- A
Delete the subscription and recreate it with a larger message retention duration.
Why wrong: Deleting the subscription loses the backlog and is not a solution. Increasing retention duration does not reduce backlog.
- B
Reduce the acknowledgment deadline to force faster processing.
Why wrong: Reducing the deadline may cause messages to be redelivered prematurely, increasing duplicates and potentially slowing down processing due to repeated messages.
- C
Change the subscription type from push to pull.
Why wrong: The type of subscription is not likely the root cause; both push and pull can handle high throughput if subscribers are adequate.
- D
Increase the number of subscribers or the throughput capacity of the existing subscribers.
Adding more subscribers (e.g., scaling out Dataflow workers) increases the rate of message processing, reducing the backlog.
PDE Maintaining and Automating Data Workloads Practice Question
This PDE practice question tests your understanding of maintaining and automating data workloads. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
A company uses Cloud Pub/Sub for a real-time data pipeline. The subscription has a backlog of millions of messages that are not being processed quickly enough. In Cloud Monitoring, you observe that the 'subscription/num_undelivered_messages' metric is high and growing, while 'subscription/oldest_unacked_message_age' is also increasing. Which action is MOST likely to reduce the backlog?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
Increase the number of subscribers or the throughput capacity of the existing subscribers.
Option D is correct because the backlog indicates that subscribers cannot keep up with the message flow. Increasing the number of subscribers or scaling their throughput capacity directly addresses the processing bottleneck, allowing messages to be pulled and acknowledged faster. Cloud Pub/Sub scales horizontally, so adding more pull subscribers or increasing the resources of existing ones (e.g., more worker threads, higher CPU/memory) reduces the backlog.
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.
- ✗
Delete the subscription and recreate it with a larger message retention duration.
Why it's wrong here
Deleting the subscription loses the backlog and is not a solution. Increasing retention duration does not reduce backlog.
- ✗
Reduce the acknowledgment deadline to force faster processing.
Why it's wrong here
Reducing the deadline may cause messages to be redelivered prematurely, increasing duplicates and potentially slowing down processing due to repeated messages.
- ✗
Change the subscription type from push to pull.
Why it's wrong here
The type of subscription is not likely the root cause; both push and pull can handle high throughput if subscribers are adequate.
- ✓
Increase the number of subscribers or the throughput capacity of the existing subscribers.
Why this is correct
Adding more subscribers (e.g., scaling out Dataflow workers) increases the rate of message processing, reducing the backlog.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that reducing the acknowledgment deadline or changing subscription type will speed up processing, when in reality these actions can increase redeliveries or do not address the root cause of insufficient subscriber capacity.
Detailed technical explanation
How to think about this question
Cloud Pub/Sub uses a pull-based model where subscribers must explicitly acknowledge messages. The 'oldest_unacked_message_age' metric increases when messages remain unacknowledged, often due to slow processing or insufficient subscriber count. Under the hood, Pub/Sub uses a flow control mechanism that can be tuned; increasing the max outstanding messages per subscriber can also help, but adding subscribers is the most direct scaling action.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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.
- →
Maintaining and Automating Data Workloads — study guide chapter
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FAQ
Questions learners often ask
What does this PDE question test?
Maintaining and Automating Data Workloads — This question tests Maintaining and Automating Data Workloads — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Increase the number of subscribers or the throughput capacity of the existing subscribers. — Option D is correct because the backlog indicates that subscribers cannot keep up with the message flow. Increasing the number of subscribers or scaling their throughput capacity directly addresses the processing bottleneck, allowing messages to be pulled and acknowledged faster. Cloud Pub/Sub scales horizontally, so adding more pull subscribers or increasing the resources of existing ones (e.g., more worker threads, higher CPU/memory) reduces the backlog.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jul 4, 2026
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.
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