The answer is to change the primary key to an auto-increment BIGINT and recreate the indexes. This is correct because UUID primary keys cause random, non-sequential writes that fragment the B-tree index, forcing frequent page splits and massive write amplification—exactly the mechanism that drives latency from 5 ms to 200 ms during flash sales. Switching to an auto-increment BIGINT enables sequential writes that fill index pages contiguously, dramatically reducing write overhead and restoring performance with minimal application changes. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of how primary key design directly impacts Aurora write performance, especially under high-concurrency workloads. A common trap is assuming read replicas or instance scaling will fix write latency, but the root cause is index fragmentation from random UUIDs. Memory tip: “UUIDs scatter, BIGINTs gather”—sequential keys keep your B-tree pages packed and your writes fast.
DBS-C01 Workload-Specific Database Design Practice Question
This DBS-C01 practice question tests your understanding of workload-specific database design. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 company runs a critical e-commerce platform on Amazon Aurora MySQL. The database is 2 TB and experiences a sudden spike in write latency during flash sales. The application uses auto-generated UUIDs as primary keys. The CPU utilization on the writer instance is 80%, and the read replicas show low utilization. Write latency has increased from 5 ms to 200 ms. The company needs to reduce write latency with minimal application changes. Which course of action is MOST effective?
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 to an auto-increment BIGINT and recreate indexes.
B is correct because UUID primary keys cause random writes that fragment the B-tree index, leading to frequent page splits and high write latency. Changing to an auto-increment BIGINT allows sequential writes, which fill index pages contiguously and reduce the write amplification that drives latency from 5 ms to 200 ms. This requires no application logic changes beyond the schema migration, making it the most effective minimal-change solution.
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.
✗
Implement sharding across multiple Aurora clusters.
Why it's wrong here
Requires significant application changes.
✓
Change the primary key to an auto-increment BIGINT and recreate indexes.
Why this is correct
Sequential keys reduce index page splits, improving write performance.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Add more read replicas and redirect write-heavy queries to replicas.
Why it's wrong here
Read replicas cannot handle writes.
✗
Upgrade the writer instance to a larger instance type with more IOPS.
Why it's wrong here
Addresses symptom, not root cause.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume scaling compute or storage (Option D) is the universal fix for write latency, but the exam specifically tests the impact of primary key design on index write amplification in Aurora MySQL.
Detailed technical explanation
How to think about this question
Aurora MySQL uses a shared-storage volume with a 6-replica quorum, but write latency is still dominated by index maintenance. UUIDs are 128-bit and randomly distributed, causing each INSERT to land on a random leaf page in the B-tree, triggering page splits and rebalancing. An auto-increment BIGINT (64-bit) appends to the rightmost leaf page, reducing page splits by over 90% and keeping the buffer pool hot for writes. In real-world flash sales, this change alone can drop write latency from 200 ms back to single-digit milliseconds without any infrastructure scaling.
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: Change the primary key to an auto-increment BIGINT and recreate indexes. — B is correct because UUID primary keys cause random writes that fragment the B-tree index, leading to frequent page splits and high write latency. Changing to an auto-increment BIGINT allows sequential writes, which fill index pages contiguously and reduce the write amplification that drives latency from 5 ms to 200 ms. This requires no application logic changes beyond the schema migration, making it the most effective minimal-change solution.
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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