PCA Promql Practice Question
How does Prometheus handle subqueries embedded within an instant query, such as rate(http_requests_total[5m])[30m:1m]?
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
✓
It runs the inner instant query at multiple evaluation timestamps over the specified range at the given resolution, returning a range vector.
A subquery evaluates an instant query expression over a given range with a specified resolution at multiple points in time, returning a range vector.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It caches the inner query results in memory for 30 minutes.
Why it's wrong here
Subqueries define an evaluation window and step size, not a caching policy.
- ✗
It increases the global scrape interval to 1 minute for the next 30 minutes.
Why it's wrong here
Subqueries do not alter global scrape configurations.
- ✓
It runs the inner instant query at multiple evaluation timestamps over the specified range at the given resolution, returning a range vector.
Why this is correct
Correct. Subqueries allow range vector functions to be applied over historical evaluated points.
- ✗
It converts the range vector into a scalar through statistical interpolation.
Why it's wrong here
Subqueries return range vectors, not scalars.
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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.