The phenomenon of software aging refers to the accumulation of errors during the execution of the software which eventually results in it's crash/hang failure. A gradual performance degradation may also accompany software aging. Pro-active fault management techniques such as "Software rejuvenation" [9] may be used to counteract aging if it exists. In this paper, we propose a methodology for detection and estimation of aging in the UNIX operating system. First, we present the design and implementation of an SNMP based, distributed monitoring tool used to collect operating system resource usage and system activity data at regular intervals, from networked UNIX workstations. Statistical trend detection techniques are applied to this data to detect/validate the existence of aging. For quantifying the effect of aging in operating system resources, we propose a metric "Estimated time to exhaustion" which is calculated using well known slope estimation techniques. Although the distributed data collection tool is specific to UNIX, the statistical techniques can be used for detection and estimation of aging in other software as well.

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Preventive maintenance of operational software systems, a novel technique for software fault tolerance, is used specifically to counteract the phenomenon of software "aging." However, it incurs some overhead. The necessity to do preventive maintenance, not only in general purpose software systems of mass use, but also in safety-critical and highly available systems, clearly indicates the need to follow an analysis based approach to determine the optimal times to perform preventive maintenance.In this paper, we present an analytical model of a software system which serves transactions. Due to aging, not only the service rate of the software decreases with time, but also the software itself experiences crash/hang failures which result in its unavailability. Two policies for preventive maintenance are modeled and expressions for resulting steady state availability, probability that an arriving transaction is lost and an upper bound on the expected response time of a transition are derived. Numerical examples are presented to illustrate the applicability of the models.

Objective-Dietary intake of polyunsaturated n-3 fatty acids has been associated with a reduced incidence of adverse cardiovascular events. The protective mechanisms involved are not fully understood, but may include anti-inflammatory factors. We sought to investigate the relationship between n-3 fatty acid levels in erythrocyte membranes and markers of systemic inflammation in 992 individuals with stable coronary artery disease.Methods-Cross-sectional associations of C-reactive protein (CRP) and Interleukin-6 (Il-6) with docosahexaenoic acid (DHA) and eicosapentaenoic acid (EHA) were evaluated in multivariable linear regression models adjusted for demographics, cardiovascular risk factors, medication use, exercise capacity, body mass index, and waist-to-hip ratio.Results-After multivariable adjustment, n-3 fatty acid levels (DHA + EPA) were inversely associated with CRP and IL-6. The inverse association of n-3 fatty acids with CRP and IL-6 was not modified by demographics, body-mass index, smoking, LDL-cholesterol, or statin use (p values for interaction > 0.1) Conclusions-In patients with stable coronary artery disease, an independent and inverse association exists between n-3 fatty acid levels and inflammatory biomarkers. These findings suggest that inhibition of systemic inflammation may be a mechanism by which n-3 fatty acids prevent recurrent cardiovascular events.