PHP/MySQL Code Optimization and Synchronization

Find why it times out when saving around 300 spare-part lines.
Optimize the PHP/MySQL code so loading and saving takes less than 5 seconds.
Add proper MySQL transactions so the operation is all-or-nothing:
Everything saves → COMMIT
Anything fails/interruption happens → ROLLBACK
Make sure Work Order and inventory quantities always stay synchronized.
Test it on their staging codebase/database, including forced interruptions and load testing.
Provide a changelog explaining:
What you changed
Why you changed it
Any PHP/MySQL configuration changes needed for deployment.
After testing, give them the verified patch so they can deploy it to production.