Contention management for distributed data replication

PhD ThesisOptimistic replication schemes provide distributed applications with access to shared data at lower latencies and greater availability. This is achieved by allowing clients to replicate shared data and execute actions locally. A consequence of this scheme raises issues regarding shared data consistency. Sometimes an action executed by a client may result in shared data that may conflict and, as a consequence, may conflict with subsequent actions that are caused by the conflicting action. This requires a client to rollback to the action that caused the conflicting data, and to execute some exception handling. This can be achieved by relying on the application layer to either ignore or handle shared data inconsistencies when they are discovered during the reconciliation phase of an optimistic protocol. Inconsistency of shared data has an impact on the causality relationship across client actions. In protocol design, it is desirable to preserve the property of causality between different actions occurring across a distributed application. Without application level knowledge, we assume an action causes all the subsequent actions at the same client. With application knowledge, we can significantly ease the protocol burden of provisioning causal ordering, as we can identify which actions do not cause other actions (even if they precede them). This, in turn, makes possible the client’s ability to rollback to past actions and to change them, without having to alter subsequent actions. Unfortunately, increased instances of application level causal relations between actions lead to a significant overhead in protocol. Therefore, minimizing the rollback associated with conflicting actions, while preserving causality, is seen as desirable for lower exception handling in the application layer. In this thesis, we present a framework that utilizes causality to create a scheduler that can inform a contention management scheme to reduce the rollback associated with the conflicting access of shared data. Our framework uses a backoff contention management scheme to provide causality preserving for those optimistic replication systems with high causality requirements, without the need for application layer knowledge. We present experiments which demonstrate that our framework reduces clients’ rollback and, more importantly, that the overall throughput of the system is improved when the contention management is used with applications that require causality to be preserved across all actions

Prioritized Transaction Management for Mobile Computing Systems

Abstract I

A cache framework for nomadic clients of web services

This research explores the problems associated with caching of SOAP Web Service request/response pairs, and presents a domain independent framework enabling transparent caching of Web Service requests for mobile clients. The framework intercepts method calls intended for the web service and proceeds by buffering and caching of the outgoing method call and the inbound responses. This enables a mobile application to seamlessly use Web Services by masking fluctuations in network conditions. This framework addresses two main issues, firstly how to enrich the WS standards to enable caching and secondly how to maintain consistency for state dependent Web Service request/response pairs

THE DESIGN OF A DIGITAL SCHEDULING SOLUTION FOR HEALING ALTERNATIVES

The focus of this senior project is to assist Healing Alternatives, an acupuncture clinic located in San Luis Obispo, in developing a business management software to fit their needs and boost their overall organization. The approach to finding the right fit for this business included assessing their current system while simultaneously investigating other providers. Once alternatives were found that met all of Healing Alternatives’ initial requirements, trial demos were generated in order to perform user experience testing. The presented final solution, a scheduling software called Acuity Scheduling, was implemented in a three-phase move plan that occurred over the period of a few weeks. This software solution was able to support all their necessary business requirements while saving them 31% on their annual operating expenses. Additionally, Healing Alternatives is able operate with increased employee efficiency in terms of client booking and inventory management

Dynamic contention management for distributed applications

PhD ThesisDistributed applications often make use of replicated state to afford a greater level of availability and throughput. This is achieved by allowing individual processes to progress without requiring prior synchronisation. This approach, termed optimistic replication, results in divergent replicas that must be reconciled to achieve an overall consistent state. Concurrent operations to shared objects in the replicas result in conflicting updates that require reconciliatory action to rectify. This typically takes the form of compensatory execution or simply undoing and rolling back client state. When considering user interaction with the application, there exists relationships and intent in the ordering and execution of these operations. The enactment of reconciliation that determines one action as conflicted may have far reaching implications with regards to the user’s original intent. In such scenarios, the compensatory action applied to a conflict may require previous operations to also be undone or compensated such that the user’s intent is maintained. Therefore, an ability to manage the contention to the shared data across the distributed application to pre-emptively lower conflicts resulting from these infringements is desirable. The aim is to not hinder throughput, achieved from the weaker consistency model known as eventual consistency. In this thesis, a model is presented for a contention management framework that schedules access using the expected execution inherent in the application domain to best inform the contention manager. A backoff scheme is employed to create an access schedule, preserving user intent for applications that require this high level of maintenance for user actions. By using such an approach, this results in a performance improvement seen in the reduction of the overall number of conflicts, while also improving overall system throughput. This thesis describes how the contention management scheme operates and, through experimentation, the performance benefits received

Mobile computing with the Rover Toolkit

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1998.Includes bibliographical references (leaves 138-147).by Anthony Douglas Joseph.Ph.D

Optimal Data Scheduling of Clients Serviced using Beamforming Antennas in Mobile Scenarios

The use of beamforming antennas has received significant attention over the last decade. I consider beamforming applied to dynamic operations such as networked UAV hubs which interconnect with users on the ground. The key problem involves understanding how to optimally manage the users' data requirements while considering mobility and a dynamic radio environment serviced by one or more hubs with beamforming antenna capability. In this work I break the problem down into scheduling, tracking and ultimately execution. I develop a regularized linear programming based scheduling algorithm along with developing a very efficient scheduling with uncertainty receding horizon based relaxation and implement them along with a capacity tracking estimation algorithm. Finally I show the results of successfully implementing this system in hardware using Fidelity Comtech's Phocus Array FCI-3100X. This implementation shows that the problem overview presented in this work provides a solid basis and defines the key components needed for a reliable electronic beamforming antenna system able to successfully service dispersed users in a mobile environment. It also shows the tools developed, refined, and integrated with respect to tracking, scheduling, and practical modifications

How To Touch a Running System

The increasing importance of distributed and decentralized software architectures entails more and more attention for adaptive software. Obtaining adaptiveness, however, is a difficult task as the software design needs to foresee and cope with a variety of situations. Using reconfiguration of components facilitates this task, as the adaptivity is conducted on an architecture level instead of directly in the code. This results in a separation of concerns; the appropriate reconfiguration can be devised on a coarse level, while the implementation of the components can remain largely unaware of reconfiguration scenarios. We study reconfiguration in component frameworks based on formal theory. We first discuss programming with components, exemplified with the development of the cmc model checker. This highly efficient model checker is made of C++ components and serves as an example for component-based software development practice in general, and also provides insights into the principles of adaptivity. However, the component model focuses on high performance and is not geared towards using the structuring principle of components for controlled reconfiguration. We thus complement this highly optimized model by a message passing-based component model which takes reconfigurability to be its central principle. Supporting reconfiguration in a framework is about alleviating the programmer from caring about the peculiarities as much as possible. We utilize the formal description of the component model to provide an algorithm for reconfiguration that retains as much flexibility as possible, while avoiding most problems that arise due to concurrency. This algorithm is embedded in a general four-stage adaptivity model inspired by physical control loops. The reconfiguration is devised to work with stateful components, retaining their data and unprocessed messages. Reconfiguration plans, which are provided with a formal semantics, form the input of the reconfiguration algorithm. We show that the algorithm achieves perceived atomicity of the reconfiguration process for an important class of plans, i.e., the whole process of reconfiguration is perceived as one atomic step, while minimizing the use of blocking of components. We illustrate the applicability of our approach to reconfiguration by providing several examples like fault-tolerance and automated resource control

Mobile Ad Hoc Networks

Guiding readers through the basics of these rapidly emerging networks to more advanced concepts and future expectations, Mobile Ad hoc Networks: Current Status and Future Trends identifies and examines the most pressing research issues in Mobile Ad hoc Networks (MANETs). Containing the contributions of leading researchers, industry professionals, and academics, this forward-looking reference provides an authoritative perspective of the state of the art in MANETs. The book includes surveys of recent publications that investigate key areas of interest such as limited resources and the mobility of mobile nodes. It considers routing, multicast, energy, security, channel assignment, and ensuring quality of service. Also suitable as a text for graduate students, the book is organized into three sections: Fundamentals of MANET Modeling and Simulation—Describes how MANETs operate and perform through simulations and models Communication Protocols of MANETs—Presents cutting-edge research on key issues, including MAC layer issues and routing in high mobility Future Networks Inspired By MANETs—Tackles open research issues and emerging trends Illustrating the role MANETs are likely to play in future networks, this book supplies the foundation and insight you will need to make your own contributions to the field. It includes coverage of routing protocols, modeling and simulations tools, intelligent optimization techniques to multicriteria routing, security issues in FHAMIPv6, connecting moving smart objects to the Internet, underwater sensor networks, wireless mesh network architecture and protocols, adaptive routing provision using Bayesian inference, and adaptive flow control in transport layer using genetic algorithms