The most likely cause of missing spans in Cloud Trace is that the trace sampling rate is set too low. Cloud Trace uses a configurable sampling rate to determine what percentage of requests are captured; when this rate is low, the majority of requests are deliberately ignored, leading to gaps where spans for a single logical trace are never recorded. This tests your understanding of how distributed tracing balances cost and completeness—on the Google Professional Cloud Developer exam, the common trap is to blame network issues or agent failures, but the real culprit is almost always an overly aggressive sampling configuration. Remember that Cloud Trace defaults to a rate that may drop spans under high throughput, so always check the sampling rate before troubleshooting instrumentation. A helpful memory tip: "Low rate, missing slate"—if your trace looks like Swiss cheese, the sampling dial is the first place to turn.
PCD Managing application performance monitoring Practice Question
This PCD practice question tests your understanding of managing application performance monitoring. 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 team is using Cloud Trace to analyze performance of a microservices application. They notice that some spans are missing from the trace. What is the most likely cause?
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 trace sampling rate is set too low
The most likely cause of missing spans in Cloud Trace is that the trace sampling rate is set too low. Cloud Trace uses a configurable sampling rate to control how many requests are traced; if the rate is low, many requests are not sampled, resulting in incomplete traces. This is a common configuration issue, not a failure to send traces or a network problem.
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 application is not sending traces for all services
Why it's wrong here
This would result in missing spans for entire services, but sampling is a more common cause of intermittent missing spans.
✗
There is a network latency issue
Why it's wrong here
Network latency affects performance but does not cause missing spans.
✗
The Cloud Trace API is disabled for some projects
Why it's wrong here
If the API were disabled, no traces would be collected, not just missing spans.
✓
The trace sampling rate is set too low
Why this is correct
Low sampling rate means only a subset of requests are traced, leading to missing spans.
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 missing spans are due to network issues or API failures, when in fact the root cause is a misconfigured sampling rate that drops spans before they are sent.
Detailed technical explanation
How to think about this question
Cloud Trace uses a probabilistic sampling mechanism where each span is independently sampled based on a configured rate (e.g., 0.1 means 10% of requests are traced). This can lead to incomplete traces when different services have different sampling rates or when the rate is too low to capture all spans in a distributed transaction. In real-world scenarios, teams often set sampling rates too low to reduce cost, inadvertently breaking trace completeness for debugging.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
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.
Managing application performance monitoring — This question tests Managing application performance monitoring — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The trace sampling rate is set too low — The most likely cause of missing spans in Cloud Trace is that the trace sampling rate is set too low. Cloud Trace uses a configurable sampling rate to control how many requests are traced; if the rate is low, many requests are not sampled, resulting in incomplete traces. This is a common configuration issue, not a failure to send traces or a network problem.
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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Question Discussion
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