Topic configuration in Kafka - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of the topic configuration command?

You run the following Kafka command to create a topic with 3 partitions and a replication factor of 2. What will be the output message?

Kafka

kafka-topics.sh --create --topic my-topic --partitions 3 --replication-factor 2 --bootstrap-server localhost:9092

A Created topic my-topic.

B Error: Replication factor larger than available brokers.

C Topic my-topic already exists.

D Warning: Partitions must be at least 1.

💡 Hint

Check if the cluster has at least 2 brokers to support replication factor 2.

If the cluster has enough brokers, the topic is created successfully with the specified partitions and replication factor.

🧠 Conceptual

intermediate

What does the 'cleanup.policy' configuration control?

In Kafka topic configuration, what is the purpose of the 'cleanup.policy' setting?

A It specifies the replication factor for the topic.

B It sets the maximum message size allowed in the topic.

C It controls how Kafka deletes or compacts old log segments.

D It defines the number of partitions for the topic.

💡 Hint

Think about how Kafka manages old data in topics.

The 'cleanup.policy' can be 'delete' to remove old data or 'compact' to keep the latest record per key.

❓ Predict Output

advanced

What is the effect of setting 'min.insync.replicas' to 2?

Given a topic with replication factor 3, what happens if 'min.insync.replicas' is set to 2 and only 1 replica is in sync during a produce request?

A The produce request fails with a NotEnoughReplicasException.

B The produce request succeeds but with a warning logged.

C The produce request succeeds normally without any issues.

D The topic automatically increases the replication factor to 4.

💡 Hint

Consider what 'min.insync.replicas' means for message durability.

If the number of in-sync replicas is less than 'min.insync.replicas', Kafka rejects produce requests to ensure durability.

❓ Predict Output

advanced

What is the output of describing a topic with a retention.ms of 604800000?

You run the command to describe a topic and see the retention.ms configuration set to 604800000. What does this value represent?

Kafka

kafka-configs.sh --describe --entity-type topics --entity-name my-topic --bootstrap-server localhost:9092

A The topic retains messages for 1 day before deletion.

B The topic retains messages for 7 days before deletion.

C The topic retains messages indefinitely.

D The topic retention is disabled.

💡 Hint

Convert milliseconds to days to understand retention time.

604800000 milliseconds equals 7 days, so messages are kept for 7 days before being deleted.

🧠 Conceptual

expert

Which configuration ensures message order within a partition?

Which Kafka topic configuration guarantees that messages are consumed in the order they were produced within a partition?

A Setting 'cleanup.policy' to 'compact'.

B Setting 'retention.ms' to a high value.

C Setting 'min.insync.replicas' to the replication factor.

D Setting 'max.in.flight.requests.per.connection' to 1.

💡 Hint

Think about how Kafka handles message sending and retries.

'max.in.flight.requests.per.connection' set to 1 ensures messages are sent one at a time, preserving order.

Practice

1. What does the retention.ms configuration control in a Kafka topic?

easy

A. How long messages are kept before deletion

B. The number of partitions in the topic

C. The replication factor of the topic

D. The maximum message size allowed

Solution

1. Step 1: Understand retention.ms meaning

   The retention.ms setting defines the time in milliseconds that Kafka retains messages before deleting them.

2. Step 2: Compare with other options

   Other options like partitions, replication factor, and message size are controlled by different configurations.

3. Final Answer:

   How long messages are kept before deletion -> Option A

4. Quick Check:

   retention.ms = message retention time [OK]

Hint: Retention means how long messages stay before removal [OK]

Common Mistakes:

• Confusing retention.ms with replication factor
• Thinking retention.ms controls partition count
• Assuming retention.ms limits message size

2. Which of the following is the correct syntax to create a Kafka topic with a replication factor of 3 using the command line?

easy

A. kafka-topics.sh --create --topic myTopic --replication-factor 3 --partitions 1 --bootstrap-server localhost:9092

B. kafka-topics.sh --create --topic myTopic --replication 3 --partitions 1 --bootstrap-server localhost:9092

C. kafka-topics.sh --create --topic myTopic --replica-factor 3 --partitions 1 --bootstrap-server localhost:9092

D. kafka-topics.sh --create --topic myTopic --replication-factor=3 --partitions 1 --bootstrap-server localhost:9092

Solution

1. Step 1: Identify correct option name

   The correct option for replication factor is --replication-factor without equals sign.

2. Step 2: Check syntax correctness

   kafka-topics.sh --create --topic myTopic --replication-factor 3 --partitions 1 --bootstrap-server localhost:9092 uses the correct syntax with spaces and proper option names; others have wrong option names or equals sign which is invalid here.

3. Final Answer:

   kafka-topics.sh --create --topic myTopic --replication-factor 3 --partitions 1 --bootstrap-server localhost:9092 -> Option A

4. Quick Check:

   Use --replication-factor with space, no equals [OK]

Hint: Use --replication-factor with space, no equals sign [OK]

Common Mistakes:

• Using --replication instead of --replication-factor
• Adding equals sign (=) after option name
• Misspelling replication-factor option

3. Given the command:
kafka-topics.sh --alter --topic logs --config retention.ms=60000 --bootstrap-server localhost:9092
What will be the effect on the topic logs?

medium

A. Messages will be retained indefinitely

B. The topic's replication factor will be set to 60000

C. The topic will be deleted after 60000 messages

D. Messages will be retained for 1 minute before deletion

Solution

1. Step 1: Understand the command's purpose

   The command alters the topic logs by setting retention.ms to 60000 milliseconds (1 minute).

2. Step 2: Interpret retention.ms effect

   This means messages older than 1 minute will be deleted automatically.

3. Final Answer:

   Messages will be retained for 1 minute before deletion -> Option D

4. Quick Check:

   retention.ms=60000 means 1 minute retention [OK]

Hint: retention.ms value is in milliseconds for message lifetime [OK]

Common Mistakes:

• Thinking retention.ms controls message count
• Confusing retention.ms with replication factor
• Assuming retention.ms disables deletion

4. You tried to set the cleanup policy of a Kafka topic with:
kafka-topics.sh --alter --topic data --config cleanup.policy=delete,compact --bootstrap-server localhost:9092
But it failed. What is the likely cause?

medium

A. The --alter command cannot change cleanup.policy

B. The cleanup.policy value is invalid; it must be either 'delete' or 'compact', not both

C. The topic name 'data' is reserved and cannot be altered

D. The bootstrap server address is incorrect

Solution

1. Step 1: Check cleanup.policy valid values

   Kafka allows cleanup.policy to be either 'delete' or 'compact' or both separated by comma, but the syntax must be exact and supported by the Kafka version.

2. Step 2: Identify common error

   Some Kafka versions or setups do not support combined policies or require no spaces; if the command failed, likely the value was invalid or syntax incorrect.

3. Final Answer:

   The cleanup.policy value is invalid; it must be either 'delete' or 'compact', not both -> Option B

4. Quick Check:

   cleanup.policy must be valid single or combined value [OK]

Hint: Check cleanup.policy values carefully; some setups disallow combined [OK]

Common Mistakes:

• Using unsupported combined cleanup policies
• Trying to alter topic with wrong bootstrap server
• Assuming topic names cannot be altered

5. You want to create a Kafka topic named events with 4 partitions, replication factor 2, and a retention time of 2 hours. Which command correctly sets all these configurations?

hard

A. kafka-topics.sh --create --topic events --partitions 4 --replication-factor 2 --config retention.ms=120 --bootstrap-server localhost:9092

B. kafka-topics.sh --create --topic events --partitions 2 --replication-factor 4 --config retention.ms=7200000 --bootstrap-server localhost:9092

C. kafka-topics.sh --create --topic events --partitions 4 --replication-factor 2 --config retention.ms=7200000 --bootstrap-server localhost:9092

D. kafka-topics.sh --create --topic events --partitions 4 --replication-factor 2 --config retention.ms=7200 --bootstrap-server localhost:9092

Solution

1. Step 1: Verify partitions and replication factor

   The topic requires 4 partitions and replication factor 2, so options with these exact values are correct.

2. Step 2: Calculate retention.ms for 2 hours

   2 hours = 2 * 60 * 60 * 1000 = 7,200,000 milliseconds. Only kafka-topics.sh --create --topic events --partitions 4 --replication-factor 2 --config retention.ms=7200000 --bootstrap-server localhost:9092 uses this correct retention.ms value.

3. Final Answer:

   kafka-topics.sh --create --topic events --partitions 4 --replication-factor 2 --config retention.ms=7200000 --bootstrap-server localhost:9092 -> Option C

4. Quick Check:

   Retention in ms for 2 hours = 7200000 [OK]

Hint: Convert hours to ms: hours * 3600000 for retention.ms [OK]

Common Mistakes:

• Mixing partitions and replication factor values
• Using retention.ms in seconds or minutes instead of ms
• Incorrect retention.ms calculation