Asynchronous vs Synchronous Kafka Producers: Which One Should You Use?

Apache Kafka is popular choice for building real-time streaming applications. One of its core components, the Kafka Producer, plays a critical role in sending messages to Kafka topics. When producing messages in Kafka, you have the option to choose between synchronous and asynchronous delivery methods, each offering unique trade-offs in terms of performance, reliability, and use case suitability.

In this blog, we’ll dive into the differences between asynchronous and synchronous Kafka producers, their advantages and disadvantages, and when to use each.

What Are Kafka Producers?

Kafka producers are responsible for publishing messages to Kafka topics. The two modes of operation, synchronous and asynchronous, determine how the producer handles the acknowledgment from Kafka after a message is sent.

Synchronous Kafka Producers

In synchronous mode, the producer waits for a response from the Kafka broker after sending a message. The producer doesn’t proceed to the next message, until it receives an response or error for the current message.

How It Works

1. The producer sends a message to Kafka.
2. Kafka acknowledges receipt (or an error is returned).
3. The producer sends the next message.

Advantages

• Predictable Behavior: Ensures a clear success or failure result for every message.
• Error Handling: Easier to handle errors as they are returned immediately.
• Message Order: Maintains the order of messages since one message is sent and acknowledged before the next.

Disadvantages

• Higher Latency: Waiting for acknowledgments adds delays.
• Slower Throughput: Each message is sent and acknowledged sequentially, making it slower.

Synchronous Producer Example

import org.apache.kafka.clients.producer.*;
import java.util.Properties;

public class SynchronousProducer {
    public static void main(String[] args) {
        Properties props = new Properties();
        props.put("bootstrap.servers", "localhost:9092");
        props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer");
        props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");

        KafkaProducer<String, String> producer = new KafkaProducer<>(props);

        try {
            ProducerRecord<String, String> record = new ProducerRecord<>("my_topic", "key", "Hello, Synchronous Kafka!");
            producer.send(record).get(); // Blocking call
            System.out.println("Message sent successfully!");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            producer.close();
        }
    }
}

}

Asynchronous Kafka Producers

In asynchronous mode, the producer sends messages to Kafka without waiting for acknowledgments. Messages are queued in a buffer and sent in batches for efficiency.

How It Works

1. The producer queues a message in memory and moves on to the next message.
2. Messages are sent in batches or as buffer memory fills up.
3. Kafka acknowledges batches, and failures are handled in the background.

Advantages

• High Throughput: Batching and non-blocking calls improve message delivery speed.
• Low Latency: Messages are queued immediately without waiting for acknowledgments.
• Better Resource Utilization: Efficient use of network and CPU due to batching.

Disadvantages

• Order Challenges: Messages may not maintain strict ordering, especially when retries occur.
• Complex Error Handling: Failures may not be immediately visible and need callbacks to handle errors.
• Potential Message Loss: If the producer crashes before sending queued messages, data can be lost.

Asynchronous Producer Example

import org.apache.kafka.clients.producer.*;
import java.util.Properties;

public class AsynchronousProducer {
    public static void main(String[] args) {
        Properties props = new Properties();
        props.put("bootstrap.servers", "localhost:9092");
        props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer");
        props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");

        KafkaProducer<String, String> producer = new KafkaProducer<>(props);

        ProducerRecord<String, String> record = new ProducerRecord<>("my_topic", "key", "Hello, Asynchronous Kafka!");
        producer.send(record, (metadata, exception) -> {
            if (exception == null) {
                System.out.println("Message sent successfully to topic: " + metadata.topic());
            } else {
                exception.printStackTrace();
            }
        });

        producer.close();
    }
}

Comparison Table: Synchronous vs. Asynchronous

Feature	Synchronous Producer	Asynchronous Producer
Throughput	Low	High
Latency	High	Low
Error Handling	Simple	Requires Callbacks
Message Ordering	Strict	May Vary
Resource Efficiency	Less Efficient	More Efficient
Use Case	Critical Operations, Debugging	High-Volume Data Streams

Conclusion

Choosing between synchronous and asynchronous Kafka producers depends on your application’s needs. Synchronous producers are ideal for scenarios where reliability and order are paramount, while asynchronous producers shine in high-throughput, low-latency use cases.

By understanding their differences, you can make informed decisions and optimize your Kafka-based applications for performance and reliability.