1A Scalable Asynchronous Cache Consistency Scheme (SACCS) for Mobile Environments

In the literature, there exit two types of cache consistency maintenance algorithms for mobile com-puting environments: stateless and stateful. In a approach, the server is unaware of the cache contents at a mobile user (MU). Even though stateless approaches employ simple database manage-ment, they lack in scalability and ability to support user disconnectedness and mobility. On the other hand, a approach is scalable for large database systems at the cost of nontrivial overhead due to server database management. In this paper, we propose a novel cache consistency maintenance al-gorithm, called ff flfiffi ! "#%$ &!$&')(ffi"* 01 (SACCS), which inherits the positive features of both stateless and stateful approaches. SACCS provides a weak cache consistency for unreliable communication environments (e.g., wireless mobile) with small stale cache hit proba-bility. Specifically, the main features of SACCS include: (1) Use of flag bits at server and MU cache (MUC); (2) Use of an identifier (ID) in MUC for each entry after its invalidation; (3) Rendering of all valid entries of MUC to an *! #2 -3 4 when an MU wakes up; and (4) Use of estimated time-to-live (TTL) for each cached entry. These four key features make the SACCS a highly scalable algorithm with minimum database management overhead. An analytical model is developed to estimate the upper bound on the stale cache hit probability. Comprehensive simulation results show that the performance of SACCS is superior to other existing stateful and stateless algorithms in both -3 5 and 04 67- cell mobile environments