What is the difference between eventual consistency and strong consistency?

Question

Accepted Answer

**Eventual Consistency** — data will converge. **Strong Consistency** — data is always up-to-date.

**Eventual Consistency:**
- Data updates propagate eventually.
- Reads may return stale data.
- Higher availability.
- Better performance.

```
Eventual Consistency:
Write to Node A → Replicate to B, C
Read from B: may see old data briefly
Eventually: all nodes converge
```

**Strong Consistency:**
- Reads always return latest data.
- Lower availability.
- Higher latency.
- Used for critical operations.

```
Strong Consistency:
Write to Node A → Wait for B, C confirmation
Read from any node: always latest data
(All nodes same data at all times)
```

**Key differences:**
- **Eventual** — data converges over time.
- **Strong** — data always current.
- **Eventual** — higher availability.
- **Strong** — higher consistency.

Systems Analyst: What is the difference between eventual consistency and strong consistency?