DBS-C01 Workload-Specific Database Design Practice Question
A company is running a MySQL database on Amazon RDS for a customer relationship management (CRM) application. The database has a table named 'contacts' with over 100 million rows. The application frequently runs queries to find contacts by email address. The email column has a B-tree index. Recently, the application started experiencing slow query performance. The team checked CloudWatch metrics and saw that the ReadIOPS for the RDS instance is consistently at 80% of the provisioned IOPS limit. The instance type is db.r5.large with 3000 provisioned IOPS (gp2). The buffer pool hit ratio is 95%. What is the most cost-effective design change to improve query performance?
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
✓
Upgrade the RDS instance to db.r5.xlarge with 6000 provisioned IOPS.
Upgrading to a db.r5.xlarge with 6,000 provisioned IOPS (gp2) doubles the IOPS capacity, directly addressing the high ReadIOPS utilization (80%) without requiring application changes. This is the most cost-effective solution as it leverages the existing RDS infrastructure. Option B is wrong because migrating to DynamoDB would require significant application rework and is not necessary when the bottleneck is IOPS. Option C is wrong because OpenSearch adds unnecessary complexity and cost for a simple email lookup. Option D is wrong because the buffer pool hit ratio is already at 95%, indicating that increasing memory would yield minimal benefit.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Upgrade the RDS instance to db.r5.xlarge with 6000 provisioned IOPS.
Why this is correct
Increases IOPS capacity, reducing IO bottleneck.
- ✗
Migrate the contacts table to Amazon DynamoDB with email as partition key.
Why it's wrong here
Requires significant application changes.
- ✗
Implement an Amazon OpenSearch Service cluster for email search.
Why it's wrong here
Adds complexity and cost; not cost-effective.
- ✗
Increase the buffer pool size by changing to a memory-optimized instance.
Why it's wrong here
Buffer pool hit ratio is already high; more memory yields diminishing returns.
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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.