Dominate the Cassandra Test 2026 – Unleash Your Big Data Brilliance!

Read repair is a mechanism used in Cassandra to ensure that data remains consistent across replicas by fixing any out-of-date or missing data when a read request is made. The specific condition in which read repair always occurs is when the consistency level is set to all.

When the consistency level is set to all, Cassandra requires a response from every replica that holds a given piece of data before it returns a result to the client. During this process, if any replicas return stale or inconsistent data, the system can detect this discrepancy and automatically trigger a repair of the data across replicas to ensure that all nodes reflect the same information. This ensures that the data is consistent not only after the read but also makes sure that it is corrected across all nodes involved in storing that piece of data.

In cases of lower consistency levels, such as one or quorum, read repair might not occur because the application does not require responses from all replicas, allowing for potential discrepancies to remain undetected until later operations. Therefore, when using the all consistency level, read repair is guaranteed to take place whenever a read occurs.