A new service needs per-item conditional updates at very high scale and predictable key-based reads. Relational joins are not required. Which database design is most appropriate?

1. Use Route 53 records as the primary transaction table.
2. Store all records in one S3 object and overwrite it for every update.
3. Use DynamoDB with keys designed for the access patterns and conditional writes for state transitions.
4. Use a single unsharded in-memory process with no durable store.