Transparently Mixing Undo Logs and Software Reversibility for State Recovery in Optimistic PDES

The rollback operation is a fundamental building block to support the correct execution of a speculative Time Warp-based Parallel Discrete Event Simulation. In the literature, several solutions to reduce the execution cost of this operation have been proposed, either based on the creation of a checkpoint of previous simulation state images, or on the execution of negative copies of simulation events which are able to undo the updates on the state. In this paper, we explore the practical design and implementation of a state recoverability technique which allows to restore a previous simulation state either relying on checkpointing or on the reverse execution of the state updates occurred while processing events in forward mode. Differently from other proposals, we address the issue of executing backward updates in a fully-transparent and event granularity-independent way, by relying on static software instrumentation (targeting the x86 architecture and Linux systems) to generate at runtime reverse update code blocks (not to be confused with reverse events, proper of the reverse computing approach). These are able to undo the effects of a forward execution while minimizing the cost of the undo operation. We also present experimental results related to our implementation, which is released as free software and fully integrated into the open source ROOT-Sim (ROme OpTimistic Simulator) package. The experimental data support the viability and effectiveness of our proposal

Value-Driven Enterprise Architecture Evaluation for the Joint Force Protection Advanced Security System

The U.S. military has placed a strong focus on the importance of operating in a joint environment, where capabilities and missions are shared between service components. Protecting U.S. forces is a major consideration in the joint environment. The Joint Force Protection Advanced Security System (JFPASS) architecture has been created to fill a critical gap in Joint Force Protection guidance for systems acquisition. The systems engineering (SE) field has made wide use of system architectures to represent complex systems. As fundamental SE principles become more widespread, analysis tools provide an objective method for the evaluation of the resulting architectural products. This study used decision analysis to develop a standardized, yet adaptable and repeatable model to evaluate the capabilities of the JFPASS for any installation or facility belonging to the United States Department of Defense (DoD). Using the Value-Focused Thinking (VFT) methods, a value hierarchy was created by consulting with subject matter experts. The resulting model, named Value-Driven Enterprise Architecture (VDEA) score, provides an analysis tool, which enables DoD decision-makers to use JFPASS architecture products to quickly and easily evaluate the value provided by the system; VDEA provides insight into the overall quality and capability of the system. Through the scoring and sensitivity analysis functions, capability gaps and potential improvements can be identified. Future studies in this area will provide a vehicle for rating not only operational level systems, but also individual functional projects against other alternatives

Benchmarking Memory Management Capabilities within ROOT-Sim

In parallel discrete event simulation techniques, the simulation model is partitioned into objects, concurrently executing events on different CPUs and/or multiple CPUCores. In such a context, run-time supports for logical time synchronization across the different simulation objects play a central role in determining the effectiveness of the specific parallel simulation environment. In this paper we present an experimental evaluation of the memory management capabilities offered by the ROme OpTimistic Simulator (ROOT-Sim). This is an open source parallel simulation environment transparently supporting optimistic synchronization via recoverability (based on incremental log/restore techniques) of any type of memory operation affecting the state of simulation objects, i.e., memory allocation, deallocation and update operations. The experimental study is based on a synthetic benchmark which mimics different read/write patterns inside the dynamic memory map associated with the state of simulation objects. This allows sensibility analysis of time and space effects due to the memory management subsystem while varying the type and the locality of the accesses associated with event processin

Attributes of fault-tolerant distributed file systems

Fault tolerance in distributed file systems will be investigated by analyzing recovery techniques and concepts implemented within the following models of distributed systems: pool-processor model and user-server model. The research presented provides an overview of fault tolerance characteristics and mechanisms within current implementations and summarizes future directions for fault tolerant distributed file systems

Building scalable digital library ingestion pipelines using microservices

CORE, a harvesting service offering access to millions of open access research papers from around the world, has shifted its harvesting process from following a monolithic approach to the adoption of a microservices infrastructure. In this paper, we explain how we rearranged and re-scheduled our old ingestion pipeline, present CORE's move to managing microservices and outline the tools we use in a new and optimised ingestion system. In addition, we discuss the ineffciencies of our old harvesting process, the advantages, and challenges of our new ingestion system and our future plans. We conclude that via the adoption of microservices architecture we managed to achieve a scalable and distributed system that would assist with CORE's future performance and evolution