Resetting Consumer Group Offsets

This process allows consumers to reprocess messages, skip past certain messages, or start processing from a different point in the topic.

1. Reprocessing Data: If there's a need to reprocess old data, such as after fixing a bug in the consumer logic.
2. Skipping Faulty Data: If certain messages caused errors and you need to skip them.
3. Starting Fresh: If the consumer group is repurposed to handle a new set of messages.
4. Recovery from Issues: After recovering from an outage or data corruption.

Kafka Consumer Group Command

• The Kafka Consumer Groups CLI can be used to reset offsets.

• Common usage: kafka-consumer-groups.sh --bootstrap-server <broker> --group <group_id> --topic <topic> --reset-offsets --to-earliest

• Options include:

  • --to-earliest: Reset offsets to the earliest available messages.
  • --to-latest: Reset offsets to the latest messages.
  • --to-datetime <timestamp>: Reset offsets to the messages at or after the specified timestamp.
  • --by-offset <num>: Reset offsets by a specific offset number.
  • --shift-by <num>: Shift current offsets forward or backward by a specified number.
  • --to-current: Reset to the current offset (useful for testing).
  • --dry-run: Simulate the reset without actually changing the offsets.

AdminClient API

The AdminClient API allows you to manage and alter consumer group offsets programmatically. This is a more flexible and powerful way to reset offsets, especially for applications that need to automate this process.

import org.apache.kafka.clients.admin.AdminClient;
import org.apache.kafka.clients.admin.AdminClientConfig;
import org.apache.kafka.clients.admin.OffsetSpec;
import org.apache.kafka.clients.admin.OffsetAndMetadata;
import org.apache.kafka.clients.admin.ListOffsetsResult;
import org.apache.kafka.clients.admin.AlterConsumerGroupOffsetsResult;
import org.apache.kafka.common.TopicPartition;

import java.util.Collections;
import java.util.Map;
import java.util.Properties;

public class OffsetResetExample {
    public static void main(String[] args) throws Exception {
        Properties props = new Properties();
        props.put(AdminClientConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
        try (AdminClient adminClient = AdminClient.create(props)) {
            String consumerGroupId = "my-group";
            TopicPartition topicPartition = new TopicPartition("my-topic", 0);

            // Example: Reset to earliest
            ListOffsetsResult listOffsetsResult = adminClient.listOffsets(
                Collections.singletonMap(topicPartition, OffsetSpec.earliest()));
            long earliestOffset = listOffsetsResult.partitionResult(topicPartition).get().offset();

            // Create the offset map to update
            Map<TopicPartition, OffsetAndMetadata> offsetsToReset = Collections.singletonMap(
                topicPartition, new OffsetAndMetadata(earliestOffset));

            // Reset offsets
            AlterConsumerGroupOffsetsResult resetOffsetsResult =
                adminClient.alterConsumerGroupOffsets(consumerGroupId, offsetsToReset);
            resetOffsetsResult.all().get ();
            System.out.println("Offsets reset successfully.");
        }
    }
}

References

• ChatGPT

Flashcards

Using the Kafka Consumer Group CLI Command, how would you reset the consumer group offsets to the earliest?:: kafka-consumer-groups.sh --bootstrap-server <broker> --group <group_id> --topic <topic> --reset-offsets --to-earliest --execute

Using AdminClient API, how would you reset the consumer group offsets to the earliest?:: adminClient.alterConsumerGroupOffsets(consumerGroupId, offsetsToReset);