Cassandra Practice Test

What does the consistency level "ONE" require in a Cassandra operation?

1. Only one node needs to acknowledge the operation

2. All nodes must acknowledge the operation

3. Half of the nodes need to acknowledge the operation

4. Any number of nodes can acknowledge the operation

The correct answer is: Only one node needs to acknowledge the operation

The consistency level "ONE" in Cassandra indicates that only one replica node must acknowledge the operation for it to be considered successful. This means that when a write is made, the system will consider it successful as long as it receives a confirmation from just one of the nodes that hold a copy of the data, regardless of the state of other nodes. This level of consistency is particularly advantageous for scenarios where lower latency is desired, as it allows for faster writes and reads at the cost of potentially returning stale data. Since only one node's acknowledgment is necessary, the application remains responsive under high load, making it suitable for many applications where some level of inconsistency is acceptable. In contrast, the other options describe different consistency levels that typically require a greater number of node acknowledgments. For example, all nodes or a majority of nodes need to acknowledge the operation in other levels of consistency, which ensures stronger data accuracy and reliability but may introduce latency and reduce throughput.