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Abstract or Table of Contents
Recent studies, and a large body of anecdotal evidence, suggest that upgrades are unreliable and often end in failure, causing downtime and data-loss. While this is sometimes due to software defects in the new version, most upgradefailures are the result of faults in the upgrade procedure, such as broken dependencies. In this paper, we present data on upgrade failures from three independent sources — a user study, a survey and a field study — and, through statistical cluster analysis, we construct a novel fault model for upgrades in distributed systems. We identify four distinct types of faults: (1) simple configuration errors (e.g., typos); (2) semantic configuration errors (e.g., misunderstood effects of parameters); (3) broken environmental dependencies (e.g., incorrect libraries, port conflicts); and (4) complex procedural errors. We estimate that, on average, Type 1 faults occur in 15.2 % of upgrades, and Type 4 faults occur in 16.8 % of upgrades.