A causal message logging protocol for mobile nodes in mobile computing systems

This paper presents a causal message logging protocol with independent checkpointing for mobile nodes with the aim of efficiently handling several constraints of the mobile nodes such as mobility and disconnection, limited life of battery power, small amount of storage and low bandwidth on wireless link. For this purpose, the protocol includes a low-cost failure-free mechanism requiring only locating the mobility agent maintaining the latest checkpoint of each process on an mobile node during its handoff process. This mechanism forces only the latest checkpoint to be maintained on the stable storage while incurring low failure-free overhead. Also, the protocol uses two garbage collection schemes to remove log information of mobile nodes. The first scheme enables each mobile node to autonomously remove useless log information in its storage by piggybacking only some additional information without requiring any extra message and forced checkpoint. The second scheme allows the mobile node to remove a part of log information in its storage if more empty storage space is required after executing the first scheme. It reduces the number of processes to participate in the garbage collection by using the size of the log information of each process. Simulation results show that the two proposed schemes significantly reduce the garbage collection overhead compared with traditional schemes. Additionally, we present an efficient recovery algorithm to avoid frequent stable storage accesses, impose no restriction on the execution of live processes during recovery and ensure consistent recovery in case of being integrated with independent checkpointing.