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Building and operationalizing data processing systems →mediumMultiple ChoiceObjective-mapped

Quick Answer

The correct answer is that the message will be redelivered after 10 seconds if not acknowledged. This occurs because Pub/Sub enforces a configurable ack deadline, defaulting to 10 seconds, during which the subscriber must send an acknowledgment; if the Dataflow streaming pipeline exceeds that window, Pub/Sub treats the message as unacknowledged and immediately redelivers it to ensure at-least-once delivery. On the Google Professional Data Engineer exam, this scenario tests your understanding of Pub/Sub’s delivery semantics and the critical role of the ack deadline in streaming pipelines, often appearing as a trap where candidates mistakenly assume a longer processing time simply delays delivery rather than triggering redelivery. A common memory tip is to think of the ack deadline as a countdown timer: if your pipeline doesn’t hit “ack” before zero, Pub/Sub hits “resend.”

PDE Practice Question: Building and operationalizing data processing systems

This PDE practice question tests your understanding of building and operationalizing data processing systems. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

Exhibit

Refer to the exhibit.

Cloud Pub/Sub subscription configuration:

{
  "name": "projects/my-project/subscriptions/my-sub",
  "topic": "projects/my-project/topics/my-topic",
  "pushConfig": {},
  "ackDeadlineSeconds": 10,
  "messageRetentionDuration": "86400s",
  "expirationPolicy": {
    "ttl": "604800s"
  },
  "enableMessageOrdering": false,
  "retryPolicy": {
    "minimumBackoff": "10s",
    "maximumBackoff": "600s"
  },
  "deadLetterPolicy": {
    "deadLetterTopic": "projects/my-project/topics/dead-letter-topic",
    "maxDeliveryAttempts": 5
  }
}

Refer to the exhibit. A Dataflow streaming pipeline subscribes to this Pub/Sub subscription. The pipeline occasionally takes more than 10 seconds to process a message. Which behavior will occur?

Question 1mediummultiple choice
Full question →

Exhibit

Refer to the exhibit.

Cloud Pub/Sub subscription configuration:

{
  "name": "projects/my-project/subscriptions/my-sub",
  "topic": "projects/my-project/topics/my-topic",
  "pushConfig": {},
  "ackDeadlineSeconds": 10,
  "messageRetentionDuration": "86400s",
  "expirationPolicy": {
    "ttl": "604800s"
  },
  "enableMessageOrdering": false,
  "retryPolicy": {
    "minimumBackoff": "10s",
    "maximumBackoff": "600s"
  },
  "deadLetterPolicy": {
    "deadLetterTopic": "projects/my-project/topics/dead-letter-topic",
    "maxDeliveryAttempts": 5
  }
}

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The message will be redelivered after 10 seconds if not acknowledged.

Option C is correct because Pub/Sub delivery requires an acknowledgment within the configurable `ackDeadlineSeconds` (default 10 seconds). If the pipeline takes longer than the ack deadline to process a message, Pub/Sub considers the message unacknowledged and redelivers it. This is the standard behavior for at-least-once delivery in Google Cloud Pub/Sub.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • ✗

    The message will be sent to the dead letter topic immediately.

    Why it's wrong here

    Dead letter only applies after maxDeliveryAttempts (5) of failed delivery.

  • ✗

    The message will be retried with exponential backoff as per retry policy.

    Why it's wrong here

    Retry policy is for push subscriptions; this is a pull subscription.

  • ✓

    The message will be redelivered after 10 seconds if not acknowledged.

    Why this is correct

    The ack deadline is 10 seconds; if processing exceeds that, Pub/Sub redelivers the message.

    Related concept

    Read the scenario before looking for a memorised answer.

  • ✗

    The message will be dropped after 10 seconds due to expiration policy.

    Why it's wrong here

    Expiration policy is about subscription lifespan, not message delivery.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Google Cloud often tests the distinction between ack deadline expiration and dead letter topics, trapping candidates who assume any processing delay immediately triggers a dead letter or that Pub/Sub uses exponential backoff like some other messaging systems.

Detailed technical explanation

How to think about this question

Under the hood, Pub/Sub uses a `modifyAckDeadline` API to extend the deadline if the subscriber needs more time; without such an extension, the server automatically redelivers the message after the original ack deadline. In a Dataflow streaming pipeline, the default `ackDeadlineSeconds` is 10 seconds, but you can increase it via pipeline options (e.g., `--ackDeadlineSeconds=60`) to avoid unnecessary redeliveries for long-running processing. A real-world scenario is a pipeline performing a heavy transformation or external API call that exceeds 10 seconds, causing duplicate processing unless the ack deadline is adjusted.

KKey Concepts to Remember

  • Read the scenario before looking for a memorised answer.
  • Find the constraint that changes the correct option.
  • Eliminate answers that are true in general but not in this case.

TExam Day Tips

  • Watch for words such as best, first, most likely and least administrative effort.
  • Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this PDE question test?

Building and operationalizing data processing systems — This question tests Building and operationalizing data processing systems — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The message will be redelivered after 10 seconds if not acknowledged. — Option C is correct because Pub/Sub delivery requires an acknowledgment within the configurable `ackDeadlineSeconds` (default 10 seconds). If the pipeline takes longer than the ack deadline to process a message, Pub/Sub considers the message unacknowledged and redelivers it. This is the standard behavior for at-least-once delivery in Google Cloud Pub/Sub.

What should I do if I get this PDE question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Last reviewed: Jun 30, 2026

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This PDE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PDE exam.