this is a classic GCP architecture decision problem. The short answer:

• Use Cloud SQL for traditional relational apps.

• Use Cloud Spanner for global, strongly consistent, horizontally scalable relational systems.

• Use Bigtable for massive, low-latency NoSQL workloads (analytics, IoT, time-series).

Now let’s break it down clearly.

☁️ Cloud SQL

Fully managed relational database (MySQL, PostgreSQL, SQL Server).

When to Use It

• Standard web/mobile apps

• SaaS backends

• E-commerce systems

• Internal business apps

• Moderate traffic workloads

• You need ACID transactions

• You want familiar SQL behavior

Good For

• Structured relational data

• Complex joins

• Traditional schemas

• Single-region deployments

• Up to tens of TB (not petabyte scale)

Not Ideal For

• Global multi-region writes

• Massive horizontal scale (millions of writes/sec)

? Cloud Spanner

Globally distributed relational database with strong consistency.

When to Use It

• Global applications

• Financial systems

• High-write distributed systems

• Mission-critical systems

• You need horizontal scaling + SQL

Good For

• Multi-region writes

• Strong consistency across regions

• Automatic horizontal scaling

• High availability (99.999%)

Example Use Cases

• Global banking systems

• Global SaaS with users worldwide

• Large e-commerce platforms

• Large-scale inventory systems

Why Not Cloud SQL Here?

Cloud SQL scales vertically (bigger machine).
Spanner scales horizontally (adds nodes).

? Bigtable

Petabyte-scale NoSQL wide-column database.

 

 

When to Use It

• Time-series data

• IoT telemetry

• Financial tick data

• Real-time analytics

• Ad tech

• ML feature storage

Good For

• Billions of rows

• Millisecond latency

• Massive write throughput

• Sparse datasets

• Event/log data

Not Good For

• Complex joins

• Relational queries

• Traditional OLTP workloads

? Quick Decision Table

? Real-World Scenarios

Scenario 1

Startup building a SaaS product →
Use Cloud SQL

Scenario 2

Global fintech app with users in US, EU, Asia →
Use Cloud Spanner

Scenario 3

IoT platform collecting billions of device readings per day →
Use Bigtable

? Easy Memory Trick

• Cloud SQL = Traditional

• Spanner = Global + Scalable + Relational

• Bigtable = Massive + NoSQL