Tuning Performance and Process

Related link: http://www.artima.com/intv/tunable.html

Artima.com has published Part VI of an interview with Martin Fowler in which he discusses balancing maintainability and efficiency, creating tunable software, the role of patterns, and the Agile Software Manifesto.

Here's an excerpt:

So you could make a performance optimization in one VM, and then bring in Hotspot, and it will actually slow Hotspot down. You've got to be very wary of that. Object pooling is a good example. A lot of people are very enamored with object pooling, yet half the time people are not measuring to that to find out whether object pooling is any good. Object pooling was very important in the early days of Java, because garbage collection wasn't terribly good. When you've got generational garbage collection, object pooling becomes a lot less effective, because short-lived objects can be collected very cheaply. It's the long-lived objects, such as ones you might pool, that are expensive to garbage collect.

So the rules keep changing. That's why you've got to be very careful to profile. If you think you can predict from the source code what the machine is doing, you've got no chance. When you're in a world of optimizing compilers and VMs, you have to profile, because the compilers and VMs are doing things that you can't even imagine. So don't predict, just measure.