The reliable execution of a mobile agent is a very important design issue to build a mobile agent system and many fault-tolerant schemes have been proposed. Hence, we present the experimental evaluation of the performance of the fault-tolerant schemes for the mobile agent environment. Our evaluation focuses on the checkpointing schemes and deals with the cooperating agents.

We evaluate the performance of checkpointing and replication schemes for the fault tolerant mobile agent system. For the quantitative comparison, we have implemented an experimental system on top of the Mole mobile agent system and also built a simulation system to include various failure cases. Our experiment aims to have the insight into the behavior of agents under two schemes and provide a guideline for the fault tolerant system design. The experimental results show that the checkpointing scheme shows a very stable performance; and for the replication scheme, some controllable system parameter values should be chosen carefully to achieve the desirable performance.

A number of checkpointing and message logging algorithms have been proposed to support fault tolerance of mobile computing systems. However, little attention has been paid to the optimistic message logging scheme. Optimistic logging has a lower failure-free operation cost compared to other logging schemes. It also has a lower failure recovery cost compared to the checkpointing schemes. This paper presents an efficient scheme to implement optimistic logging for the mobile computing environment. In the proposed scheme, the task of logging is assigned to the mobile support station so that volatile logging can be utilized. In addition, to reduce the message overhead, the mobile support station takes care of dependency tracking and the potential dependency between mobile hosts is inferred from the dependency between mobile support stations. The performance of the proposed scheme is evaluated by an extensive simulation study. The results show that the proposed scheme requires a small failure-free overhead and the cost of unnecessary rollback caused by the imprecise dependency is adjustable by properly selecting the logging frequency.

This paper presents an efficient recovery scheme based on checkpointing and message logging for mobile computing systems. For the efficient management of checkpoints and message logs, a movement-based scheme is proposed. Mobile hosts carrying their recovery information to the nearby mobile support station can recover instantly in case of a failure, however, the cost to transfer the recovery information must be high. On the other hand, the recovery information remaining dispersed over a number of support stations visited by mobile hosts must incur very high recovery cost. To balance the failure-free operation cost and the recovery cost, in the proposed scheme, the recovery information of a mobile host remains at the visited support stations while the host moves within a certain range. Only when the host moves out of the range, the recovery information is transferred to a nearby mobile support station. As a result, the proposed scheme can control the information transfer cost as well as the recovery cost.

This paper presents a new checkpoint scheme that utilizes the memory usage profile and time series analysis for low-overhead checkpoint. The proposed checkpoint scheme checks current and future checkpoint overhead based on the on the changes of the memory size and the expected checkpoint overhead using memory profile and adaptive time series analysis when it decides whether or not to take a checkpoint. Unlike the previous works that do not utilize the memory usage profile, it is possible to reduce the total overhead of the execution time. We also present experimental results which show that the checkpoint overhead of the proposed scheme is reduced compared with the previously developed checkpoint scheme.

This paper presents region-based storage management schemes, which support the efficient implementation of checkpointing and message logging for fault tolerant mobile computing systems. In the proposed schemes, a recovery manager assigned for a group of cells takes care of the recovery for the mobile hosts within the region. As a result, the recovery information of a mobile host, which may be dispersed over the network due to the mobility of the host, can efficiently be handled.

This paper presents an asynchronous recovery scheme to provide fault-tolerance for mobile computing systems. The proposed scheme is based on optimistic message logging, since the checkpointing-only schemes are not suitable for the mobile environment in which unreliable mobile hosts and fragile network connection may hinder any kind of coordination for checkpointing and recovery. Also, in order to reduce the overhead imposed on mobile hosts, mobile support stations take charge of logging and dependency tracking, and mobile hosts maintain only a small amount of information for mobility tracking. As a result, truly asynchronous recovery for mobile systems can be achieved with little overhead.

This paper presents a causal logging scheme for the lazy release consistent distributed shared memory systems. Causal logging is a very attractive approach to provide fault tolerance for distributed systems, since it eliminates the need for stable logging. However since interprocess dependency must causally be transferred with the normal messages, the excessive message overhead has been a drawback of this approach. In order to achieve an efficient implementation of causal logging for distributed shared memory systems, the data structures and the operations supported by the lazy release consistency memory model are utilized. For example, to implement the sender-based logging of the message contents, the diff structure is utilized, and for the causal logging of the dependency information, the operations to support the causal propagation of the write notices are utilized. As a result, the causal logging for the lazy release consistent distributed shared memory system can be implemented with a very low overhead. The simulation results using parallel applications show only 1%-4.4% increases in the execution time.

Causal message logging has many good properties such as nonblocking message logging and no rollback propagation. However, it requires a large amount of information to be piggybacked on each message, which may incur severe performance degradation. This paper presents an efficient causal logging algorithm based on the new message log structure, LogOn, which represents the causal interprocess dependency relation with much smaller overhead compared to the existing algorithms. The proposed algorithm is efficient in the sense that it requires no additional information other than LogOn to be carried in each message, while the other algorithms require extra information other than the message log, to eliminate the duplicates in log entries. Moreover, in those algorithms, as more extra information is added into the message, more duplicates can be detected. However, the proposed algorithm achieves the same degree of efficiency using only the message log carried in each message, without any extra information.

The paper presents a new logging scheme for recoverable distributed shared memory systems. In previous schemes, the logging is performed whenever a new data item is accessed or written by a process. However, in the proposed scheme, only the data item accessed by multiple processes is logged when it is invalidated by the overwritten. Moreover, the logging is performed at one process responsible for that data item, unlike the other schemes in which every process accessing the data item performs the logging. As a result, the amount and the frequency of logging can be significantly reduced. The performance of the proposed scheme is analyzed using extensive simulation study and our new logging scheme shows superior performance in various system environments.

This paper presents a checkpointing recovery scheme which effectively copes with media failures in distributed database systems, under the two-phase locking policy. Our scheme utilizes both the current database area and the checkpoint area, so that the transactions whose effects are to be included in the checkpoint and the ones whose effects are to be excluded from the checkpoint can separately reflect their effects. Hence, the check pointing process under our scheme is executed concurrently with normal transactions, without aborting or delaying any of them. Unlike the existing schemes, each data item needs to be read at most once for checkpointing without the maintenance of the before-images of the data items.>

The authors present an efficient synchronized checkpointing protocol that exploits the dependency relation between processes in distributed systems. In this protocol, a process takes a checkpoint when it knows that all processes on which it computationally depends took their checkpoints, hence the process need not always wait for the decision made by the checkpointing coordinator as in the conventional synchronized protocols. As a result, the checkpointing coordination time is substantially reduced and the possibility of total abort of the checkpointing coordination is reduced.>

The authors present an efficient software application of a distributed system for area-wide traffic control. This system, called area-wide real-time traffic control (ARTC), can provide orderly movement of traffic, shorten average vehicle delay, prevent congestion, and improve road utilization. The signal controllers in ARTC, which are microcomputers, are interconnected through a computer network. By exchanging traffic flow information among the signal controllers, ARTC provides a novel concept in traffic control by using the computer network. Simulation results of the ARTC prototype control algorithm are presented. The results show substantial improvement over an optimized fixer time control. The signal controllers and the computer network were designed to support real-time communication requirements and a sufficient level of fault tolerance.>