delivery capabilities. During this time, the large majority of users that attempt to get these objects face the frustrating experience of not being able to retrieve the content they want while still being able to communicate effectively with all other parts of the network. In this paper, we examine whether simple, undirected peer-to-peer search protocols can be used as a backup to deliver content whose popularity suddenly spikes. We model a simple, representative, undirected peer-to-peer search protocol in which clients cache only those objects they have explicitly requested. Because the object that becomes hot initially has limited popularity, the number of cache points, were they to remain fixed, would be insufficient to handle the level of demand during the flash crowd. However, as searches complete, more copies of the object become available. We analyze this natural scaling phenomenon and show that during the flash crowd, copies are distributed to requesting clients at a fast enough rate such that these simple protocols can indeed be used to scalably retrieve content that suddenly becomes "hot." © 2005 IEEE.