The answer is to increase the DMS replication instance size to a larger class with more memory. This resolves the 'Memory limit exceeded' error because DMS buffers change data capture (CDC) events in memory before applying them to DocumentDB, and a write-heavy workload with many small updates can overwhelm the limited memory of a dms.r5.large instance, causing the buffer to overflow and the task to fail. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of DMS resource sizing for CDC performance—a common trap is to restart the task or tweak batch sizes, but those don't fix the underlying memory bottleneck. Remember the mnemonic "More Memory for Migrations": when DMS fails with memory errors during CDC, scale up the instance, not the configuration.
DBS-C01 Deployment and Migration Practice Question
This DBS-C01 practice question tests your understanding of deployment and migration. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 is migrating a 500 GB MongoDB database to Amazon DocumentDB. The migration is done using AWS DMS with full load and ongoing replication. The full load completes successfully, but during CDC, the DMS task logs show 'Memory limit exceeded' errors and the task fails repeatedly. The DMS replication instance is a dms.r5.large. The source MongoDB has a write-heavy workload with many small updates. The DBA needs to fix the migration without restarting from scratch. Which action should the DBA take?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Increase the DMS replication instance size to a larger instance class with more memory.
Option C is correct. The 'Memory limit exceeded' error often occurs when DMS cannot keep up with the volume of changes, especially for write-heavy workloads. Increasing the replication instance size provides more memory for buffering. Option A is wrong because stopping and restarting the task does not address the root cause. Option B is wrong because reducing the batch size may not help; the issue is memory capacity. Option D is wrong because enabling multi-AZ does not increase memory; it provides high availability.
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.
✓
Increase the DMS replication instance size to a larger instance class with more memory.
Why this is correct
More memory allows DMS to buffer more changes and handle the workload.
Related concept
Read the scenario before looking for a memorised answer.
✗
Reduce the DMS task's 'BatchApplyEnabled' setting to apply transactions individually.
Why it's wrong here
This may increase memory usage, not decrease it.
✗
Stop and restart the DMS task to clear the cache.
Why it's wrong here
Restarting does not prevent the memory limit from being exceeded again.
✗
Enable Multi-AZ on the DMS replication instance to distribute the load.
Why it's wrong here
Multi-AZ is for failover, not for increasing memory capacity.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Identify which DBS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Deployment and Migration — This question tests Deployment and Migration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Increase the DMS replication instance size to a larger instance class with more memory. — Option C is correct. The 'Memory limit exceeded' error often occurs when DMS cannot keep up with the volume of changes, especially for write-heavy workloads. Increasing the replication instance size provides more memory for buffering. Option A is wrong because stopping and restarting the task does not address the root cause. Option B is wrong because reducing the batch size may not help; the issue is memory capacity. Option D is wrong because enabling multi-AZ does not increase memory; it provides high availability.
What should I do if I get this DBS-C01 question wrong?
Identify which DBS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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