QuAD: A Quorum Protocol for Adaptive Data Management in the Cloud

More and more companies move their data to the Cloud which is able to cope with the high scalability and availability demands due to its pay-as-you-go cost model. For this, databases in the Cloud are distributed and replicated across different data centers. According to the CAP theorem, distributed data management is governed by a trade-off between consistency and availability. In addition, the stronger the provided consistency level, the higher is the generated coordination overhead and thus the impact on system performance. Nevertheless, many OLTP applications demand strong consistency and use ROWA(A) for replica synchronization. ROWA(A) protocols eagerly update all (or all available) replicas and thus generate a high overhead for update transactions. In contrast, quorum-based protocols consider only a subset of sites for eager commit. This reduces the overhead for update transactions at the cost of reads, as the latter also need to access several sites. Existing quorum-based protocols do not consider the load of sites when determining the quorums; hence, they are not able to adapt at run-time to load changes. In this paper, we present QuAD, an adaptive quorum-based replication protocol that constructs quorums by dynamically selecting the optimal quorum configuration w.r.t. load and network latency. Our evaluation of QuAD based on Amazon EC2 shows that it considerably outperforms both static quorum protocols and dynamic protocols that neglect site properties in the quorum construction process

Icarus: Towards a Multistore Database System

The last years have seen a vast diversification on the database market. In contrast to the "one-size-fits-all" paradigm according to which systems have been designed in the past, today's database management systems (DBMSs) are tuned for particular workloads. This has led to DBMSs optimized for high performance, high throughput read/write workload in online transaction processing (OLTP) and systems optimized for complex analytical queries (OLAP). However, this approach reaches a limit when systems have to deal with mixed workloads that are neither pure OLAP nor pure OLTP workloads. In such cases, polystores are increasingly gaining popularity. Rather than supporting one single database paradigm and addressing one particular workload, polystores encompass several DBMSs that store data in different schemas and allow to route requests at a per-query-level to the most appropriate system. In this paper, we introduce the polystore Icarus. In our evaluation based on a workload that combines OLTP and OLAP elements, We show that Icarus is able to speed-up queries up to a factor of 3 by properly routing queries to the best underlying DBMS

Seismic Response of Single-storey Steel Buildings

Nonlinear time step dynamic analyses have been performed on 24 rectangular single-storey steel framed buildings including a metal roof deck diaphragm and steel bracing bays along their exterior walls. The structures were designed according to current Canadian codes and were subjected to site specific ensembles of historical earthquake accelerograms. The analyses indicated that larger in-plane deformations and bending moments developed in the diaphragm compared to the values expected from the equivalent lateral force procedure commonly used in design. The distribution of the shear forces in the diaphragm was also found to deviate significantly from the linear distribution assumed in design. In addition, the ductility demand in the bracing bents exceeded the amount predicted by nonlinear analyses performed on equivalent single-degree of freedom systems. Based on these results, preliminary design guidelines have been proposed for predicting the deformations, moments and shear forces in roof diaphragm as well as for confining inelastic action in the vertical bracing elements

Analyzing the Performance of Data Replication and Data Partitioning in the Cloud: the Beowulf Approach

Applications deployed in the Cloud usually come with dedicated performance and availability requirements. This can be achieved by replicating data across several sites and/or by partitioning data. Data replication allows to parallelize read requests and thus to decrease data access latency, but induces significant overhead for the synchronization of updates. Partitioning, in contrast, is highly beneficial if all the data accessed by an application is located at the same site, but again necessitates coordination if distributed transactions are needed to serve applications. In this paper, we analyze three protocols for distributed data management in the Cloud, namely Read-One Write-All-Available (ROWAA), Majority Quorum (MQ) and Data Partitioning (DP) - all in a configuration that guarantees strong consistency. We introduce Beowulf, a meta protocol based on a comprehensive cost model that integrates the three protocols and that dynamically selects the protocol with the lowest latency for a given workload. In the evaluation, we compare the prediction of the Beowulf cost model with a baseline evaluation. The results nicely show the effectiveness of the analytical model and the precision in selecting the best suited protocol for a given workload

Johannes Verkuyl (1908-2001): een leven lang zending en dialoog: De ontwikkeling van zijn visie op andere godsdiensten en levensbeschouwingen

Vroom, H.M. [Promotor

Chronos: The Swiss Army Knife for Database Evaluations

Systems evaluations are an important part of empirical research in computer science. Such evaluations encompass the systematic assessment of the run-time characteristics of systems based on one or several parameters. Considering all possible parameter settings is often a very tedious and time-consuming task with many manual activities, or at least the manual creation of evaluation scripts. Ideally, the thorough evaluation of a complete evaluation space can be fully automated. This includes the set-up of the evaluation, its execution, and the subsequent analysis of the results. In this paper, we introduce Chronos, a system for the automation of the entire evaluation workflow. While Chronos has originally been built for database systems evaluations, its generic approach also allows its usage in other domains. We show how Chronos can be deployed for a concrete database evaluation, the comparative performance analysis of different storage engines in MongoDB

Comparison of Eager and Quorum-based Replication in a Cloud Environment

Most applications deployed in a Cloud require a high degree of availability. For the data layer, this means that data have to be replicated either within a data center or across Cloud data centers. While replication also allows to increase the performance of applications if data is read as the load can be distributed across replica sites, updates need special coordination among the sites and may have an adverse effect on the overall performance. The actual effects of data replication depend on the replication protocol used. While ROWAA (readone-write-all-available) prefers read operations, quorum-based replication protocols tend to prefer write operations as not all replica sites need to be updated synchronously. In this paper, we provide a detailed evaluation of ROWAA and quorum-based replication protocols in an amazon AWS Cloud environment on the basis of the TPC-C benchmark and different transaction mixes. The evaluation results for single data center and multi data center environments show that in general the influence of transaction coordination significantly grows with the number of update sites and a growing number of update transactions. However, not all quorum-based protocols are well suited for high update loads as they may create a hot spot that again significantly impacts performance

A narrative pastoral care approach to a school outreach programme at a private school in Gauteng

Part of my responsibilities as Life Orientation teacher at Sagewood School is the Community Outreach Programme. In particular encouraging participation and ensuring that learners enjoy a life giving and reciprocal experience as they focus beyond themselves in the wider community. Information for this research was gathered from other independent schools, parents and learners from Sagewood. Sources included answers to questionnaires, class discussions and feedback from past experiences. My focus included a study of the history of outreach, works on postmodernism, social construction, practical theology and my position of co-constructor with the learners. Important outcomes included ensuring that the voices of the learners are heard in decision making and planning for future outreach activities. Given the constantly changing nature of society such activities need to be evaluated regularly. Lastly, people care in different ways and about different things and we need to encourage learners to care, in their own unique way.Philosophy, Practical and Systematic TheologyM.Th. (Specialisation in Pastoral Therapy

Numerical modeling of phase-separation in binary media based on the cahn-hilliard equation

In the article numerical procedure for solution of the Cahn-Hilliard equation which is based on the forward Euler method in time and mixed (due to 4th order nature of differential operator) linear finite element formulation in space is described. Numerical examples consist of idealized model with double well potential (in 2 and 3 spatial dimensions) and more physically relevant model with logarithmic potential (in 2D only).У статті описано процедуру наближеного рішення рівняння Кана-Хіллярда в частинних похідних 4-го порядку, котра базується на явному методі Ейлера в часі та змішаній постановці з білінійними скінченими елементами в просторі. Наведено чисельні рішення для ідеалізованої моделі з двуямним потенціалом (в 2-х та 3-х просторових вимірах) та більш фізично релевантної моделі з логарифмічним потенціалом (тільки в 2-х просторових вимірах)

Mathematical optimization and machine learning to support PCB topology identification

In this paper, we study an identification problem for schematics with different concurring topologies. A framework is proposed, that is both supported by mathematical optimization and machine learning algorithms. Through the use of Python libraries, such as scikit-rf, which allows for the emulation of network analyzer measurements, and a physical microstrip line simulation on PCBs, data for training and testing the framework are provided. In addition to an individual treatment of the concurring topologies and subsequent comparison, a method is introduced to tackle the identification of the optimum topology directly via a standard optimization or machine learning setup: An encoder-decoder sequence is trained with schematics of different topologies, to generate a flattened representation of the rated graph representation of the considered schematics. Still containing the relevant topology information in encoded (i.e., flattened) form, the so obtained latent space representations of schematics can be used for standard optimization of machine learning processes. Using now the encoder to map schematics on latent variables or the decoder to reconstruct schematics from their latent space representation, various machine learning and optimization setups can be applied to treat the given identification task. The proposed framework is presented and validated for a small model problem comprising different circuit topologies.</p