What defines the "Consistency Level" in Cassandra?

The "Consistency Level" in Cassandra is defined by the number of replicas that must respond to read or write requests in order for the operation to be considered successful. This concept is crucial because it allows users to configure the balance between consistency and availability depending on the requirements of their application.

When setting a consistency level, you can make trade-offs; for example, a higher consistency level, which requires a response from more replicas, ensures that clients receive the most recent data. Conversely, a lower consistency level can increase availability and reduce latency, as it may allow a request to be considered successful even if not all replicas respond.

This flexibility in choosing consistency levels—such as ONE, QUORUM, or ALL—enables Cassandra to be adaptable in various use cases, striking the right balance between strong consistency and system performance according to the needs of the application.