Exactly-once semantics (EOS) in Kafka - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to enable exactly-once semantics in Kafka producer configuration.

Kafka

Properties props = new Properties();
props.put("enable.idempotence", [1]);

Drag options to blanks, or click blank then click option'

A"maybe"

B"false"

C"yes"

D"true"

Attempts:

3 left

💡 Hint

Common Mistakes

Using false disables idempotence, so exactly-once is not guaranteed.

Using invalid strings causes configuration errors.

Setting enable.idempotence to true enables exactly-once semantics in Kafka producer.

2fill in blank

medium

Complete the code to set the transaction ID for Kafka producer to support EOS.

Kafka

props.put("transactional.id", [1]);

Drag options to blanks, or click blank then click option'

A"txn-123"

Bnull

C""

D123

Attempts:

3 left

💡 Hint

Common Mistakes

Setting transactional.id to null disables transactions.

Using empty string disables transactions.

The transactional.id must be a unique string to enable transactions for exactly-once semantics.

3fill in blank

hard

Fix the error in the code to begin a Kafka transaction correctly.

Kafka

producer.[1]();

Drag options to blanks, or click blank then click option'

AbeginTransaction

BstartTransaction

CinitTransaction

DopenTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Using startTransaction causes a compilation error.

initTransaction and openTransaction do not exist.

The correct method to start a transaction in Kafka producer is beginTransaction().

4fill in blank

hard

Fill both blanks to commit a Kafka transaction and close the producer.

Kafka

producer.[1]();
producer.[2]();

Drag options to blanks, or click blank then click option'

AcommitTransaction

Bclose

Cflush

DabortTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Calling abortTransaction instead of commitTransaction.

Closing producer before committing transaction.

First commit the transaction with commitTransaction(), then close the producer with close().

5fill in blank

hard

Fill all three blanks to configure Kafka consumer for exactly-once semantics with isolation level and auto commit disabled.

Kafka

props.put("isolation.level", [1]);
props.put("enable.auto.commit", [2]);
props.put("auto.offset.reset", [3]);

Drag options to blanks, or click blank then click option'

A"read_committed"

B"false"

C"earliest"

D"true"

Attempts:

3 left

💡 Hint

Common Mistakes

Setting isolation.level to 'read_uncommitted' breaks EOS.

Enabling auto commit causes duplicate processing.

Using 'latest' for auto.offset.reset may skip messages.

To ensure exactly-once semantics, set isolation.level to read_committed, disable auto commit by setting enable.auto.commit to false, and set auto.offset.reset to earliest to read from the beginning if no offset is found.

Practice

1. What is the main goal of Exactly-once semantics (EOS) in Kafka?

easy

A. To compress messages for storage efficiency

B. To prevent duplicate or lost messages during data processing

C. To allow multiple consumers to read the same message simultaneously

D. To increase the speed of message delivery

Solution

1. Step 1: Understand the purpose of EOS

   Exactly-once semantics ensures that each message is processed exactly one time, avoiding duplicates or losses.

2. Step 2: Compare options with EOS goal

   Options A, B, and C describe other Kafka features but not EOS's main goal.

3. Final Answer:

   To prevent duplicate or lost messages during data processing -> Option B

4. Quick Check:

   EOS = prevent duplicates/losses [OK]

Hint: EOS means no duplicates or lost messages [OK]

Common Mistakes:

• Confusing EOS with message speed optimization
• Thinking EOS allows multiple consumers to read simultaneously
• Mixing EOS with message compression features

2. Which configuration must be enabled in a Kafka producer to support Exactly-once semantics?

easy

A. max.poll.records = 500

B. acks = 0

C. compression.type = gzip

D. enable.idempotence = true

Solution

1. Step 1: Identify EOS required producer setting

   Enabling idempotence (enable.idempotence = true) is necessary for EOS to avoid duplicates.

2. Step 2: Review other options

   Options B, C, and D relate to acknowledgments, compression, and consumer polling, not EOS.

3. Final Answer:

   enable.idempotence = true -> Option D

4. Quick Check:

   Idempotence enabled = EOS support [OK]

Hint: Enable idempotence for EOS in producer config [OK]

Common Mistakes:

• Setting acks to 0 disables guarantees
• Confusing compression with EOS
• Using consumer settings instead of producer

3. Given the following Kafka producer code snippet with transactions enabled, what will happen if producer.commitTransaction() is not called after producer.send()?

producer.initTransactions();
producer.beginTransaction();
producer.send(record);
// Missing commitTransaction call
producer.close();

medium

A. The transaction will be aborted and messages will not be committed

B. Messages will be committed automatically on close

C. Messages will be duplicated in the topic

D. Producer will throw a syntax error

Solution

1. Step 1: Understand transaction lifecycle in Kafka

   After beginning a transaction and sending messages, commitTransaction() must be called to finalize the transaction.

2. Step 2: Effect of missing commitTransaction()

   If commitTransaction() is not called, the transaction is aborted on close, so messages are not committed.

3. Final Answer:

   The transaction will be aborted and messages will not be committed -> Option A

4. Quick Check:

   Missing commitTransaction = abort transaction [OK]

Hint: Always commit or abort transactions explicitly [OK]

Common Mistakes:

• Assuming close commits automatically
• Expecting duplicates without commit
• Thinking missing commit causes syntax error

4. You have enabled EOS in your Kafka producer but notice duplicate messages in the topic. Which of the following is the most likely cause?

medium

A. Producer did not call initTransactions() before starting transactions

B. Producer set enable.idempotence to true

C. Consumer group is reading messages multiple times

D. Topic has replication factor set to 3

Solution

1. Step 1: Check EOS setup requirements

   initTransactions() must be called before using transactions to ensure EOS works properly.

2. Step 2: Analyze other options

   Producer set enable.idempotence to true is correct config, A relates to consumers not producers, D is unrelated to duplicates.

3. Final Answer:

   Producer did not call initTransactions() before starting transactions -> Option A

4. Quick Check:

   Missing initTransactions() causes duplicates [OK]

Hint: Call initTransactions() before transactions for EOS [OK]

Common Mistakes:

• Confusing consumer behavior with producer duplicates
• Assuming replication factor affects duplicates
• Thinking idempotence alone fixes all issues

5. You want to implement a Kafka producer that writes messages exactly once to multiple partitions atomically. Which combination of settings and steps is required to achieve this?

hard

A. Disable idempotence, send messages asynchronously, then flush producer

B. Set acks=0, send messages to partitions, then close producer

C. Enable idempotence, initialize and begin transactions, send messages, then commit transaction

D. Use synchronous sends without transactions and rely on consumer deduplication

Solution

1. Step 1: Identify EOS requirements for atomic writes

   Enable idempotence and use transactions to ensure atomic writes across partitions.

2. Step 2: Follow correct transaction steps

   Initialize transactions, begin transaction, send messages, then commit transaction to finalize.

3. Step 3: Evaluate other options

   Options B, C, and D lack idempotence or transactions, so they cannot guarantee exactly-once atomic writes.

4. Final Answer:

   Enable idempotence, initialize and begin transactions, send messages, then commit transaction -> Option C

5. Quick Check:

   Idempotence + transactions = atomic exactly-once writes [OK]

Hint: Use idempotence + transactions for atomic exactly-once writes [OK]

Common Mistakes:

• Ignoring transaction lifecycle steps
• Relying on consumer deduplication only
• Disabling idempotence for performance