503 research outputs found
Agent-Based Query Optimization in a Grid Environment
No full textThe next generation experiments in High Energy Physics are the driving force for setting up an International Data Grid at CERN, the European Organization for Nuclear Research. Hundreds of Petabytes of data will be distributed and replicated all over the globe starting from 2005. In order to analyse this massive set of distributed data efficiently, we propose a hierarchical query optimisation architecture based on multi-agent technology. The architecture is optimised for the High Energy Physics community but is representative also for other data intensive scientific applications that use distributed data stores and mass storage system
Replica consistency in a Data Grid
No full textA Data Grid is a wide area computing infrastructure that employs Grid technologies to provide storage capacity and processing power to applications that handle very large quantities of data. Data Grids rely on data replication to achieve better performance and reliability by storing copies of data sets on different Grid nodes. When a data set can be modified by applications, the problem of maintaining consistency among existing copies arises. The consistency problem also concerns metadata, i.e., additional information about application data sets such as indices, directories, or catalogues. This kind of metadata is used both by the applications and by the Grid middleware to manage the data. For instance, the Replica Management Service (the Grid middleware component that controls data replication) uses catalogues to find the replicas of each data set. Such catalogues can also be replicated and their consistency is crucial to the correct operation of the Grid. Therefore, metadata consistency generally poses stricter requirements than data consistency. In this paper we report on the development of a Replica Consistency Service based on the middleware mainly developed by the European Data Grid Project. The paper summarises the main issues in the replica consistency problem, and lays out a high-level architectural design for a Replica Consistency Service. Finally, results from simulations of different consistency models are presented
Achievement emotions and well-being at school: Transitioning from primary to secondary school
No full textAchievement emotions play a key role in students’ well-being and learning. In line with the control-value theory, many studies support the relevance of achievement emotions for achievement. However, scarce attention has been devoted to school-related achievement emotions and well-being in the transition from primary to secondary school. We examined the psychometric properties of two brief scales assessing achievement emotions and well-being using Rasch modelling, possible grade-level and gender differences in emotions and well-being, and their relations with achievement. We sampled 432 fourth and seventh-graders. At T1 we assessed school-related achievement emotions (Achievement Emotions Adjective List–Brief version, AEAL–B, Raccanello et al., 2013) and well-being (School-Related Well-Being Scale, SWBS, Loderer et al., 2016). At T2 we gathered data on grades. First, our findings confirmed the goodness of two brief instruments to measure achievement emotions and well-being at school. Through Rasch modelling, we transformed the two scales in two instruments that respect the properties of the fundamental measurement. Second, grade-level differences emerged, with a general decrease of positive emotions and well-being that attests a maladaptive trend. Moreover, females reported lower anger, hopelessness, and boredom, and higher well-being. Third, a path analysis revealed that some school-related negative emotions, namely anger, hopelessness, and boredom, are detrimental for achievement, while well-being at school was positively associated to achievement. This study highlights the need for developing interventions to support students in the transition from primary to secondary school, which is such a pivotal time in their learning path
Towards an Economy-Based Optimisation of File Access and Replication on a Data Grid
No full textWe are working on a system for the optimised access and replication of data on a Data Grid. Our approach is based on the use of an economic model that includes the actors and the resources in the Grid. Optimisation is obtained via interaction of the actors in the model, whose goals are maximising the profits and minimising the costs of data resource management. In the system, local optimisation results in global optimisation through emergent marketplace behaviour. In this paper we give an overview of our model and present part of the complex economic reasoning required to support this desired marketplace interaction model
Formal analysis of an agent-based optimisation strategy for Data Grids
No full textIn a world-wide computational Grid, thousands of users compete for computing, storage and network facilities, so optimising the use of these resources is critical for both the users and resource providers. Users typically want their jobs to be executed as fast as possible, while the goal of a Grid infrastructure is to assure some specific quality of service for all users. We have developed an optimisation strategy based on an economic model where data-seeking agents trade with data-storing agents in order to negotiate optimal prices for exchanging data files. We have gained considerable experience of the performance of this model through detailed simulation studies; however, simulation studies alone cannot give formal verification of its properties. Here we provide a formalisation of the auction protocol that is the basis of the economic model and prove some of its properties, namely that it is free from deadlocks and that it always terminates. We model the auction protocol using Petri nets, a formal and graphical language that is well suited for modelling concurrent distributed system
Grid Performance Measurements with OptorSim
No full textGrid computing is fast emerging as the solution to the problems posed by the massive computational and data handling requirements of many current international scientific projects. Simulation of the Grid environment is important to evaluate the impact of potential data handling strategies before being deployed on the Grid. In this paper, we look at the effects of various data replication strategies and compare them in a variety of Grid scenarios, evaluating several performance metrics. We use the Grid simulator OptorSim, and base our simulations on a world-wide Grid testbed for data intensive high energy physics experiments. Our results show that the choice of scheduling and data replication strategies can have a large effect on both job throughput and the overall consumption of Grid resource
Evaluating Scheduling and Replica Optimisation Strategies in OptorSim
No full textGrid computing is fast emerging as the solution to the problems posed by the massive computational and data handling requirements of many current international scientific projects. Simulation of the Grid environment is important to evaluate the impact of potential data handling strategies before being deployed on the Grid. In this paper, we look at the effects of various job scheduling and data replication strategies and compare them in a variety of Grid scenarios, evaluating several performance metrics. We use the Grid simulator OptorSim, and base our simulations on a world-wide Grid testbed for data intensive high energy physics experiments.
Our results show that the choice of scheduling and data replication strategies can have a large effect on both job throughput and the overall consumption of Grid resource
CBF gene copy number variation at Frost Resistance-2 is associated with levels of freezing tolerance in temperate-climate cereals
No full textFrost Resistance-1 (FR-1) and FR-2 are two loci affecting freezing tolerance and winterhardiness of the temperate-climate cereals. FR-1 is hypothesized to be due to thepleiotropic effects of VRN-1. FR-2 spans a cluster of C-Repeat Binding Factor (CBF)genes. These loci are genetically and functionally linked. Recent studies indicate CBFtranscripts are down-regulated by the VRN-1 encoded MADS-box protein or a factor inthe VRN-1 pathway. Here we report that barley genotypes ‘Dicktoo’ and ‘Nure’ carryinga vrn-H1 winter allele at VRN-H1 harbor increased copy numbers of CBF codingsequences relative to Vrn-H1 spring allele genotypes ‘Morex’ and ‘Tremois’. Sequencingbacteriophage lambda genomic clones from these four genotypes alongside DNA blothybridizations indicate approximately half of the eleven CBF orthologs at FR-H2 areduplicated in individual genomes. One of these duplications discriminates vrn-H1genotypes from Vrn-H1 genotypes. The vrn-H1 winter allele genotypes harbor tandemsegmental duplications through the CBF2A–CBF4B genomic region and maintain twodistinct CBF2 paralogs, while the Vrn-H1 spring allele genotypes harbor single copies ofCBF2 and CBF4. An additional CBF gene, CBF13, is a pseudogene interrupted bymultiple nonsense codons in ‘Tremois’ whereas CBF13 is a complete uninterruptedcoding sequence in ‘Dicktoo’ and ‘Nure’. DNA blot hybridization with wheat DNAsreveals greater copy numbers of CBF14 also occurs in winter wheats than in springwheats. These data indicate that variation in CBF gene copy numbers is widespread in theTriticeae and suggest selection for winter hardiness co-selects winter alleles at both VRN-1 and FR-2
Optorsim: A Grid Simulator for Studying Dynamic Data Replication Strategies
No full textComputational grids process large, computationally intensive problems on small data sets. In contrast, data grids process large computational problems that in turn require evaluating, mining and producing large amounts of data. Replication, creating geographically disparate identical copies of data, is regarded as one of the major optimization techniques for reducing data access costs. In this paper, several replication algorithms are discussed. These algorithms were studied using the Grid simulator: OptorSim. OptorSim provides a modular framework within which optimization strategies can be studied under different Grid configurations. The goal is to explore the stability and transient behaviour of selected optimization techniques. We detail the design and implementation of OptorSim and analyze various replication algorithms based on different Grid workloads
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