- A
Use subcollections to organize related data
Subcollections enable scalable data modeling.
- B
Avoid large arrays to prevent document size limits
Large arrays can cause performance degradation.
- C
Denormalize data to reduce the need for joins
Denormalization improves read performance.
- D
Use nested maps for deeply structured data
Why wrong: Deeply nested maps are difficult to query and index.
- E
Always use transactional writes to ensure consistency
Why wrong: Transactions are useful but not required for all writes.
Question 30 of 1,000
PCDE Design and implement database schemas Practice Question
This PCDE practice question tests your understanding of design and implement database schemas. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which THREE are considerations when designing a schema for Cloud Firestore?
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
✓
Use subcollections to organize related data
Option A is correct because subcollections in Cloud Firestore allow you to organize related data hierarchically within a document, enabling efficient queries and scalability without hitting the 1 MiB document size limit. This structure is ideal for data like user posts or product reviews, where each subcollection can grow independently.
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.
- ✓
Use subcollections to organize related data
Why this is correct
Subcollections enable scalable data modeling.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Avoid large arrays to prevent document size limits
Why this is correct
Large arrays can cause performance degradation.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Denormalize data to reduce the need for joins
Why this is correct
Denormalization improves read performance.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use nested maps for deeply structured data
Why it's wrong here
Deeply nested maps are difficult to query and index.
- ✗
Always use transactional writes to ensure consistency
Why it's wrong here
Transactions are useful but not required for all writes.
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common trap in Google exams is the misconception that nested maps are a good alternative to subcollections for deeply structured data, but they ignore Firestore's indexing and size limitations that make subcollections the correct choice for scalability.
Detailed technical explanation
How to think about this question
Firestore's subcollections are stored as separate collections under a parent document, allowing for efficient querying and automatic scaling without affecting the parent document's size. Denormalization (Option C) is a common NoSQL pattern to avoid joins, but it requires careful management of data duplication and consistency, often using batched writes or background functions. The 1 MiB document size limit and 20,000 field index limit are hard constraints that influence schema design, making subcollections and denormalization critical for large-scale applications.
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.
TExam Day Tips
- 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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this PCDE question test?
Design and implement database schemas — This question tests Design and implement database schemas — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use subcollections to organize related data — Option A is correct because subcollections in Cloud Firestore allow you to organize related data hierarchically within a document, enabling efficient queries and scalability without hitting the 1 MiB document size limit. This structure is ideal for data like user posts or product reviews, where each subcollection can grow independently.
What should I do if I get this PCDE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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