Getting Your Priorities Straight. Scalability and Performance are the Least of your Worries.

Back in my Contractor days, I would occasionally take a job bringing a bunch of C++ guys up to speed in C# and ASP.NET. Invariably, I would have to break them of old habits that they had picked up back in the days when memory and hard drive space were expensive, and applications had to run in real time. Most of these little battles were quickly won, so flat files were replaced by relational databases, bit masks gave way to association tables, and data access code was pulled out into its own layer.

But one thing never went over well. Performance. Speed is largely irrelevant for a web application. Sure, it's important that your thing run fast, but there are a half dozen other things that are more important for a big web application. This is difficult to hear if your major skill is writing inline assembly for critical routines, but it's still the truth. Readability, Debugability, Maintainability and Development Pace are much more important than raw speed.

To deal with this rift, I would ask the developers to list out the most important qualities of a piece of software, and to rank those qualities in order. I've hinted at my answer above, but I'll take a few minutes to list them out below. Everything you see in the list is important, but the things toward the top are relatively more important than the ones towards the bottom. For what it's worth, we're talking about Web Applications here, so clearly this list does not apply to Game Development or even Windows Apps. Here goes:

Readability

In my mind, this is the single most important quality of a piece of software. Assuming your thing is going to be around for a while, you're always going to need to return to a given piece of code from time to time and make modifications. The faster you can read and understand what's going on, the sooner you will be able to start making modifications and adding new functionality. Better still, if you can quickly figure out what the code is doing and why, you'll be less likely to break anything in the process.

Debugability

Your code is going to break. Often. That's how it goes, so you'd better structure things so that it's easy to step through and figure out what's going on. That means declaring variables instead of stringing together 17 object methods on a single line. That means using real IF/THEN/ELSE blocks with squiggly brackets instead of inlined immediate if's. And it means thinking twice before committing to some automagically generated database framework that sniffs out all your column names, writes its own SQL, and keeps your data in ArrayLists of ArrayLists.

Keep your design simple enough that any exception will drop you into the debugger looking at a single line of code that does a single thing. Even if it turns out it's doing that single thing wrong, at least you'll be able to find and fix it.

Maintainability

Over time, new features are going to get added and old features are going to get dropped. Some of those new features will be stupid ones, with dorky business logic that rubs the fur the wrong way in your elegantly designed class structure. You want to be able to make those changes quickly, without breaking anything else. This means you need unit testing. You'll also want to refactor large sections of your backend to work in ways you had never anticipated, and you'll need to propagate those changes all the way out to the client code. For that, you'll need even more unit tests (and some good tools), but also you'll need an architecture that doesn't fall apart when you rip chunks out of it.

Development Pace

Modern applications are big and complicated. It doesn't matter how nicely written your thing is or how many simultaneous users it can support if you never manage to get it out the door. If you want to get your application shipped, you're going to need to put out a ton of code in a hurry. That means you're going to need the best tools available, and the most productive environment that you can find.

Keeping the above points in mind, you're going to want a development framework of some description. Here at Expat, we've rolled our own specifically to keep us fast without sacrificing Readability, Debugability, or Maintainability. I'd recommend doing the same, but there are any number of 3rd party frameworks out there that might fit the bill. Just make sure you keep those three qualities in mind when you are evaluating any new framework.

Scalability

At some point, your thing is going to get popular. Actually, chances are it won't, but you shouldn't architect your thing to preclude the possibility that people might start using it in the Millions. So how do you pull that off without undoing all those Important Things further up this list? Simple. Just be aware that one day you might need the ability to add more database and web servers to the mix. Add a few little abstractions such as a Database Connection Factory, and a Session wrapper that you can replace someday with something BEEFY. For now, they don't have to do anything fancier than wrapping the existing stuff in whatever framework you're using. But if you're diligent in using these wherever you would normally use the framework components, you might end up saving yourself a lot of headache down the road.

For the most part though, don't worry too much about scalability. Having a million people that want to use your thing on a single day is a good thing. If you've done a little homework, you'll work things out when the time comes.

Performance

Computers are fast. Seriously, computers are faster than you think. If you try to imagine which piece of your application is slow, you're probably wrong. I once worked with a developer who spent the better part of 6 months hand optimizing an algorithm to do fast fuzzy string comparisons. It turned out that the server doing the text processing was only spending about 10% of its time actually processing text (even with a simplified, non-optimized algorithm), and 90% of its time battling database locks to get the results put away. He could have figured this out in one day with a profiler, and then spent a few hours tweaking database indices and optimizing queries. Instead, he spent half a year solving the wrong problem.

So yeah, keep a profiler handy, and if you see something that is obviously taking a lot of extra time, go ahead and fix it. But don't spend too much time sweating performance issues. At least, wait until they present themselves as issues before you start sweating them!

Life imitates Rant...

As I write this, Blogabond (one of my diversions from real work) is starting to show its first signs of scaling pain. Every once in a while, a misbehaved crawler will swing by and hit it 500 times in a second, causing SQL Server to time out on a specific long-running query. This is a good thing in my mind, as it gives me a chance to tackle a potential bottleneck before it starts affecting real users.

Still, Blogabond has been up and running for almost two years now, and it is only now that I'm having to think about performance at all. Those other qualities though: Readability, Debugability, Maintainability, Development Pace. I'm seeing benefits from them every day.

Discuss on hacker news