Replication factor in Kafka - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the replication factor in Kafka?

The replication factor is the number of copies of each partition that Kafka keeps across different brokers to ensure data durability and availability.

beginner

Why is having a replication factor greater than 1 important?

It helps protect data from loss if a broker fails by keeping copies on other brokers, so the system can continue working without losing messages.

beginner

What happens if the replication factor is set to 1?

There is only one copy of each partition, so if the broker holding that partition fails, the data is lost and unavailable until the broker recovers.

intermediate

How does Kafka decide which brokers hold replicas of a partition?

Kafka distributes replicas across brokers to balance load and increase fault tolerance, ensuring replicas are on different brokers to avoid single points of failure.

intermediate

What is the relationship between replication factor and fault tolerance?

Higher replication factor means more copies of data, which increases fault tolerance because the system can survive more broker failures without losing data.

What does a replication factor of 3 mean in Kafka?

A Each partition has 3 copies on different brokers

B There are 3 partitions in the topic

C The topic can only have 3 messages

D The broker can handle 3 clients

Replication factor 3 means each partition is copied 3 times on different brokers for safety.

If a broker fails, what helps Kafka keep data available?

A Disabling replication

B Replication factor greater than 1

C Using a single broker

D Having only one partition

Replication factor > 1 means copies exist on other brokers, so data stays available.

What risk does a replication factor of 1 pose?

A Data loss if the broker fails

B Too many copies of data

C Slower message delivery

D More disk space used

With only one copy, if the broker fails, data is lost.

How does Kafka improve fault tolerance with replication?

A By limiting the number of partitions

B By deleting old messages

C By storing replicas on different brokers

D By using a single broker

Replicas on different brokers prevent single points of failure.

What is a downside of increasing the replication factor?

A Fewer brokers needed

B Less data safety

C Messages get lost faster

D More disk space and network usage

More replicas use more disk space and network resources.

Explain what the replication factor is and why it matters in Kafka.

Think about how Kafka keeps copies of data to avoid losing it.

Describe what happens when the replication factor is set to 1 and a broker fails.

Consider what happens if there is no backup copy.

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