Caching can reduce the bandwidth requirement in a wireless computing environment as well as minimize the energy consumption of wireless portable computers. To facilitate mobile clients in ascertaining the validity of their cache content, servers periodically broadcast cache invalidation reports that contain information of data that has been updated. However, as mobile clients may operate in a doze or even totally disconnected mode (to conserve energy), it is possible that some reports may be missed and the clients are forced to discard the entire cache content. In this paper, we reexamine the issue of designing cache invalidation strategies. We identify the basic issues in designing cache invalidation strategies. From the solutions to these issues, a large set of cache invalidation schemes can be constructed. We evaluate the performance of four representative algorithms-two of which are known algorithms (i.e., Dual-Report Cache Invalidation and Bit-Sequences) while the other two are their counterparts that exploit selective tuning (namely, Selective Dual-Report Cache Invalidation and Bit-Sequences with Bit Count). Our study shows that the two proposed schemes are not only effective in salvaging the cache content but consume significantly less energy than their counterparts. While the Selective Dual-Report Cache Invalidation scheme performs best in most cases, it is inferior to the Bit-Sequences with the Bit-Count scheme under high update rates.

Re-examines the cache coherency problem in a mobile computing environment in the context of relational operations (i.e. selection, projection and join). We propose a taxonomy of cache coherency schemes, and as case studies, we pick several schemes for further study. These schemes are novel in several ways. First, they are incremental. Second, they are an integration of (and built on) techniques in view maintenance in centralized systems and cache invalidation in client-server computing environments. We conducted extensive studies based on a simulation model. Our study shows the effectiveness of these algorithms in reducing uplink transmission and average access times. Moreover, the class of algorithms that exploit collaboration between the client and server performs best in most cases. We also study extended versions of this class of algorithms to further cut down on the work performed by the server.