Question 788 of 1,663
Diagnosing High Write Latency in Amazon DocumentDB
A company uses Amazon DocumentDB (with MongoDB compatibility) for its application. The application is experiencing high write latency. The DB cluster has one primary instance and two replicas. Which action should be taken to identify the cause?
Quick Answer
The correct action is to enable Enhanced Monitoring and review OS-level metrics like CPU, memory, and I/O. This is because high write latency in Amazon DocumentDB often stems from resource contention on the primary instance, and OS-level metrics reveal whether the bottleneck is CPU saturation, memory pressure, or disk I/O limits—details that database-level logs alone cannot provide. On the AWS Certified Database Specialty DBS-C01 exam, this question tests your understanding that troubleshooting write latency requires isolating infrastructure-level constraints before considering query optimization or scaling. A common trap is to jump to profiling slow queries, but those logs capture query duration, not the underlying OS resource starvation that delays writes. Remember the memory tip: “OS first, queries second”—always check the operating system’s health before blaming the database engine.
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
✓
Enable Enhanced Monitoring and review OS-level metrics like CPU, memory, and I/O.
Enabling Enhanced Monitoring at the instance level provides OS-level metrics (CPU, memory, I/O) that can help identify resource bottlenecks causing high write latency on the primary instance. Option A is incorrect because switching to Amazon DynamoDB is a major architectural change, not a troubleshooting step. Option B is incorrect because adding read replicas does not reduce write latency on the primary; replicas handle read traffic, not writes. Option D is incorrect because while slow query logging can identify poorly performing queries, high write latency may also be caused by OS-level resource contention, which Enhanced Monitoring captures.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Migrate the database to Amazon DynamoDB for better write performance.
Why it's wrong here
Migrating is a drastic change, not a troubleshooting step.
- ✗
Add more read replicas to distribute the load.
Why it's wrong here
Read replicas do not help with write latency on the primary.
- ✓
Enable Enhanced Monitoring and review OS-level metrics like CPU, memory, and I/O.
Why this is correct
Enhanced Monitoring provides granular OS metrics to pinpoint bottlenecks.
- ✗
Enable slow query logging and analyze slow queries.
Why it's wrong here
Slow queries may contribute but not necessarily the root cause of high 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 DocumentDB cluster. The application is experiencing high write latency. The cluster has a single instance. What should be done to identify the cause of the latency?
hard- A.Upgrade the instance to a larger size.
- ✓ B.Enable Performance Insights and review the top wait events.
- C.Add a replica to distribute the write load.
- D.Change the storage type to Provisioned IOPS.
Why B: Enabling Performance Insights for Amazon DocumentDB allows you to monitor the database load and review top wait events, which helps identify the specific causes of high write latency, such as lock contention or I/O bottlenecks. Option A is wrong because simply upgrading to a larger instance size addresses symptoms but does not identify the root cause. Option C is wrong because adding a replica does not reduce write latency on the primary instance; it only offloads read traffic. Option D is wrong because changing to Provisioned IOPS may improve I/O performance but does not diagnose the underlying issue causing latency.
Last reviewed: Jun 20, 2026
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