The answer is to check the DMS task logs, because when rows are missing after a migration, the task logs are the definitive source for identifying rows that failed to apply due to data type conversion errors. AWS DMS logs every skipped or rejected row during the apply phase, so a mismatch in row counts almost always points to conversion failures that were recorded but not written to the target. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of DMS error handling and the importance of monitoring task logs rather than assuming a successful task status means complete data transfer. A common trap is to look at table-level statistics or validation reports first, but those only show counts, not the specific failed rows. Memory tip: “Logs catch the lost rows” — if the target has fewer rows, the task logs will show you exactly which ones were dropped.
DEA-C01 Data Operations and Support Practice Question
This DEA-C01 practice question tests your understanding of data operations and support. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 uses AWS Database Migration Service (DMS) to migrate an on-premises Oracle database to Amazon RDS for PostgreSQL. The migration completes successfully, but the data engineer notices that some tables have fewer rows in the target than the source. Which DMS setting should be checked to ensure full data migration?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The task logs show that some rows failed to apply due to data type conversion errors.
Option B is correct because if some rows failed to apply due to data type conversion errors, those rows would be logged as errors and not written to the target, resulting in fewer rows. AWS DMS task logs capture these failures, and checking them is the direct way to identify rows that were skipped or rejected during migration. This is the most common cause of row count mismatches after a successful DMS task.
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.
✗
The LOB mode is set to 'Limited LOB mode' instead of 'Full LOB mode'.
Why it's wrong here
LOB mode affects how large objects are handled, not regular rows.
✓
The task logs show that some rows failed to apply due to data type conversion errors.
Why this is correct
Failed rows would be logged and can be reviewed.
Related concept
Read the scenario before looking for a memorised answer.
✗
The 'Enable validation' option is turned off.
Why it's wrong here
Validation checks data after migration, does not affect migration completeness.
✗
The 'Parallel Apply' feature is disabled, slowing down the migration.
Why it's wrong here
Speed, not completeness.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume row count mismatches are always due to LOB settings or validation being off, but the most direct cause is data type conversion errors logged in the task logs, which DMS does not surface in the task status summary.
Detailed technical explanation
How to think about this question
Under the hood, AWS DMS uses a task-level error handling policy that can be set to 'Stop', 'Ignore', or 'Log' on data conversion failures. By default, DMS logs data type conversion errors and continues, so rows that fail conversion are recorded in the task logs but not applied to the target. In real-world migrations, subtle type mismatches (e.g., Oracle NUMBER with no precision mapping to PostgreSQL NUMERIC) can silently drop rows if the error handling is not set to fail the task.
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.
Data Operations and Support — This question tests Data Operations and Support — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The task logs show that some rows failed to apply due to data type conversion errors. — Option B is correct because if some rows failed to apply due to data type conversion errors, those rows would be logged as errors and not written to the target, resulting in fewer rows. AWS DMS task logs capture these failures, and checking them is the direct way to identify rows that were skipped or rejected during migration. This is the most common cause of row count mismatches after a successful DMS task.
What should I do if I get this DEA-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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