PromptTech/docs/reports/PERFORMANCE_FIXES.md

Performance Fixes Applied - January 11, 2026

Issues Identified

1. Infinite Loop in CartContext (CRITICAL)

Problem: The frontend was making hundreds of /api/cart requests per second, causing severe performance degradation.

Root Cause: In frontend/src/context/CartContext.js, the useEffect hook had fetchCart in its dependency array, but fetchCart was recreated on every render, causing an infinite loop.

Solution:

• Wrapped fetchCart function with useCallback hook to memoize it with proper dependencies
• This ensures the function is only recreated when isAuthenticated or token changes

2. Missing Product Images in Cart Query

Problem: The backend cart endpoint wasn't preloading product images, causing N+1 query issues.

Solution:

• Updated /api/cart endpoint in backend/server.py to use selectinload(CartItem.product).selectinload(Product.images)
• This loads all product images in a single query instead of making separate queries for each product

3. Deprecated FastAPI Event Handlers

Problem: Backend was using deprecated @app.on_event("startup") and @app.on_event("shutdown") decorators, causing deprecation warnings.

Solution:

• Migrated to modern lifespan context manager pattern
• Created @asynccontextmanager function that handles startup and shutdown
• Passed lifespan to FastAPI app initialization

Files Modified

Frontend

• frontend/src/context/CartContext.js
  • Added useCallback import
  • Wrapped fetchCart with useCallback hook
  • Simplified useEffect dependencies

Backend

• backend/server.py
  • Added asynccontextmanager import
  • Created lifespan function for app lifecycle management
  • Updated cart query to preload product images
  • Removed deprecated @app.on_event decorators
  • Moved logging configuration before app creation

Performance Improvements

Before Fixes

• Cart Requests: 100+ requests per second (infinite loop)
• Backend Logs: Flooded with cart requests
• Page Load Time: Extremely slow, site unresponsive
• Database Queries: N+1 issues with product images

After Fixes

• Cart Requests: 1-2 requests on page load/navigation (expected behavior)
• Backend Logs: Clean, only showing necessary requests
• Page Load Time: Fast and responsive
• Database Queries: Optimized with eager loading

Testing Performed

1. ✅ Frontend build completed successfully
2. ✅ Backend server starts without deprecation warnings
3. ✅ Cart requests reduced from hundreds to 1-2 per page load
4. ✅ Both servers running and communicating properly
5. ✅ No infinite loops detected in monitoring

Additional Optimizations Applied

• Product images are now preloaded in all product queries using selectinload(Product.images)
• Cart endpoint now loads product images in a single query
• FastAPI app uses modern lifespan events for better async handling

Verification Steps

To verify the fixes are working:

1. Check Backend Logs:

   tail -f /proc/$(pgrep -f "python server.py")/fd/1
   

   Should see only occasional cart requests, not continuous spam

2. Monitor Cart Requests:

   watch -n 1 'tail -50 /proc/$(pgrep -f "python server.py")/fd/1 | grep "/api/cart" | wc -l'
   

   Count should remain low (0-2), not increasing rapidly

3. Frontend Console:

   • Open browser DevTools → Network tab
   • Filter by "cart"
   • Should see only 1-2 requests when navigating pages

Recommended Next Steps

1. Production Build: Test with production build for maximum performance
2. Caching: Consider adding Redis caching for frequently accessed data
3. Database Indexing: Verify all foreign keys and frequently queried columns have indexes
4. Load Testing: Perform load testing to ensure system handles concurrent users

References

• React useCallback Hook
• FastAPI Lifespan Events
• SQLAlchemy Eager Loading