1,117 research outputs found
Optimizing the Replication of Multi-Quality Web Applications Using ACO and WoLF
This thesis presents the adaptation of Ant Colony Optimization to a new NP-hard problem involving the replication of multi-quality database-driven web applications (DAs) by a large application service provider (ASP). The ASP must assign DA replicas to its network of heterogeneous servers so that user demand is satisfied and replica update loads are minimized. The algorithm proposed, AntDA, for solving this problem is novel in several respects: ants traverse a bipartite graph in both directions as they construct solutions, pheromone is used for traversing from one side of the bipartite graph to the other and back again, heuristic edge values change as ants construct solutions, and ants may sometimes produce infeasible solutions. Experiments show that AntDA outperforms several other solution methods, but there was room for improvement in the convergence rates of the ants. Therefore, in an attempt to achieve the goals of faster convergence and better solution values for larger problems, AntDA was combined with the variable-step policy hill-climbing algorithm called Win or Learn Fast (WoLF). In experimentation, the addition of this learning algorithm in AntDA provided for faster convergence while outperforming other solution methods
On the cost of database clusters reconfiguration
Database clusters based on share-nothing replication techniques are currently widely accepted as a practical solution to scalability and availability of the data tier. A key issue when planning such systems is the ability to meet service level agreements when load spikes occur or cluster nodes fail. This translates into the ability to provision and deploy additional nodes. Many current research efforts focus on designing autonomic controllers to perform such reconfiguration, tuned to quickly react to system changes and spawn new replicas based on resource usage and performance measurements. In contrast, we are concerned about the inherent impact of deploying an additional node to an online cluster, considering both the time required to finish such an action as well as the impact on resource usage and performance of the cluster as a whole. If noticeable, such impact hinders the practicability of self-management techniques, since it adds an additional dimension that has to be accounted for. Our approach is to systematically benchmark a number of different reconfiguration scenarios to assess the cost of bringing a new replica online. We consider factors such as: workload characteristics, incremental and parallel recovery, flow control and outdatedness of the recovering replica. As a result, we show that research should be refocused from optimizing the capture and transmition of changes to applying them, which in a realistic setting dominates the cost of the recovery operation.Work supported by the Spanish Government under research grant TIN2006-14738-C02-02
Improving The Fault Tolerance of Ad Hoc Routing Protocols using Aspect-oriented Programming
[ES] Las redes ad hoc son redes inalámbricas distribuidas formadas por nodos móviles que se ubican
libremente y dinámicamente, capaces de organizarse de manera propia en topologías arbitrarias y
temporales, a través de la actuación de los protocolos de encaminamiento. Estas redes permiten a las
personas y dispositivos conectarse sin problemas rápidamente, en áreas sin una infraestructura de
comunicaciones previa y con un bajo coste. Muchos estudios demuestran que los protocolos de
encaminamiento ad hoc se ven amenazados por una variedad de fallos accidentales y maliciosos, como
la saturación de vecinos, que puede afectar a cualquier tipo de red ad hoc, y el ruido ambiental, que
puede afectar en general a todas las redes inalámbricas. Por lo tanto, el desarrollo y la implementación
de estrategias de tolerancia a fallos para mitigar el efecto de las fallos, es esencial para el uso práctico
de este tipo de redes. Sin embargo, los mecanismos de tolerancia a fallos suelen estar implementados
de manera específica, dentro del código fuente de los protocolos de encaminamiento que hace que i)
ser reescrito y reorganizado cada vez que una nueva versión de un protocolo se libera, y ii) tener un
carácter completamente remodelado y adaptado a las nuevas versiones de los protocolos. Esta tesis de
máster explora la viabilidad de utilizar programación orientada a aspectos (AOP), para desarrollar e
implementar los mecanismos de tolerancia a fallos adecuados para toda una familia de protocolos de
encaminamiento, es decir, las versiones actuales y futuras de un protocolo determinado (OLSR en este
caso). Por otra parte, se propone una nueva metodología para ampliar estos mecanismos a diferentes
familias de protocolos proactivos (OLSR, BATMAN y Babel) con un nuevo concepto de AOP, el metaaspecto.
La viabilidad y efectividad de la propuesta se ha evaluado experimentalmente, estableciendo
así un nuevo método para mejorar la implementación de la portabilidad y facilidad de mantenimiento
de los mecanismos de tolerancia a fallos en los protocolos de enrutamiento ad hoc y, por lo tanto, la
fiabilidad de las redes ad hoc.[EN] Ad hoc networks are distributed networks consisting of wireless mobile nodes that can freely and
dynamically self-organize into arbitrary and temporary topologies, through the operation of routing
protocols. These networks allow people and devices to seamlessly interconnect rapidly in areas with no
pre-existing communication infrastructure and with a low cost. Many studies show that ad hoc routing
protocols are threatened by a variety of accidental and malicious faults, like neighbour saturation,
which may affect any kind of ad hoc network, and ambient noise, which may impact all wireless
networks in general. Therefore, developing and deploying fault tolerance strategies to mitigate the
effect of such faults is essential for the practical use of this kind of networks. However, those fault
tolerance mechanisms are usually embedded into the source code of routing protocols which causes
that i) they must be rewritten and redeployed whenever a new version of a protocol is released, and ii)
they must be completely redeveloped and adapted to new routing protocols. This master thesis
explores the feasibility of using Aspect-Oriented Programming (AOP) to develop and deploy fault
tolerance mechanisms suitable for a whole family of routing protocols, i.e. existing and future versions
of a given protocol (OLSR in this case). Furthermore, a new methodology is proposed to extend these
mechanisms to different families of proactive protocols (OLSR, B.A.T.M.A.N and Babel) using a new
concept in AOP, the meta-aspect. The feasibility and effectiveness of the proposal is experimentally
assessed, thus establishing a new method to improve the deployment, portability, and maintainability
of fault tolerance mechanisms for ad hoc routing protocols and, therefore, the dependability of ad hoc
networks.Bustos Rodríguez, AJ. (2012). Improving The Fault Tolerance of Ad Hoc Routing Protocols using Aspect-oriented Programming. http://hdl.handle.net/10251/18421Archivo delegad
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