The answer is to change the primary key from UUID to an auto-increment integer while keeping the index on tracking_number. This is correct because UUID primary keys cause random writes and severe index fragmentation in the clustered index, leading to frequent page splits and degraded insert performance as the table grows; switching to a sequential auto-increment integer allows ordered writes that minimize overhead and improve throughput. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of how primary key design impacts write-heavy workloads on RDS for MySQL, with a common trap being to assume that adding more storage or CPU will fix the root cause of fragmentation. A useful memory tip is “UUID for uniqueness, but auto-increment for speed”—when inserts dominate, sequential keys outperform random ones.
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 logistics company uses Amazon RDS for MySQL to track package shipments. The 'shipments' table contains 200 million rows and has a primary key on 'shipment_id' (UUID). The application frequently queries for shipments by 'tracking_number', which is a unique string of 20 characters. The DBA created a B-tree index on tracking_number. The queries by tracking_number are fast, but inserts are becoming slower over time. The table has 50 GB of data. The company plans to double the insert rate next month. The database is a db.r5.large instance with 500 GB of Provisioned IOPS SSD storage. The instance's CPU utilization is below 30%, and there is no lock contention. What should the database specialist do to improve insert performance?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Change the primary key from UUID to an auto-increment integer, and keep the tracking_number index.
Option C is correct because UUID primary keys cause random writes and index fragmentation, degrading insert performance as the table grows. Switching to an auto-increment integer primary key allows sequential writes to the clustered index, reducing page splits and improving insert throughput. The B-tree index on tracking_number remains to support fast queries, while the new primary key eliminates the UUID write overhead.
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.
✗
Add a read replica and route insert queries to the replica.
Why it's wrong here
Read replicas are for read scaling, not for improving write performance.
✗
Drop the index on tracking_number to reduce write overhead.
Why it's wrong here
Dropping the index would slow down queries by tracking_number, which is a frequent access pattern.
✓
Change the primary key from UUID to an auto-increment integer, and keep the tracking_number index.
Why this is correct
An auto-increment primary key allows sequential inserts, reducing page splits and improving insert speed.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Increase the provisioned IOPS to 20,000.
Why it's wrong here
IOPS is not the bottleneck; the issue is index fragmentation due to random primary key.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often focus on index overhead or IOPS as the cause of slow inserts, overlooking the fundamental impact of UUID fragmentation on clustered index write performance.
Detailed technical explanation
How to think about this question
In InnoDB, the primary key is a clustered index, so UUID inserts cause random page splits and excessive B-tree rebalancing, increasing write amplification. An auto-increment integer primary key ensures sequential insertion order, minimizing page splits and reducing index maintenance overhead. The tracking_number index remains a secondary B-tree index, which is efficient for lookups and does not suffer from the same fragmentation issue because it is not the clustering key.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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: Change the primary key from UUID to an auto-increment integer, and keep the tracking_number index. — Option C is correct because UUID primary keys cause random writes and index fragmentation, degrading insert performance as the table grows. Switching to an auto-increment integer primary key allows sequential writes to the clustered index, reducing page splits and improving insert throughput. The B-tree index on tracking_number remains to support fast queries, while the new primary key eliminates the UUID write overhead.
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.
Are there clue words in this question I should notice?
Yes — watch for: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
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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