Hacker News Reader

Comment by codethief | Hacker News Reader

That same Wikipedia page also states:

> There is a rare alternative definition for the bus factor, namely: the number of people who are indispensable for the project.[2] In other words, it is the minimum number of people who are a single point of failure. If using this definition, then a high bus factor is considered a bad thing (since the loss of any person included destroys the project), and zero is considered the ideal bus factor.

View on HN

That's true, and in fact I'd prefer it if that was the mainstream definition. Given that it isn't, there may be better replacements for the headline, along the lines of "maintainable by one person".

That alternative definition seems less useful, because quite often there are two people who can individually maintain a project, and in that scenario the bus factor is 0 even though there is a risk that both of them will leave the project.

These two measures are probably ended up conflated because they're two ends of the same metric. "How many people need to be hit by a bus", which for simplicity I'll call the "bus factor", measures unusually high levels of resilience, but it doesn't go lower than 0 so it can't measure how fragile a fragile project is. "How many people are indispensable", which for simplicity I'll call "inverse bus factor", measures unusually low levels of resilience, but it doesn't meaningfully go below 0 so it can't measure how resilient a resilient project is. The thing is, a bus factor >= 2 necessarily indicates an inverse bus factor = 0 (if you need to hit two people with buses to take the project down then nobody is indispensable) while an inverse bus factor >= 1 necessarily indicates a bus factor = 1 (if anyone exists that is indispensable, then hitting exactly them with a bus takes the project down). In other words, bus factor = 1 and inverse bus factor = 1 could be viewed as being the same point in the middle of a line on which all projects fall, same way zero is the center between positive and negative numbers.

>same way zero is the center between positive and negative numbers.

More like the way 1 is halfway between 0 and infinity. I think you're nearly there, and the answer to the dilemma is that fractional bus factors are possible. A bus factor of 0.5 means there are two indispensable people.

We might disambiguate the two conflicting definitions by renaming them with suitably inverse words - "redundancy" and "fragility" perhaps (though I suspect the latter is unneccesary). This is basically the terminology we use for RAID arrays and servers.

> 1 is halfway between 0 and infinity

That would be true if "infinity" meant 2.

I agree that fractional bus factors would be better if we could completely redefine the metric, yes - they do a much better job conveying the fact that doubling your bus factor does way more than halve your likelihood of actually getting stopped by losing a contributor. I was stuck reinterpreting existing definitions when I wrote that post, though, so /shrug

Reply on news.ycombinator.com