Weighing ACID guarantees and availability against each other

ACID compliance and availability are key criteria for choosing a Google Cloud data store, and the exam expects you to match workload requirements (transactional integrity vs. massive scale/availability) to the right product. Understanding which services offer full ACID guarantees versus eventual consistency or limited transactional scope is essential for designing correct, resilient data pipelines.

Must-know

• Cloud Spanner offers strong external consistency and full ACID transactions (including multi-row, multi-table) with horizontal scalability and high availability (up to 99.999% with multi-region configs), making it the choice when you need both ACID and global scale.
• Cloud SQL provides full ACID compliance via standard relational engines (MySQL, PostgreSQL, SQL Server) but is limited to regional availability and vertical scaling, so it's not suited for workloads needing horizontal write scale or multi-region durability.
• BigQuery supports ACID transactions at the row level within a single table via DML statements (INSERT/UPDATE/DELETE/MERGE), but it is not designed for high-frequency transactional workloads, it's optimized for analytical (OLAP) queries, not OLTP.
• Bigtable is not ACID-compliant across rows; it only guarantees atomicity for single-row mutations, making it suitable for high-throughput NoSQL use cases (time series, IoT) rather than multi-row transactional integrity.
• Firestore provides ACID transactions across multiple documents/collections and offers strong consistency plus multi-region availability, making it a good fit for mobile/web app backends needing transactional correctness at scale.
• A common exam gotcha: 'high availability' and 'ACID compliance' are independent axes, a system can be highly available but eventually consistent (e.g., Bigtable single-cluster) or strongly consistent but with lower availability guarantees than a distributed system like Spanner, so always evaluate both dimensions separately when architecting a solution.

Coverage checked against the published exam guide on Aug 11, 2026.

These are independent practice questions, written against this certification's published exam guide. They are not the certification vendor's own questions, and not the real exam.