Software defects and their impact on system 118 availability

In recent years, software defects have become the dominant cause of customer outage, and improvements in software relia-bility and quality have not kept pace with those of hardware. Yet, software defects are not well enough understood to provide a clear methodology for avoiding or recovering from them. To gain the necessary insight, we study defects reported between 1986 and 1889 from a on a high-end operating system product. We compare a typical defect (regular) to one that corrupts a program’s memory (overlay) given that overlays are considered by field services to be particularly hard to find and fix. This paper: g Shows that the impact of an overlay defect is, on aver-age, much higher than that of a regular defect. g Defines error types to classify the programming mis-takes that cause software to fail. g Defines error trigger to classify the events that cause latent errors in programs to surface. The error trigger dis-tribution weights events and environments that are prob-ably inadequately tested. g Shows that boundary conditions and allocation management are the major causes of overlay defects, not timing. (bu Shows that most overlays are small and not too far from their intended destination. Further analysis are provided on defects in fixes to other defects, symptoms, and an assessment of their impact. These results provide a base line understanding useful to designers and developers. The data will also help develop realistic fault models for use in fault-injection experiments. 1