You need to design a globally distributed system that can handle millions of read and write operations per second, and you also need strong consistency. Which GCP database service is suitable for this?

Cloud Spanner is the correct choice because it is a globally distributed, strongly consistent, and horizontally scalable relational database service. It is designed for high-transaction workloads and offers unlimited scalability with transactional consistency, making it ideal for millions of reads and writes per second across global regions. Cloud Bigtable is a NoSQL wide-column store, excellent for analytical workloads and high throughput, but it does not offer strong consistency across global regions in the same way Spanner does for transactional data. Cloud Firestore and Cloud Datastore are NoSQL document databases, suitable for mobile and web applications, but they are not designed for the extreme scale and strong global consistency of transactional workloads that Spanner provides. Cloud SQL is a regional relational database service, offering strong consistency within a region, but it lacks the global distribution and horizontal scalability required for millions of operations per second across the globe.