UWSpace

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Recent Submissions

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    Lanternfish: Better random networks through optics
    (University of Waterloo, 2015-07-23) Szepesi, Tyler; Wond, Bernard; Kazhami, Fiodar; Rizvi, Sajjad; Brecht, Tim
    Current random datacenter network designs, such as Jellyfish, directly wire top-of-rack switches together randomly, which is difficult even when using best-practice cable management techniques. Moreover, these are static designs that cannot adapt to changing workloads. In this paper, we introduce Lanternfish, a new approach to building random datacenter networks using an optical ring that significantly reduces wiring complexity and provides the opportunity for reconfigurability. Unlike previous optical ring designs, Lanternfish does not require wavelength planning because it is specifically designed to provide random connectivity between switches. This design choice further reduces the difficulty of deploying a Lanternfish network, making random datacenter networks more practical. Our experimental results using both simulations and network emulation show that Lanternfish can effectively provide the same network properties as Jellyfish. Additionally, we demonstrate that by replacing passive optical components with active optical components at each switch, we can dynamically reconfigure the network topology to better suit the workload while remaining cost competitive. Lanternfish is able to construct workload specific topologies that provide as much as half the average pathlength than a Jellyfish deployment with twice as many switch-to-switch connections.
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    Mayflower: Improving distributed filesystem performance through SDN/filesystem co-design
    (University of Waterloo, 2015-07-23) Rizvi, Sajjad; Li, Xi; Wong, Bernard; Cao, Xiao; Cassell, Benjamin
    The increasing prevalence of oversubscribed networks and fast solid-state storage devices in the datacenter has made the network the new performance bottleneck for many distributed filesystems. As a result, distributed filesystems need to be network-aware in order to make more effective use of available network resources. In this paper, we introduce Mayflower, a new distributed filesystem that is not only network-aware, it is co-designed from the ground up to work together with a network control plane. In addition to the standard distributed filesystem components, Mayflower has a flow monitor and manager running inside a software-defined networking controller. This tight coupling with the network controller enables Mayflower to make intelligent replica selection and flow scheduling decisions based on both filesystem and network information. It also enables Mayflower to perform global optimizations that are unavailable to conventional distributed filesystems and network control planes. Our evaluation results from both simulations and a prototype implementation show that Mayflower reduces average read completion time by more than 25% compared to current state-of-the-art distributed filesystems with an independent network flow scheduler, and more than 80% compared to HDFS with ECMP.
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    Nessie: A decoupled, client-driven, key-value store using RDMA
    (University of Waterloo, 2015-07-22) Szepesi, Tyler; Cassell, Benjamin; Wong, Bernard; Brecht, Tim; Liu, Xiaoyi
    The increasing use of key-value storage systems in performance-critical data centre applications has motivated new storage system designs that use Remote Direct Memory Access (RDMA) to reduce communication overhead. However, existing approaches that achieve low latency and high throughput do so by dedicating entire cores to PDMA message handling, including polling local memory for incoming RDMA messages. In this paper we describe and demonstrate why polling-based RDMA is not suitable for many data centre applications with significant data processing and data storage requirements. We then propose, design, implement and evaluate an alternative communication approach that strictly uses one-sided RDMA operations, which eliminates polling on the server-side and is therefore a serverless (client-driven) design. This approach is used to build Nessie, a distributed client-driven RDMA-enabled key-value store that uses native RDMA compare-and-swap operations to co-ordinate conflicting operations between clients. Nessie further reduces communication requirements by decoupling the key-value location from the key lookup mechanism, which enables local write operations, thus avoiding comparatively expensive RDMA operations. Nessie's one-sided design ensures that only the clients in the system consume any CPU, which in turn allows it to maintain high performance despite the need for computation by the application utilizing the key-value store or contention from other applications.
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    CrossStitch: An efficient transaction processing framework for geo-distributed system
    (University of Waterloo, 2015-07-28) Choy, Sharon; Wong, Bernard; Cui, Xu; Liu, Xiaoyi
    Current transaction system for geo-distributed datastores either have high transaction processing latencies or are unable to support general transactions with dependent operations. In this paper, we introduce CrossStitch, an efficient transaction processing framework that reduces latency by restructuring each transaction into a chain of state transitions, where each state consists of a key operation and computation. Transaction states are processed sequentially, and the transaction code and data is sent directly to the next hop in the chain. CrossStitch transactions can be organized such that all states in a location are processed before transitioning to a state in a different location. This allows CrossStitch to significantly reduce the number of inter-location crossings compared to transaction systems that retrieve remote data to a single location for processing. To provide transactional properties while preserving the chain communication pattern, CrossStitch introduces a pipelined commit protocol that executes in parallel with the transaction and does not require any centralized co-ordination. Our evaluation results show that CrossStitch can reduce the latency of geo-distributed transactions when compared to a traditional 2PC-based distributed transaction system. We demonstrate that CrossStitch can reduce the number of round trips by more than half for TPC-C-like transactions.
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    Equity in Policy and Health: Examining Inequalities in Job Quality of Caregivers, Refugees’ Health Care Access, and the Health Disparity of Health Care Workers in Canada
    (University of Waterloo, 2026-07-31) Mursal, Adam
    This dissertation examines how structural inequities in Canada’s health and labour systems shape the well-being and inclusion of marginalized populations, with a focus on the convergence of migration, social policy, and health. Across three chapters, it integrates qualitative, policy, and quantitative analyses to explore how institutions and labour markets perpetuate health disparities among Personal Support Workers (PSWs), refugees, and immigrant or visible minority health care workers. Together, the studies demonstrate ways that systemic inequality, policy design, and institutional neglect sustain vulnerabilities that undermine both population health and workforce stability. Chapter 2 is a qualitative study that investigates the multidimensional challenges of frontline eldercare work and the job quality of personal support workers (PSWs). The study employs semi-structured interviews with participants who played different roles at eldercare settings (N = 8). The sample included personal support workers (PSWs), Directors of Care (DOCs), and other frontline and supervisory eldercare personnel. Applying the OECD Job Quality Framework, the study finds that PSWs and other eldercare staff experience chronic employment insecurity, emotional exhaustion, and limited institutional recognition. All these conditions worsened during the COVID-19 pandemic. Participants reported heightened physical and psychological strain, severe shortage of staffing, and inequitable workloads, particularly in long-term care facilities. The study highlights how gendered and racialized or visible minority jobs reinforce structural and systemic inequities. The findings of this study suggest that the sustainability of eldercare depends on comprehensive policy reforms that address wages, regulation, and professional recognition. Chapter 3 is a study that applies social justice theories to critique the equity implications of federal refugee health care policy reforms. It critically assesses the 2012 IFHP cuts, which restricted refugees’ access to health care services, and the 2016 reinstatement that only partially restored refugees’ health care coverage. The analysis situates these policy shifts within Canada’s neoliberal transformation toward market-oriented governance, emphasizing cost containment over social equity. Drawing on migration studies literature, the chapter demonstrates how refugee health care policy operates as a mechanism of “differential inclusion”, where societal status hierarchy (i.e., citizen, claimant, asylum seeker) determines access to care. These exclusions reinforce health inequities among refugees and contravene Canada’s stated commitments to health care’s universality and health care as human rights. The study concludes that equitable health care access to all is both a social justice imperative and a public health necessity. Chapter 4 is a quantitative study on health care workers’ health disparity in Canada. It utilizes data from the Survey on Health Care Workers' Experiences During the Pandemic (SHCWEP) to examine how immigration background and visible minority status are associated with perceived health. Using survey-multivariate logistic regression, the study finds that both immigrant and visible minority health care workers have significantly higher odds of reporting poorer perceived health compared to their non-immigrant, non-visible minority counterparts. Findings reveal that immigrant visible minority health care workers experience the greatest disadvantage. Socioeconomic and age gradients were also observed and were consistent with existing literature. Overall study results demonstrate that systemic inequalities within health care institutions mirror that of broader society, which underscores the need for inclusive policies and targeted supports.