Topic deletion and cleanup in Kafka - Cheat Sheet & Quick Revision

Recall & Review

beginner

What happens when you delete a Kafka topic?

Deleting a Kafka topic removes all its data and metadata from the cluster. This means all messages, partitions, and offsets are permanently lost.

beginner

How do you enable topic deletion in Kafka?

You enable topic deletion by setting the broker configuration delete.topic.enable=true. Without this, topic deletion requests are ignored.

intermediate

What is the role of the log.retention.ms setting in topic cleanup?

The log.retention.ms setting controls how long Kafka keeps messages before deleting them during cleanup. It helps manage disk space by removing old data.

intermediate

Explain the difference between topic deletion and log cleanup in Kafka.

Topic deletion removes the entire topic and all its data permanently. Log cleanup removes old messages based on retention policies but keeps the topic and newer messages intact.

beginner

What happens if delete.topic.enable is set to false and you try to delete a topic?

If delete.topic.enable is false, Kafka ignores delete requests. The topic remains active and data is not removed.

Which Kafka broker setting must be enabled to allow topic deletion?

A delete.topic.enable=true

B log.retention.ms=0

C auto.create.topics.enable=true

D log.cleanup.policy=delete

The setting delete.topic.enable=true allows Kafka to delete topics when requested.

What does Kafka do when a topic is deleted?

A Disables the topic but keeps data

B Removes all data and metadata for the topic

C Only deletes messages older than retention period

D Archives the topic data for backup

Deleting a topic removes all its data and metadata permanently from Kafka.

What controls how long Kafka keeps messages before cleanup?

A auto.offset.reset

B delete.topic.enable

C log.retention.ms

D log.segment.bytes

log.retention.ms sets the time Kafka retains messages before deleting them.

If delete.topic.enable is false, what happens when you try to delete a topic?

A The topic is deleted immediately

B The topic is archived

C Kafka throws an error

D The delete request is ignored

Kafka ignores delete requests if delete.topic.enable is false.

Which of the following is NOT true about Kafka topic deletion?

A It only deletes messages older than retention time

B It can be disabled via broker config

C It permanently removes all topic data

D It removes topic metadata

Topic deletion removes the entire topic, not just old messages.

Describe the process and configuration needed to delete a Kafka topic safely.

Think about broker settings and what happens to data.

Explain the difference between Kafka topic deletion and log cleanup.

Focus on what is removed and what remains.

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