What can a snowblower tell us about software?

If you’re in the north eastern United States, you’re probably thinking about snow right now. And if you’re responsible for clearing the snow from your drive or walkways you might also be all too familiar with time behind a snow blower. For years I hand shoveled my walkways, but when we moved to this new house they were simply far too long for that.

It takes me about an hour to do all the clearing I am responsible for, so that’s a lot of time to think, which isn’t necessarily a bad thing. This particular snow is the deepest we’ve had yet. My snowblower has three forward speeds on it and presumably you use a slower speed when you have more snow to clear. The slower speed allows the auger to clear the snow before it gets all backed up.

So, as I was clearing the drive, I noticed something. Even at the lowest speed there was enough snow that some of it was being simply pushed out of the way by the blower. That meant that I’d have to do clean-up passes just to get that little bit of snow that the blower wouldn’t get on the first pass. And that got me to thinking. What if I just went faster? After all, if I was going to have to make a second pass anyway, who cares if it’s a tiny bit of snow or a little bit more?

And that got me to thinking about software. One approach might be to take it slow and carefully, but if you’re going to create bugs anyway, then perhaps going that slow isn’t the right answer. You’re still going to need the clean-up pass so you might as well let it happen and just clean up a bit more, right?

That sort of makes sense, if you think a second pass over the code is as effective as a second pass with the snow blower. In terms of dealing with snow, the blower is relentless. If it goes over the same ground twice it will do so with the same vigor as before. On the other hand, testing is imperfect. Each pass only gets about 35-50% of the defects (tending towards the 35% end). It isn’t like a snow blower at all. If you push aside a relatively big pile of snow with the a snow blower, it’ll get it on the second go. If you create a big pile of bugs in the code on your first go, a round of testing will likely reduce the pile by less than half. Then you need another pass, and another just to get to an industry average 85%.

There’s one other thing about going too fast that I learned with my snow blower. Some times you get a catastrophic failure. In my case, going too fast with the snow blower broke the shear pin on the auger. It’s a safety feature to prevent damage to the engine but it does make it impossible to keep using it to move snow. And software is a bit like that too. Go too fast and you may introduce a major issue that you’ll spend a whole lot of time cleaning up. It is not all about speed.

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