- A
Write a security rule that checks if request.auth.uid == resource.data.user_id
This rule ensures the authenticated user can only access documents where user_id matches their UID.
- B
Enable Datastore mode instead of Native mode
Why wrong: Datastore mode uses IAM and Cloud Firestore APIs differently; not required for this.
- C
Assign the roles/datastore.user IAM role to each user
Why wrong: IAM roles are for project-level access, not document-level granularity; security rules should be used.
- D
Ensure the app passes the user's UID in the document's user_id field
The security rule compares request.auth.uid to this field; it must be populated correctly.
- E
Create a composite index on user_id and timestamp
Why wrong: Indexes improve query performance but are not required for security rules.
PCD Practice Question: Design Scalable and Highly Available Cloud Database Solutions
This PCD practice question tests your understanding of design scalable and highly available cloud database solutions. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 company uses Firestore in Native mode for a mobile app. They need to enforce security rules to allow users to read and write only their own data. Which TWO steps are required? (Select TWO.)
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
Write a security rule that checks if request.auth.uid == resource.data.user_id
Firestore Security Rules use the request.auth object to identify the user. Use resource.data.user_id to match the document's owner field. The rules must check request.auth.uid against the document's field. Configuring IAM roles at the project level is not granular enough. Enabling Datastore mode changes the API.
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.
- ✓
Write a security rule that checks if request.auth.uid == resource.data.user_id
Why this is correct
This rule ensures the authenticated user can only access documents where user_id matches their UID.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Enable Datastore mode instead of Native mode
Why it's wrong here
Datastore mode uses IAM and Cloud Firestore APIs differently; not required for this.
- ✗
Assign the roles/datastore.user IAM role to each user
Why it's wrong here
IAM roles are for project-level access, not document-level granularity; security rules should be used.
- ✓
Ensure the app passes the user's UID in the document's user_id field
Why this is correct
The security rule compares request.auth.uid to this field; it must be populated correctly.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create a composite index on user_id and timestamp
Why it's wrong here
Indexes improve query performance but are not required for security rules.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- 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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Identify which PCD exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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Design Scalable and Highly Available Cloud Database Solutions — study guide chapter
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FAQ
Questions learners often ask
What does this PCD question test?
Design Scalable and Highly Available Cloud Database Solutions — This question tests Design Scalable and Highly Available Cloud Database Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Write a security rule that checks if request.auth.uid == resource.data.user_id — Firestore Security Rules use the request.auth object to identify the user. Use resource.data.user_id to match the document's owner field. The rules must check request.auth.uid against the document's field. Configuring IAM roles at the project level is not granular enough. Enabling Datastore mode changes the API.
What should I do if I get this PCD question wrong?
Identify which PCD exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jul 4, 2026
This PCD 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 PCD exam.
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