Initial commit - PromptTech

docs/reports/PERFORMANCE_FIXES.md

@@ -0,0 +1,119 @@
+# 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**:
+
+   ```bash
+   tail -f /proc/$(pgrep -f "python server.py")/fd/1
+   ```
+
+   Should see only occasional cart requests, not continuous spam
+
+2. **Monitor Cart Requests**:
+
+   ```bash
+   watch -n 1 'tail -50 /proc/$(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](https://react.dev/reference/react/useCallback)
+- [FastAPI Lifespan Events](https://fastapi.tiangolo.com/advanced/events/)
+- [SQLAlchemy Eager Loading](https://docs.sqlalchemy.org/en/20/orm/queryguide/relationships.html)