System Design: Exactly-Once Creation by Name on Cassandra, Deletes, and Read API Design

Context

You run a Java web API on Kubernetes backed by a Cassandra 4.x cluster. Users create artifacts identified by a user-provided unique name. The system must ensure each name is created exactly once under concurrent requests. Later, a Delete feature is added. Finally, you must design the Read API for low latency and high throughput while controlling consistency.

Assume a single region with 3 Availability Zones, NetworkTopologyStrategy, RF=3 per DC, and cross-AZ traffic allowed. Payload size fits Cassandra best practices; if not, store only metadata in Cassandra and the payload in blob storage.

Tasks

a) Creation concurrency control

• Define the table schemas and primary keys.
• Specify idempotency keys.
• Choose a concurrency-control mechanism (e.g., Cassandra LWT with IF NOT EXISTS, unique-name reservation rows, or a distributed lock), and describe retry behavior and failure modes.

b) Delete and re-add semantics

• Model deletes to avoid races and duplicates, including soft deletes, tombstones, TTL/grace period, name reuse policy, and tombstone compaction considerations.

c) Read API design

• Design and optimize the Read API for latency/throughput while controlling consistency (read CLs, caching, pagination, read repair/repairs, replication, hot-partition mitigation, and fallbacks during partial outages).