Stefano Russo

Software Reliability and Testing Time Allocation: An Architecture-Based Approach

With software systems increasingly being employed in critical contexts, assuring high reliability levels for large, complex systems can incur huge verification costs. Existing standards usually assign predefined risk levels to components in the design phase, to provide some guidelines for the verification. It is a rough-grained assignment that does not consider the costs and does not provide sufficient modeling basis to let engineers quantitatively optimize resources usage. Software reliability allocation models partially address such issues, but they usually make so many assumptions on the input parameters that their application is difficult in practice. In this paper, we try to reduce this gap, proposing a reliability and testing resources allocation model that is able to provide solutions at various levels of detail, depending upon the information the engineer has about the system. The model aims to quantitatively identify the most critical components of software architecture in order to best assign the testing resources to them. A tool for the solution of the model is also developed. The model is applied to an empirical case study, a program developed for the European Space Agency, to verify models prediction abilities and evaluate the impact of the parameter estimation errors on the prediction accuracy.

A survey of software aging and rejuvenation studies

Software aging is a phenomenon plaguing many long-running complex software systems, which exhibit performance degradation or an increasing failure rate. Several strategies based on the proactive rejuvenation of the software state have been proposed to counteract software aging and prevent failures. This survey article provides an overview of studies on Software Aging and Rejuvenation (SAR) that have appeared in major journals and conference proceedings, with respect to the statistical approaches that have been used to forecast software aging phenomena and to plan rejuvenation, the kind of systems and aging effects that have been studied, and the techniques that have been proposed to rejuvenate complex software systems. The analysis is useful to identify key results from SAR research, and it is leveraged in this article to highlight trends and open issues.

Indoor and outdoor location based services for portable wireless devices

Designing and developing location-aware portable software applications is challenging, since most location-estimation methods i) require non-standard features either in the mobile terminal or in the network infrastructure, and ii) they are specifically designed for either indoor or outdoor. Moreover, installing and tuning systems that rely on such location methods may be quite a complex operation. In this paper we propose a software architecture that makes a combined use of indoor and outdoor location-sensing technologies. On top of the architecture there is a generic API, aimed at supporting the development of hybrid (indoor/outdoor) applications at a high level of abstraction, independent of the location technology. The API is meant to support applications for which the exact position of a mobile terminal is not a primary requirement, but it suffices to identify the terminal position in a known set of zones (e.g., rooms indoor, or pre-defined outdoor areas). The software architecture is designed: i) to ensure compliance with emerging positioning standards and commercial devices, in order to leverage the interoperability with third-party developed services, and ii) to be based on low-cost and easily deployable and tunable indoor positioning infrastructures. An implementation of the architecture is described, based on Bluetooth and GPS technologies, so as to outline the major implementation issues.

Scalable Analytics for IaaS Cloud Availability

In a large Infrastructure-as-a-Service (IaaS) cloud, component failures are quite common. Such failures may lead to occasional system downtime and eventual violation of Service Level Agreements (SLAs) on the cloud service availability. The availability analysis of the underlying infrastructure is useful to the service provider to design a system capable of providing a defined SLA, as well as to evaluate the capabilities of an existing one. This paper presents a scalable, stochastic model-driven approach to quantify the availability of a large-scale IaaS cloud, where failures are typically dealt with through migration of physical machines among three pools: hot (running), warm (turned on, but not ready), and cold (turned off). Since monolithic models do not scale for large systems, we use an interacting Markov chain based approach to demonstrate the reduction in the complexity of analysis and the solution time. The three pools are modeled by interacting sub-models. Dependencies among them are resolved using fixed-point iteration, for which existence of a solution is proved. The analytic-numeric solutions obtained from the proposed approach and from the monolithic model are compared. We show that the errors introduced by interacting sub-models are insignificant and that our approach can handle very large size IaaS clouds. The simulative solution is also considered for the proposed model, and solution time of the methods are compared.

Software Aging Analysis of the Linux Operating System

Software systems running continuously for a long time tend to show degrading performance and an increasing failure occurrence rate, due to error conditions that accrue over time and eventually lead the system to failure. This phenomenon is usually referred to as \textit{Software Aging}. Several long-running mission and safety critical applications have been reported to experience catastrophic aging-related failures. Software aging sources (i.e., aging-related bugs) may be hidden in several layers of a complex software system, ranging from the Operating System (OS) to the user application level. This paper presents a software aging analysis at the Operating System level, investigating software aging sources inside the Linux kernel. Linux is increasingly being employed in critical scenarios; this analysis intends to shed light on its behaviour from the aging perspective. The study is based on an experimental campaign designed to investigate the kernel internal behaviour over long running executions. By means of a kernel tracing tool specifically developed for this study, we collected relevant parameters of several kernel subsystems. Statistical analysis of collected data allowed us to confirm the presence of aging sources in Linux and to relate the observed aging dynamics to the monitored subsystems behaviour. The analysis output allowed us to infer potential sources of aging in the kernel subsystems.

Survey On reliability in publish/subscribe services

Modern large-scale mission-critical systems demand efficient and robust multi-point data dissemination infrastructures. Since such infrastructures have to exhibit good performance when scaling up the number of interacting entities and managing large amounts of data, publish/subscribe services represent a suitable middleware solution due to their decoupling properties. However, since data are conveyed by networks where failures may occur, and since nodes may present a faulty behavior, such services also have to adopt proper mechanisms to deal with several kinds of failures and to guarantee event dissemination despite their occurrence. Although significant efforts have been made on this topic, many issues are still open. This article covers an introduction to the principles of assuring event notification even in the presence of faults, and an analysis of relevant state-of-the-art by both surveying the academic literature over the period 2000-2011 on reliable publish/subscribe services and overviewing current marketed products. Then, it presents the main challenges that are still unresolved and are worth being addressed in future research efforts.

Software Aging and Rejuvenation: Where We Are and Where We Are Going

After 16 years, a significant body of knowledge has been established in the area of Software Aging and Rejuvenation (SAR). In this paper, we survey papers about SAR that appeared in IEEE conferences and journals, identify where SAR research has been mostly focused, and highlight some aspects deserving more attention, with the aim to provoke a constructive discussion among SAR researches about where SAR has arrived and where it should be headed in the next future.

Characterizing Aging Phenomena of the Java Virtual Machine

In this work we investigate software aging phenomena inside the Java Virtual Machine (JVM). Starting from an experimental campaign on real world testbeds, this work isolates the contribution of the JVM to the overall aging trend, and identifies, through statistical methods, which workload parameters are more relevant to aging dynamics. Experimental results show that the Sun Hotpost JVM experiences software aging phenomena. A consistent memory depletion trend (up to 50 KB/min) has been observed during periods of low garbage collector activity; the Just-In-Time compiler is also responsible for a lighter, but not negligible, memory depletion trend; finally, a consistent throughput loss (up to 24 KB/min) has been observed.

Failure classification and analysis of the Java Virtual Machine

This paper presents a failure analysis of the Java Virtual Machine providing useful insights into the nature of reported failures and to improve the understanding of its dependability aspects. Failure data is extracted from publicly available bug databases, where developers and users of Java applications usually submit failures/bugs. Presented results clearly indicate that much more efforts have still to be done in order to improve the dependability of the JVM. In particular, the conducted analysis revealed that i) builtin error detection mechanism are characterized by a low coverage; ii) the JVM does not achieve the same levels of dependability across different platforms iii) developers have to pursue a tradeoff between performance and reliability. Finally, code fragments reproducing failures submitted in bug database are injected into Java Applications. Preliminary results show that often these faults could be removed changing the environment of the JVM.

Improving dependability of service oriented architectures for pervasive computing

Service oriented programming - which combines distributed object computing, component-based and Web-based concepts - has recently emerged as a promising approach to develop dynamic and heterogeneous service provision environments. Such systems are referenced in literature as service oriented architectures. Classic strategies to address dependability in distributed object computing middleware may not be straightforwardly applied to service oriented architectures (SOAs) for pervasive computing, since they operate in quite different contexts compared to traditional DOC middleware. In this paper, our focus is on dependability issues of SOAs. In particular, we identify dependability requirements of such systems during their life cycle showing how these requirements may change depending on the time phase (discovery, lookup, setup, delivery). We also explore the suitability of Jini technology as an enabling infrastructure to improve availability and reliability, describing both the benefits and drawbacks of a Jini-based solution in the context of a case study application, namely PRINCEPS.