What do transactions in Kafka provide? What are they used for?

Transactions in Kafka allow guaranteeing the atomicity of operations when writing messages to multiple topics or partitions. This means that either all messages within a transaction are successfully written and visible to consumers, or none of them are.

Main advantages of transactions in Kafka:

• Atomicity: multiple write operations are combined into a single transaction.
• Avoidance of duplication: using transactions, idempotent processing can be implemented, which is important for precise message delivery.
• Data consistency: it is guaranteed that consumers will see either all changes or none.

Transactions are especially useful when ensuring consistency across multiple topics or when a producer writes and commits consumption offsets simultaneously (e.g., in stream processing).

Example of using transactions in Kafka Producer in Java:

producer.initTransactions();
try {
    producer.beginTransaction();
    producer.send(new ProducerRecord<>("topic1", "key", "value1"));
    producer.send(new ProducerRecord<>("topic2", "key", "value2"));
    producer.commitTransaction();
} catch (Exception e) {
    producer.abortTransaction();
}