Enhanced Scalable Asynchronous Cache Consistency Scheme for Mobile Environments

An important technique to reduce the contention on the limited bandwidth of wireless channels between mobile units and base stations is caching frequently accessed data items. In the literature, two approaches were proposed for cache consistency: Stateful and Stateless. In the Stateful approach, the server has to keep information about all the mobile units in its cell. On the other hand, in the stateless approach, the server does not store any information about clients. In this paper, we propose a hybrid cache consistency approach which combines the advantages of both Stateless and Stateful approaches; our approach has several characteristics in common with the Scalable Algorithm for Cache Consistency Scheme “SACCS”, which has been reported to have advantages compared to some major previous algorithms, including TimeStamps, Signatures, Amnesic Terminals and Asynchronous Stateful. The proposed approach reduces the side-effect of the sleep-wakeup patterns, and uses new communication messages intended to invalidate only the entries changed during the sleep time. Further, we propose a better replacement policy for the mobile unit cache, which considers the size of the removed entry to improve channel utilization. Experimental results show that the proposed approach increases the mobile cache hit, reduces the delay time of queries and reduces traffic in both uplink and downlink channels. Keyword: mobile databases, cache consistency, invalidation report, cache invalidation scheme.