- A
Create a GSI with user_id as the partition key and timestamp as the sort key.
Why wrong: A GSI would work but is overkill and adds cost compared to an LSI.
- B
Use DynamoDB Streams to populate an Amazon Elasticsearch cluster for search queries.
Why wrong: This adds unnecessary complexity; the LSI is simpler and sufficient.
- C
Create an LSI with user_id as the partition key and timestamp as the sort key.
An LSI uses the same partition key and a different sort key, enabling efficient range queries.
- D
Query the base table using the sort key timestamp with a limit of 10.
Why wrong: Without an LSI, the query would require a full scan of all items for the user.
Question 932 of 1,730
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 social media application stores user posts in a DynamoDB table with a partition key of user_id and a sort key of timestamp. The most frequent query is to retrieve the 10 most recent posts for a given user. Which secondary index design would optimize this query?
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
✓
Create an LSI with user_id as the partition key and timestamp as the sort key.
Option C is correct because a Local Secondary Index (LSI) on the base table with the same partition key (user_id) and a sort key of timestamp allows efficient retrieval of the 10 most recent posts for a given user. An LSI shares the same partition key as the base table, so querying by user_id with ScanIndexForward=false and Limit=10 returns the most recent items without needing to replicate data or incur additional write costs.
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.
- ✗
Create a GSI with user_id as the partition key and timestamp as the sort key.
Why it's wrong here
A GSI would work but is overkill and adds cost compared to an LSI.
- ✗
Use DynamoDB Streams to populate an Amazon Elasticsearch cluster for search queries.
Why it's wrong here
This adds unnecessary complexity; the LSI is simpler and sufficient.
- ✓
Create an LSI with user_id as the partition key and timestamp as the sort key.
Why this is correct
An LSI uses the same partition key and a different sort key, enabling efficient range queries.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Query the base table using the sort key timestamp with a limit of 10.
Why it's wrong here
Without an LSI, the query would require a full scan of all items for the user.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may choose Option A (GSI) because they think a GSI is always the answer for query optimization, but they overlook that an LSI is more appropriate when the partition key is the same as the base table and the query pattern is a simple range query on an existing attribute, avoiding unnecessary cost and complexity.
Detailed technical explanation
How to think about this question
An LSI is defined at table creation and allows an alternate sort key on the same partition key, enabling efficient range queries without data duplication. When querying an LSI with ScanIndexForward=false and Limit=10, DynamoDB retrieves only the 10 most recent items for that user_id from the index, which is physically co-located with the base table data, minimizing read latency. In contrast, a GSI would require separate storage and write capacity, and the base table query (Option D) is not a secondary index design, which is what the question explicitly asks for.
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 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.
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FAQ
Questions learners often ask
What does this DBS-C01 question test?
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: Create an LSI with user_id as the partition key and timestamp as the sort key. — Option C is correct because a Local Secondary Index (LSI) on the base table with the same partition key (user_id) and a sort key of timestamp allows efficient retrieval of the 10 most recent posts for a given user. An LSI shares the same partition key as the base table, so querying by user_id with ScanIndexForward=false and Limit=10 returns the most recent items without needing to replicate data or incur additional write costs.
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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Last reviewed: Jul 4, 2026
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