Topic deletion and cleanup in Kafka - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of the Kafka topic deletion command?

Given the command to delete a Kafka topic, what will be the output if the topic exists and deletion is successful?

Kafka

kafka-topics.sh --delete --topic my-topic --bootstrap-server localhost:9092

A Topic 'my-topic' marked for deletion.

B Error: Topic 'my-topic' does not exist.

C Topic 'my-topic' deleted immediately.

D Warning: Topic deletion is disabled.

💡 Hint

Think about how Kafka handles topic deletion asynchronously.

Kafka marks the topic for deletion but the actual removal happens asynchronously. The command outputs a confirmation that the topic is marked for deletion.

🧠 Conceptual

intermediate

What happens if topic deletion is disabled in Kafka?

If the Kafka broker configuration has 'delete.topic.enable=false', what will happen when you try to delete a topic?

A The topic will remain and no deletion occurs.

B The topic will be marked for deletion but not removed.

C The deletion command will fail with an error.

D The topic will be deleted immediately.

💡 Hint

Consider the effect of disabling topic deletion in Kafka broker settings.

When 'delete.topic.enable' is false, Kafka ignores delete requests and the topic remains intact without any deletion.

🔧 Debug

advanced

Why does the topic not get deleted after issuing the delete command?

You ran the command to delete a Kafka topic, but the topic still appears in the list. What could be the reason?

Kafka

kafka-topics.sh --delete --topic test-topic --bootstrap-server localhost:9092
kafka-topics.sh --list --bootstrap-server localhost:9092

A The topic is marked for deletion but the broker has not completed cleanup yet.

B The topic name was misspelled in the delete command.

C The topic has active consumers preventing deletion.

D The Kafka broker has 'delete.topic.enable' set to false.

💡 Hint

Check the broker configuration related to topic deletion.

If 'delete.topic.enable' is false, Kafka will not delete topics even if the delete command is issued, so the topic remains listed.

📝 Syntax

advanced

Which command correctly deletes a Kafka topic named 'orders'?

Choose the correct syntax to delete the Kafka topic 'orders' using kafka-topics.sh with bootstrap server localhost:9092.

A kafka-topics.sh --remove --topic orders --bootstrap-server localhost:9092

B kafka-topics.sh --delete --topic orders --bootstrap-server localhost:9092

C kafka-topics.sh --delete-topic orders --server localhost:9092

D kafka-topics.sh --delete orders --bootstrap-server localhost:9092

💡 Hint

Check the official kafka-topics.sh command syntax for deleting topics.

The correct syntax uses '--delete' and '--topic' flags with '--bootstrap-server' to specify the broker.

🚀 Application

expert

How to ensure complete cleanup of deleted Kafka topics?

After deleting a Kafka topic, which steps ensure that all data and metadata related to the topic are fully cleaned up from the Kafka cluster?

A Run kafka-topics.sh with --force-delete flag to remove topic instantly.

B Restart all Kafka brokers immediately after issuing the delete command.

C Wait for Kafka to asynchronously delete topic data, then manually delete topic directories from brokers if needed.

D Delete the topic and then run kafka-configs.sh to remove topic configs.

💡 Hint

Think about Kafka's asynchronous deletion and broker storage cleanup.

Kafka deletes topic data asynchronously. Sometimes manual cleanup of topic directories on brokers is needed if deletion is stuck or incomplete.

Practice

1. What is the correct Kafka configuration to enable topic deletion?

easy

A. topic.delete.enabled=false

B. enable.topic.removal=false

C. delete.topic.enable=true

D. allow.topic.delete=no

Solution

1. Step 1: Understand Kafka topic deletion setting

   The Kafka broker must have a configuration that explicitly allows topic deletion.

2. Step 2: Identify the correct configuration key

   The correct key is delete.topic.enable and it must be set to true to allow deletion.

3. Final Answer:

   delete.topic.enable=true -> Option C

4. Quick Check:

   Topic deletion enabled = delete.topic.enable=true [OK]

Hint: Look for 'delete.topic.enable' set to true in config [OK]

Common Mistakes:

• Confusing the config key name
• Setting the value to false
• Assuming deletion works without config change

2. Which command correctly deletes a Kafka topic named my-topic?

easy

A. kafka-delete-topic.sh --topic my-topic

B. kafka-topics.sh --delete --topic my-topic

C. kafka-topics.sh --remove --topic my-topic

D. kafka-topics.sh --drop --topic my-topic

Solution

1. Step 1: Identify the correct Kafka topic deletion command

   The official Kafka command to delete a topic uses kafka-topics.sh with the --delete flag.

2. Step 2: Verify the command syntax

   The correct syntax is kafka-topics.sh --delete --topic my-topic.

3. Final Answer:

   kafka-topics.sh --delete --topic my-topic -> Option B

4. Quick Check:

   Delete topic command = kafka-topics.sh --delete --topic [OK]

Hint: Use --delete flag with kafka-topics.sh to remove topics [OK]

Common Mistakes:

• Using wrong flags like --remove or --drop
• Using a non-existent script
• Omitting the --topic option

3. After running kafka-topics.sh --delete --topic test-topic, which command confirms the topic is deleted?

medium

A. kafka-topics.sh --alter --topic test-topic

B. kafka-topics.sh --describe --topic test-topic

C. kafka-topics.sh --create --topic test-topic

D. kafka-topics.sh --list

Solution

1. Step 1: Understand how to check existing topics

   Listing topics shows all current topics in Kafka, so deleted topics won't appear.

2. Step 2: Choose the command that lists topics

   kafka-topics.sh --list lists all topics, confirming if test-topic is gone.

3. Final Answer:

   kafka-topics.sh --list -> Option D

4. Quick Check:

   List topics to confirm deletion = kafka-topics.sh --list [OK]

Hint: List topics to verify deletion, deleted ones won't show [OK]

Common Mistakes:

• Using describe which errors if topic missing
• Trying to create or alter instead of checking
• Assuming deletion is immediate without checking

4. You tried to delete a topic but it still appears in the list. What is the most likely cause?

medium

A. The broker configuration delete.topic.enable is set to false

B. You used the wrong topic name in the delete command

C. Kafka does not support topic deletion

D. The topic is currently being produced to

Solution

1. Step 1: Check broker configuration for topic deletion

   If delete.topic.enable is false, Kafka ignores delete commands and topics remain.

2. Step 2: Understand other options

   Wrong topic name causes error, Kafka supports deletion if enabled, and producing to topic doesn't block deletion.

3. Final Answer:

   The broker configuration delete.topic.enable is set to false -> Option A

4. Quick Check:

   Deletion blocked if delete.topic.enable=false [OK]

Hint: Check delete.topic.enable=true to allow deletion [OK]

Common Mistakes:

• Assuming Kafka never supports deletion
• Ignoring broker config settings
• Thinking active producers block deletion

5. You want to automate cleanup of unused topics older than 30 days. Which approach best uses Kafka's topic deletion and cleanup features?

hard

A. Enable delete.topic.enable=true and run a script that lists topics, checks their creation date, and deletes old ones

B. Set log.retention.ms to 30 days and rely on Kafka to delete topics automatically

C. Manually delete topics from Kafka config files after 30 days

D. Disable topic deletion and archive topics instead

Solution

1. Step 1: Understand Kafka's automatic cleanup capabilities

   Kafka deletes old log segments inside topics but does not delete entire topics automatically based on age.

2. Step 2: Choose an automation method for topic deletion

   Enabling delete.topic.enable=true and scripting topic listing with date checks allows controlled deletion of old topics.

3. Final Answer:

   Enable delete.topic.enable=true and run a script that lists topics, checks their creation date, and deletes old ones -> Option A

4. Quick Check:

   Automate deletion with config + script, not just retention settings [OK]

Hint: Use delete.topic.enable plus scripts for automated topic cleanup [OK]

Common Mistakes:

• Expecting Kafka to delete topics automatically by age
• Editing config files manually for topic deletion
• Disabling deletion and expecting cleanup