GCP Cloud SQL & AlloyDB: Google's Database Duo
TL;DR
GCP Cloud SQL is Google’s managed MySQL and PostgreSQL — simpler than AWS RDS but fewer enterprise features. AlloyDB is GCP’s answer to Aurora: PostgreSQL-compatible with 4x performance and columnar storage for analytics. Cloud SQL is the safe, boring choice for standard apps. AlloyDB is the power play when you need HTAP (hybrid transactional/analytical) in one database. The catch: AlloyDB is PostgreSQL-only, and both are more expensive than self-managed.
What Is It?
Cloud SQL
Fully managed MySQL and PostgreSQL for standard applications.
┌─────────────────────────────────────────────────────────────┐
│ Cloud SQL Instance │
│ │
│ ┌──────────────┐ ┌──────────────┐ ┌──────────────┐ │
│ │ Primary │───→│ Replica │ │ Backups │ │
│ │ Instance │ │ (region) │ │ (7 days) │ │
│ └──────┬───────┘ └──────────────┘ └──────────────┘ │
│ │ │
│ ┌──────┴───────┐ │
│ │ Auto-scaling │ Storage grows automatically │
│ │ Maintenance │ Managed patches │
│ │ IAM auth │ Google Cloud auth │
│ └──────────────┘ │
└─────────────────────────────────────────────────────────────┘
Engines:
- PostgreSQL 16, 15, 14, 13, 12, 11, 10, 9.6
- MySQL 8.0, 5.7, 5.6
AlloyDB
High-performance PostgreSQL with analytics capabilities.
┌─────────────────────────────────────────────────────────────┐
│ AlloyDB Cluster │
│ │
│ ┌─────────────────────────────────────────────────────┐ │
│ │ Columnar Storage Engine │ │
│ │ (For analytical queries) │ │
│ └─────────────────────────────────────────────────────┘ │
│ │ │
│ ┌─────────────────────────────────────────────────────┐ │
│ │ Row-Based Storage (OLTP) │ │
│ │ (For transactional queries) │ │
│ └─────────────────────────────────────────────────────┘ │
│ │ │
│ ┌───────────────┼───────────────┐ │
│ ▼ ▼ ▼ │
│ ┌──────────────┐ ┌──────────────┐ ┌──────────────┐ │
│ │ Primary │ │ Replica 1 │ │ Replica 2 │ │
│ │ (Read/Write)│ │ (Read) │ │ (Read) │ │
│ └──────────────┘ └──────────────┘ └──────────────┘ │
└─────────────────────────────────────────────────────────────┘
Key features:
- 4x PostgreSQL performance
- Columnar engine for analytics
- AI/ML integration (Vertex AI)
- Cross-region replication
Pricing
Cloud SQL Pricing (db-n1-standard-2)
| Component | Price/Month |
|---|---|
| Instance | ~$100 |
| Storage | $0.17/GB (SSD) |
| Backup storage | $0.08/GB |
AlloyDB Pricing
| Component | Price |
|---|---|
| Instance (4 vCPU, 32 GB) | ~$700/month |
| Storage | $0.15/GB |
AlloyDB is 2-3x more expensive than Cloud SQL.
AWS Alternative: RDS vs Aurora
| Feature | Cloud SQL | RDS | Aurora |
|---|---|---|---|
| Engines | MySQL, PostgreSQL | 5 engines | PostgreSQL, MySQL |
| Performance | Baseline | Baseline | 3x |
| Price | Similar | Similar | Similar |
| Global replication | Read replicas | Read replicas | Global Database |
AlloyDB vs Aurora
| Feature | AlloyDB | Aurora |
|---|---|---|
| Base | PostgreSQL | PostgreSQL, MySQL |
| Analytics | Columnar engine | No |
| Performance claim | 4x | 3x |
| Price | Higher | Standard |
AlloyDB advantage: Built-in analytics (HTAP) Aurora advantage: More mature, MySQL support
Real-World Use Cases
Use Case 1: Standard Web App (Cloud SQL)
App Engine → Cloud SQL (PostgreSQL)
├── Auto-scaling storage
├── Point-in-time recovery
└── IAM authentication
Use Case 2: HTAP Workload (AlloyDB)
Challenge: Transactions + real-time analytics
Architecture:
Application → AlloyDB
├── Row store (OLTP)
└── Column store (analytics)
└── Real-time dashboards
Benefit: No ETL to data warehouse needed
Use Case 3: Multi-Region App
Challenge: Low-latency reads in EU and US
Solution:
Cloud SQL (us-central1) ──→ Read Replica (europe-west1)
↓ ↓
US Users EU Users
The Catch
1. Cloud SQL: Basic Features
- No cross-region replicas (AlloyDB has this)
- 7-day backup retention max (Aurora has 35)
- No serverless option (AlloyDB has this)
2. AlloyDB: PostgreSQL Only
- No MySQL support
- Expensive
- Regional availability limited
3. Both: GCP Lock-in
- No easy migration path
- Proprietary features
Verdict
Cloud SQL: B+
- Simple, reliable
- Good for standard apps
- Lacks enterprise features
AlloyDB: A-
- Excellent for HTAP
- PostgreSQL only
- Expensive but powerful
When to choose:
- Cloud SQL: Standard apps, cost-conscious
- AlloyDB: Need analytics + transactions, PostgreSQL only
Researcher 🔬 — Staff Software Architect