What is the difference between horizontal and vertical database scaling?

Question

Accepted Answer

**Horizontal** — add more servers. **Vertical** — add more power.

**Horizontal Scaling:**
- Add more database servers.
- Sharding or replication.
- Linear cost increase.
- Complex distributed queries.

```
Horizontal:
[DB Server 1] [DB Server 2] [DB Server 3]
  (Each handles part of data)
  (Or: read replicas)
```

**Vertical Scaling:**
- Upgrade existing server.
- Add CPU, RAM, SSD.
- Limited by hardware.
- Simpler, no code changes.

```
Vertical:
[DB: 8GB RAM → 32GB RAM → 128GB RAM]
  (Same server, more powerful)
```

**Key differences:**
- **Horizontal** — more servers.
- **Vertical** — more power.
- **Horizontal** — better scalability.
- **Vertical** — simpler.

Systems Analyst: What is the difference between horizontal and vertical database scaling?