Checkpoint Requests Research Articles

A LOW OVERHEAD MINIMUM PROCESS GLOBAL SNAPSHOT COLLECTION ALGORITHM FOR MOBILE DISTRIBUTED SYSTEM

Coordinated checkpointing is an effective fault tolerant technique in distributed system as it avoids the domino effect and require minimum storage requirement. Most of the earlier coordinated checkpoint algorithms block their computation during checkpointing and forces minimum-process or non-blocking but forces all nodes to takes checkpoint even though many of them may not be necessary or non-blocking minimum-process but takes useless checkpoints or reduced useless checkpoint but has higher synchronization message overhead or has high checkpoint request propagation time. Hence in mobile distributed systems there is a great need of minimizing the number of communication message and checkpointing overhead as it raise new issues such as mobility, low bandwidth of wireless channels, frequently disconnections, limited battery power and lack of reliable stable storage on mobile nodes. In this paper, we propose a minimum-process coordinated checkpointing algorithm for mobile distributed system where no useless checkpoints are taken, no blocking of processes takes place and enforces a minimum-number of processes to take checkpoints. Our algorithm imposes low memory and computation overheads on MH's and low communication overheads on wireless channels. It avoids awakening of an MH if it is not required to take its checkpoint and has reduced latency time as each process involved in a global checkpoint can forward its own decision directly to the checkpoint initiator.

Low-Overhead Non-Blocking Checkpointing Scheme for Mobile Computing Systems

When applied to mobile computing systems, checkpoint protocols for distributed computing systems would face many new challenges, such as low wireless bandwidth, frequent disconnections, and lack of stable storage at mobile hosts. This paper proposes a novel checkpoint protocol to effectively reduce the coordinating overhead. By using a communication vector, only a few processes participate in the checkpointing event. During checkpointing, the scheme can save the time used to trace the dependency tree by sending checkpoint requests to dependent processes at once. In addition, processes are non-blocking in this scheme, since the inconsistency is resolved by the piggyback technique. Hence the unnecessary and orphan messages can be avoided. Compared with the traditional coordinated checkpoint approach, the proposed non-blocking algorithm obtains a minimal number of processes to take checkpoints. It also reduces the checkpoint latency, which brings less overhead to mobile host with limited resources.

Multiprogrammed non-blocking checkpoints in support of optimistic simulation on myrinet clusters

CCL (checkpointing and communication library) is a software layer in support of optimistic parallel discrete event simulation (PDES) on myrinet-based COTS clusters. Beyond classical low latency message delivery functionalities, this library implements CPU offloaded, non-blocking (asynchronous) checkpointing functionalities based on data transfer capabilities provided by a programmable DMA engine on board of myrinet network cards. These functionalities are unique since optimistic simulation systems conventionally rely on checkpointing implemented as a synchronous, CPU-based data copy. Releases of CCL up to v2.4 only support monoprogrammed non-blocking checkpoints. This forces re-synchronization between CPU and DMA activities, which is a potential source of overhead, each time a new checkpoint request must be issued at the simulation application level while the last issued one is still being carried out by the DMA engine. In this paper we present a redesigned release of CCL (v3.0) that, exploiting hardware capabilities of more advanced myrinet clusters, supports multiprogrammed non-blocking checkpoints. The multiprogrammed approach allows higher degree of concurrency between checkpointing and other simulation specific operations carried out by the CPU, with benefits on performance. We also report the results of the experimental evaluation of those benefits for the case of a Personal Communication System (PCS) simulation application, selected as a real world test-bed.

A synchronous checkpointing protocol for mobile distributed systems: probabilistic approach

Coordinated checkpointing is a method that minimises number of processes to checkpoint for an initiation. It may require blocking of processes, extra synchronisation messages or useless checkpoints. We propose a minimum process coordinated checkpointing algorithm where the number of useless checkpoints and blocking are reduced using a probabilistic approach that computes an interacting set of processes on checkpoint initiation. A process checkpoints if the probability that it will get a checkpoint request in current initiation is high. A few processes may be blocked but they can continue their normal computation and may send messages. We also modified methodology to maintain exact dependencies.

Design and Evaluation of a Low-Latency Checkpointing Scheme for Mobile Computing Systems

Fault-tolerant mobile computing systems have different requirements and restrictions, not taken into account by conventional distributed systems. This paper presents a coordinated checkpointing scheme which reduces the delay involved in a global checkpointing process for mobile systems. A piggyback technique is used to track and record the checkpoint dependency information among processes during normal message transmission. During checkpointing, a concurrent checkpointing technique is designed to use the pre-recorded process dependency information to minimize process blocking time by sending checkpoint requests to dependent processes at once, hence saving the time to trace the dependency tree. We show that our checkpoint algorithm forces a minimum number of processes to take checkpoints, which is an important property for checkpointing mobile applications. Via probability-based analysis, we show that our scheme can significantly reduce the latency associated with checkpoint request propagation, compared with traditional coordinated checkpointing approaches. Experimental results indicate that we have <2% overhead in transmitting piggybacked information during normal runtime. However, we can achieve up to a 60% reduction in checkpoint latency time.

High Assurance Software Systems

The last few decades are marked by an unprecedented increase in the complexity and consequence of information technology systems. High assurance software systems must satisfy basic functional service properties that the system intends to deliver, as well as guarantee desirable system properties such as security, safety, timeliness and reliability. Examples of high assurance software systems include command and control systems, nuclear power plants, electronic banking, aerospace systems, automated manufacturing and medical systems. One of the major challenges in high assurance software engineering is to develop well-founded methods for system construction, verification and validation, so they provide critical services with a high degree of confidence in their correctness and quality. The goal of the special issue is to bring together innovative research ideas and advances in the field of high assurance software systems to address these challenges. To this end, the guest editors invited six papers published in the 29th IEEE Annual International Computer Software and Applications Conference (COMPSAC 2005) in the conference theme of High Assurance Software Systems to submit to this special issue, from which four papers after a rigorous review process have been selected to appear in the special issue. In their paper ‘An Empirical Performance Study on PSIM’, Jinchun Xia, Carl K. Chang, Jeff Wise and Yujia Ge [1] address performance evaluation of software architecture designs. They describe a PSIM (Performance SImulation and Modeling) tool that integrates performance properties into software architecture specifications expressed in UML syntax. PSIM models can be transformed into Colored GSPN (Colored Generalized Stochastic Petri nets) via an automated tool. As a result, the Colored GSPN models can be simulated to perform model-based performance evaluation. PSIM is shown to be effective in predicting system performance and identifying system performance bottlenecks to address the timeliness property of high assurance software systems early in the development lifecycle. High assurance mobile computing systems often have fault tolerance and timeliness requirements which exceed those encountered in conventional distributed systems. The second paper ‘Design and Evaluation of a Low-Latency Checkpointing Scheme for Mobile Computing Systems’ by Guohui Li and Lihchyun Shu [2] presents a coordinated checkpointing scheme which reduces the latency in global checkpointing for failure recovery of high assurance mobile systems. The method proposed significantly reduces the latency associated with checkpoint request propagation. Experimental results indicate that an improvement of up to a 60% reduction in latency can be achieved with <2% extra overhead incurred during runtime to provide timely failure recovery for high assurance mobile systems. The third paper ‘A Blocking-Based Approach to Protocol Validation’ by Qizhi Ye, Yu Lei and David Kung [3] reports a new analysis method for protocol validation. Their method, based on reachability analysis, guarantees to detect protocol logical errors including deadlocks, unspecified receptions and channel overflows prior to actual system deployment. The authors apply the analysis method to 160 synthesized protocols as well as two real protocols to demonstrate its applicability to high assurance software systems that rely on these protocols. Its performance is especially sound when the non-blocking ratio of a protocol is high. Phishing is a form of online identity theft that aims to steal sensitive information such as online banking passwords and credit card information from users. The last paper ‘Protecting Users against Phishing Attacks’ by Engin Kirda and Christopher Kruegel [4] presents a novel method that protects users against spoofed web-based phishing attacks. Their tool called AntiPhish tracks the sensitive information of a user and generates warnings whenever the user attempts to transmit this information to a website that is considered untrusted. AntiPhish is a step in the right direction for protecting software systems against spoofed website-based phishing attacks. We would like to thank the reviewers for their superb work of refereeing and improving the quality as well as the presentation of the four papers selected in this special issue.