Reactor Kafka: Exactly Once Processing Sample

Question

I\'ve read many articles where there are many different configurations to achieve exactly once processing.

Here is my producer config:

final Map

        

Answer 1

See the javadocs for receiveExactlyOnce

/**
 * Returns a {@link Flux} of consumer record batches that may be used for exactly once
 * delivery semantics. A new transaction is started for each inner Flux and it is the
 * responsibility of the consuming application to commit or abort the transaction
 * using {@link TransactionManager#commit()} or {@link TransactionManager#abort()}
 * after processing the Flux. 

begin() has already been called so you don't need to call it.

@Override
public Flux<Flux<ConsumerRecord<K, V>>> receiveExactlyOnce(TransactionManager transactionManager) {
    this.ackMode = AckMode.EXACTLY_ONCE;
    Flux<ConsumerRecords<K, V>> flux = withDoOnRequest(createConsumerFlux());
    return  flux.map(consumerRecords -> transactionManager.begin()
                             .then(Mono.fromCallable(() -> awaitingTransaction.getAndSet(true)))
                             .thenMany(transactionalRecords(transactionManager, consumerRecords)))
                             .publishOn(transactionManager.scheduler());
}