Kafka: 3 ways to delete committed offsets for a consumer group

Overview

Managing consumer groups and offsets is a crucial aspect of using Apache Kafka effectively. At times you might need to reset the offsets for a consumer group to a previous state, perhaps for reprocessing messages or recovering from an error. In this article, we will cover several ways to delete committed offsets for a consumer group. Each approach caters to different scenarios and comes with its own set of pros and cons.

Solution 1: Kafka Consumer Groups CLI

The Kafka Consumer Groups command-line interface (CLI) is an in-built tool that comes with Kafka and allows for management of consumer groups and their offsets. This is the most straightforward way of resetting offsets.

1. Identify the consumer group for which you wish to delete the offsets.
2. Determine the topic and the partitions whose offsets need to be reset.
3. Use the kafka-consumer-groups.sh script to reset the offsets to the desired value, either to the earliest, latest, or to a specific timestamp.

Example:

# Delete committed offsets for a consumer group
kafka-consumer-groups.sh --bootstrap-server localhost:9092 --group my-consumer-group --topic my-topic --reset-offsets --to-earliest --execute

# Output
# Consumer group 'my-consumer-group' has no active members.
# GROUP                          TOPIC                          PARTITION  NEW-OFFSET
# my-consumer-group              my-topic                       0          0

Notes: Using the CLI is quick and effective for manual offset management. The primary limitation is that it tends to be less practical for a large number of offsets or in automated settings. It is also limited by the user’s access to and familiarity with the Kafka command line tools.

Solution 2: Programmatically Using Kafka Consumer API

Kafka’s Consumer API allows for finer control through code. This is useful when you want to integrate offset deletion as a part of a larger automated process or system.

1. Set up a Kafka consumer using the appropriate configuration for your consumer group.
2. Fetch the committed offsets you wish to delete.
3. Invoke commitSync with an empty map or with specific offsets to reset to indicate deletion.

Example:

// Assume Kafka consumer setup is completed
Map<TopicPartition, OffsetAndMetadata> offsetsToReset = new HashMap<>();
// Define the partitions and corresponding empty OffsetAndMetadata
offsetsToReset.put(new TopicPartition("my-topic", 0), new OffsetAndMetadata(0));
// Commit the new offset, effectively deleting the previous one
consumer.commitSync(offsetsToReset);

Notes: This solution allows for automation and can be seamlessly integrated. However, it may require more Kafka expertise, and caution must be taken when manipulating offsets programmatically to avoid data loss or duplication.

Solution 3: Using Kafka Admin API

Kafka’s Admin API supports offset deletion through code as well. Compared to using the Consumer API, this method is better for handling offsets without having to manage active consumer instances.

1. Instantiate an instance of KafkaAdminClient.
2. Invoke the alterConsumerGroupOffsets method with the consumer group and map of partitions to empty offsets.

Example:

Properties props = new Properties();
props.setProperty(AdminClientConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");

try (AdminClient admin = KafkaAdminClient.create(props)) {
    Map<TopicPartition, OffsetAndMetadata> offsets = Collections.emptyMap();
    admin.alterConsumerGroupOffsets("my-consumer-group", offsets).all().get();
}

Notes: The Admin API offers a programmatic approach which is more nuanced and is particularly useful for administration tasks where greater control or integration with other administrative processes is required.

Conclusion

In conclusion, deleting Kafka committed offsets for a consumer group can be approached in multiple ways, each with its advantages and use cases. It’s critical to understand and conscientize the behavior of consumer offsets within your Kafka topology to choose the right method for your specific need. While CLI tools are ideal for quick and manual interventions, the Consumer and Admin APIs offer more flexibility for programmatic management. Understanding the implications of offset deletion, like potential reprocessing or data loss, is also essential when employing any of these methods.