Interview Tales I – The Bathtub Curve

I’ve been to a few interviews recently, most of which have been bizarrely enjoyable affairs where I’ve had the opportunity to discover much about how things work elsewhere. However, I recently went to an interview for an organisation which has suffered some pretty high profile  system failures recently which I timidly pointed out; hoping not to offend. The response was, in my view, both arrogant and ignorant – perhaps I did offend…

I was informed; rather snootily, that this incident was a one-off having occurred just once in the 15+ year experience of the interviewer and couldn’t happen again. Humm… I raised the point having worked on a number of technology refresh projects and being familiar with the Bathtub Curve (shown below – image courtesy of Engineering Statistics Handbook).

bathtub2

What this shows is how during the early life of a system failures are common (new build, many defects etc.). Things then settle down to a fairly stable; but persistent, level of failures for the main life of the system before things start to wear out and the number of incidents increases again – ultimately becoming catastrophic.

This is kind of obvious for mechanical devices (cars and the like) but perhaps not so much for software. I still have an old ’80s book on software engineering which states that “software doesn’t decay!”. However, as pointed out previously, software is subject to change from a variety of sources, change brings decay and decay increases failure rates. Bathtub curve applies.

Now the reason I mentioned the failure in the first place was because the press I had read pointed towards a combination of ageing systems and complex integration solutions holding things together. I was therefore expecting an answer along the lines of “yes, we need to work to make sure it doesn’t happen again” and “that’s why we’re hiring because we need to address these issues”. This could then lead on and I could relate my experiences on refresh projects, hurrah!… It didn’t work out like that even though it did seem that the raison d’être behind the role itself was precisely because they didn’t have a good enough grip on the existing overall IT environment.

It’s entirely possible that the interviewer is correct (or gets lucky). However, given there has actually been a couple of such incidents at the same organisation recently – two individually unique issues of course – I’m kind of suspicious that what they’re actually seeing is the start of the ramp up in incidents that is typified by the Bathtub Curve. Time will tell.

I wasn’t offered the job, but then again, I didn’t want it either so I think we’re happy going our separate ways.