How to Get the Number of Messages in a Kafka Topic

One key aspect of ensuring a well-managed and maintained Kafka cluster is monitoring the number of messages in a topic. By keeping an eye on the message count, you can ensure your system is operating smoothly and detect potential issues.

There are a number of ways to get the message count for a topic, and we'll do our best to cover the most popular ways. Some of these methods include using Kafka's built-in command-line tools, leveraging the Consumer API, or using third-party tools. Of course, each method has its pros and cons, which we'll also briefly take a look at.

In this article, we'll discuss various methods to help you get the number of messages in a Kafka topic with ease.

Using Kafka Command-Line Tools

Kafka comes bundled with a set of useful command-line tools that can be used for a number of different tasks, like creating topics, and managing and monitoring your cluster. These tools are very convenient when it comes to retrieving information about your cluster, like message counts. Here we'll focus on using these built-in command-line tools to get the number of messages in a topic.

To get the number of messages, you can use the kafka-run-class.sh script along with the kafka.tools.GetOffsetShell class. The command looks like this:

$ ./bin/kafka-run-class.sh kafka.tools.GetOffsetShell --broker-list <your_broker_list> --topic <your_topic_name> --time -1

Replace <your_broker_list> with the list of your brokers, and <your_topic_name> with the name of the topic you want to fetch the message count for. The --time -1 parameter tells the tool to fetch the latest offsets for each partition in the topic.

After executing the command, you'll see output formatted like this:

<your_topic_name>:<partition_id>:<latest_offset>

For example, it might look like this:

my_topic:0:450
my_topic:1:500
my_topic:2:550

To get the total message count, you need to add up the <latest_offset> values for each partition. Keep in mind that this method shows the count of messages currently available in the topic, and any messages that have been removed due to retention policies, for example, will not be included.

Using the Kafka Consumer API

Another approach to getting the number of messages in a Kafka topic is by using the Kafka Consumer API. The Consumer API is a programming interface that allows you to get messages from topics in various programming languages. In this section, we'll show how to use the Consumer API in Python to count the messages in a topic. You can adapt this method for other languages, such as Java, as needed.

First, you'll need to install the kafka-python library if you haven't already. You can do this using pip:

$ pip install kafka-python

Next, import the necessary libraries in your Python script:

from kafka import KafkaConsumer
import time

Next we'll need to configure the consumer properties. Replace <your_broker_list> with the list of your brokers and <your_topic_name> with the name of the topic you want to fetch the message count for.

consumer = KafkaConsumer(
    '<your_topic_name>',
    bootstrap_servers='<your_broker_list>',
    auto_offset_reset='earliest',
    enable_auto_commit=False,
    group_id=None,
)

With the consumer set up, we can now read messages from the topic:

now = time.time()
message_count = 0
for message in consumer:
    message_count += 1
    if (message.timestamp / 1000) - now > 60:
        break

This code will count messages for the next 60 seconds before stopping. You can adjust the time interval as needed.

Finally, print the message count to the console:

print(f"Total message count: {message_count}")

Now, when you run the script, it will consume messages from the topic and display the total message count after the given time interval.

Note: Keep in mind that using the Consumer API to count messages might not be the most efficient method, especially for topics with a large number of messages. This method actually requires consuming all messages in the topic, which can take a lot of time.

Using Kafka Monitoring Tools

In addition to the command-line tools and Kafka Consumer API, you can also use various monitoring tools to get the number of messages in a topic. These tools are typically user-friendly and have advanced features to help you manage clusters. Some popular Kafka monitoring tools include Confluent Control Center, CMAK, and Kafdrop. In this section, we will walk you through the process of obtaining message count using Confluent Control Center and CMAK.

For both Confluent Control Center and CMAK (Cluster Manager for Apache Kafka, formerly known as Kafka Manager), you'll need to start by configuring and connecting to your Kafka cluster. Follow the official documentation for each tool to set up the connection:

• Confluent Control Center documentation
• CMAK documentation

Once connected to your cluster, you can navigate to the topic whose message count you want to retrieve.

• In Confluent Control Center, go to the "Topics" tab and select the desired topic.
• In CMAK, choose the cluster and then click on the "Topic List" link. Locate your topic and click on it.

After navigating to the topic, you can retrieve the message count:

• In Confluent Control Center, check the "Messages" field in the "Overview" tab. This field should show the total number of messages in the topic.
• In CMAK, look for the "Total Size" field in the "Topic Identity" section on the topic's detail page. This field displays the total number of messages in the topic.

Conclusion

In this article, we looked at a few ways to get the number of messages in a Kafka topic. We started with Kafka's built-in command-line tools, as well as the Consumer API and other popular 3rd party tools like Confluent Control Center and CMAK.

Ultimately, the best method for getting the number of messages in a topic depends on your specific use-case and infrastructure. Be sure to weigh the pros and cons of each approach, like performance and ease-of-use