Consumer acknowledgment strategies in RabbitMQ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to acknowledge a message manually in RabbitMQ consumer.

RabbitMQ

channel.basic_ack(delivery_tag=[1])

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

Amessage

Bchannel

Cmethod.delivery_tag

Dqueue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'channel' or 'queue' instead of the delivery tag.

Trying to acknowledge without specifying the delivery tag.

The delivery_tag uniquely identifies the message to acknowledge. It is accessed via method.delivery_tag in the callback.

2fill in blank

medium

Complete the code to enable automatic acknowledgment in RabbitMQ consumer.

RabbitMQ

channel.basic_consume(queue='task_queue', on_message_callback=callback, auto_ack=[1])

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

ATrue

BFalse

CNone

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Setting auto_ack to False when automatic ack is desired.

Using None or 0 which are invalid for this parameter.

Setting auto_ack=True tells RabbitMQ to automatically consider messages acknowledged once delivered.

3fill in blank

hard

Fix the error in the manual acknowledgment code by completing the blank.

RabbitMQ

def callback(ch, method, properties, body):
    print(f"Received {body}")
    ch.basic_ack(delivery_tag=[1])

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

Ach.delivery_tag

Bproperties.delivery_tag

Cbody.delivery_tag

Dmethod.delivery_tag

Attempts:

3 left

💡 Hint

Common Mistakes

Using properties or body to get delivery_tag.

Trying to access delivery_tag from the channel object.

The delivery_tag is part of the method parameter, not properties or others.

4fill in blank

hard

Fill both blanks to reject a message and requeue it in RabbitMQ consumer.

RabbitMQ

channel.basic_reject(delivery_tag=[1], requeue=[2])

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

Amethod.delivery_tag

BTrue

CFalse

Dchannel

Attempts:

3 left

💡 Hint

Common Mistakes

Using channel instead of delivery_tag.

Setting requeue to False which discards the message.

To reject and requeue a message, use method.delivery_tag and set requeue=True.

5fill in blank

hard

Fill all three blanks to consume messages with manual ack and reject unprocessable messages without requeue.

RabbitMQ

def callback(ch, method, properties, body):
    try:
        process(body)
        ch.basic_ack(delivery_tag=[1])
    except Exception:
        ch.basic_reject(delivery_tag=[2], requeue=[3])

channel.basic_consume(queue='jobs', on_message_callback=callback, auto_ack=False)

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

Amethod.delivery_tag

BTrue

CFalse

Dproperties.delivery_tag

Attempts:

3 left

💡 Hint

Common Mistakes

Using properties.delivery_tag instead of method.delivery_tag.

Setting requeue to True which requeues the message.

Use method.delivery_tag for both ack and reject. Set requeue=False to discard unprocessable messages.

Practice

1. What does setting autoAck=false in a RabbitMQ consumer do?

easy

A. It pauses message delivery until the consumer is ready.

B. It automatically acknowledges messages as soon as they are received.

C. It rejects messages immediately without processing.

D. It requires the consumer to manually acknowledge messages after processing.

Solution

1. Step 1: Understand autoAck parameter

   The autoAck flag controls if messages are acknowledged automatically or manually.

2. Step 2: Effect of setting autoAck to false

   When autoAck=false, the consumer must explicitly send an acknowledgment after processing each message.

3. Final Answer:

   It requires the consumer to manually acknowledge messages after processing. -> Option D

4. Quick Check:

   autoAck=false means manual ack [OK]

Hint: autoAck=false means manual message acknowledgment [OK]

Common Mistakes:

• Thinking autoAck=false auto-acknowledges messages
• Confusing autoAck with message rejection
• Assuming autoAck pauses message delivery

2. Which of the following is the correct way to send a manual acknowledgment in RabbitMQ using the client library?

easy

A. channel.acknowledge(deliveryTag);

B. channel.basicAck(deliveryTag, false);

C. channel.sendAck(deliveryTag, true);

D. channel.confirm(deliveryTag);

Solution

1. Step 1: Identify the correct method name

   The RabbitMQ client uses basicAck to acknowledge messages manually.

2. Step 2: Understand parameters of basicAck

   The first parameter is the deliveryTag identifying the message; the second is multiple flag, usually false for single ack.

3. Final Answer:

   channel.basicAck(deliveryTag, false); -> Option B

4. Quick Check:

   Manual ack uses basicAck method [OK]

Hint: Manual ack uses basicAck(deliveryTag, false) [OK]

Common Mistakes:

• Using non-existent methods like acknowledge or sendAck
• Confusing confirm with ack
• Passing wrong parameters to basicAck

3. Given the following code snippet, what will happen if the consumer crashes before calling channel.basicAck(deliveryTag, false);?

channel.basicConsume(queueName, false, consumerTag, new DefaultConsumer(channel) {
  public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) {
    // process message
    // no ack sent yet
  }
});

medium

A. The message will be requeued and delivered again to another consumer.

B. The message will be lost and never delivered again.

C. The message will be acknowledged automatically despite no ack call.

D. The consumer will block and wait indefinitely.

Solution

1. Step 1: Understand manual ack behavior on consumer crash

   If a consumer crashes before sending basicAck, RabbitMQ considers the message unacknowledged.

2. Step 2: RabbitMQ requeues unacknowledged messages

   Unacknowledged messages are requeued and delivered to other consumers to avoid message loss.

3. Final Answer:

   The message will be requeued and delivered again to another consumer. -> Option A

4. Quick Check:

   Unacked message + crash = requeue [OK]

Hint: Unacked messages get requeued on consumer crash [OK]

Common Mistakes:

• Assuming message is lost without ack
• Thinking message auto-acks on crash
• Believing consumer blocks indefinitely

4. You have a consumer with autoAck=false but forgot to call basicAck after processing messages. What problem will this cause?

medium

A. Messages will pile up as unacknowledged and may block new deliveries.

B. Messages will be acknowledged automatically anyway.

C. RabbitMQ will delete the queue automatically.

D. The consumer will crash immediately.

Solution

1. Step 1: Effect of missing manual acknowledgments

   Without calling basicAck, messages remain unacknowledged in RabbitMQ.

2. Step 2: Consequence of unacknowledged messages

   Unacknowledged messages accumulate and can block further message delivery due to prefetch limits.

3. Final Answer:

   Messages will pile up as unacknowledged and may block new deliveries. -> Option A

4. Quick Check:

   No ack + autoAck=false = message pileup [OK]

Hint: No ack with autoAck=false causes message buildup [OK]

Common Mistakes:

• Assuming messages auto-acknowledge anyway
• Thinking RabbitMQ deletes queues automatically
• Believing consumer crashes without ack

5. You want to ensure that a batch of 5 messages is processed before sending a single acknowledgment to RabbitMQ. Which strategy should you use?

hard

A. Set autoAck=true to acknowledge messages automatically.

B. Call basicAck(deliveryTag, false) after each message individually.

C. Call basicAck(deliveryTag, true) after processing the 5th message to acknowledge all previous messages.

D. Call basicReject(deliveryTag, false) after processing the batch.

Solution

1. Step 1: Understand the multiple flag in basicAck

   Setting the second parameter of basicAck to true acknowledges all messages up to the given deliveryTag.

2. Step 2: Use batch acknowledgment for efficiency

   After processing 5 messages, calling basicAck(deliveryTag, true) acknowledges all 5 at once, improving performance.

3. Final Answer:

   Call basicAck(deliveryTag, true) after processing the 5th message to acknowledge all previous messages. -> Option C

4. Quick Check:

   Batch ack uses basicAck with multiple=true [OK]

Hint: Use basicAck with multiple=true for batch ack [OK]

Common Mistakes:

• Calling basicAck with multiple=false for batch
• Using autoAck=true when manual control needed
• Confusing basicReject with acknowledgment