Mobile App Performance: Optimizing for 100K+ Users

The Challenge

We built a marketplace mobile app (iOS and Android) that connects service providers with customers. As the user base grew to 100,000+ active users, we started experiencing performance issues: slow load times, laggy scrolling, crashes on older devices, and high battery consumption.

Performance Optimizations

1. Image Optimization

Images were the biggest performance bottleneck. We implemented:

• Lazy loading for images below the fold
• Multiple image sizes served based on device pixel density
• WebP format with fallback to JPEG
• Image caching with 7-day expiration
• Progressive image loading for better perceived performance

Result: 70% reduction in image load time and 40% reduction in data usage.

2. Code Splitting & Bundle Optimization

We restructured the React Native app to use code splitting:

• Route-based code splitting — only load code for current screen
• Lazy loading of heavy libraries (maps, charts)
• Tree shaking to remove unused code
• Bundle size reduced from 12MB to 6MB

3. State Management Optimization

We migrated from Redux to Zustand for simpler state management and better performance:

• Reduced boilerplate code by 60%
• Faster state updates and re-renders
• Better memory management

4. API Optimization

Backend API improvements:

• GraphQL with field-level selection to reduce payload size
• Response caching for frequently accessed data
• Pagination for large lists (20 items per page)
• Request batching to reduce network calls

5. Native Performance

For critical performance paths, we used native modules:

• Native image processing for filters and effects
• Native animations for smooth 60fps scrolling
• Background task optimization to reduce battery drain

Results

Key Takeaways

• Performance optimization is an ongoing process, not a one-time task
• Measure first — use profiling tools to identify real bottlenecks
• Optimize for the lowest common denominator (older devices)
• User experience matters more than perfect code architecture
• Regular performance audits prevent regression