Message retention and acknowledgment in GCP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

Message acknowledgment timing in Pub/Sub

In Google Cloud Pub/Sub, when a subscriber receives a message, what happens if the subscriber does not acknowledge the message within the acknowledgment deadline?

A The message is redelivered to the subscriber or another subscriber after the acknowledgment deadline expires.

B The message is immediately deleted from the subscription and not redelivered.

C The message is moved to a dead-letter topic automatically without redelivery.

D The message acknowledgment deadline is extended indefinitely until the subscriber acknowledges.

💡 Hint

Think about what happens when a message is not confirmed as processed in time.

If a subscriber does not acknowledge a message within the acknowledgment deadline, Pub/Sub assumes the message was not processed and makes it available for redelivery to the same or another subscriber.

❓ Architecture

intermediate

Configuring message retention duration

You want to ensure that unacknowledged messages in a Pub/Sub subscription are retained for 7 days before being deleted. Which configuration should you set?

A Set the topic's <code>messageRetentionDuration</code> to 7 days.

B Set the subscription's <code>ackDeadlineSeconds</code> to 7 days.

C Set the topic's <code>ackDeadlineSeconds</code> to 7 days.

D Set the subscription's <code>messageRetentionDuration</code> to 7 days.

💡 Hint

Retention duration controls how long messages stay in the subscription after delivery.

The messageRetentionDuration on the subscription controls how long unacknowledged messages are retained before deletion. Setting it to 7 days keeps messages for that duration.

❓ security

advanced

Preventing message loss with acknowledgment deadlines

You have a subscriber that processes messages slowly, sometimes taking longer than the default acknowledgment deadline. What is the best practice to prevent message loss or duplicate processing?

A Use the subscriber client to extend the acknowledgment deadline dynamically while processing.

B Set the subscription's message retention duration to zero.

C Disable message acknowledgment to avoid redelivery.

D Increase the subscription's acknowledgment deadline to a very high value (e.g., 1 hour).

💡 Hint

Think about how to keep the message invisible to others while processing.

Extending the acknowledgment deadline dynamically allows the subscriber to keep the message invisible to others while processing, preventing premature redelivery and duplicate processing.

🧠 Conceptual

advanced

Dead-letter topic behavior in Pub/Sub

What happens to a message in a Pub/Sub subscription configured with a dead-letter topic if the message is not acknowledged after the maximum delivery attempts?

A The message is redelivered indefinitely until acknowledged.

B The message is deleted permanently without being sent anywhere else.

C The message is sent to the dead-letter topic for further inspection or processing.

D The message is automatically acknowledged to prevent further delivery.

💡 Hint

Dead-letter topics are used to handle problematic messages.

When a message exceeds the maximum delivery attempts without acknowledgment, Pub/Sub sends it to the configured dead-letter topic for separate handling.

✅ Best Practice

expert

Designing a reliable message processing system with Pub/Sub

You are designing a system that must process messages exactly once using Google Cloud Pub/Sub. Which combination of features and practices will best help achieve this?

A Acknowledge messages immediately upon receipt without processing to speed up throughput.

B Use at-least-once delivery with message deduplication logic in the subscriber and enable dead-letter topics for failed messages.

C Use exactly-once delivery mode in Pub/Sub and disable dead-letter topics to prevent message loss.

D Set acknowledgment deadline to zero and disable message retention to avoid duplicates.

💡 Hint

Consider how to handle duplicates and failures safely.

Pub/Sub provides at-least-once delivery, so to achieve exactly-once processing, the subscriber must handle duplicates. Using dead-letter topics helps manage failed messages safely.