Ramon Puigjaner

An up-to-date survey in web load balancing

This survey is an up-to-date state-of-the-art in Web load balancing mechanisms that includes all the possible classifications and focuses on the advantages of using load balancing solutions to increase the performance of the Web system. A general description of the Web load balancing solutions is included and organised by differentiating the OSI protocol stack layer the load balancing is based on. The most important request distributing polices that are proposed in the literature are also included. This article summarises all previous surveys on the Web load balancing subject and updates the state-of-the-art with the most recent load balancing proposals.

Performance Model Interchange Format (PMIF 2): A comprehensive approach to Queueing Network Model interoperability

The Performance Model Interchange Format (PMIF) provides a mechanism for transferring the system model information among performance modeling tools requiring only that the tools either internally support PMIF or provide an interface that reads/writes model specifications from/to a file. This paper presents the latest version of the specification (PMIF 2): a metamodel defining the information requirements and the corresponding XML schema. It defines the semantic properties for a pmif.xml interchange, the prescribed validation order, errors and warnings, and a tool and Web service implementation. Import and export prototypes for two different types of tools prove the concept. Generally available examples are used for repeatability.

Performance-related ontologies and semantic web applications for on-line performance assessment intelligent systems

Several techniques and applications have been proposed to aid the decision taking process in the system performance domain. Most of these techniques have depicted the performance model of systems through annotations of performance measurements coming from specific software descriptive syntactical languages. However, the semantic representation of performance information provides the possibility of its ulterior machine-processable logical interpretation and therefore the applicability of inference rules about a particular domain. Moreover, ontologies ease the interchange and reuse of knowledge of particular domains, e.g. system performance. In this work, we propose a performance ontology together with the system performance analysis technique as an example of framework building for intelligent applications based on semantic web. The paper also shows the construction of performance rules through OWL to automatically infer new performance constraints and QoS knowledge about the system on execution.

Adaptive admission control algorithm in a QoS-aware Web system

Internet traffic tends to show significant growth of demand at certain times of the day, or in response to special events. The consequence of these traffic peaks is that Web systems that are responding to user demands are congested due to their inability to serve a large volume of requests. The case for admission control in these situations is even stronger when Quality of Service (QoS) is considered as a primary objective in the Web system. In this work, we address two issues: on one hand, we consider and compare five throughput predictors to be used in a Web system in order to track its performance and, on the other hand, we propose a QoS-aware admission control and load balancing algorithm that prevents the Web system from sudden overload. The admission control algorithm is based on a resource allocation scheme that includes a throughput predictor. In order to obtain a low overhead, the monitoring of traffic arriving at the Web system is performed following an adaptive time slot scheduling based on the burstiness factor that we defined in previous work. Results show the benefits of our adaptive time slot scheduling compared to a fixed time scheduling. A discussion of the results of the five throughput predictors and the admission control algorithm is provided. We also compare the performance of our algorithm with Intelligent Queue-based Request Dispatcher (IQRD). The algorithm is designed to be included in a Web system composed by a set of Web servers distributed locally, which can also form part of a wider geographically distributed load balancing architecture.

Performance assessment on ambient intelligent applications through ontologies

This paper brings together the performance assessment of ambient intelligence architectures systems with ontology engineering. Thus, firstly appropriate description methods for distributed intelligent applications are summarized. Derived from the system characterization, typical software performance engineering techniques are based on the augmented description of the model regarding performance annotations. However, these annotations are only related with the syntactical view of the software architecture. In the next generation of performance assessment tools for ambient intelligent systems, the description of the system would be capable of reasoning and acquiring knowledge about performance. Having an appropriate architectural description including performance aspects, any possible design options for intelligent distributed applications can be evaluated according to their performance impact. Therefore, we propose the use of an ontology with performance-related information not only to possible evaluate the architecture through the common off-line procedure but also the first step to build a broker that assesses the performance of the system during its execution.

Interchange Formats for Performance Models: Experimentation and Ouput

XML-based interchange formats for performance models provide a mechanism whereby performance model information may be transferred among modeling tools. For example, the PMIF allows diverse tools to exchange queueing network model information. Formats have also been defined for the interchange of LQN, UML, Petri Nets, and others. These formats specify the model and a set of parameters for one run. For model studies, however, it is useful to be able to specify multiple runs, or experiments, for the model. This paper presents an XML interchange schema extension for defining a set of model runs and the output desired from them. It has the expressive power to specify iterations, alternations, assignments of values, actions based on model results and more. Examples illustrate how the experiment interchange extension can be used with a wide variety of performance modeling paradigms. A prototype proves the concept.

A general performance model interchange format

A common, XML-based interface between specifications of quantitative system models and programmed solutions is developed and illustrated with several examples. It is based on the PMIF (Performance Model Interchange Format), which allows queueing network models to be specified in XML and solved by calling any appropriate modelling tool, such as Qnap. The definition of PMIF specifications is generalised by considering more abstract collections of interacting nodes, using concepts compatible with the Reversed Compound Agent Theorem (RCAT). The interactions are more general in that they synchronise transitions in a pair of nodes rather than being restricted to describing traffic flows. The generalised nodes are characterised by the interactions in which they participate, together with their rates and reversed rates, which may be implicit. In this way, generalised queueing networks with negative customers and triggers can be incorporated and fixpoint models can also be handled uniformly through the use of symbolic variables.

An approach to ontology-aided performance engineering through NFR framework

In this article we intend to make an attempt to formalize the Software Performance Engineering Body of Knowledge (SPEBoK) by means of the formal semantics of an ontology written in OWL. We do not claim that our SPEBoK is complete nor the information contained correct. Rather we propose the structure of an ontological database to contain it. This structure allows the Performance Engineering issues to be related among themselves and even to other non-functional requirements with which they may interact. Our work uses the NFR Framework.

A unified approach to modelling the performance of concurrent systems

Abstract Quantitative design is crucial to ICT and it is therefore important to integrate performance modelling techniques into support environments that facilitate the correct construction of computer systems. We consider Performance Modelling Interchange Formats (PMIFs), which allow models to be specified in a uniform way and ported to a number of tools that solve them. We focus on extending the class of models describable in a PMIF that can be solved analytically – specifically, yielding a product-form solution for their equilibrium state probabilities. We use an extension of an established theorem, called the ‘reversed compound agent theorem’ (RCAT) as the basis of the analytical modelling tool into which the extended PMIF feeds models. We describe the RCAT methodology in practical terms, how it is integrated into an extended PMIF, and illustrate our methodology with three examples.

Comparison of predictive techniques in cluster-based network servers with resource allocation

Predictive algorithms play a crucial role in system management by alerting it to future events that may degrade the global performance of the system. Our paper proposes a predictive algorithm for a Web switch that manages a cluster of Web servers. Several throughput predictive techniques have been studied to balance the workload dynamically according to a predetermined quality of service for different types of users, and finally we have obtained the best that fits in our algorithm. In order to reduce the checking time, estimations are only computed in a variable slot scheduling.