How I cut a fintech app's startup time by 40%

A fintech client's Android app was slow to start and the UI was lagging. I found memory leaks and heavy work on the main thread, fixed the startup sequence, and cut startup time by 40%.

The problem

A fintech client's Android app was slow to start and the UI was lagging. Users were complaining, and the reviews were starting to show it. The team had already tried to fix it themselves, but nothing worked.

What I found

• Memory leaks: I added LeakCanary, and on its first run it flagged several memory leaks. Objects were held in memory long after they should have been released, so the app carried dead weight every time it launched.
• A blocked main thread: I used ANR-WatchDog to find exactly where the app was freezing. Database reads, network calls and heavy setup code were all running on the main thread at startup. The app was trying to do too much before it even showed the first screen.

What I did

• Moved all heavy work off the main thread.
• Restructured the startup sequence so the app loads only what it needs to show the first screen. Everything else waits.
• Fixed the memory leaks LeakCanary found.
• Cleaned up the setup code that was running unnecessary work on every launch.

The result

App startup time dropped by 40%.

Most Android performance problems are not a mystery. They follow the same patterns: memory leaks, work on the main thread, and too much happening at startup. The hard part is knowing where to look.

Is your app slow to start? Check these

• Application.onCreate() runs before anything else. Keep only what is needed to launch.
• Main-thread work: move database reads, network calls and heavy setup to a background thread with coroutines.
• Defer what can wait: analytics, crash reporting and push notification setup can start after the first screen is visible. If you use Hilt or Dagger, don't build everything at launch.
• Use the tools: the Jetpack App Startup library controls what starts at launch and in what order, and Android Studio's startup profiler will almost always find something.