Cloud Spanner: ACE Exam Study Guide (2026)
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1. Core Overview
- Database Type: Fully managed, enterprise-grade relational database (RDBMS) with global scale.
- Key Features: Horizontal scalability, strong global consistency, and high availability (up to 99.999% SLA).
- Language: Supports Standard SQL (Google Standard SQL) and PostgreSQL-dialect.
2. When to Choose Cloud Spanner (Exam Scenarios)
- Massive Scale: Your relational database exceeds Cloud SQL storage limits (typically > 64 TB) or requires tens of thousands of reads/writes per second.
- Horizontal Scaling: You need a relational database that can scale horizontally (by adding more nodes/PUs) for both reads and writes.
- Global Geography: You need a globally distributed database with strong consistency across regions (e.g., global financial ledger, worldwide inventory system).
- Graph and Relational: With Spanner Graph, you can now store and query graph data alongside relational data in the same database using the ISO GQL standard.
3. Cloud Spanner vs. Cloud SQL vs. AlloyDB
The ACE exam frequently tests your ability to choose between these two services.
Cloud SQL vs AlloyDB vs Cloud Spanner (ACE Summary)
| Feature | Cloud SQL | AlloyDB | Cloud Spanner |
|---|---|---|---|
| Scope | Regional | Regional | Global / Multi‑regional |
| Scaling | Vertical (downtime) | Horizontal read scaling (read pools) | Horizontal read + write scaling |
| Performance | Standard | Much faster than Cloud SQL | Highest, globally consistent |
| Compatibility | MySQL / PostgreSQL / SQL Server | PostgreSQL‑compatible | Spanner SQL |
| Availability | HA optional (regional) | HA with primary + read pools | Built‑in global HA |
| Storage | Limited | High-performance, auto‑scaling | Virtually unlimited |
| Best For | Typical web apps, standard DB workloads | High‑performance transactional apps | Massive, global, mission‑critical systems |
4. Architecture and Compute
- Processing Units (PUs) and Nodes: Compute capacity is measured in PUs or nodes. 1 node = 1000 PUs.
- Scaling and Storage Limits (2026 Standards):
- Zero Downtime: Scaling nodes/PUs up or down is instantaneous and happens while the database is serving traffic.
- Storage Limit: Each 1,000 PUs (1 node) now supports up to 10 TB of storage in modern configurations. If your database grows beyond this, you MUST add more nodes even if CPU usage is low.
- Interleaved Tables: A unique Spanner feature where a child table’s rows are physically stored with the parent table’s rows. This drastically improves performance for related data joins by ensuring data is co-located on the same split.
- High Availability (SLA):
- Regional: 99.99% availability.
- Multi-regional: 99.999% availability (the famous five nines).
5. IAM and Security
- Access Control: IAM roles can be granted at the project, instance, or database level.
- Common Roles:
roles/spanner.admin: Full control of all Spanner resources.roles/spanner.databaseAdmin: Manage databases and schema, but cannot create/delete the Spanner instance itself.roles/spanner.databaseReader: Read data and schema.roles/spanner.viewer: View instance and database metadata (read-only).
- Security Features: Integrates with Cloud Audit Logs and supports CMEK (Customer-Managed Encryption Keys).
6. Backups and Recovery
- Point-in-Time Recovery (PITR): Allows you to read data from a specific microsecond in the past. The maximum retention period for PITR is 7 days.
- Backups: You can take on-demand backups of your database. These backups are retained for up to 1 year and are stored in the same geographic location as the database instance.
- Export/Import: Uses Dataflow to move data between Spanner and Cloud Storage (Avro or CSV formats).
7. Interacting with Cloud Spanner (CLI)
For the ACE exam, know the gcloud spanner command group:
gcloud spanner instances list: List all instances in a project.gcloud spanner databases create [DB_NAME] --instance=[INSTANCE_NAME]: Create a new database.gcloud spanner instances update [INSTANCE_NAME] --nodes=[COUNT]: Scale an instance horizontally.