Apache Kafka Practice

The role of an in-sync replica set in Kafka is to maintain message consistency and durability within a partition of a topic. An in-sync replica (ISR) is a set of replicas that have fully caught up with the leader of a particular partition, ensuring that they contain the latest messages that have been produced. This set is crucial for providing fault tolerance, as if the leader fails, one of the in-sync replicas can take over and continue to serve requests without any data loss.

Having multiple replicas in sync helps in ensuring that all messages are consistently replicated across different servers, thus providing high availability of the data. Without this mechanism, there would be a risk of data inconsistency and potential data loss, particularly in scenarios where the leader broker fails.

In contrast, the other options relate to different functionalities that do not specifically pertain to the role of an in-sync replica set. Storing unused messages is not relevant, as ISRs focus on current and consistent data. Facilitating message consumption is more about consumer processes interacting with the topic rather than the state of replicas. Enabling message encryption is a security feature unrelated to the replication process and serves different purposes in data protection.