Cassandra Practice Test

What does the consistency level "ALL" mean in Cassandra?

1. Only one node needs to acknowledge the operation

2. Half of the nodes must acknowledge the operation

3. All nodes involved must acknowledge the operation

4. Any node can acknowledge the operation

The correct answer is: All nodes involved must acknowledge the operation

The consistency level "ALL" in Cassandra signifies that all nodes involved in a given operation need to acknowledge it before it is considered successful. This approach ensures the highest level of data consistency, as it requires every replica of the data to confirm the write or read operation. Consequently, this means that any possible response from a node (whether it's a write acknowledgment or read response) is invalid unless every single node involved in that data has participated and positively acknowledged the operation. However, it's important to recognize that while this level of consistency guarantees that all copies of the data across nodes are up-to-date, it can also lead to latency issues and unavailability in situations where one or more nodes are down or unreachable. This is an essential trade-off in distributed databases like Cassandra, where different operations may require varying levels of consistency based on application needs. The other options suggest different scenarios regarding node acknowledgment but do not align with the strict requirement of "ALL," highlighting the unique role this consistency level plays in ensuring data reliability across the entire cluster.