Among the numerous DAG scheduling heuristics suitable for heterogeneous systems, the Heterogeneous Earliest Finish Time (HEFT) heuristic is known to give good results in short time. In this paper, we propose an improvement of HEFT, where the locally optimal decisions made by the heuristic do not rely on estimates of a single task only, but also look ahead in the schedule and take into account information about the impact of this decision to the children of the task being allocated. Preliminary simulation results indicate that the lookahead variation of HEFT can effectively reduce the makespan of the schedule in most cases without making the algorithm’s execution time prohibitively high.

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DAG Scheduling Using a Lookahead Variant of the Heterogeneous Earliest Finish Time Algorithm

A storage system maintains a journal of journal entries and at lease one snapshot of one or more data volumes. By assigning a unique sequence number to journal and snapshot, it is easy to find a journal which can be applied to the snapshot. A technique is described for detecting an overflow condition of running out of journal space and recovering the journal space.

Method and apparatus for backup and recovery using storage based journaling

In this paper, we analyze the robustness of 20 static, makespan-centric, DAG scheduling heuristics of the literature. We also study if dynamically changing the order of the tasks on their assigned processor improves the robustness. Based on experimental results we investigate how robustness and makespan are correlated. Finally, the heuristics are experimentally evaluated and ranked according to their performance in terms of both robustness and makespan.

/pdf/comparative-evaluation-of-the-robustness-of-dag-scheduling-3339cizwie.pdf

Comparative Evaluation Of The Robustness Of DAG Scheduling Heuristics

A host and a storage system each keep a shared identifier indicating a state of a system. The storage system acquires, at update of data, a data pair including data for a change through processing of the host and data before the update. The storage system relates the data pair to a shared identifier. When the host indicates an identifier, the storage system restores data using the data pair.

Data restoring method and an apparatus using journal data and an identification information

A first storage system stores information relating to the updating of data stored in that system as a journal. More specifically, the journal is composed of a copy of data that was used for updating and update information such as a write command used during updating. Furthermore, the second storage system acquires the journal via a communication line between the first storage system and the second storage system. The second storage system holds a duplicate of the data held by the first storage system and updates the data corresponding to the data of the first storage system in the data update order of the first storage system by using the journal.

Data replication among storage systems

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.

An efficient recovery scheme for mobile computing environments

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.

An efficient optimistic message logging scheme for recoverable mobile computing systems

Fault-tolerance is an essential element to the distributed system which requires the reliable computation environment. In spite of extensive researches over two decades, practical fault-tolerance systems have not been provided. It is due to the high overhead and the unhandiness of the previous fault-tolerance systems. In this paper, we propose MPICH-GF, a user-transparent checkpointing system for grid-enabled MPICH. Our objectives are to fill the gap between the theory and practice of fault-tolerance systems and to provide a checkpointing-recovery system for grids. To build a fault-tolerant MPICH version, we have designed task migration, dynamic process management for MPI and message queue management. MPICH-GF requires no modification of application source codes and affects the MPICH communication as less as possible. The features of MPICH-GF are that it supports the direct message transfer mode and that all of the implementation has been done at the lower layer, that is, the virtual device level. We have evaluated MPICH-GF with NPB applications on Globus middleware.

MPICH-GF: Transparent Checkpointing and Rollback-Recovery for Grid-Enabled MPI Processes

An efficient recovery scheme for fault-tolerant mobile computing systems

This paper presents the design and impementation of MPI_Rejoin() for MPICH-GF, a grid-enabled fault tolerant MPICH implementation. To provide fault tolerance to the MPI applications, it is mandatory for a failed process to recover and continue execution. However, current MPI implementations do not support dynamic process management and it is not possible to restore the information regarding communication channels. The ‘rejoin’ operation allows the restored process to rejoin the existing group by updating the corresponding entries of the channel table with the new physical address. We have verified that our implementation can correctly reconstruct the MPI communication structure by running NPB applications. We also report on the cost of ‘rejoin’ operation.

Namyoon Woo

Papers

An efficient recovery scheme for mobile computing environments

An efficient optimistic message logging scheme for recoverable mobile computing systems

MPICH-GF: Transparent Checkpointing and Rollback-Recovery for Grid-Enabled MPI Processes

An efficient recovery scheme for fault-tolerant mobile computing systems

Design and Implementation of Dynamic Process Management for Grid-Enabled MPICH