Auto-commit vs manual commit in Kafka - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to enable auto-commit in Kafka consumer configuration.

Kafka

props.put("enable.auto.commit", [1]);

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

A"true"

B"auto"

C"false"

D"manual"

Attempts:

3 left

💡 Hint

Common Mistakes

Using false disables auto-commit.

Using 'auto' or 'manual' are invalid values.

Setting enable.auto.commit to true enables Kafka consumer to commit offsets automatically.

2fill in blank

medium

Complete the code to manually commit offsets synchronously in Kafka consumer.

Kafka

consumer.[1]();

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

Acommit

BcommitSync

CcommitAsync

DcommitManual

Attempts:

3 left

💡 Hint

Common Mistakes

Using commitAsync commits asynchronously, not synchronously.

Using commit or commitManual are not valid Kafka consumer methods.

commitSync() commits offsets synchronously, blocking until the commit is acknowledged.

3fill in blank

hard

Fix the error in the code to disable auto-commit in Kafka consumer configuration.

Kafka

props.put("enable.auto.commit", [1]);

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

A"false"

Bfalse

CFalse

DFALSE

Attempts:

3 left

💡 Hint

Common Mistakes

Using boolean false without quotes causes errors.

Using capitalized False or FALSE are invalid.

The value must be a string "false" to properly disable auto-commit in Kafka consumer properties.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps topic partitions to their latest committed offsets.

Kafka

offsets = {tp: consumer.[1](tp) for tp in consumer.[2]() if tp is not None}

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

Acommitted

Bassignment

Csubscription

Dpartitions

Attempts:

3 left

💡 Hint

Common Mistakes

Using subscription or partitions instead of assignment for getting assigned partitions.

Using wrong method names for committed offsets.

consumer.committed(tp) gets the committed offset for a topic partition, and consumer.assignment() returns the set of partitions assigned to the consumer.

5fill in blank

hard

Fill all three blanks to commit offsets asynchronously with a callback that prints success or error.

Kafka

consumer.[1](offsets, new OffsetCommitCallback() {
    public void onComplete(Map<TopicPartition, OffsetAndMetadata> offsets, Exception e) {
        if (e == null) {
            System.out.println("Commit successful for [2]");
        } else {
            System.err.println("Commit failed: " + [3]);
        }
    }
});

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

AcommitAsync

Boffsets

Ce.getMessage()

DcommitSync

Attempts:

3 left

💡 Hint

Common Mistakes

Using commitSync instead of commitAsync for asynchronous commit.

Printing the exception object directly instead of its message.

commitAsync commits offsets asynchronously. The callback receives the offsets and an exception e. If e is null, commit succeeded; otherwise, print the error message with e.getMessage().

Practice

1. What is the main difference between auto-commit and manual commit in Kafka consumer offset management?

easy

A. Auto-commit requires manual calls to commit offsets, manual commit commits automatically.

B. Auto-commit disables offset tracking, manual commit enables it.

C. Auto-commit commits offsets automatically at intervals, manual commit requires explicit commit calls.

D. Auto-commit commits offsets only after consumer shutdown, manual commit commits continuously.

Solution

1. Step 1: Understand auto-commit behavior

   Auto-commit commits offsets automatically at regular intervals without user intervention.

2. Step 2: Understand manual commit behavior

   Manual commit requires the consumer to explicitly call commit() after processing messages.

3. Final Answer:

   Auto-commit commits offsets automatically at intervals, manual commit requires explicit commit calls. -> Option C

4. Quick Check:

   Auto-commit = automatic, Manual commit = explicit call [OK]

Hint: Auto-commit is automatic; manual commit needs your call [OK]

Common Mistakes:

• Confusing which method commits automatically
• Thinking manual commit disables offset tracking
• Believing auto-commit commits only on shutdown

2. Which of the following is the correct way to disable auto-commit in Kafka consumer configuration?

easy

A. "enable.auto.commit" : false

B. "auto.commit.enable" : false

C. "auto.commit" : "disable"

D. "enable.auto.commit" : true

Solution

1. Step 1: Identify the correct config key

   The correct Kafka consumer config key to control auto-commit is "enable.auto.commit".

2. Step 2: Identify the correct value to disable auto-commit

   Setting "enable.auto.commit" to false disables auto-commit.

3. Final Answer:

   "enable.auto.commit" : false -> Option A

4. Quick Check:

   Disable auto-commit = enable.auto.commit = false [OK]

Hint: Use "enable.auto.commit" = false to disable auto-commit [OK]

Common Mistakes:

• Using wrong config key names
• Setting true instead of false to disable
• Using string values instead of boolean

3. Given this Kafka consumer code snippet with manual commit:

consumer.poll(Duration.ofMillis(100)).forEach(record -> {
    process(record);
});
consumer.commitSync();

What happens if commitSync() is called before processing the records?

medium

A. Offsets are committed before processing, risking message loss on failure.

B. Offsets are committed after processing, ensuring safe processing.

C. commitSync() throws an exception if called before processing.

D. Offsets are not committed at all.

Solution

1. Step 1: Understand commitSync timing

   commitSync() commits the current offsets to Kafka immediately when called.

2. Step 2: Analyze calling commitSync before processing

   If commitSync() is called before processing, offsets are saved before messages are handled, risking data loss if processing fails.

3. Final Answer:

   Offsets are committed before processing, risking message loss on failure. -> Option A

4. Quick Check:

   Commit before processing = risk of message loss [OK]

Hint: Commit offsets only after processing messages [OK]

Common Mistakes:

• Assuming commitSync waits for processing
• Thinking commitSync throws error if called early
• Believing offsets commit automatically without call

4. You have disabled auto-commit and use manual commit in your Kafka consumer. You notice some offsets are not committed, causing message reprocessing. What is the likely cause?

medium

A. Kafka broker is down, so commits fail silently.

B. Auto-commit is enabled, causing conflicts.

C. You called commit() before processing messages.

D. You forgot to call commit() after processing messages.

Solution

1. Step 1: Check manual commit requirements

   When auto-commit is disabled, the consumer must call commit() explicitly after processing.

2. Step 2: Identify cause of missing commits

   If offsets are not committed, likely commit() was not called after processing, causing reprocessing.

3. Final Answer:

   You forgot to call commit() after processing messages. -> Option D

4. Quick Check:

   Manual commit needs explicit commit() call [OK]

Hint: Always call commit() after processing when auto-commit is off [OK]

Common Mistakes:

• Assuming auto-commit still works when disabled
• Blaming Kafka broker without checking code
• Calling commit() before processing messages

5. You want to ensure exactly-once processing in a Kafka consumer application. Which commit strategy is safer and why?

hard

A. Auto-commit, because it commits offsets automatically without extra code.

B. Manual commit, because you commit offsets only after successful processing.

C. Auto-commit, because it commits offsets after processing each message.

D. Manual commit, because it commits offsets before processing messages.

Solution

1. Step 1: Understand exactly-once processing needs

   Exactly-once means processing each message once and committing offset only after success.

2. Step 2: Compare commit strategies

   Auto-commit commits offsets automatically at intervals, risking committing before processing completes. Manual commit lets you commit only after successful processing.

3. Final Answer:

   Manual commit, because you commit offsets only after successful processing. -> Option B

4. Quick Check:

   Exactly-once needs manual commit after success [OK]

Hint: Commit manually after success for exactly-once processing [OK]

Common Mistakes:

• Assuming auto-commit guarantees exactly-once
• Committing offsets before processing
• Ignoring commit timing importance