Your company is developing a new global transactional application that must be ACID-compliant and have 99.999% availability. You are responsible for selecting the appropriate Google Cloud database to serve as a datastore for this new application. What should you do?

Cloud Spanner is the only Google Cloud database that satisfies all the stated requirements. It is designed as a global, horizontally scalable, and strongly consistent relational database. It provides full ACID compliance for transactions with external consistency, which is critical for transactional applications. Furthermore, a multi-region Cloud Spanner configuration offers a 99.999% availability Service Level Agreement (SLA), meeting the stringent uptime requirement. Its ability to handle global traffic with low latency and strong consistency makes it the most suitable choice.

A. Use Firestore. Firestore is a NoSQL document database. While it offers a 99.999% SLA in multi-region mode and supports transactions, Cloud Spanner's relational structure and global external consistency are better suited for this use case.
C. Use Cloud SQL. Cloud SQL is a regional service and its high availability configuration only provides a 99.95% SLA, which falls short of the 99.999% requirement. It is not designed for global scale.
D. Use Bigtable. Bigtable is a NoSQL wide-column store that does not support multi-row ACID transactions, a fundamental requirement for the described transactional application. ---

1. Cloud Spanner Documentation - "What is Cloud Spanner?": "Spanner is a distributed SQL database management and storage service. [...] It is a fully managed service that provides relational semantics, ACID transactions, schemas, SQL, and automatic, synchronous replication for high availability."

Source: Google Cloud Documentation, "What is Cloud Spanner?".

2. Cloud Spanner Service Level Agreement (SLA): "For a multi-region instance configuration, the Monthly Uptime Percentage is ≥99.999%."

Source: Google Cloud Legal, "Cloud Spanner Service Level Agreement (SLA)".

3. Cloud SQL Service Level Agreement (SLA): "For a High Availability configuration of a Cloud SQL instance... the Monthly Uptime Percentage is ≥99.95%."

Source: Google Cloud Legal, "Cloud SQL Service Level Agreement (SLA)".

4. Cloud Bigtable Documentation - "About Cloud Bigtable": "Bigtable is not a relational database and it does not support SQL queries or multi-row transactions."

Source: Google Cloud Documentation, "About Cloud Bigtable".

5. Google Cloud Documentation - "Choosing a storage option": This guide positions Cloud Spanner for "Global-scale, strongly consistent, relational database service" and highlights its use for "high availability with strong consistency."

Source: Google Cloud Documentation, "Choosing a storage option".