Cassandra Practice Test

A lightweight transaction in Cassandra is primarily characterized by its ability to check a specific condition before executing an update or insert operation. This mechanism is crucial because it allows for conditional updates, ensuring that an operation is only performed if certain criteria are met. This functionality is enabled through the use of a "conditional update," which involves comparing the current value of a column against a specified value before proceeding with the change, thus supporting a sort of optimistic concurrency control. While lightweight transactions do offer some level of consistency — which could suggest ACID (Atomicity, Consistency, Isolation, Durability) compliance at a broader level — they do not guarantee full ACID properties at the table level. Instead, lightweight transactions are more focused on ensuring that specific conditions are satisfied during data manipulation. Furthermore, the requirement for all data to be unique is not a characteristic of lightweight transactions. Instead, uniqueness can be managed through primary keys and other database constraints within Cassandra. Lastly, the concept of immediate visibility of changes is not inherently guaranteed by lightweight transactions as well; visibility can depend on factors like consistency levels and the state of the cluster. Thus, the correct characterization of a lightweight transaction is that it checks a condition before performing an update or insert, which highlights the transaction's role