Adaptive fault tolerant checkpointing algorithm for cluster based mobile Ad Hoc networks

Mobile Ad hoc NETwork (MANET) is a type of wireless network consisting of a set of self-configured mobile hosts that can communicate with each other using wireless links without the assistance of any fixed infrastructure. This has made possible to create a distributed mobile computing application and has also brought several new challenges in distributed algorithm design. Checkpointing is a well explored fault tolerance technique for the wired and cellular mobile networks. However, it is not directly applicable to MANET due to its dynamic topology, limited availability of stable storage, partitioning and the absence of fixed infrastructure. In this paper, we propose an adaptive, coordinated and non-blocking checkpointing algorithm to provide fault tolerance in cluster based MANET, where only minimum number of mobile hosts in the cluster should take checkpoints. The performance analysis and simulation results show that the proposed scheme performs well compared to works related

ParaMedic: Heterogeneous Parallel Error Correction

Processor error detection can be reduced in cost significantly by exploiting the parallelism that exists in a repeated copy of an execution, which may not exist in the original code, to split up the redundant work on a large number of small, highly efficient cores. However, such schemes don't provide a method for automatic error recovery. We develop ParaMedic, an architecture to allow efficient automatic correction of errors detected in a system by using parallel heterogeneous cores, to provide a full fail-safe system that does not propagate errors to other systems, and can recover without manual intervention. This uses logging to roll back any computation that occurred after a detected error, along with a set of techniques to provide error-checking parallelism while still preventing the escape of incorrect processor values in multicore environments, where ordering of individual processors' logs is not enough to be able to roll back execution. Across a set of single and multi-threaded benchmarks, we achieve 3.1\% and 1.5\% overhead respectively, compared with 1.9\% and 1\% for error detection alone.Arm Lt

Using migratable objects to enhance fault tolerance schemes in supercomputers

Supercomputers have seen an exponential increase in their size in the last two decades. Such a high growth rate is expected to take us to exascale in the timeframe 2018-2022. But, to bring a productive exascale environment about, it is necessary to focus on several key challenges. One of those challenges is fault tolerance. Machines at extreme scale will experience frequent failures and will require the system to avoid or overcome those failures. Various techniques have recently been developed to tolerate failures. The impact of these techniques and their scalability can be substantially enhanced by a parallel programming model called migratable objects. In this paper, we demonstrate how the migratable-objects model facilitates and improves several fault tolerance approaches. Our experimental results on thousands of cores suggest fault tolerance schemes based on migratable objects have low performance overhead and high scalability. Additionally, we present a performance model that predicts a significant benefit of using migratable objects to provide fault tolerance at extreme scale

A new approach to reversible computing with applications to speculative parallel simulation

In this thesis, we propose an innovative approach to reversible computing that shifts the focus from the operations to the memory outcome of a generic program. This choice allows us to overcome some typical challenges of "plain" reversible computing. Our methodology is to instrument a generic application with the help of an instrumentation tool, namely Hijacker, which we have redesigned and developed for the purpose. Through compile-time instrumentation, we enhance the program's code to keep track of the memory trace it produces until the end. Regardless of the complexity behind the generation of each computational step of the program, we can build inverse machine instructions just by inspecting the instruction that is attempting to write some value to memory. Therefore from this information, we craft an ad-hoc instruction that conveys this old value and the knowledge of where to replace it. This instruction will become part of a more comprehensive structure, namely the reverse window. Through this structure, we have sufficient information to cancel all the updates done by the generic program during its execution. In this writing, we will discuss the structure of the reverse window, as the building block for the whole reversing framework we designed and finally realized. Albeit we settle our solution in the specific context of the parallel discrete event simulation (PDES) adopting the Time Warp synchronization protocol, this framework paves the way for further general-purpose development and employment. We also present two additional innovative contributions coming from our innovative reversibility approach, both of them still embrace traditional state saving-based rollback strategy. The first contribution aims to harness the advantages of both the possible approaches. We implement the rollback operation combining state saving together with our reversible support through a mathematical model. This model enables the system to choose in autonomicity the best rollback strategy, by the mutable runtime dynamics of programs. The second contribution explores an orthogonal direction, still related to reversible computing aspects. In particular, we will address the problem of reversing shared libraries. Indeed, leading from their nature, shared objects are visible to the whole system and so does every possible external modification of their code. As a consequence, it is not possible to instrument them without affecting other unaware applications. We propose a different method to deal with the instrumentation of shared objects. All our innovative proposals have been assessed using the last generation of the open source ROOT-Sim PDES platform, where we integrated our solutions. ROOT-Sim is a C-based package implementing a general purpose simulation environment based on the Time Warp synchronization protocol

Using Rollback Avoidance to Mitigate Failures in Next-Generation Extreme-Scale Systems

High-performance computing (HPC) systems enable scientists to numerically model complex phenomena in many important physical systems. The next major milestone in the development of HPC systems is the construction of the first supercomputer capable executing more than an exaflop, 10^18 floating point operations per second. On systems of this scale, failures will occur much more frequently than on current systems. As a result, resilience is a key obstacle to building next-generation extreme-scale systems. Coordinated checkpointing is currently the most widely-used mechanism for handling failures on HPC systems. Although coordinated checkpointing remains effective on current systems, increasing the scale of today\u27s systems to build next-generation systems will increase the cost of fault tolerance as more and more time is taken away from the application to protect against or recover from failure. Rollback avoidance techniques seek to mitigate the cost of checkpoint/restart by allowing an application to continue its execution rather than rolling back to an earlier checkpoint when failures occur. These techniques include failure prediction and preventive migration, replicated computation, fault-tolerant algorithms, and software-based memory fault correction. In this thesis, I examine how rollback avoidance techniques can be used to address failures on extreme-scale systems. Using a combination of analytic modeling and simulation, I evaluate the potential impact of rollback avoidance on these systems. I then present a novel rollback avoidance technique that exploits similarities in application memory. Finally, I examine the feasibility of using this technique to protect against memory faults in kernel memory

Implementing fault tolerance in a 64-bit distributed operating system

This thesis explores the potential of 64-bit processors for providing a different style of distributed operating system. Rather than providing another reworking of the UNIX model, the use of the large address space for unifying volatile memory (virtual memory), persistent memory (file systems) and distributed network access is examined and a novel operating system, Arius, is proposed. The concepts behind the design of ARIUS are briefly reviewed, and then the reliability of such a system is examined in detail. The unified nature of the architecture makes it possible to use a reliable single address space to provide a completely reliable system without the addition of other mechanisms. Protocols are proposed to provide locally scalable distributed shared memory and these are then augmented to handle machine failures transparently though the use of distributed checkpoints and rollback. The checkpointing system makes use of the caching mechanism in DSM to provide data duplication for failure recovery. By using distributed memory for checkpoints, recovery from machine faults may be handled seamlessly. To cope with more “complete” failures, persistent storage is also included in the failure mechanism. These protocols are modelled to show their operability and to determine the cost they incur in various types of parallel and serial programs. Results are presented to demonstrate these costs

Master/worker parallel discrete event simulation

The execution of parallel discrete event simulation across metacomputing infrastructures is examined. A master/worker architecture for parallel discrete event simulation is proposed providing robust executions under a dynamic set of services with system-level support for fault tolerance, semi-automated client-directed load balancing, portability across heterogeneous machines, and the ability to run codes on idle or time-sharing clients without significant interaction by users. Research questions and challenges associated with issues and limitations with the work distribution paradigm, targeted computational domain, performance metrics, and the intended class of applications to be used in this context are analyzed and discussed. A portable web services approach to master/worker parallel discrete event simulation is proposed and evaluated with subsequent optimizations to increase the efficiency of large-scale simulation execution through distributed master service design and intrinsic overhead reduction. New techniques for addressing challenges associated with optimistic parallel discrete event simulation across metacomputing such as rollbacks and message unsending with an inherently different computation paradigm utilizing master services and time windows are proposed and examined. Results indicate that a master/worker approach utilizing loosely coupled resources is a viable means for high throughput parallel discrete event simulation by enhancing existing computational capacity or providing alternate execution capability for less time-critical codes.Ph.D.Committee Chair: Fujimoto, Richard; Committee Member: Bader, David; Committee Member: Perumalla, Kalyan; Committee Member: Riley, George; Committee Member: Vuduc, Richar

Standart-konformes Snapshotting für SystemC Virtuelle Plattformen

The steady increase in complexity of high-end embedded systems goes along with an increasingly complex design process. We are currently still in a transition phase from Hardware-Description Language (HDL) based design towards virtual-platform-based design of embedded systems. As design complexity rises faster than developer productivity a gap forms. Restoring productivity while at the same time managing increased design complexity can also be achieved through focussing on the development of new tools and design methodologies. In most application areas, high-level modelling languages such as SystemC are used in early design phases. In modern software development Continuous Integration (CI) is used to automatically test if a submitted piece of code breaks functionality. Application of the CI concept to embedded system design and testing requires fast build and test execution times from the virtual platform framework. For this use case the ability to save a specific state of a virtual platform becomes necessary. The saving and restoring of specific states of a simulation requires the ability to serialize all data structures within the simulation models. Improving the frameworks and establishing better methods will only help to narrow the design gap, if these changes are introduced with the needs of the engineers and developers in mind. Ultimately, it is their productivity that shall be improved. The ability to save the state of a virtual platform enables developers to run longer test campaigns that can even contain randomized test stimuli. If the saved states are modifiable the developers can inject faulty states into the simulation models. This work contributes an extension to the SoCRocket virtual platform framework to enable snapshotting. The snapshotting extension can be considered a reference implementation as the utilization of current SystemC/TLM standards makes it compatible to other frameworkds. Furthermore, integrating the UVM SystemC library into the framework enables test driven development and fast validation of SystemC/TLM models using snapshots. These extensions narrow the design gap by supporting designers, testers and developers to work more efficiently.Die stetige Steigerung der Komplexität eingebetteter Systeme geht einher mit einer ebenso steigenden Komplexität des Entwurfsprozesses. Wir befinden uns momentan in der Übergangsphase vom Entwurf von eingebetteten Systemen basierend auf Hardware-Beschreibungssprachen hin zum Entwurf ebendieser basierend auf virtuellen Plattformen. Da die Entwurfskomplexität rasanter steigt als die Produktivität der Entwickler, entsteht eine Kluft. Die Produktivität wiederherzustellen und gleichzeitig die gesteigerte Entwurfskomplexität zu bewältigen, kann auch erreicht werden, indem der Fokus auf die Entwicklung neuer Werkzeuge und Entwurfsmethoden gelegt wird. In den meisten Anwendungsgebieten werden Modellierungssprachen auf hoher Ebene, wie zum Beispiel SystemC, in den frühen Entwurfsphasen benutzt. In der modernen Software-Entwicklung wird Continuous Integration (CI) benutzt um automatisiert zu überprüfen, ob eine eingespielte Änderung am Quelltext bestehende Funktionalitäten beeinträchtigt. Die Anwendung des CI-Konzepts auf den Entwurf und das Testen von eingebetteten Systemen fordert schnelle Bau- und Test-Ausführungszeiten von dem genutzten Framework für virtuelle Plattformen. Für diesen Anwendungsfall wird auch die Fähigkeit, einen bestimmten Zustand der virtuellen Plattform zu speichern, erforderlich. Das Speichern und Wiederherstellen der Zustände einer Simulation erfordert die Serialisierung aller Datenstrukturen, die sich in den Simulationsmodellen befinden. Das Verbessern von Frameworks und Etablieren besserer Methodiken hilft nur die Entwurfs-Kluft zu verringern, wenn diese Änderungen mit Berücksichtigung der Bedürfnisse der Entwickler und Ingenieure eingeführt werden. Letztendlich ist es ihre Produktivität, die gesteigert werden soll. Die Fähigkeit den Zustand einer virtuellen Plattform zu speichern, ermöglicht es den Entwicklern, längere Testkampagnen laufen zu lassen, die auch zufällig erzeugte Teststimuli beinhalten können oder, falls die gespeicherten Zustände modifizierbar sind, fehlerbehaftete Zustände in die Simulationsmodelle zu injizieren. Mein mit dieser Arbeit geleisteter Beitrag beinhaltet die Erweiterung des SoCRocket Frameworks um Checkpointing Funktionalität im Sinne einer Referenzimplementierung. Weiterhin ermöglicht die Integration der UVM SystemC Bibliothek in das Framework die Umsetzung der testgetriebenen Entwicklung und schnelle Validierung von SystemC/TLM Modellen mit Hilfe von Snapshots

Optimizing recovery protocols for replicated database systems

En la actualidad, el uso de tecnologías de informacíon y sistemas de cómputo tienen una gran influencia en la vida diaria. Dentro de los sistemas informáticos actualmente en uso, son de gran relevancia los sistemas distribuidos por la capacidad que pueden tener para escalar, proporcionar soporte para la tolerancia a fallos y mejorar el desempeño de aplicaciones y proporcionar alta disponibilidad. Los sistemas replicados son un caso especial de los sistemas distribuidos. Esta tesis está centrada en el área de las bases de datos replicadas debido al uso extendido que en el presente se hace de ellas, requiriendo características como: bajos tiempos de respuesta, alto rendimiento en los procesos, balanceo de carga entre las replicas, consistencia e integridad de datos y tolerancia a fallos. En este contexto, el desarrollo de aplicaciones utilizando bases de datos replicadas presenta dificultades que pueden verse atenuadas mediante el uso de servicios de soporte a mas bajo nivel tales como servicios de comunicacion y pertenencia. El uso de los servicios proporcionados por los sistemas de comunicación de grupos permiten ocultar los detalles de las comunicaciones y facilitan el diseño de protocolos de replicación y recuperación. En esta tesis, se presenta un estudio de las alternativas y estrategias empleadas en los protocolos de replicación y recuperación en las bases de datos replicadas. También se revisan diferentes conceptos sobre los sistemas de comunicación de grupos y sincronia virtual. Se caracterizan y clasifican diferentes tipos de protocolos de replicación con respecto a la interacción o soporte que pudieran dar a la recuperación, sin embargo el enfoque se dirige a los protocolos basados en sistemas de comunicación de grupos. Debido a que los sistemas comerciales actuales permiten a los programadores y administradores de sistemas de bases de datos renunciar en alguna medida a la consistencia con la finalidad de aumentar el rendimiento, es importante determinar el nivel de consistencia necesario. En el caso de las bases de datos replicadas la consistencia está muy relacionada con el nivel de aislamiento establecido entre las transacciones. Una de las propuestas centrales de esta tesis es un protocolo de recuperación para un protocolo de replicación basado en certificación. Los protocolos de replicación de base de datos basados en certificación proveen buenas bases para el desarrollo de sus respectivos protocolos de recuperación cuando se utiliza el nivel de aislamiento snapshot. Para tal nivel de aislamiento no se requiere que los readsets sean transferidos entre las réplicas ni revisados en la fase de cetificación y ya que estos protocolos mantienen un histórico de la lista de writesets que es utilizada para certificar las transacciones, este histórico provee la información necesaria para transferir el estado perdido por la réplica en recuperación. Se hace un estudio del rendimiento del protocolo de recuperación básico y de la versión optimizada en la que se compacta la información a transferir. Se presentan los resultados obtenidos en las pruebas de la implementación del protocolo de recuperación en el middleware de soporte. La segunda propuesta esta basada en aplicar el principio de compactación de la informacion de recuperación en un protocolo de recuperación para los protocolos de replicación basados en votación débil. El objetivo es minimizar el tiempo necesario para transfeir y aplicar la información perdida por la réplica en recuperación obteniendo con esto un protocolo de recuperación mas eficiente. Se ha verificado el buen desempeño de este algoritmo a través de una simulación. Para efectuar la simulación se ha hecho uso del entorno de simulación Omnet++. En los resultados de los experimentos puede apreciarse que este protocolo de recuperación tiene buenos resultados en múltiples escenarios. Finalmente, se presenta la verificación de la corrección de ambos algoritmos de recuperación en el Capítulo 5.Nowadays, information technology and computing systems have a great relevance on our lives. Among current computer systems, distributed systems are one of the most important because of their scalability, fault tolerance, performance improvements and high availability. Replicated systems are a specific case of distributed system. This Ph.D. thesis is centered in the replicated database field due to their extended usage, requiring among other properties: low response times, high throughput, load balancing among replicas, data consistency, data integrity and fault tolerance. In this scope, the development of applications that use replicated databases raises some problems that can be reduced using other fault-tolerant building blocks, as group communication and membership services. Thus, the usage of the services provided by group communication systems (GCS) hides several communication details, simplifying the design of replication and recovery protocols. This Ph.D. thesis surveys the alternatives and strategies being used in the replication and recovery protocols for database replication systems. It also summarizes different concepts about group communication systems and virtual synchrony. As a result, the thesis provides a classification of database replication protocols according to their support to (and interaction with) recovery protocols, always assuming that both kinds of protocol rely on a GCS. Since current commercial DBMSs allow that programmers and database administrators sacrifice consistency with the aim of improving performance, it is important to select the appropriate level of consistency. Regarding (replicated) databases, consistency is strongly related to the isolation levels being assigned to transactions. One of the main proposals of this thesis is a recovery protocol for a replication protocol based on certification. Certification-based database replication protocols provide a good basis for the development of their recovery strategies when a snapshot isolation level is assumed. In that level readsets are not needed in the validation step. As a result, they do not need to be transmitted to other replicas. Additionally, these protocols hold a writeset list that is used in the certification/validation step. That list maintains the set of writesets needed by the recovery protocol. This thesis evaluates the performance of a recovery protocol based on the writeset list tranfer (basic protocol) and of an optimized version that compacts the information to be transferred. The second proposal applies the compaction principle to a recovery protocol designed for weak-voting replication protocols. Its aim is to minimize the time needed for transferring and applying the writesets lost by the recovering replica, obtaining in this way an efficient recovery. The performance of this recovery algorithm has been checked implementing a simulator. To this end, the Omnet++ simulating framework has been used. The simulation results confirm that this recovery protocol provides good results in multiple scenarios. Finally, the correction of both recovery protocols is also justified and presented in Chapter 5.García Muñoz, LH. (2013). Optimizing recovery protocols for replicated database systems [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/31632TESI