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We consider an environment in which a collection of mobile clients accesses a stationary database server via a wireless channel. Due to the limited bandwidth of a wireless channel and the instability of the wireless network, caching of frequently accessed data items in a client's local storage becomes especially important for improving the performance and data availability of data access queries. However, the network stability and high transmission bandwidth requirements of existing caching mechanisms for conventional clientserver and distributed database applications conflict with the mobility nature of mobile clients as well as the low-bandwidth of wireless channel. In this paper, we investigate issues that need to be addressed in caching mechanisms for a mobile environment and propose an adaptive caching mechanism that could cope with the nature of a mobile environment as well as the low-bandwidth wireless media. The results of some preliminary exploratory experiments will also be illustrated to demonstrate the feasibility of our mechanism.

Recovery by checkpointing on distributed shared memory systems is investigated in this paper. The notion of corwzstent global states on a sequentially consistent shared memory system is defined. We investigate how consistent checkpoints can be obtained in these systems. In addition, a novel lazy checkpointing approach is proposed. It allows a cent rolled degree of concurrency and, at the same time, limits the amount of rollback propagation during recovery. Correctness requirements for efficient checkpointing are explored first and algorithms satisfying the requirements are developed subsequently. Several interesting properties of checkpointing on distributed shared memory systems are discovered. In particular, we show that for low levels of laziness, one can achieve better concurrency with more stable storage.