- A
Amazon DynamoDB with a single table and scan operation for the global feed
Why wrong: Scan operations are inefficient and should be avoided for frequent queries.
- B
Amazon S3 with a metadata index in DynamoDB
Why wrong: This adds complexity and latency; DynamoDB alone can handle the workload.
- C
Amazon DynamoDB with user_id as partition key and timestamp as sort key, plus a GSI on timestamp
This design efficiently supports both query patterns.
- D
Amazon RDS for PostgreSQL with indexes on user_id and timestamp
Why wrong: RDS can handle the workload but may not scale as easily as DynamoDB for high write throughput.
Question 1,412 of 1,730
DynamoDB Table Design: Partition Key, Sort Key, and GSI
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 company stores user posts in a database. Each post has a unique ID, content, and timestamp. The application frequently queries posts by user ID and also needs to support a global feed sorted by timestamp. Which database design is most efficient?
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
✓
Amazon DynamoDB with user_id as partition key and timestamp as sort key, plus a GSI on timestamp
Option C is correct because it uses user_id as the partition key and timestamp as the sort key for efficient per-user queries, while the Global Secondary Index (GSI) on timestamp allows the global feed to be sorted by timestamp without a costly scan. This design leverages DynamoDB's key-value and query capabilities to support both access patterns with low latency and minimal read capacity consumption.
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.
- ✗
Amazon DynamoDB with a single table and scan operation for the global feed
Why it's wrong here
Scan operations are inefficient and should be avoided for frequent queries.
- ✗
Amazon S3 with a metadata index in DynamoDB
Why it's wrong here
This adds complexity and latency; DynamoDB alone can handle the workload.
- ✓
Amazon DynamoDB with user_id as partition key and timestamp as sort key, plus a GSI on timestamp
Why this is correct
This design efficiently supports both query patterns.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Amazon RDS for PostgreSQL with indexes on user_id and timestamp
Why it's wrong here
RDS can handle the workload but may not scale as easily as DynamoDB for high write throughput.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a relational database with indexes is always the best for sorted queries, but DynamoDB's GSI and sort key design can handle both access patterns more efficiently at scale, and the exam tests understanding of when to use NoSQL over SQL for high-throughput workloads.
Detailed technical explanation
How to think about this question
Under the hood, DynamoDB's GSI is a sparse index that replicates data to a separate partition space, allowing queries on timestamp with eventual consistency; the base table's sort key on timestamp ensures that per-user queries return results in chronological order without sorting. In a real-world scenario, a social media platform with millions of posts per second would benefit from DynamoDB's partition-based scaling, where the GSI distributes the global feed workload across partitions, avoiding hot keys that could occur with a single-indexed timestamp column in a relational database.
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: Amazon DynamoDB with user_id as partition key and timestamp as sort key, plus a GSI on timestamp — Option C is correct because it uses user_id as the partition key and timestamp as the sort key for efficient per-user queries, while the Global Secondary Index (GSI) on timestamp allows the global feed to be sorted by timestamp without a costly scan. This design leverages DynamoDB's key-value and query capabilities to support both access patterns with low latency and minimal read capacity consumption.
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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