Disseminating Updates on Broadcast Disks
Swarup Acharya, Michael J. M. Franklin, Stanley B. Zdonik · 1996
Lately there has been increasing interest in the use of data dissemination as a means for delivering data from servers to clients in both wired and wireless environ-ments. Using data dissemination, the transfer of data is initiated by servers, resulting in a reversal of the tra-ditional relationship between clients and servers. In previous papers, we have proposed Broadcast Disks as a model for structuring the repetitive transmission of data in a broadcast medium. Broadcast Disks are in-tended for use in environments where, for either phys-ical or application-dependent reasons, there is asym-metry in the communication capacity between clients and servers. Examples of such environments include wireless networks with mobile clients, cable and direct satellite broadcast, and information dispersal applica-tions. Our initial studies of Broadcast Disks focused on the performance of the mechanism when the data be-ing broadcast did not change. In this paper, we extend those results to incorporate the impact of updates. We first propose several alternative models for updates and examine the fundamental tradeoff that arises between the currency of data and performance. We then propose and analyze mechanisms for implementing these vari-ous models. The performance results show that, even in a model where updates must be transmitted immedi-ately, the performance of the Broadcast Disks technique can be made quite mbust through the use of simple tech-niques for propagating and prefetching data items.