# 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)
