The answer is to increase the instance size to db.r5.xlarge. This is correct because Amazon DocumentDB write performance scaling is tied directly to the primary instance’s compute resources; writes are processed exclusively by the primary node, so upgrading from an r5.large to an r5.xlarge provides more CPU and memory, which directly reduces write latency during peak loads. On the AWS Certified Database Specialty DBS-C01 exam, this question tests your understanding that DocumentDB’s write path is single-threaded through the primary, making instance scaling the only effective lever for write throughput—adding read replicas or scaling storage are common traps that do not improve write performance. A key memory tip: think of DocumentDB writes as a single-lane road—widening the lane (bigger instance) is the only way to move more traffic, while adding parallel lanes (read replicas) only helps reads.
DBS-C01 Workload-Specific Database Design Practice Question
This DBS-C01 practice question tests your understanding of workload-specific database design. 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.
A company is running a MongoDB-compatible workload on Amazon DocumentDB. They are experiencing high write latency during peak hours. The current cluster has one instance (db.r5.large) with 100 GB storage. Which change is most likely to improve write performance?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Increase the instance size to db.r5.xlarge
DocumentDB writes are handled by the primary instance. Since the instance is r5.large, increasing instance size provides more CPU and memory, improving write throughput. Adding read replicas does not help writes. Scaling storage does not directly improve write latency. Enabling Multi-AZ adds a standby but does not improve write performance.
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.
✗
Increase storage to 500 GB
Why it's wrong here
Storage scaling does not directly improve write latency; DocumentDB storage is automatically scaled.
✗
Enable Multi-AZ deployment
Why it's wrong here
Multi-AZ provides high availability but does not improve write performance.
✓
Increase the instance size to db.r5.xlarge
Why this is correct
A larger instance provides more CPU and memory, which can improve write performance.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
Add a read replica in a different Availability Zone
Why it's wrong here
Read replicas handle read traffic only, not writes.
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 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.
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 DBS-C01 NAT questions on configuration and troubleshooting.
Workload-Specific Database Design — This question tests Workload-Specific Database Design — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Increase the instance size to db.r5.xlarge — DocumentDB writes are handled by the primary instance. Since the instance is r5.large, increasing instance size provides more CPU and memory, improving write throughput. Adding read replicas does not help writes. Scaling storage does not directly improve write latency. Enabling Multi-AZ adds a standby but does not improve write performance.
What should I do if I get this DBS-C01 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 DBS-C01 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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