Subscribe in a readerI recently took my first serious look at Traceview, and it occurred to me, first, that there are probably a few other Android developers who haven’t used it and, second, that this is an opportunity to lecture sternly on one of my favorite subjects: performance improvement and profiling. This is perhaps a little bit Android-101; If you already know all about Traceview, you can stop here and go back to coding.
Making Apps Fast
Here’s a belief that I think I share with most experienced developers: For any app that is even moderately complex, you’re not smart enough to predict what the slow parts are going to be, because nobody is smart enough to predict where software bottlenecks will turn up.
So the smart way to write a fast app is to build it in the simplest way that could possibly work, avoiding egregiously-stupid thing like order-N-squared algorithms and doing I/O on the Android UI thread. Who knows, it might be fast enough, and then you’re done!
If it isn’t fast enough, don’t guess why. Measure it and find out, using a profiler. Actually I’ve been known to do this, when backed into a corner, using things like System.err.println("Entered at" + System.currentTimeMillis()); Fortunately, Android comes with a reasonably decent profiler, so you don’t have to get ugly like that.
Case Study: LifeSaver 2
I have this little utility in Android Market called LifeSaver 2, the details are on my personal blog. At one point, it reads the SMS and phone-call logs out of the system and persists them in a JSON text file on the SD card. Since this is kind of slow, it shows a nice dynamic progress bar. It occurred to me to wonder why it was kind of slow to write a few hundred records into a text file on a device that, after all, has a gigahertz processor.
Somebody who foolishly disregarded my advice above might assume that the slowdown had to be due to the ContentProvider Cursor machinery reading the system logs, or failing that, the overhead of writing to the SD card. A wiser person would instrument the code and find out. Let’s do that.
