Coordination-Free Byzantine Replication with Minimal Communication Costs

State-of-the-art fault-tolerant and federated data management systems rely on fully-replicated designs in which all participants have equivalent roles. Consequently, these systems have only limited scalability and are ill-suited for high-performance data management. As an alternative, we propose a hierarchical design in which a Byzantine cluster manages data, while an arbitrary number of learners can reliable learn these updates and use the corresponding data. To realize our design, we propose the delayed-replication algorithm, an efficient solution to the Byzantine learner problem that is central to our design. The delayed-replication algorithm is coordination-free, scalable, and has minimal communication cost for all participants involved. In doing so, the delayed-broadcast algorithm opens the door to new high-performance fault-tolerant and federated data management systems. To illustrate this, we show that the delayed-replication algorithm is not only useful to support specialized learners, but can also be used to reduce the overall communication cost of permissioned blockchains and to improve their storage scalability

Middleware-based Database Replication: The Gaps between Theory and Practice

The need for high availability and performance in data management systems has been fueling a long running interest in database replication from both academia and industry. However, academic groups often attack replication problems in isolation, overlooking the need for completeness in their solutions, while commercial teams take a holistic approach that often misses opportunities for fundamental innovation. This has created over time a gap between academic research and industrial practice. This paper aims to characterize the gap along three axes: performance, availability, and administration. We build on our own experience developing and deploying replication systems in commercial and academic settings, as well as on a large body of prior related work. We sift through representative examples from the last decade of open-source, academic, and commercial database replication systems and combine this material with case studies from real systems deployed at Fortune 500 customers. We propose two agendas, one for academic research and one for industrial R&D, which we believe can bridge the gap within 5-10 years. This way, we hope to both motivate and help researchers in making the theory and practice of middleware-based database replication more relevant to each other.Comment: 14 pages. Appears in Proc. ACM SIGMOD International Conference on Management of Data, Vancouver, Canada, June 200

Re-examining And Extending Penrose's Growth Theory: Updating Penrose For The 21St Century

Edith Penrose argued that firms face a constraint on organic growth because of growth activities in previous periods. Central to her ideas about growth is the distinction between managerial and entrepreneurial capabilities. Growth in previous periods creates adjustment costs which are associated with managerial capabilities and impacts on the growth opportunities which are associated with entrepreneurial capabilities. In this paper we revisit Penrose’s work to examine how the nature of growth in previous periods may effect growth in the current period. Employing a panel of all commercially active enterprises in the private (non-government) sector in Sweden over a 10 year period our results indicate that previous organic growth acts as a constraint on organic growth, however, acquisitive growth may act as a catalyst for organic growth. Based on these findings, we suggest extensions Penrose’s to growth theory

Complex situations: Economic insecurity, mental health, and substance use among pregnant women who consider - but do not have - abortions.

We examine characteristics and experiences of women who considered, but did not have, an abortion for this pregnancy. Participants were recruited at prenatal care clinics in Louisiana and Maryland for a mixed-methods study (N = 589). On self-administered surveys and structured interviews, participants were asked if they had considered abortion for this pregnancy and, if so, reasons they did not obtain one. A subset (n = 83), including participants who considered abortion for this pregnancy, completed in-depth phone interviews. Multivariable logistic regression analyses examined characteristics associated with having considered abortion and experiencing a policy-related barrier to having an abortion; analyses focused on economic insecurity and of mental health/substance use as main predictors of interest. Louisiana interviews (n = 43) were analyzed using modified grounded theory to understand concrete experiences of policy-related factors. In regression analyses, women who reported greater economic insecurity (aOR 1.21 [95% CI 1.17, 1.26]) and more mental health diagnoses/substance use (aOR 1.29 [1.16, 1.45] had higher odds of having considered abortion. Those who reported greater economic insecurity (aOR 1.50 [1.09, 2.08]) and more mental health diagnoses/substance use (aOR 1.45 [95% CI 1.03, 2.05] had higher odds of reporting policy-related barriers. Interviewees who considered abortion and were subject to multiple restrictions on abortion identified material and instrumental impacts of policies that, collectively, contributed to them not having an abortion. Many described simultaneously navigating economic insecurity, mental health disorders, substance use, and interpersonal opposition to abortion from family and the man involved in the pregnancy. Current restrictive abortion policies appear to have more of an impact on women who report greater economic insecurity and more mental health diagnoses/substance use. These policies work in concert with each other, with people's individual complex situations-including economic insecurity, mental health, and substance use-and with anti-abortion attitudes of other people to make abortion care impossible for some pregnant women to access