Chapter 10. Performance
One of us had a computer science lecturer who began one class by saying, “You should never, ever, ever try to optimize your code. But when you do optimize your code, here’s how you should do it.”
Premature optimization, as Donald Knuth once said, is the root of all evil. It would be best if you first made your code work. Then make your code maintainable. And only then—if you have a problem—should you worry about making your code fast. Slow code that works will always beat fast code that doesn’t.
That said, there are times when performance can be a significant issue. If your application takes more than a few seconds to load, you may lose users who will never return. Slow can become unusable on low-powered devices. This chapter will take what we like to call an essentialist approach to performance. You should rarely tune your code, but when you do, you should tune the right code. We look at various tools and techniques that will allow you to track down and measure performance bottlenecks so that if you do need to apply performance fixes, they will be in the right place, and you will have some way of measuring the difference they make.
All performance fixes come at a cost. If you make your client code faster, it might cost more memory or more server time. You will almost always have to add more code and more complexity.
The recipes in this chapter follow the order in which we would suggest you approach performance problems. We begin with high-level measurements ...
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