Human Readability of Log Files and Voodoo Operations

Human factors

Above all else, log files are human-readable. That means they constitute a human-computer interface and should be examined in terms of human factors. This might sound trivial, even laughable, but in a stressful situation, such as a Severity 1 incident, human misinterpretation of status information can prolong or aggravate the problem. Operators for the Three Mile Island reactor misinterpreted the meaning of coolant pressure and temperature values, leading them to take exactly the wrong action at every turn (see Inviting Disaster [Chi01] ). Although most of our systems will not vent radioactive steam when they break, they will expel our money and our reputation.

Therefore, we should ensure that log files convey clear, accurate, and actionable information to the humans who read them. If log files are a human interface, then they should also be written such that humans can recognize and interpret them as rapidly as possible. The format should be as readable as possible. Formats that break columns and create a ragged left-to-right scanning pattern are not human-readable.