Acknowledgment modes (acks=0, 1, all) in Kafka - Step-by-Step Execution

Process Flow - Acknowledgment modes (acks=0, 1, all)

Producer sends message

↓

Check acks setting

Shows how Kafka producer waits for acknowledgments based on the acks setting before continuing.

Execution Sample

Kafka

producer.send(record, acks=0)
producer.send(record, acks=1)
producer.send(record, acks='all')

Sends messages with different acknowledgment modes to Kafka.

Process Table

Step	acks value	Action	Wait for	Result	Continue
1	0	Send message	No one	No confirmation	Immediately
2	1	Send message	Leader broker	Leader confirms	After leader ack
3	all	Send message	All in-sync replicas	All confirm	After all acks
4	-	Stop	-	No more messages	-

💡 Producer stops sending after all messages are sent with specified acks.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
acks	-	0	1	all	all
confirmation_received	false	false	true	true	true
producer_continues	true	true	true	true	true

Key Moments - 3 Insights

Why does acks=0 not wait for any confirmation?

Because as shown in execution_table row 1, acks=0 means the producer sends the message and immediately continues without waiting for any broker acknowledgment.

What does acks=1 guarantee about the message?

As per execution_table row 2, acks=1 waits for the leader broker to confirm the message, ensuring it is received by the leader but not necessarily replicated yet.

How does acks='all' improve message durability?

According to execution_table row 3, acks='all' waits for all in-sync replicas to confirm, ensuring the message is fully replicated and durable before continuing.

Visual Quiz - 3 Questions

Look at the execution_table, at which step does the producer wait for all replicas to confirm?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Check the 'Wait for' column in execution_table row 3.

According to variable_tracker, what is the value of 'confirmation_received' after step 1?

A false

B true

C 'all'

D undefined

💡 Hint

Look at the 'confirmation_received' row under 'After Step 1' in variable_tracker.

If acks is set to 1, when does the producer continue sending messages?

A After all replicas confirm

B Immediately after sending

C After leader broker confirms

D Never continues

💡 Hint

Refer to execution_table row 2 under 'Continue' column.

Concept Snapshot

Kafka producer acks modes:
acks=0: No wait, no confirmation, fastest but risky.
acks=1: Wait for leader ack, safer.
acks=all: Wait for all replicas, safest.
Choose based on durability vs latency needs.

Full Transcript

This visual execution shows how Kafka producer's acknowledgment modes control message sending. When acks=0, the producer sends and continues immediately without waiting for confirmation. With acks=1, it waits for the leader broker to confirm receipt before continuing. With acks='all', it waits for all in-sync replicas to confirm, ensuring full replication. Variables like 'confirmation_received' track if acknowledgments arrived. This helps balance speed and safety in message delivery.

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