The answer is that the ackDeadlineSeconds setting of 10 is too short, causing frequent message redelivery. When your subscriber cannot process and acknowledge a message within that 10-second window, Cloud Pub/Sub assumes the message was lost and immediately redelivers it, creating a loop of duplicate processing that directly increases Pub/Sub latency. This is a classic trap on the Google Professional Cloud Developer exam: candidates often overlook the ackDeadlineSeconds as a latency culprit, instead blaming the network or the publisher. The exam tests your understanding that a short deadline forces unnecessary redeliveries, which delays final consumption and degrades throughput. A good memory tip is to think of the ack deadline as a “patience timer”—if your subscriber needs more time to finish work, increase the timer to avoid redundant work. For most workloads, start with 60 seconds and adjust based on your processing time, not the default 10.
PCD Integrating Google Cloud services Practice Question
This PCD practice question tests your understanding of integrating google cloud services. 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.
Your application runs on Compute Engine and uses Cloud Pub/Sub to receive messages from a third-party service. Recently, the message delivery latency has increased significantly. The third-party reports no issues on their end. You notice that the Pub/Sub subscription's 'ackDeadlineSeconds' is set to 10. What is the most likely cause of the latency?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The ackDeadlineSeconds is too short, causing frequent message redelivery.
A is correct because a 10-second ackDeadlineSeconds is very short. If your subscriber cannot process and acknowledge messages within 10 seconds, Pub/Sub will consider them unacknowledged and redeliver them. This redelivery causes duplicate processing and increases overall latency as messages are repeatedly sent back to the subscriber, delaying their final consumption.
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 ackDeadlineSeconds is too short, causing frequent message redelivery.
Why this is correct
Short ack deadline leads to redelivery before processing completes.
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.
✗
The topic's message retention duration is too long.
Why it's wrong here
Retention duration does not affect latency.
✗
The push endpoint is not responding, causing Pub/Sub to retry.
Why it's wrong here
The subscription is pull, not push.
✗
The subscription has an exponential backoff policy that is too aggressive.
Why it's wrong here
Exponential backoff would reduce retries.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between push and pull subscriptions; the trap here is that candidates may incorrectly assume a push endpoint issue (Option C) without recognizing that the question implies a pull subscription by stating 'receives messages' rather than 'receives pushed messages'.
Detailed technical explanation
How to think about this question
Under the hood, Pub/Sub uses a lease-based mechanism: when a message is delivered via pull, the subscriber must extend the lease by modifying ackDeadline or acknowledge the message before the deadline expires. If the deadline is too short, the message becomes available for redelivery, leading to duplicate processing and increased end-to-end latency. In real-world scenarios, a common best practice is to set ackDeadlineSeconds to at least 60 seconds for typical workloads, and to use streaming pull or asynchronous processing to avoid blocking.
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.
Integrating Google Cloud services — This question tests Integrating Google Cloud services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The ackDeadlineSeconds is too short, causing frequent message redelivery. — A is correct because a 10-second ackDeadlineSeconds is very short. If your subscriber cannot process and acknowledge messages within 10 seconds, Pub/Sub will consider them unacknowledged and redeliver them. This redelivery causes duplicate processing and increases overall latency as messages are repeatedly sent back to the subscriber, delaying their final consumption.
What should I do if I get this PCD 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.
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This PCD 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 PCD exam.
Question Discussion
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