Apache Kafka Practice Test 2025 – 400 Free Practice Questions to Pass the Exam

When there are fewer in-sync replicas than configured in a Kafka setup, the producer will not receive acknowledgments from all required replicas, meaning it will not be able to complete the write operation successfully. As a result, the producer will buffer messages instead of confirming their delivery. This behavior is a safeguard to ensure that data isn't lost due to an insufficient number of copies of the message being available in the Kafka cluster.

Buffered messages remain in the producer's memory until the number of in-sync replicas meets the configured acknowledgment requirements. This allows the producer to maintain a level of durability and reliability, as it can retry sending messages later once the system stabilizes, rather than acknowledging potentially incomplete writes.

This option highlights an important aspect of Kafka's design, which emphasizes data durability and consistency even in the face of partial system failures. The other options do not represent the operational realities of how Kafka manages message acknowledgment and replication under these conditions.