Strong consistency:
- Reads always return latest write
- Requires coordination between nodes
- Higher latency, lower availability
- Use for: Financial transactions, inventory counts
Eventual consistency:
- Reads may return stale data temporarily
- System converges to consistent state
- Lower latency, higher availability
- Use for: Social feeds, view counts, recommendations
In interviews:
- Default to eventual unless business requires strong
- Specify which operations need which level
- Consider hybrid: Strong for writes, eventual for reads
Consistency is per-operation, not per-system.