Advanced
A cart that never forgets
Shoppers add items to their cart and sometimes see them disappear on the next page. The cart lives in a Cassandra cluster. At 11:00 a node will fail. Make the cart consistent and keep it available.
This is CAP and PACELC in practice: the consistency level decides how many replicas must answer each read and write.
What your design must achieve
- Stale reads < 0.01 %
- Availability ≥ 99.95 %
- Latency p99 < 150 ms