How to create kafka compacted topic

Question

I have a Kafka application that has a producer who produces messages to a topic. A consumer then takes the messages from the topic, does some logic to the given messages and then produces them to another topic. I'm using ProducerRecord and ConsumerRecords.

I want my app to create 2 compacted topics and then use them. If the compacted topics already exist, just display a message and continue.

My SimpleProducer class:

  package com.kafkatest.demo;

import java.util.*;

import org.apache.kafka.clients.producer.*;
public class SimpleProducer extends Thread{

   public static void main(String[] args) throws Exception{

      String topicName = "nodesTopic";
      String key = "Key1";
      String value = "Value-1";

      String key1 = "Key2";
      String value1 = "Value-2";



      Properties props = new Properties();
      props.put("bootstrap.servers", "localhost:9092,localhost:9093");
      props.put("key.serializer","org.apache.kafka.common.serialization.StringSerializer");         
      props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");

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

      ProducerRecord<String, String> record = new ProducerRecord<>(topicName,key,value);
      producer.send(record);


      ProducerRecord<String, String> record2 = new ProducerRecord<>(topicName,key1,value1);
      producer.send(record2);


      ProducerRecord<String, String> record3 = new ProducerRecord<>(topicName,key,value);
      producer.send(record3);


      ProducerRecord<String, String> record4 = new ProducerRecord<>(topicName,key,value);
      producer.send(record4);


      ProducerRecord<String, String> record5 = new ProducerRecord<>(topicName,key,value);
      producer.send(record5);


      ProducerRecord<String, String> record6 = new ProducerRecord<>(topicName,key,value);
      producer.send(record6);
      producer.close();

      System.out.println("SimpleProducer Completed.");
   }
}

My SimpleConsumer class:

   package com.kafkatest.demo;

import java.time.Duration;
import java.time.temporal.ChronoUnit;
import java.util.Arrays;
import java.util.Properties;

import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.Producer;
import org.apache.kafka.clients.producer.ProducerRecord;

public class SimpleConsumer extends Thread{

    public static void main(String[] args) {

    Properties props1 = new Properties();
    props1.put("bootstrap.servers", "localhost:9092,localhost:9093");
    props1.put("key.serializer","org.apache.kafka.common.serialization.StringSerializer");         
    props1.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");

    Producer<String, String> producer = new KafkaProducer <>(props1);

    Duration duration = Duration.of(2, ChronoUnit.MINUTES);
    String topicName = "nodesTopic";

    Properties props = new Properties();
    props.put("bootstrap.servers", "localhost:9092");
    props.put("group.id", "consumer-tutorial");
    props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
    props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
    KafkaConsumer<String, String> consumer = new KafkaConsumer<>(props); 

    consumer.subscribe(Arrays.asList(topicName));

    try {
        while (true) {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        consumer.beginningOffsets(consumer.assignment());
          ConsumerRecords<String, String> records = consumer.poll(duration);
          for (ConsumerRecord<String, String> record : records) {
            System.out.println(record.offset() + ": " + record.value());
            System.out.println("Record: " + record.value().toLowerCase());
            ProducerRecord<String, String> record1 = new ProducerRecord<>("forecastTopic", "Key", record.offset() + ". " + record.value().toLowerCase());
            String a = "" + records.count();
            ProducerRecord<String, String> record2 = new ProducerRecord<>("forecastTopic", "Key", record.offset() + ". " + a);
            producer.send(record1);
            producer.send(record2);
          }
        }
      } finally {
        producer.close();
        consumer.close();
      }

    }

}

When I run bin/kafka-console-consumer.sh --bootstrap-server localhost:9092 --topic forecastTopic --from-beginning and I run my producer a couple of time, I get

0. value-1
0. 6
1. value-2
1. 6
2. value-1
2. 6
3. value-1
3. 6
4. value-1
4. 6
5. value-1
5. 6
6. value-1
6. 6
7. value-2
7. 6
8. value-1
8. 6
9. value-1
9. 6
10. value-1
10. 6
11. value-1
11. 6
12. value-1
12. 6
13. value-2
13. 6
14. value-1
14. 6
15. value-1
15. 6
16. value-1
16. 6
17. value-1
17. 6
18. value-1
18. 6
19. value-2
19. 6
20. value-1
20. 6
21. value-1
21. 6
22. value-1
22. 6
23. value-1
23. 6
24. value-1
24. 6
25. value-2
25. 6
26. value-1
26. 6
27. value-1
27. 6
28. value-1
28. 6
29. value-1
29. 6
30. value-1
30. 6
31. value-2
31. 6
32. value-1
32. 6
33. value-1
33. 6
34. value-1
34. 6
35. value-1
35. 6
36. value-1
36. 6
37. value-2
37. 6
38. value-1
38. 6
39. value-1
39. 6
40. value-1
40. 6
41. value-1
41. 6
42. value-1
42. 6
43. value-2
43. 6
44. value-1
44. 6
45. value-1
45. 6
46. value-1
46. 6
47. value-1
47. 6
48. value-1
48. 12
49. value-2
49. 12
50. value-1
50. 12
51. value-1
51. 12
52. value-1
52. 12
53. value-1
53. 12
54. value-1
54. 12
55. value-2
55. 12
56. value-1
56. 12
57. value-1
57. 12
58. value-1
58. 12
59. value-1
59. 12
60. value-1
60. 6
61. value-2
61. 6
62. value-1
62. 6
63. value-1
63. 6
64. value-1
64. 6
65. value-1
65. 6
66. value-1
66. 6
67. value-2
67. 6
68. value-1
68. 6
69. value-1
69. 6
70. value-1
70. 6
71. value-1
71. 6
72. value-1
72. 6
73. value-2
73. 6
74. value-1
74. 6
75. value-1
75. 6
76. value-1
76. 6
77. value-1
77. 6
78. value-1
78. 6
79. value-2
79. 6
80. value-1
80. 6
81. value-1
81. 6
82. value-1
82. 6
83. value-1
83. 6

I put the log.cleanup.policy=compact in the server.properties file, but it doesn't seem to work, because I have all the 83 offsets in the topic.

Thank you.

Answer 1

Just in case somebody finds this helpful, this is the actual CLI command to use if you want to make a specific topic compacted, and don't want to set all your topics to compacted at the server level.

bin/kafka-topics --alter --topic my_topic_name --zookeeper my_zookeeper:2181 --config cleanup.policy=compact

Assuming the above is being run from the confluent base directory. I believe you have to change the command to call bin/kafka-topics.sh if using just a regular Apache Kafka distribution.