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Quality Time: Intermittent problems

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So, what we typically call an intermittent problem is: a mysterious and undesirable behavior of a system, observed at least once, that we cannot yet manifest on demand.

Some Principles of Intermittent Problems:

• Be comforted: the cause is probably not evil spirits.
• If it happened once, it will probably happen again.
• If a bug goes away without being fixed, it probably didn’t go away for good.
• Be wary of any fix made to an intermittent bug. By definition, a fixed bug and an unfixed intermittent bug are indistinguishable over some period of time and/or input space.
• Any software state that takes a long time to occur, under normal circumstances, can also be reached instantly, by unforeseen circumstances.
• Complex and baffling behavior often has a simple underlying cause.
• Complex and baffling behavior sometimes has a complex set of causes.
• Intermittent problems often teach you something profound about your product.
• It’s easy to fall in love with a theory of a problem that is sensible, clever, wise, and just happens to be wrong.
• The key to your mystery might be resting in someone else’s common knowledge.
• An intermittent problem in the lab might be easily reproducible in the field.
• The Pentium Principle of 1994: an intermittent technical problem may pose a *sustained and expensive* public relations problem.
• The problem may be intermittent, but the risk of that problem is ever present.
• The more testability is designed into a product, the easier it is to investigate and solve intermittent problems.
• When you have eliminated the impossible, whatever remains, however improbable, could have done a lot of damage by then! So, don’t wait until you’ve fully researched an intermittent problem before you report it.
• If you ever get in trouble an intermittent problem that you could not lock down before release, you will fare a lot better if you made a faithful, thoughtful, vigorous effort to find and fix it. The journey can be the reward, you might say.

Author: James Bach full article at

http://www.satisfice.com/blog/archives/34

-Peter Tennekes