A logistics company is building a new fleet-management backend on Google Cloud. The application must store structured shipment records with a well-defined relational schema, support ACID transactions across multiple tables, and serve a moderate but steady workload from a single region. The engineering team wants a fully managed database and expects data to grow to a few hundred gigabytes, with no requirement for global distribution or horizontal write scaling beyond a single primary. Which storage service best meets these requirements at the lowest operational and licensing overhead?