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 company uses Amazon DynamoDB to store user posts. The table has a partition key of 'user_id' and a sort key of 'post_timestamp'. Each item is about 10 KB. The application needs to retrieve all posts for a given user within a date range. The company recently added a new feature that allows users to 'like' posts, and they store the like count as an attribute in the post item. The like count is updated frequently. The application experiences high write throttling on the table. The table has 1000 WCUs provisioned. The write pattern is bursty. Which design change would MOST effectively reduce write throttling?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a random suffix to the user_id partition key to distribute writes across multiple partitions.
Option C is correct because the write throttling is caused by a 'hot partition' — all writes for a given user_id go to the same partition, and the bursty write pattern (e.g., many likes on a single post) exceeds the partition's 1,000 WCU limit (1,000 write capacity units per partition). Adding a random suffix to the user_id partition key distributes writes across multiple partitions, effectively increasing the write throughput for that logical user's data. This is a common design pattern for DynamoDB to handle high-traffic items without increasing provisioned capacity.
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.
✗
Increase the WCUs to 5000.
Why it's wrong here
Increasing capacity helps but is not the most efficient; sharding is more cost-effective.
✗
Enable DynamoDB Accelerator (DAX) to cache writes.
Why it's wrong here
DAX is a read cache, it does not help write throttling.
✓
Add a random suffix to the user_id partition key to distribute writes across multiple partitions.
Why this is correct
Sharding spreads the write load evenly across partitions, reducing throttling.
Related concept
Read the scenario before looking for a memorised answer.
✗
Create a Global Secondary Index (GSI) on the like count attribute.
Why it's wrong here
A GSI does not reduce write throttling on the base table.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume increasing provisioned capacity (Option A) is the universal fix for throttling, but AWS specifically tests the understanding that DynamoDB's partition-level throughput limits require data distribution changes, not just capacity increases.
Detailed technical explanation
How to think about this question
Under the hood, DynamoDB partitions data based on the partition key's hash value; a single partition can sustain up to 1,000 WCUs (or 3,000 RCUs) before throttling. By adding a random suffix (e.g., user_id + random number from 1 to N), you spread writes for the same user across N partitions, effectively multiplying the write throughput for that user by N. However, this complicates reads — you must query all suffix variants and merge results, which is acceptable for the described 'retrieve all posts within a date range' use case if you use a scatter-gather pattern.
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 a random suffix to the user_id partition key to distribute writes across multiple partitions. — Option C is correct because the write throttling is caused by a 'hot partition' — all writes for a given user_id go to the same partition, and the bursty write pattern (e.g., many likes on a single post) exceeds the partition's 1,000 WCU limit (1,000 write capacity units per partition). Adding a random suffix to the user_id partition key distributes writes across multiple partitions, effectively increasing the write throughput for that logical user's data. This is a common design pattern for DynamoDB to handle high-traffic items without increasing provisioned capacity.
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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