PCDE Design and implement database schemas Practice Question
This PCDE practice question tests your understanding of design and implement database schemas. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 considerations are important when designing a schema for Cloud Firestore to ensure scalability?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Design collections to avoid high read/write rates on a single document.
Options A, C, and E are correct. Option A: Avoiding document growth near 1 MiB prevents performance issues. Option C: Using composite indexes for common queries avoids full scans. Option E: Sharding writes for a collection with high write throughput avoids hotspotting. Option B is wrong because subcollections cannot be deeply nested (max 20 levels). Option D is wrong because regular (not collection group) indexes require specific fields.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Design collections to avoid high read/write rates on a single document.
Why this is correct
Hot documents cause contention; distribute writes across documents.
Related concept
Static NAT maps one inside address to one outside address.
✓
Create composite indexes tailored to the application's query patterns.
Why this is correct
Composite indexes improve query performance and reduce costs.
Related concept
Static NAT maps one inside address to one outside address.
✗
Nest subcollections up to 10 levels deep to model complex hierarchies.
Why it's wrong here
Deep nesting is allowed but not recommended; depth limit is 20; but design should be flat.
✗
Use collection group indexes for all queries to avoid manual index creation.
Why it's wrong here
Collection group indexes are for queries across subcollections; not needed for all queries.
✓
Limit document size to avoid exceeding the 1 MiB limit.
Why this is correct
Large documents cause slow reads and writes; best to keep them small.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCDE NAT questions on configuration and troubleshooting.
Design and implement database schemas — This question tests Design and implement database schemas — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Design collections to avoid high read/write rates on a single document. — Options A, C, and E are correct. Option A: Avoiding document growth near 1 MiB prevents performance issues. Option C: Using composite indexes for common queries avoids full scans. Option E: Sharding writes for a collection with high write throughput avoids hotspotting. Option B is wrong because subcollections cannot be deeply nested (max 20 levels). Option D is wrong because regular (not collection group) indexes require specific fields.
What should I do if I get this PCDE question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCDE NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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