Mobile Agent Fault Tolerance for Information Retrieval Applications: An Exception Handling Approach

Maintaining mobile agent availability in the presence of agent server crashes is a challenging issue since developers normally have no control over remote agent servers. A popular technique is that a mobile agent injects a replica into stable storage upon its arrival at each agent server. However, a server crash leaves the replica unavailable, for an unknown time period, until the agent server is back on-line. This paper uses exception handling to maintain the availability of mobile agents in the presence of agent server crash failures. Two exception handler designs are proposed. The first exists at the agent server that created the mobile agent. The second operates at the previous agent server visited by the mobile agent. Initial performance results demonstrate that although the second design is slower it offers the smaller trip time increase in the presence of agent server crashes.