Frequent releases reduce risk



Let’s think about what we mean by risk.

What is risk?


Risk = Likelihood of failure x Worst case impact of failure





Large, infrequent releases are riskier


Small, frequent releases reduce the likelihood of a failure





One Comment

  1. Hi Chris

    This is a great introduction to the counter-intuitive truth that smaller, more frequent changes reduce risk.

    You are entirely right that smaller changes reduce the probability of a failure, as splitting a large experiment into smaller independent experiments reduces variation in outcomes i.e. by dividing up the risk associated with a release into smaller releases, we can more accurately estimate where failure probability truly resides and act upon that new information.

    However, saying “there is no way to reduce the impact of a failure” is incorrect – smaller, frequent changesets can also reduce the cost of failure as well as the probability of failure. I outline why in my Release Testing Is Risk Management Theatre talk (see 35:17 of The cost of a failure is also two-dimensional – the economic impact of failure and the duration of failure. The former is hard to influence let alone control due to external market forces, but duration is easy to control due to Little's Law – less WIP means a lower lead time, which means a lower failure duration, which means a lower cost.

    That is why production defect fixes always go out in small changesets – to minimise the opportunity cost of the current defect, *and* to reduce the probability of causing further defects with the fix.




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