- Availability means the system always responds, even if some data is outdated.
- Consistency means all users see the same, most recent data.
- Availability favors uptime; consistency favors correctness.
- Increasing availability may sacrifice consistency (eventual consistency).
- Increasing consistency may reduce availability (fail fast if data mismatch).
- Example:
- Availability-focused: DNS, shopping cart during sales.
- Consistency-focused: Banking systems, inventory management.