The answer is to add read replicas to the DocumentDB cluster. This is the most effective action because read replicas offload read-heavy traffic from the primary instance, directly reducing read latency during peak hours. In DocumentDB, up to 15 read replicas are kept in sync via the cluster’s storage-based replication, meaning your application’s frequent fetches by document ID can be distributed across multiple endpoints, preventing the primary from becoming a bottleneck. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of scaling read capacity horizontally versus vertical scaling or caching—common traps include choosing to increase instance size or enable encryption, which do not address read load distribution. Remember, for read-heavy workloads with large documents, replicas are the go-to solution. Memory tip: “Replicas for reads, primary for writes—spread the load to beat the peak.”
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 runs a document management system using Amazon DocumentDB (with MongoDB compatibility). The application stores large documents (up to 5 MB each) and frequently fetches them by document ID. The team notices increased latency during peak hours. They need to reduce read latency. Which action is MOST effective?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add read replicas to the cluster
Adding read replicas to the DocumentDB cluster is the most effective action because it offloads read traffic from the primary instance, directly reducing read latency during peak hours. DocumentDB supports up to 15 read replicas that are kept in sync via the cluster's replication mechanism, and the application's frequent fetches by document ID are read-heavy operations that benefit from distributing the load across multiple replicas.
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.
✓
Add read replicas to the cluster
Why this is correct
Read replicas offload read traffic and reduce latency.
Related concept
Read the scenario before looking for a memorised answer.
✗
Shard the collection across multiple DocumentDB clusters
Why it's wrong here
Sharding adds complexity; not needed for this simple access pattern.
✗
Implement Amazon ElastiCache for Redis in front of DocumentDB
Why it's wrong here
Adds complexity and requires application changes.
✗
Increase the instance class of the primary instance
Why it's wrong here
Vertical scaling helps but not as cost-effective as horizontal scaling.
Common exam traps
Common exam trap: answer the scenario, not the keyword
AWS often tests the misconception that scaling up the primary instance (Option D) is equivalent to scaling out read capacity, but in DocumentDB, read replicas are the correct solution for read-heavy workloads because they provide horizontal read scaling without overloading the primary.
Detailed technical explanation
How to think about this question
DocumentDB read replicas are implemented as separate instances in the same cluster that share the same underlying storage volume, allowing them to serve read requests with minimal replication lag (typically under 100 ms). The application's read-heavy workload benefits from this architecture because the replicas can handle read operations in parallel, and the cluster endpoint automatically distributes reads across replicas when using the reader endpoint. In real-world scenarios, this approach is most effective when the read-to-write ratio is high, as is common in document management systems.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Workload-Specific Database Design — This question tests Workload-Specific Database Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add read replicas to the cluster — Adding read replicas to the DocumentDB cluster is the most effective action because it offloads read traffic from the primary instance, directly reducing read latency during peak hours. DocumentDB supports up to 15 read replicas that are kept in sync via the cluster's replication mechanism, and the application's frequent fetches by document ID are read-heavy operations that benefit from distributing the load across multiple replicas.
What should I do if I get this DBS-C01 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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Question Discussion
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