Troubleshooting High Write Latency in Amazon Aurora MySQL
A company has an Amazon Aurora MySQL DB cluster with a primary instance and two Aurora Replicas. The application is experiencing high write latency. The primary instance's CPU utilization is at 90%, while the replicas are at 30%. The DB cluster parameter group has the default values. Which change is most likely to reduce write latency?
Quick Answer
The correct answer is to disable the binary log (binlog) on the DB cluster. This is the most effective solution because, by default, Amazon Aurora MySQL enables binlog for compatibility with MySQL, but it forces the primary instance to perform additional disk I/O and CPU-intensive logging for every write operation, directly causing high write latency when CPU is already saturated at 90%. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of Aurora’s architecture—specifically that binlog is unnecessary for replication in Aurora (which uses its own storage-based replication) and that disabling it frees CPU cycles for transaction processing. A common trap is assuming you need to scale up the instance or add storage, but the replicas’ low CPU usage confirms the bottleneck is on the primary’s logging overhead, not hardware capacity. Memory tip: “Binlog is a burden on the primary—Aurora replicates without it.”
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
✓
Disable the binary log (binlog) on the DB cluster.
High CPU utilization on the primary instance is often caused by the binary log (binlog) being enabled, which is enabled by default for Aurora MySQL. Binlog generation adds overhead to write operations. Disabling binlog reduces CPU usage on the primary, thereby reducing write latency. Increasing the instance class (Option A) could help but is not as directly targeted as disabling binlog. Adding more Aurora Replicas (Option B) does not reduce write latency on the primary because replicas handle read traffic only. Increasing allocated storage (Option D) does not affect CPU or write latency.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the DB instance class of the primary instance.
Why it's wrong here
While this could help, it is more costly and not the first step.
- ✗
Add more Aurora Replicas to distribute the write load.
Why it's wrong here
Aurora Replicas are read-only and do not handle writes.
- ✓
Disable the binary log (binlog) on the DB cluster.
Why this is correct
Binary logging adds CPU overhead; disabling it can reduce write latency.
- ✗
Increase the allocated storage of the cluster.
Why it's wrong here
Storage size does not directly affect CPU usage or write latency.
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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 company is running an Amazon Aurora MySQL database cluster. The database specialist notices that the write latency is high during peak hours. The cluster consists of one writer and two reader instances. Which action should the specialist take to reduce write latency?
medium- A.Enable Auto Scaling on the cluster to automatically adjust capacity.
- ✓ B.Increase the instance class of the writer instance to a larger size.
- C.Enable Multi-AZ deployment for the cluster.
- D.Add more reader instances to distribute the read load.
Why B: Increasing the instance class of the writer instance provides more CPU and memory resources, which can directly improve write throughput and reduce write latency during peak loads. Option A is incorrect because Auto Scaling in Aurora adjusts the number of reader instances, not the writer capacity. Option C is incorrect because Multi-AZ is already inherent in Aurora; enabling Multi-AZ does not affect write latency. Option D is incorrect because adding more reader instances distributes read traffic but does not reduce write latency on the writer.
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.