DBS-C01 Workload-Specific Database Design Practice Question
A company runs an online auction platform on AWS. The application uses Amazon DynamoDB as the primary database, with a table 'Auctions' that has a partition key 'auction_id' (String) and sort key 'end_time' (Number). The table also has a global secondary index (GSI) on 'status' (String) and 'current_bid' (Number). The application frequently queries for active auctions sorted by current bid. Recently, the team noticed that queries on the GSI for active auctions with a high current_bid are returning results slowly. The DynamoDB table has 10,000 write capacity units (WCU) and 30,000 read capacity units (RCU) provisioned. The GSI has 5,000 RCU provisioned. The team suspects throttling on the GSI. What is the most likely cause of the slow queries?
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
✓
The GSI's provisioned RCU is insufficient due to hot partitions.
The GSI has 5,000 RCU provisioned, but if the GSI's partition key (status) and sort key (current_bid) lead to a hot partition—for example, many active auctions have the same status and similar current_bid—that single partition can throttle even if the total RCU is not fully utilized. This is because DynamoDB distributes RCU evenly across partitions, and a hot partition can exceed its allocated RCU, causing throttling on that partition. Option B is incorrect because the index key schema (status, current_bid) is actually appropriate for querying active auctions sorted by current bid; the issue is hot partitions, not inefficiency. Option C is incorrect because WCU throttling does not directly affect read performance on the GSI. Option D is incorrect because the table's RCU is separate from the index's RCU, and the index's RCU is the relevant factor.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The GSI's provisioned RCU is insufficient due to hot partitions.
Why this is correct
Hot partitions can throttle even if total RCU is not fully used.
- ✗
The GSI key schema is inefficient for the query pattern.
Why it's wrong here
The schema is appropriate; throttling is the issue.
- ✗
The table's WCU is too low, causing throttling on writes that affects reads.
Why it's wrong here
Write throttling does not directly cause read throttling on index.
- ✗
The table's RCU is too low for the application's read load.
Why it's wrong here
Table RCU is separate from index RCU.
Go deeper
Related to this question
About these practice questions
One of 1,663 original DBS-C01 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more way this is tested on DBS-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A web application uses Amazon DynamoDB as its database. The application frequently queries items using a secondary index. The index's partition key has high cardinality, but the query latency is higher than expected. Which action would MOST likely improve query performance?
easy- A.Use a Scan operation instead of Query to retrieve items from the index.
- B.Add additional sort key attributes to the index to better distribute the data.
- C.Convert the global secondary index to a local secondary index.
- ✓ D.Increase the read capacity units (RCU) for the global secondary index.
Why D: A Global Secondary Index (GSI) has its own provisioned read capacity, separate from the base table. If the GSI's read capacity units (RCU) are insufficient to handle the query workload, requests may be throttled, leading to higher latency. Increasing the RCU for the GSI directly addresses this bottleneck by allowing more concurrent read operations against the index.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DBS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DBS-C01 exam.