How to handle backpressure when using Reactor Kafka? - reactive-programming

Question

I'm using Reactor Kafka to both consume and produce Kafka events. In the case of consuming events my consumer is slow and therefor I need to handle backpressure.
However, I experience that no matter what I call Subscription.request() with, the publisher will publish all events from the topic immediately, therefor overwhelming the consumer.
I'm using a custom Subscriber, setting a small number of initial request by calling Subscription.request(), when I subscribe to KafkaReceiver.receive() to do this. To my understanding this is how I tell the publisher how many events my consumer initially wants.
My subscriber:
public class KafkaEventSubscriber extends BaseSubscriber {
private final int numberOfItemsToRequestOnSubscribe;
private final int numberOfItemsToRequestOnNext;
public KafkaEventSubscriber(int numberOfItemsToRequestOnSubscribe,
int numberOfItemsToRequestOnNext) {
this.numberOfItemsToRequestOnSubscribe = numberOfItemsToRequestOnSubscribe;
this.numberOfItemsToRequestOnNext = numberOfItemsToRequestOnNext;
}
#Override
protected void hookOnSubscribe(Subscription subscription) {
subscription.request(numberOfItemsToRequestOnSubscribe);
}
#Override
protected void hookOnNext(EnrichedMetadata value) {
request(numberOfItemsToRequestOnNext);
}
}
How I use the subscriber:
kafkaReceiver.receive().map(ReceiverRecord::value).map(KafkaConsumer::acknowledge).subscribe(new KafkaEventSubscriber(10, 1));
I expect the KafkaReceiver to output 10 events before any call to the subscribers onNext() method is done, but the KafkaReceiver outputs all events that are not already ACK:ed from the topic.
I experience that no matter what we call Subscription.request() with, the publisher will publish all events from the topic immediately, not respecting the backpressure measures I've been taking.