Cassandra Read Consistency ONE vs QUORUM for RF 3

Goal: select a read consistency level for a three-node Cassandra 4.x cluster with replication factor 3 that serves user-profile reads. The application must avoid stale reads, but the p99 latency budget is tight.

Local single-node testing with consistency ONE hides replication lag because the only replica satisfies the read requirement. In production, ONE can return stale or missing data if the contacted replica is behind or down, especially during a network partition. QUORUM requires responses from two of three replicas, improving read-your-writes visibility, but increases latency and reduces availability when a node is unavailable.

Unresolved: whether the consistency and availability trade-off justifies QUORUM for all reads, or whether ONE with targeted read repair is acceptable for this workload.

• Does a QUORUM read return the most recent write when writes are issued at consistency ANY?
• Which level meets a sub-100 ms p99 read SLA while preventing stale reads during a single-node partition?
• Can read repair reliably converge replicas after reads served at consistency ONE?