Pointer arithmetic and dynamic HTML generation FTW–at 2 AM

time to read 2 min | 388 words

I just finished writing the following code, the time is 2 AM local time, and I am chasing a conceptual issue deep in the guts of Voron (RavenDB’s internal storage system).


By any measure of the word, this code should frighten anyone who reads it. For what I think can we can all safely assume are self evident reasons.

So why am I so very happy about this kind of code? Because the output of this code is this:


This is pretty trivial tree view for internal data structures inside of Voron.

But the point here isn’t that this code is probably going to be a no-go zone by tomorrow morning. This is code explicitly designed for that. In fact, the calling method for this is:


So this is a piece of code that we are trying very hard to ensure that will never be called unless we are actively requesting it in a debug session. In other words, this isn’t production code. It is scaffolding code. The code that you’ll call when you lost your way, and can no longer figure out what is going on using the standard tools.

This kind of visualization is cheap & dirty trick, but it means that instead of having to reason about this kind of thing, I can immediately see what is going on.

For that matter, if you look closely at the visualization, you might be able to see the bug in question. It is pretty obvious, once we are able to look at the entire data set in one go. The more complex the algorithm, the harder it is to conceptualize it. But in most cases, if we could but look at the data in a way that would make sense to us, we will be able to immediately see what we did wrong.