Exactly-once stream processing in Kafka - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Exactly-Once Semantics in Kafka

Which Kafka feature ensures that messages are processed exactly once in a stream processing application?

A Kafka Transactions

B Kafka Consumer Groups

C Kafka Partitions

D Kafka Replication

💡 Hint

Think about what mechanism allows atomic writes and commits in Kafka.

Kafka Transactions allow producers and consumers to write and read messages atomically, ensuring exactly-once processing.

💻 Command Output

intermediate

Kafka Producer Transaction Initialization Output

What is the expected output when a Kafka producer successfully initializes transactions?

Kafka

producer.initTransactions();
System.out.println("Transactions initialized");

A Transactions initialized

B Exception: Transactions not supported

C No output

D Error: Producer not configured

💡 Hint

Consider what happens when the initTransactions method completes without error.

If the producer is configured correctly, initTransactions completes successfully and the message is printed.

🔀 Workflow

advanced

Correct Order of Steps for Exactly-Once Processing in Kafka Streams

Arrange the following steps in the correct order to achieve exactly-once processing in a Kafka Streams application.

A 1,3,2,4

B 2,1,3,4

C 1,2,3,4

D 2,3,1,4

💡 Hint

Think about starting the transaction before processing and committing after sending output.

The transaction must start before processing input and committing after output to ensure atomicity.

❓ Troubleshoot

advanced

Identifying the Cause of Duplicate Messages in Exactly-Once Kafka Streams

A Kafka Streams application configured for exactly-once processing is producing duplicate output messages. What is the most likely cause?

A The producer is not using transactions

B The application is using at-least-once processing mode

C The input topic has multiple partitions

D The consumer group ID is not set

💡 Hint

Consider the processing guarantee mode configured in the application.

Using at-least-once mode can cause duplicates because it retries processing without atomic commits.

✅ Best Practice

expert

Best Practice for Configuring Kafka Producer for Exactly-Once Semantics

Which configuration is essential to enable exactly-once semantics in a Kafka producer?

A linger.ms=1000 and max.in.flight.requests.per.connection=5

B acks=0 and retries=0

C compression.type=none and batch.size=0

D enable.idempotence=true and transaction.id set

💡 Hint

Think about settings that prevent duplicate sends and enable transactions.

enable.idempotence=true prevents duplicates and setting transaction.id enables transactions for atomic writes.