Cloud SQL vs Cloud Spanner: Key Differences and When to Use Each

Cloud SQL is a managed relational database service best for traditional SQL workloads with moderate scale, while Cloud Spanner is a globally distributed database designed for high scale and strong consistency across regions. Choose Cloud SQL for simpler, smaller apps and Cloud Spanner for large, globally available applications needing horizontal scaling.

Quick Comparison

Here is a quick side-by-side look at key features of Cloud SQL and Cloud Spanner.

Feature	Cloud SQL	Cloud Spanner
Database Type	Relational (MySQL, PostgreSQL, SQL Server)	Relational, horizontally scalable, globally distributed
Scalability	Vertical scaling (scale-up)	Horizontal scaling (scale-out) across regions
Consistency	Strong consistency within single region	Strong global consistency across regions
Use Case	Traditional apps, moderate traffic	Global apps, high traffic, mission-critical
Pricing Model	Instance-based, simpler	Node-based, higher cost but scalable
Automatic Sharding	No	Yes

Key Differences

Cloud SQL is a managed service for popular relational databases like MySQL and PostgreSQL. It is designed for applications that need a traditional SQL database with vertical scaling, meaning you increase the power of a single server. It offers strong consistency but mainly within a single region.

Cloud Spanner is a unique database that combines relational structure with horizontal scaling and global distribution. It automatically shards data across many servers and regions, providing strong consistency worldwide. This makes it ideal for large, globally distributed applications that require high availability and low latency everywhere.

While Cloud SQL is simpler and cheaper for small to medium workloads, Cloud Spanner supports complex, mission-critical systems with massive scale and global reach. The tradeoff is higher cost and more complex setup.

Code Comparison

Here is how you create a simple table and insert data in Cloud SQL using PostgreSQL syntax.

sql

CREATE TABLE users (
  id SERIAL PRIMARY KEY,
  name VARCHAR(100),
  email VARCHAR(100) UNIQUE
);

INSERT INTO users (name, email) VALUES ('Alice', '[e-mail]');

SELECT * FROM users;

Output

id | name  | email
---+-------+-------------------
1  | Alice | [e-mail]

Cloud Spanner Equivalent

Here is how you create a similar table and insert data in Cloud Spanner using its SQL dialect.

sql

CREATE TABLE users (
  id INT64 NOT NULL,
  name STRING(100),
  email STRING(100)
) PRIMARY KEY(id);

INSERT INTO users (id, name, email) VALUES (1, 'Alice', '[e-mail]');

SELECT * FROM users;

Output

id: 1
name: Alice
email: [e-mail]

When to Use Which

Choose Cloud SQL when you have a traditional application that needs a managed relational database with moderate traffic and simpler setup. It is cost-effective for single-region workloads and supports popular databases like MySQL and PostgreSQL.

Choose Cloud Spanner when your application requires global scale, high availability, and strong consistency across multiple regions. It fits mission-critical systems with heavy traffic and complex transactions that need horizontal scaling.

Key Takeaways

Cloud SQL is best for traditional, single-region relational databases with moderate scale.

Cloud Spanner offers global distribution and horizontal scaling with strong consistency.

Use Cloud SQL for simpler, cost-effective workloads and Cloud Spanner for large, global apps.

Cloud Spanner automatically shards data; Cloud SQL does not.

Pricing and complexity are higher with Cloud Spanner but support massive scale.