Provyn Prep · System Design competency
Availability & consistency in the System Design assessment
Availability & consistency is one of the areas a Provyn System Design credential scores separately, so a recruiter can see it on its own rather than averaged into one number. This guide explains what it covers, how it is tested and what to practice.
What it covers
Trade-offs between availability and consistency, replication, idempotency, service-level objectives and recovering from failure.
Topics in the practice set for this area
- consistency / CAP
- reliability
- idempotency
- SLAs
- event sourcing
How it is tested
In the timed assessment, questions in this area use these formats: fill-in-the-blank code, incident walkthrough, multiple choice, short answer, written scenario. Each attempt draws its own set of questions, and this area gets its own sub-score on the credential when the attempt includes enough questions from it. The assessment questions themselves are never published; the practice set below is written separately for study.
What to practice
- Explain the CAP trade-off using a real system you know.
- Design an idempotent payment or order endpoint and say how retries are made safe.
- Turn an availability target into an error budget per month.
Try a practice question
From the free practice set (7 questions in this area). Answers and explanations are in the practice set.
- CAP theorem says you must give up:
- Write-ahead log's purpose:
- Idempotency is best implemented via:
Practice before the real thing
Both are free and use practice questions only, never questions from the real assessment.
More System Design study guides
Last reviewed 2026-10-06.