PCA Promql Practice Question
An operator writes a query to calculate error percentage: sum(rate(errors[5m])) / sum(rate(total[5m])) * 100. What happens if the denominator evaluates to zero or has no matching time series?
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 query returns an empty vector (no data points).
Division by zero or division by an empty vector in PromQL results in an empty vector output.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Prometheus throws a fatal query evaluation runtime exception.
Why it's wrong here
PromQL handles math errors gracefully without crashing.
- ✗
The query returns NaN for all series.
Why it's wrong here
Empty vectors are omitted entirely rather than returning NaN.
- ✗
The query automatically returns infinity.
Why it's wrong here
PromQL does not return infinity for vector division by zero; it returns empty.
- ✓
The query returns an empty vector (no data points).
Why this is correct
Correct. Division by zero or empty vectors results in an empty result in PromQL.
About these practice questions
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed August 2026 · checked against the official CNCF / Linux Foundation exam blueprint
This PCA practice question is part of Courseiva's free CNCF / Linux Foundation 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 PCA exam.