DBS-C01 Workload-Specific Database Design Practice Question
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?
⚠ Common exam trap
Many exam-takers 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.
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
✓
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.
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.
- ✗
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.
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