Acknowledgment modes (acks=0, 1, all) in Kafka - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does acks=0 mean in Kafka producer configuration?

acks=0 means the producer does not wait for any acknowledgment from the broker after sending a message. It sends the message and moves on immediately.

This is the fastest mode but risks message loss if the broker fails.

beginner

Explain acks=1 in Kafka producer settings.

acks=1 means the producer waits for acknowledgment from the leader broker only.

The leader confirms it received the message, but followers might not have replicated it yet.

This balances speed and reliability.

beginner

What does acks=all (or acks=-1) guarantee in Kafka?

acks=all means the producer waits for acknowledgment from all in-sync replicas.

This ensures the message is fully replicated and is the safest mode against data loss.

It is slower but more reliable.

beginner

Which acknowledgment mode offers the fastest message sending but the least reliability?

acks=0 offers the fastest sending because the producer does not wait for any confirmation.

However, it risks losing messages if the broker fails before storing them.

intermediate

Why might you choose acks=all despite its slower speed?

You choose acks=all to ensure maximum data safety.

It waits for all replicas to confirm the message, reducing the chance of data loss even if some brokers fail.

What does acks=0 mean in Kafka?

A Producer waits for leader acknowledgment only

B Producer retries sending messages indefinitely

C Producer waits for all replicas acknowledgment

D Producer does not wait for any acknowledgment

acks=0 means the producer sends messages without waiting for any confirmation from brokers.

Which acks setting waits for the leader broker's confirmation only?

A acks=all

B acks=0

C acks=1

D acks=-1

acks=1 waits for the leader broker to confirm the message.

What is the main advantage of acks=all?

A Waits for all in-sync replicas to confirm

B No message loss risk

C No acknowledgments needed

D Fastest message sending

acks=all waits for all in-sync replicas to confirm, ensuring full replication.

If you want the fastest sending speed and can tolerate some message loss, which acks value should you use?

A acks=all

B acks=0

C acks=1

D acks=-1

acks=0 does not wait for any acknowledgment, so it is the fastest but least reliable.

What does acks=-1 mean in Kafka?

A Same as acks=all

B Same as acks=1

C Same as acks=0

D Disables acknowledgments

acks=-1 is an alias for acks=all, waiting for all replicas to confirm.

Describe the differences between acks=0, acks=1, and acks=all in Kafka producer configuration.

Think about how much the producer waits before considering a message sent.

Why would a Kafka producer choose acks=all over acks=1 or acks=0?

Consider what happens if a broker fails after receiving a message.

Practice

1. Which acks mode in Kafka provides the fastest message sending but with the least safety?

easy

A. acks=0

B. acks=1

C. acks=all

D. None of the above

Solution

1. Step 1: Understand acks=0 behavior

   This mode means the producer does not wait for any acknowledgment from the broker, so it sends messages fastest but with no guarantee of delivery.

2. Step 2: Compare with other modes

   acks=1 waits for leader confirmation, and acks=all waits for all replicas, both slower but safer.

3. Final Answer:

   acks=0 -> Option A

4. Quick Check:

   Fastest but least safe = acks=0 [OK]

Hint: No wait for confirmation means fastest mode is acks=0 [OK]

Common Mistakes:

• Confusing acks=0 with acks=1
• Thinking acks=all is fastest
• Assuming acks=0 waits for leader

2. Which of the following is the correct way to set the acknowledgment mode to wait for all replicas in Kafka producer configuration?

easy

A. "acks=1"

B. "acks=0"

C. "acks=all"

D. "ack=all"

Solution

1. Step 1: Recall correct property name and value

   The property is acks (plural), and to wait for all replicas, the value is all.

2. Step 2: Check options for syntax correctness

   "acks=all" uses correct key and value: "acks=all". "ack=all" has a typo "ack" instead of "acks".

3. Final Answer:

   "acks=all" -> Option C

4. Quick Check:

   Wait for all replicas = acks=all [OK]

Hint: Remember plural 'acks' and value 'all' for all replicas [OK]

Common Mistakes:

• Using 'ack' instead of 'acks'
• Confusing 'acks=1' with 'acks=all'
• Setting 'acks=0' for all replicas

3. Consider this Kafka producer code snippet:

props.put("acks", "1");
producer.send(record);
System.out.println("Message sent");

What does acks=1 guarantee before printing "Message sent"?

medium

A. Message is stored only in producer buffer

B. No guarantee; message may be lost

C. All replicas have confirmed the message

D. Leader broker has confirmed the message

Solution

1. Step 1: Understand acks=1 meaning

   This mode waits for the leader broker to confirm the message is received and written to its log.

2. Step 2: Compare with other options

   acks=0 gives no guarantee, acks=all waits for all replicas, and producer buffer storage is unrelated.

3. Final Answer:

   Leader broker has confirmed the message -> Option D

4. Quick Check:

   acks=1 means leader confirmation [OK]

Hint: acks=1 waits for leader confirmation only [OK]

Common Mistakes:

• Thinking acks=1 waits for all replicas
• Assuming no guarantee with acks=1
• Confusing producer buffer with broker confirmation

4. You have this Kafka producer configuration:

props.put("acks", "alll");

What is the problem with this configuration?

medium

A. Typo in the value; should be "all"

B. Typo in the key; should be "ack"

C. No problem; "alll" is valid

D. Should be an integer, not a string

Solution

1. Step 1: Check the value spelling

   The correct value for waiting all replicas is "all", but here it is misspelled as "alll" with an extra 'l'.

2. Step 2: Verify key and value types

   The key "acks" is correct and the value should be a string. So the problem is only the typo in the value.

3. Final Answer:

   Typo in the value; should be "all" -> Option A

4. Quick Check:

   Value must be "all", not "alll" [OK]

Hint: Check spelling of 'all' carefully in acks value [OK]

Common Mistakes:

• Assuming 'alll' is valid
• Changing key to 'ack' instead of 'acks'
• Using integer instead of string for acks

5. You want to ensure maximum data safety in Kafka producer but can tolerate some delay. Which acks setting should you use and why?

hard

A. acks=1 because leader confirmation is enough

B. acks=all because it waits for all replicas

C. acks=0 because it is fastest

D. acks=-1 because it disables acknowledgments

Solution

1. Step 1: Identify safety vs speed tradeoff

   acks=all waits for all replicas to confirm, ensuring maximum data safety but slower performance.

2. Step 2: Evaluate other options

   acks=0 is fastest but unsafe, acks=1 waits only for leader, and acks=-1 is invalid or equivalent to acks=all but less clear.

3. Final Answer:

   acks=all because it waits for all replicas -> Option B

4. Quick Check:

   Max safety = acks=all [OK]

Hint: Max safety means waiting for all replicas: acks=all [OK]

Common Mistakes:

• Choosing acks=0 for safety
• Confusing acks=-1 as disabling acknowledgments
• Thinking leader confirmation is max safety