Manual Offset Committing
Implement manual control over offset commits to achieve precise control over message processing guarantees and avoid data loss or duplication.
Manual Offset Committing is a free Advanced Spring Boot 4: Event-Driven Architecture (Kafka) lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Advanced Spring Boot 4: Event-Driven Architecture (Kafka) learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Why Manual Commits?
In Kafka, an offset marks the last message a consumer group has successfully processed from a topic partition. Committing an offset tells Kafka: "I've handled messages up to this point."
By default, Spring Kafka uses auto-commit, where offsets are committed periodically in the background. While convenient, this can sometimes lead to data loss or duplication if your application crashes mid-processing.
Manual offset committing gives you precise control, allowing you to decide exactly when an offset is marked as processed. This is crucial for ensuring message processing guarantees.
Auto-Commit: A Quick Look
With auto-commit, Kafka automatically commits offsets at a set interval (e.g., every 5 seconds). This means:
- Messages are processed.
- Offsets are committed later by Kafka.
If your application processes a message but crashes *before* Kafka's auto-commit interval passes, that message's offset might not be committed. When the application restarts, it will re-read and re-process that message, leading to potential duplicates (at-least-once processing).
Switching to Manual Mode
To take control of offset management, you need to disable auto-commit in your Spring Boot application's Kafka configuration. This is typically done by setting the AckMode.
The AckMode determines when a consumer acknowledges messages. For manual control, we'll use MANUAL_IMMEDIATE or MANUAL.
Here's how you might configure it in application.properties:
spring.kafka.consumer.enable-auto-commit=false
spring.kafka.listener.ack-mode=MANUAL_IMMEDIATEThe Acknowledgment Object
When ack-mode is set to a manual option, your @KafkaListener method can receive an additional parameter: the Acknowledgment object.
This object is your direct interface to signal to Kafka that you have successfully processed a message (or a batch of messages) and its offset can now be committed.
You'll call its acknowledge() method when you're ready.
Basic Manual Commit Example
Let's see a simple example where we manually commit the offset after processing each message. Notice the Acknowledgment acknowledgment parameter.
Run this code, then stop and restart. You'll see messages are not re-processed if committed.
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.kafka.annotation.KafkaListener;
import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.kafka.support.Acknowledgment;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
@SpringBootApplication
public class ManualCommitApp implements CommandLineRunner {
@Autowired
private KafkaTemplate<String, String> kafkaTemplate;
public static void main(String[] args) {
SpringApplication.run(ManualCommitApp.class, args);
}
@Override
public void run(String... args) throws Exception {
System.out.println("Sending message...");
kafkaTemplate.send("my-topic", "Hello CoddyKit!");
System.out.println("Message sent.");
}
@KafkaListener(topics = "my-topic", groupId = "manual-group")
public void listen(String message, Acknowledgment acknowledgment) {
System.out.println("Received: " + message);
// Simulate processing
try {
Thread.sleep(500);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
System.out.println("Processed: " + message + ", committing offset.");
acknowledgment.acknowledge(); // Manual commit
}
}Configuring for the Example
For the previous example to work, you'd need a src/main/resources/application.properties file with Kafka broker details and the manual ack mode:
spring.kafka.bootstrap-servers=localhost:9092(or your Kafka broker)spring.kafka.consumer.enable-auto-commit=falsespring.kafka.listener.ack-mode=MANUAL_IMMEDIATEspring.kafka.producer.key-serializer=org.apache.kafka.common.serialization.StringSerializerspring.kafka.producer.value-serializer=org.apache.kafka.common.serialization.StringSerializerspring.kafka.consumer.key-deserializer=org.apache.kafka.common.serialization.StringDeserializerspring.kafka.consumer.value-deserializer=org.apache.kafka.common.serialization.StringDeserializer
Remember to have a local Kafka running!
When to Acknowledge?
The core principle for manual committing is: commit only after your business logic has successfully completed.
- After each message: As shown in the previous example. Good for low throughput or critical messages.
- After a batch: Process multiple messages, then commit once for the entire batch. This is more efficient for high throughput.
- After external interactions: If you write data to a database, commit the offset *only after* the database transaction is successful.
Choosing the right strategy depends on your application's requirements for performance and data consistency.
Batch Processing & Manual Commit
When your listener consumes a batch of messages (e.g., List<String>), you should commit the offset only after *all* messages in that batch have been successfully processed. The Acknowledgment object still works for the entire batch.
This is often combined with AckMode.BATCH, though MANUAL_IMMEDIATE also works.
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.kafka.annotation.KafkaListener;
import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.kafka.support.Acknowledgment;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import java.util.List;
@SpringBootApplication
public class BatchManualCommitApp implements CommandLineRunner {
@Autowired
private KafkaTemplate<String, String> kafkaTemplate;
public static void main(String[] args) {
SpringApplication.run(BatchManualCommitApp.class, args);
}
@Override
public void run(String... args) throws Exception {
System.out.println("Sending 3 messages...");
kafkaTemplate.send("my-batch-topic", "Batch Msg 1");
kafkaTemplate.send("my-batch-topic", "Batch Msg 2");
kafkaTemplate.send("my-batch-topic", "Batch Msg 3");
System.out.println("Messages sent.");
}
// Ensure spring.kafka.listener.ack-mode=MANUAL_IMMEDIATE in properties
@KafkaListener(topics = "my-batch-topic", groupId = "batch-manual-group")
public void listenBatch(List<String> messages, Acknowledgment acknowledgment) {
System.out.println("Received batch of " + messages.size() + " messages.");
for (String msg : messages) {
System.out.println(" Processing: " + msg);
// Simulate processing each message in the batch
try {
Thread.sleep(100);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
}
System.out.println("Finished processing batch. Committing offset.");
acknowledgment.acknowledge(); // Commit once for the entire batch
}
}Handling Errors & Reprocessing
What happens if an error occurs during message processing *before* acknowledgment.acknowledge() is called?
Since the offset was not committed, Kafka considers the message (or batch) as not processed. Upon restart or rebalance, the consumer will re-fetch and re-process those messages. This is the foundation of at-least-once processing semantics.
While this guarantees no data loss, it requires your message processing logic to be idempotent, meaning processing the same message multiple times has the same effect as processing it once.
Trade-offs & Best Practices
Manual offset committing offers control but comes with considerations:
- Overhead: Committing too frequently can add network and Kafka broker overhead.
- Reprocessing Scope: Committing too infrequently means more messages might be reprocessed if a failure occurs.
- Idempotency: Always design your consumers to be idempotent when using manual commits to handle potential duplicates gracefully.
- Error Handling: Combine manual commits with robust exception handling (e.g., retries, Dead Letter Topics) to manage failures effectively.
Quick Check: Manual Commits
You are using manual offset committing in your Spring Kafka consumer. If an error occurs while processing a message, and the acknowledgment.acknowledge() method is NOT called for that message, what will happen?
Recap: Manual Offset Control
We've explored manual offset committing, a powerful technique for precise control over message processing in Spring Kafka.
- It disables auto-commit, giving you control.
- You use the
Acknowledgmentobject to explicitly commit offsets. - Committing should happen only after successful business logic execution.
- It enables at-least-once processing, but requires idempotent consumers.
This fine-grained control is vital for building robust and reliable event-driven applications.
Frequently asked questions
Is the “Manual Offset Committing” lesson free?
Yes — the full text of “Manual Offset Committing” is free to read here on the web, and the Advanced Spring Boot 4: Event-Driven Architecture (Kafka) course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Advanced Spring Boot 4: Event-Driven Architecture (Kafka) course, upgrade to CoddyKit PRO.
What will I learn in “Manual Offset Committing”?
Implement manual control over offset commits to achieve precise control over message processing guarantees and avoid data loss or duplication. You practise Advanced Spring Boot 4: Event-Driven Architecture (Kafka) with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Advanced Spring Boot 4: Event-Driven Architecture (Kafka)?
No prior experience is required. Advanced Spring Boot 4: Event-Driven Architecture (Kafka) on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Manual Offset Committing” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Advanced Spring Boot 4: Event-Driven Architecture (Kafka) lesson?
Yes. Every Advanced Spring Boot 4: Event-Driven Architecture (Kafka) lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.