Replication factor in Kafka - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What does the replication factor control in Kafka?

In Kafka, the replication factor is a key configuration. What does it control?

A The number of consumers in a consumer group

B The number of partitions in a topic

C The maximum size of a message in bytes

D The number of copies of each partition across different brokers

💡 Hint

Think about data safety and availability in Kafka.

The replication factor sets how many copies of each partition exist on different brokers. This helps with fault tolerance.

❓ Predict Output

intermediate

Output of creating a topic with replication factor 3

Given the following Kafka topic creation command, what will be the replication factor of the topic?

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

A The topic will have 3 copies of each partition on different brokers

B The topic will have 2 copies of each partition

C The topic will have 1 copy of each partition

D The command will fail because replication factor cannot be 3

💡 Hint

Replication factor is set explicitly in the command.

The replication factor option sets the number of copies per partition. Here it is 3, so each partition has 3 copies.

❓ Predict Output

advanced

What happens if replication factor is higher than available brokers?

Consider a Kafka cluster with 2 brokers. What happens if you try to create a topic with replication factor 3?

A The topic creation fails with an error about insufficient brokers

B The topic is created with replication factor 2 automatically

C The topic is created with replication factor 3 but some replicas are on the same broker

D The topic is created with replication factor 1

💡 Hint

Replication factor cannot exceed the number of brokers.

Kafka requires the replication factor to be less than or equal to the number of brokers. Otherwise, topic creation fails.

🧠 Conceptual

advanced

Why is a higher replication factor beneficial?

What is the main benefit of setting a higher replication factor for a Kafka topic?

A Simpler consumer group management

B Reduced disk usage on brokers

C Improved fault tolerance and data availability

D Faster message processing speed

💡 Hint

Think about what happens if a broker fails.

A higher replication factor means more copies of data exist on different brokers, so if one broker fails, data is still available.

🚀 Application

expert

Calculate minimum in-sync replicas for replication factor 5

You have a Kafka topic with replication factor 5. To ensure strong durability, you want to set the minimum in-sync replicas (min.insync.replicas) to the highest number that still allows the leader to acknowledge writes if one broker fails. What should this value be?

A 2

B 4

C 5

D 3

💡 Hint

min.insync.replicas must be less than or equal to replication factor minus one to tolerate one failure.

With replication factor 5, setting min.insync.replicas to 4 means the leader requires 4 replicas to acknowledge writes. This allows one broker to fail and still maintain durability.

Practice

1.

What does the replication factor in Kafka control?

easy

A. The size limit of each partition

B. The number of copies of each partition stored across brokers

C. The number of partitions in a topic

D. The number of consumers in a consumer group

Solution

1. Step 1: Understand replication factor meaning

   The replication factor defines how many copies of each partition Kafka keeps on different brokers.

2. Step 2: Differentiate from other Kafka settings

   Partitions count and consumer group size are unrelated to replication factor.

3. Final Answer:

   The number of copies of each partition stored across brokers -> Option B

4. Quick Check:

   Replication factor = number of copies [OK]

Hint: Replication factor = copies of data stored [OK]

Common Mistakes:

• Confusing replication factor with partition count
• Thinking replication factor controls consumer groups
• Assuming replication factor limits partition size

2.

Which of the following is the correct way to set the replication factor when creating a Kafka topic using the command line?

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

easy

A. --replication-factor 3

B. --replication-factor=3

C. --replication_factor 3

D. --replicationFactor 3

Solution

1. Step 1: Check Kafka CLI syntax for replication factor

   The correct flag is --replication-factor with a space before the value.

2. Step 2: Identify incorrect options

   Options with underscores or camelCase are invalid flags; equals sign is not used here.

3. Final Answer:

   --replication-factor 3 -> Option A

4. Quick Check:

   Use double dash and hyphen for replication factor [OK]

Hint: Use double dash and hyphen for flags in Kafka CLI [OK]

Common Mistakes:

• Using underscore instead of hyphen
• Using equals sign instead of space
• Using camelCase flag names

3.

Given a Kafka topic created with --partitions 2 and --replication-factor 3, how many total replicas will Kafka store across the cluster?

medium

A. 6

B. 3

C. 5

D. 2

Solution

1. Step 1: Calculate replicas per partition

   Each partition has 3 replicas because replication factor is 3.

2. Step 2: Multiply by number of partitions

   2 partitions x 3 replicas each = 6 total replicas.

3. Final Answer:

   6 -> Option A

4. Quick Check:

   Partitions x Replication factor = Total replicas [OK]

Hint: Multiply partitions by replication factor [OK]

Common Mistakes:

• Confusing replication factor with total partitions
• Adding instead of multiplying partitions and replicas
• Ignoring replication factor in calculation

4.

What is wrong with this Kafka topic creation command?

kafka-topics.sh --create --topic logs --partitions 3 --replication-factor 5 --bootstrap-server localhost:9092

Assuming the Kafka cluster has only 3 brokers.

medium

A. Partitions must be equal to replication factor

B. Topic name cannot be 'logs'

C. Bootstrap server address is incorrect

D. Replication factor cannot be greater than the number of brokers

Solution

1. Step 1: Understand replication factor limits

   Replication factor must be less than or equal to the number of brokers to ensure each replica is on a different broker.

2. Step 2: Check cluster size vs replication factor

   Replication factor 5 is greater than 3 brokers, which is invalid.

3. Final Answer:

   Replication factor cannot be greater than the number of brokers -> Option D

4. Quick Check:

   Replication factor ≤ brokers [OK]

Hint: Replication factor must not exceed broker count [OK]

Common Mistakes:

• Thinking partitions must equal replication factor
• Ignoring cluster size limits
• Assuming topic names have restrictions here

5.

You want to create a Kafka topic with 4 partitions and a replication factor of 3 for high availability. However, your cluster has only 2 brokers. What is the best solution?

hard

A. Create the topic with 1 partition and replication factor 3

B. Set replication factor to 4 to match partitions

C. Increase the number of brokers to at least 3

D. Create the topic with replication factor 2 instead

Solution

1. Step 1: Check replication factor vs brokers

   Replication factor 3 requires at least 3 brokers to store replicas on different machines.

2. Step 2: Evaluate options

   Reducing replication factor lowers availability; increasing brokers meets requirement.

3. Final Answer:

   Increase the number of brokers to at least 3 -> Option C

4. Quick Check:

   Replication factor ≤ brokers for high availability [OK]

Hint: Match replication factor to broker count for safety [OK]

Common Mistakes:

• Setting replication factor higher than brokers
• Reducing partitions instead of brokers
• Ignoring availability requirements