Optimising data centre operation by removing the transport bottleneck

Data centres lie at the heart of almost every service on the Internet. Data centres are used to provide search results, to power social media, to store and index email, to host “cloud” applications, for online retail and to provide a myriad of other web services. Consequently the more efficient they can be made the better for all of us. The power of modern data centres is in combining commodity off-the-shelf server hardware and network equipment to provide what Google’s Barrosso and Ho ̈lzle describe as “warehouse scale” computers. Data centres rely on TCP, a transport protocol that was originally designed for use in the Internet. Like other such protocols, TCP has been optimised to maximise throughput, usually by filling up queues at the bottleneck. However, for most applications within a data centre network latency is more critical than throughput. Consequently the choice of transport protocol becomes a bottleneck for performance. My thesis is that the solution to this is to move away from the use of one-size-fits-all transport protocols towards ones that have been designed to reduce latency across the data centre and which can dynamically respond to the needs of the applications. This dissertation focuses on optimising the transport layer in data centre networks. In particular I address the question of whether any single transport mechanism can be flexible enough to cater to the needs of all data centre traffic. I show that one leading protocol (DCTCP) has been heavily optimised for certain network conditions. I then explore approaches that seek to minimise latency for applications that care about it while still allowing throughput-intensive applications to receive a good level of service. My key contributions to this are Silo and Trevi. Trevi is a novel transport system for storage traffic that utilises fountain coding to max- imise throughput and minimise latency while being agnostic to drop, thus allowing storage traffic to be pushed out of the way when latency sensitive traffic is present in the network. Silo is an admission control system that is designed to give tenants of a multi-tenant data centre guaranteed low latency network performance. Both of these were developed in collaboration with others

Software-Oriented Distributed Shared Cache Management for Chip Multiprocessors

This thesis proposes a software-oriented distributed shared cache management approach for chip multiprocessors (CMPs). Unlike hardware-based schemes, our approach offloads the cache management task to trace analysis phase, allowing flexible management strategies. For single-threaded programs, a static 2D page coloring scheme is proposed to utilize oracle trace information to derive an optimal data placement schema for a program. In addition, a dynamic 2D page coloring scheme is proposed as a practical solution, which tries to ap- proach the performance of the static scheme. The evaluation results show that the static scheme achieves 44.7% performance improvement over the conventional shared cache scheme on average while the dynamic scheme performs 32.3% better than the shared cache scheme. For latency-oriented multithreaded programs, a pattern recognition algorithm based on the K-means clustering method is introduced. The algorithm tries to identify data access pat- terns that can be utilized to guide the placement of private data and the replication of shared data. The experimental results show that data placement and replication based on these access patterns lead to 19% performance improvement over the shared cache scheme. The reduced remote cache accesses and aggregated cache miss rate result in much lower bandwidth requirements for the on-chip network and the off-chip main memory bus. Lastly, for throughput-oriented multithreaded programs, we propose a hint-guided data replication scheme to identify memory instructions of a target program that access data with a high reuse property. The derived hints are then used to guide data replication at run time. By balancing the amount of data replication and local cache pressure, the proposed scheme has the potential to help achieve comparable performance to best existing hardware-based schemes.Our proposed software-oriented shared cache management approach is an effective way to manage program performance on CMPs. This approach provides an alternative direction to the research of the distributed cache management problem. Given the known difficulties (e.g., scalability and design complexity) we face with hardware-based schemes, this software- oriented approach may receive a serious consideration from researchers in the future. In this perspective, the thesis provides valuable contributions to the computer architecture research society

Structural Style And Stratigraphic Architecture Of The Northeastern Brooks Range, Alaska

The Arctic Alaska–Chukotka microplate is a large Mesozoic–Cenozoic composite terrane that resides at the northern limit of the North American Cordillera. Although its Mesozoic origins are assuredly linked to the opening of the Amerasian Basin of the Arctic Ocean, its Paleozoic origins can be linked to at least three separate paleocontinents, including northern Laurentia, Baltica, and Siberia. Across the Arctic Alaska portion of the microplate, an internal, mid-Paleozoic suture zone presumably separates rocks of the North Slope subterrane (Laurentian affinity) from a collection of smaller subterranes in the southern Brooks Range and Seward Peninsula (Baltic affinity). The mountains of the northeastern Brooks Range expose a thick assemblage of Neoproterozoic–Lower Cretaceous rocks that belong to the North Slope subterrane. New data from geological mapping, coupled with zircon U-Pb and muscovite 40Ar/39Ar radiometric ages, reveal that the Neoproterozoic–Ordovician rocks in the NE Brooks Range, assigned to the Firth River Group, Neruokpuk Formation, and the informal Leffingwell formation, record deep-water, slope- to basin-floor sedimentation along the ancient passive margin of northern Laurentia. Stata of the Ordovician–Lower Devonian(?) Clarence River Group (new name) disconformably overlie these passive margin units and record a major shift in the sedimentary source. Detrital zircon U-Pb ages from Clarence River Group strata closely resemble the deep-water, syn-orogenic strata exposed in the Franklinian Basin of northern Ellesmere Island, and are interpreted to reflect erosion and transport of sediment sourced from the Caledonian orogen. A rootless thrust sheet places a Cambrian–Middle Ordovician structural complex of basalt, limestone and chert, herein named the Whale Mountain allochthon, above the upper strata of the Clarence River Group. Igneous geochemistry and trilobite paleontology suggest that the Whale Mountain allochthon formed as a series of remote volcanic islands or seamounts that established outboard the Laurentian margin. The emplacement of the allochthon occurred in concert with the locally-defined, Early–Middle Devonian Romanzof orogeny, and it may be linked to the closure of the Iapetus Ocean and the collision between Baltica and Laurentia in the Caledonian orogeny. This major collisional event is responsible for the assembly of the Arctic Alaska–Chukotka microplate, implicating the Whale Mountain allochthon as a potential relic to the suture zone that separates the North Slope subterrane from the rest of Arctic Alaska and Chukotka

Evidence and methods required to evaluate the impact for patients who use social prescribing : a rapid systematic review and qualitative interviews

Background Social prescribing encourages health-care and other professionals to refer patients to a link worker, who will develop a personalised plan to improve the patient’s health and well-being. We explore the feasibility of evaluating the service. Objective The objective was to answer the following research questions. (1) What are the most important evaluation questions that an impact study could investigate? (2) What data are already available at a local or national level and what else would be needed? (3) Are there sites delivering at a large enough scale and in a position to take part in an impact study? (4) How could the known challenges to evaluation (e.g. information governance and identifying a control group) be addressed? Data sources Data sources included MEDLINE ALL (via Ovid), searched from inception to 14 February 2019, and the first 100 hits of a Google (Google Inc., Mountain View, CA, USA) search. Review methods Rapid systematic review – electronic searches up to February 2019. Studies included any study design or outcomes. Screening was conducted by one reviewer; eligibility assessment and data extraction were undertaken by two reviewers. Data were synthesised narratively. Qualitative interviews – data from 25 participants in different regions of England were analysed using a pragmatic framework approach across 12 areas including prior data collection, delivery sites, scale and processes of current service delivery, and known challenges to evaluation. Views of key stakeholders (i.e. patients and academics) were captured. Results Rapid systematic review – 27 out of 124 studies were included. We identified outcomes and highlighted research challenges. Important evaluation questions included identification of the most appropriate (1) outcomes and (2) methods for dealing with heterogeneity. Qualitative interviews – social prescribing programmes are holistic in nature, covering domains such as social isolation and finance. Service provision is heterogeneous. The follow-on services that patients access are often underfunded or short term. Available data – there was significant heterogeneity in data availability, format and follow-up. Data were collected using a range of tools in ad hoc databases across sites. Non-attendance data were frequently not captured. Service users are more deprived and vulnerable than the overall practice population. Feasibility and potential limitations of an evaluation – current data collection is limited in determining the effectiveness of the link worker social prescribing model; therefore, uniform data collection across sites is needed. Standardised outcomes and process measures are required. Cost–utility analysis could provide comparative values for assessment alongside other NHS interventions. Limitations This was a rapid systematic review that did not include a systematic quality assessment of studies. COVID-19 had an impact on the shape of the service. We were not able to examine the potential causal mechanisms in any detail. Conclusions We describe possible future research approaches to determine effectiveness and cost-effectiveness evaluations; all are limited in their application. (1) Evaluation using currently available, routinely collected health-care, costing and outcomes data. (2) Evaluative mixed-methods research to capture the complexity of social prescribing through understanding heterogeneous service delivery across comparative settings. Cost-effectiveness evaluation using routinely available costing and outcomes data to supplement qualitative data. (3) Interventional evaluative research, such as a cluster randomised controlled trial focused on the link worker model. Cost-effectiveness data collected as part of the trial. Future work Mature data are currently not available. There needs to be an agreement across schemes on the key outcomes that need to be measured, harmonisation of data collection, and follow-up referrals (how and when). Funding This project was funded by the National Institute for Health and Care Research (NIHR) Health and Social Care Delivery Research programme and will be published in full in Health and Social Care Delivery Research; Vol. 10, No. 29. See the NIHR Journals Library website for further project information

Towards environmental sustainability in the Niger Delta region of Nigeria: a theological framework for broader involvement of the Presbyterian Church of Nigeria

The Niger Delta environmental crisis fuelled principally by the degration from oil and gas exploration activities has had negative impact on the sustainability of the region into the long-term future. The fallout of the frequent confrontations between the government and oil companies on one hand and the communities (supported by the so-called Niger Delta militants) on the other has had adverse consequences on the wellbeing of the people and the environment. Tracing the issues that posed threats to the sustainability of the Niger Delta environment led to the discovery of a complex mix of bio-physical, economic, and socio-political factors. These factors have compounded the state of degradation. In this thesis, the response of the Presbyterian Church of Nigeria (PCN) to these problems was brought under scrutiny in the light of the failure of key stakeholders, namely, the government, the oil companies and the local communities, to resolve the issues. The results from the fieldwork show that the PCN is not engaging with these issues in a rigorous and systematic manner. The thesis unravels factors militating against the PCN’s participation, and reveals opportunities open to the church. However, what is lacking is a conscious effort by the PCN to pull together a local ecological theology of creation from its inherited theology and from local wisdom. A framework for such a local holistic ecotheology (LHE) is therefore suggested to drive PCN’s involvement, and potentially step into the void left by the earlier-mentioned stakeholders. The LHE is designed to be practical and contextual, having its starting point in the local socio-cultural, economic, political, and ecclesiastical context. It draws from elements of local cultures and tradition, the lived experiences of the people at the grassroots, and from Christian theology. It is proposed as a holistic framework that factors in the challenges facing the people and the environment, and proffers practical suggestions towards resolving the problems

Modeling, Predicting and Capturing Human Mobility

Realistic models of human mobility are critical for modern day applications, specifically for recommendation systems, resource planning and process optimization domains. Given the rapid proliferation of mobile devices equipped with Internet connectivity and GPS functionality today, aggregating large sums of individual geolocation data is feasible. The thesis focuses on methodologies to facilitate data-driven mobility modeling by drawing parallels between the inherent nature of mobility trajectories, statistical physics and information theory. On the applied side, the thesis contributions lie in leveraging the formulated mobility models to construct prediction workflows by adopting a privacy-by-design perspective. This enables end users to derive utility from location-based services while preserving their location privacy. Finally, the thesis presents several approaches to generate large-scale synthetic mobility datasets by applying machine learning approaches to facilitate experimental reproducibility

An integrated strings model of transnational advocacy: case studies from Romania and the United Kingdom

Studies of transnational advocacy mainly explore separate processes – e.g. the use of persuasion, socialization, leverage, incentives and penalties – through which specific actors influence policy and law at national and transnational levels. These processes can be seen as strings pulled by the actors involved in order to promote their aims. However, the existing literature stops short of explaining the dynamics of advocacy across time, the number of strings necessary for inducing change and the failure of advocacy. In order to address these shortcomings this thesis analyses the interactions between various processes that constitute transnational advocacy and proposes a conceptual model – labelled the integrated strings model of advocacy – to facilitate the understanding of the dynamics of advocacy. This model suggests that transnational advocacy is constituted by the following interlinked processes, labelled stages and strings in order to emphasize their dynamics: - The stages are: the making of pilot or past solutions-in-practice, problematization, the development of a common frame for possible solutions, the creation of solutions-on-paper and the making of solutions-in-practice; - These stages are constituted by six strings: the creation of social enterprises, the use of expertise, regulations, technology, the formation of alliances and the marketization of ideas and services. This model provides a more comprehensive understanding of the dynamics of advocacy than the existing literature and explains why some advocacy processes were successful while other failed. The model is illustrated through three case studies of advocacy focused on: (a) heritage conservation and sustainable development in Romania; (b) children’s rights in Romania; and (c) access to the UK’ labour market for Romanian migrants in Britain. The integrated model was developed through empirical multi-sited research conducted in Romania and the UK. My methodology was influenced by multi-sited ethnography (Marcus 1998), grounded theory (Strauss and Corbin 1990) and actor-network theory (Callon 1986; Latour 2005)

On the Theory of Ethnic Conflict

We present a theory of ethnic conflict in which coalitions formed along ethnic lines compete for the economy's resources. The role of ethnicity is to enforce coalition membership: in ethnically homogeneous societies members of the losing coalition can defect to the winners at low cost, and this rules out conflict as an equilibrium outcome. We derive a number of implications of the model relating social, political, and economic indicators such as the incidence of conflict, the distance among ethnic groups, group sizes, income inequality, and expropriable resources.ethnic distance, exploitation