Optimistic Parallel State-Machine Replication

State-machine replication, a fundamental approach to fault tolerance, requires replicas to execute commands deterministically, which usually results in sequential execution of commands. Sequential execution limits performance and underuses servers, which are increasingly parallel (i.e., multicore). To narrow the gap between state-machine replication requirements and the characteristics of modern servers, researchers have recently come up with alternative execution models. This paper surveys existing approaches to parallel state-machine replication and proposes a novel optimistic protocol that inherits the scalable features of previous techniques. Using a replicated B+-tree service, we demonstrate in the paper that our protocol outperforms the most efficient techniques by a factor of 2.4 times

Parallel Deferred Update Replication

Deferred update replication (DUR) is an established approach to implementing highly efficient and available storage. While the throughput of read-only transactions scales linearly with the number of deployed replicas in DUR, the throughput of update transactions experiences limited improvements as replicas are added. This paper presents Parallel Deferred Update Replication (P-DUR), a variation of classical DUR that scales both read-only and update transactions with the number of cores available in a replica. In addition to introducing the new approach, we describe its full implementation and compare its performance to classical DUR and to Berkeley DB, a well-known standalone database

Rethinking State-Machine Replication for Parallelism

State-machine replication, a fundamental approach to designing fault-tolerant services, requires commands to be executed in the same order by all replicas. Moreover, command execution must be deterministic: each replica must produce the same output upon executing the same sequence of commands. These requirements usually result in single-threaded replicas, which hinders service performance. This paper introduces Parallel State-Machine Replication (P-SMR), a new approach to parallelism in state-machine replication. P-SMR scales better than previous proposals since no component plays a centralizing role in the execution of independent commands---those that can be executed concurrently, as defined by the service. The paper introduces P-SMR, describes a "commodified architecture" to implement it, and compares its performance to other proposals using a key-value store and a networked file system

LEARNING STYLES AND METACOGNITION

In this paper we introduce the results of a research that involved 60 primary school pupils. Attention is drawn to a relevant issue in instructional research: the potential value to learners of metacognitive awareness. Some implications of these issues for learning styles research are then discussed. The purpose of this study was to investigate how students perceive learning and their learning styles preferences. Through a reflection on relations between the personalization of education and knowledge of learning styles, we will emphasize how the very important issue, for a teacher, is to create his own working knowledge on his students' learning styles, if he really wants effectively stimulate their learning process through activities normally done at school. We will consider Kolb's learning styles model and will analyze how a teacher, minding the diversity of students' learning styles, will be able to make his own teaching more effective. Regarding the pupils, we will try to show how the awareness of one's learning style can help to guide the self-regulation on learning and personal development. Research about metacognition and its implications for learning and instruction has become a central issue in education. The call for teaching metacognitive skills is considered one of main implications for instruction that emerged from over three decades of research about how people learn. Learning how to learn has been identified by the EU as one of eight key competences. This study is aimed to compare how students think what they learn to their learning styles preferences. The metacognitive model is used to describe how fundamental concepts of experiential learning theory can guide metacognitive monitoring and control of learning. Metacognitive strategies to help pupils to improve their learning effectiveness are outlined. We will analyze relationship between learning styles and teaching methods highlighting how one of the teacher's educational role is helping each student to find the right balance between intellectual abilities and learning style. Learners can chart their path on the learning way by developing their metacognitive learning capacities, and educators can pave the way for placing learning about learning on the agenda of their educational programs

Ressenyes

Obra ressenyada: Aurora GARCÍA BALLESTEROS (coord.), Métodos y técnicas cualitativas en geografía social. Barcelona: Oikos-Tau, 1998

State autonomy, political power and public policy : a study of Brazilian development.

Political ScienceDoctor of Philosophy (PhD