Google PCA Practice Question: Analysing and Optimising Technical and Business Processes
A team wants to define an SLO for a service that requires 99.9% availability over a 30-day window. They need to measure the ratio of successful requests to total requests. Which SLI should they use?
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
✓
Request success rate
An SLI is a measure of service performance. For availability, the standard SLI is the proportion of successful requests (e.g., HTTP 2xx) to total requests. Latency SLI measures response times. Error budget is derived from SLO. SRE is the practice.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Request success rate
Why this is correct
Request success rate measures the proportion of successful requests against total requests, expressed as a ratio. This directly satisfies the stem's 99.9% availability SLO over a 30-day window, since availability is defined by served versus total valid requests.
- ✗
SRE
Why it's wrong here
SRE is a discipline and role, not a measurable indicator, so it cannot express successful requests divided by total requests. It is tempting because SRE teams define SLOs and SLIs, and SRE would be the correct answer if the question asked who owns the reliability target rather than which metric to measure.
- ✗
Request latency
Why it's wrong here
Request latency measures duration, not the proportion of successful requests, so it cannot represent a 99.9% availability ratio. It is tempting because latency is a common SLI and would be the correct choice if the SLO concerned response-time thresholds, such as the percentage of requests served under 200 ms.
- ✗
Error budget
Why it's wrong here
An error budget is a derived allowance of permitted failures, not a measurement of the ratio itself, so it cannot serve as the SLI. It is tempting because error budgets are calculated from the same success ratio and drive SLO enforcement, and an error budget would be the correct answer if the question asked what to track against a 99.9% target.
Go deeper
Related to this question
Learn chapter
IAM Policies, Service Accounts, and Auditing
Key term
SLI
An SLI (Service Level Indicator) is a carefully chosen metric that measures one specific aspect of a service's performance, such as request latency or error rate, to help determine whether the service is meeting its reliability goals.
Key term
SLO
A Service Level Objective is a measurable target for a specific aspect of a service's performance or reliability that a team commits to meeting over a defined period.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCA 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 PCA exam.