Explain the concept of manual commit in Kafka

In Kafka, manual commit is the process of explicitly acknowledging message processing by the consumer, where the developer manually controls when the message offset is committed in Kafka.

By default, Kafka can automatically commit offsets at regular intervals (auto-commit). However, manual commit allows:

• Ensuring that the offset is only committed after successful message processing.
• Avoiding message loss or reprocessing in case of failures.

In Kafka clients for Go (e.g., sarama or confluent-kafka-go), manual commit is usually implemented by calling a function that saves the current offset after processing a message.

Example (pseudo-code):

for msg := range consumer.Messages() {
    process(msg)
    consumer.MarkMessage(msg, "") // manual commit offset
}

Thus, manual commit provides full control over message acknowledgment, which is important for ensuring data reliability and consistency.