Cassandra Practice Test

What does the consistency level "QUORUM" require for acknowledgment of an operation?

1. All nodes must acknowledge the operation

2. At least half of the nodes need to acknowledge the operation

3. More than half of the nodes need to acknowledge the operation

4. Only one node is required to acknowledge the operation

The correct answer is: More than half of the nodes need to acknowledge the operation

The consistency level "QUORUM" requires that more than half of the nodes in a given replication group must acknowledge the operation for it to be considered successful. This approach helps to ensure that the read and write operations are consistent and reliable, as it minimizes the likelihood of discrepancies that could arise from failures or network partitions. In a distributed system like Cassandra, having a QUORUM means that if a cluster has, for example, 5 replicas for a piece of data, at least 3 nodes must respond positively to the write or read request. This method enhances fault tolerance and ensures that operations reflect a majority consensus among the nodes, promoting data integrity even in the event of some nodes being down. The other choices do not meet the criteria for QUORUM. For instance, acknowledging by all nodes would require complete availability and is impractical in distributed environments, while requiring acknowledgment from only one node would not ensure any level of data consistency. Similarly, acknowledging by only half would fall short of the majority required to satisfy the QUORUM level, leading to potential inconsistencies.