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

What Keeps Social Documentaries from Audiences -- And How to Fix It

Offers an analysis and set of recommendations on how to improve today's market for social documentaries and make them far more accessible to people who want to use them

INVESTIGATION OF THE RELATIONSHIP BETWEEN DIGITAL HOARDING, INFORMATION TECHNOLOGIES SELF-EFFICACY, AND ANXIETY

As digital tools expand in daily life; the accumulation of digital files has become a notable problem. Considering the negative impact of digital hoarding behavior, developing a measurement tool to measure the extent of digital hoarding among individuals is essential. For the Digital Hoarding Questionnaire, developed as part of this research, the scale was adapted to the Turkish target language, and the adapted scale was applied to college students. The adapted scale was a valid and reliable measurement tool. This study also aimed to determine the relationship and interaction between participants' digital hoarding behaviors, IT self-efficacy, and IT anxiety. A survey research method was conducted to examine the research subject. The study was conducted with 478 college students. According to the research findings, the participants’ accumulated photo files the most, and the most important reason for not deleting files was the belief they might be helpful in the future. All relationships between IT self-efficacy, IT anxiety, and digital hoarding were significant. According to the results, accumulating files makes no difference in hoarding behavior, while not deleting files makes a difference. When IT anxiety was controlled, gender made no significant difference in IT self-efficacy and digital hoarding behavior. Therefore, it is believed that the scale and results of this study will be an introductory research guide for studies that focus on determining digital file hoarding behavior.  Article visualizations

Supporting disconnected operations in mobile computing

Mobile computing has enabled users to seamlessly access databases even when they are on the move. However, in the absence of readily available high-quality communication, users are often forced to operate disconnected from the network. As a result, software applications have to be redesigned to take advantage of this environment while accommodating the new challenges posed by mobility. In particular, there is a need for replication and synchronization services in order to guarantee availability of data and functionality, (including updates) in disconnected mode. To this end we propose a scalable and highly available data replication and management service. The proposed replication technique is compared with a baseline replication technique and shown to exhibit high availability, fault tolerance and minimal access times of the data and services, which are very important in an environment with low-quality communication links.<br /

Memory Management Support for Multi-Programmed Remote Direct Memory Access (RDMA) Systems

Current operating systems offer basic support for network interface controllers (NICs) supporting remote direct memory access (RDMA). Such support typically consists of a device driver responsible for configuring communication channels between the device and user-level processes but not involved in data transfer. Unlike standard NICs, RDMA-capable devices incorporate significant memory resources for address translation purposes. In a multi-programmed operating system (OS) environment, these memory resources must be efficiently shareable by multiple processes. For such sharing to occur in a fair manner, the OS and the device must cooperate to arbitrate access to NIC memory, similar to the way CPUs and OSes cooperate to arbitrate access to translation lookaside buffers (TLBs) or physical memory. A problem with this approach is that today’s RDMA NICs are not integrated into the functions provided by OS memory management systems. As a result, RDMA NIC hardware resources are often monopolized by a single application. In this paper, I propose two practical mechanisms to address this problem: (a) Use of RDMA only in kernel-resident I/O subsystems, transparent to user-level software; (b) An extended registration API and a kernel upcall mechanism delivering NIC TLB entry replacement notifications to user-level libraries. Both options are designed to re-instate the multiprogramming principles that are violated in early commercial RDMA systems

Opportunities for information sharing: case studies

Personal information provided to government and non-government service providers is highly sensitive. Appropriate collection, management and storage of personal information are critical elements to citizen trust in the public sector. However, misconceptions about the frameworks governing sharing personal information can impact on the coordination of services, case management and policy development. &nbsp; The NSW Department of Premier &amp; Cabinet engaged the Social Policy Research Centre to develop three case studies that identified the challenges to sharing information appropriately, and the opportunities for better personal information sharing between government agencies and non-government organisations. Improved sharing of personal information in these areas can support more effective policy development, leading to improved service delivery performance and coordination. &nbsp; The Social Policy Research Centre identified the legislative and policy framework for each case study, conducted qualitative research on the interpretation of this framework, and developed three case study reports

Making space for the future: the importance of deletion for LIS and the information society

The information society generally, and information studies specifically, are understandably concerned with productive actions done with data and information, like preservation, access, and (re)use over time. While such concerns are important and their related activities are clearly valuable, we will soon be facing limits to storage and related resources, and so information scholars and practitioners must more fully consider and support the complementary part of the information lifecycle: deletion. We outline the growing necessity of data and information deletion for social and environmental sustainability through several example concerns. We then consider several challenges of and to deleting that must be considered and addressed, from societal to individual scales, by drawing on works in information behaviour, personal information management, human-computer interaction, and the history, philosophy, and ethics of information. Deletion is an understudied phenomenon of growing importance, and although it has a broadly negative perception in comparison to preservation, it has some notable advantages for individuals and society. Information scholars and practitioners have an important role to play in understanding and supporting deletion; recommendations for each are provided here.Peer Reviewe

Model-driven dual caching For nomadic service-oriented architecture clients

Mobile devices have evolved over the years from resource constrained devices that supported only the most basic tasks to powerful handheld computing devices. However, the most significant step in the evolution of mobile devices was the introduction of wireless connectivity which enabled them to host applications that require internet connectivity such as email, web browsers and maybe most importantly smart/rich clients. Being able to host smart clients allows the users of mobile devices to seamlessly access the Information Technology (IT) resources of their organizations. One increasingly popular way of enabling access to IT resources is by using Web Services (WS). This trend has been aided by the rapid availability of WS packages/tools, most notably the efforts of the Apache group and Integrated Development Environment (IDE) vendors. But the widespread use of WS raises questions for users of mobile devices such as laptops or PDAs; how and if they can participate in WS. Unlike their “wired” counterparts (desktop computers and servers) they rely on a wireless network that is characterized by low bandwidth and unreliable connectivity.The aim of this thesis is to enable mobile devices to host Web Services consumers. It introduces a Model-Driven Dual Caching (MDDC) approach to overcome problems arising from temporarily loss of connectivity and fluctuations in bandwidth