I optimized a high-traffic web app by identifying bottlenecks through profiling. I improved database performance with indexing, caching (Redis), and query optimization, reducing query time by 60%. On the front end, I used code-splitting, lazy loading, and minimized re-renders, cutting page load times. API efficiency improved with batch requests and GraphQL. Server-side, I implemented load balancing and async processing with message queues, handling high concurrency efficiently. These optimizations led to a 70% faster response time and 40% cost reduction, ensuring a smoother user experience.