DEA-C01 Data Operations and Support Practice Question
A data engineer is using AWS Database Migration Service (AWS DMS) to migrate an on-premises Oracle database to Amazon Aurora PostgreSQL. The migration is ongoing, and the engineer notices that some transactions are not being replicated to the target. The DMS task is configured for full load plus change data capture (CDC). Which action should the engineer take to troubleshoot the missing transactions?
⚠ Common exam trap
The trap here is assuming that performance tuning or validation will fix missing transactions, when the real issue is often logged errors that need to be addressed.
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
✓
Check the DMS task's CloudWatch logs for errors related to unsupported data types or DDL changes.
When AWS DMS CDC skips transactions, it is often due to errors such as unsupported data types or DDL changes. These errors are logged in CloudWatch Logs. Reviewing the logs allows the engineer to identify the specific cause and take corrective action, such as excluding the problematic table or adjusting the task settings. This is the most direct troubleshooting step.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Check the DMS task's CloudWatch logs for errors related to unsupported data types or DDL changes.
Why this is correct
AWS DMS logs errors for issues like unsupported data types, DDL changes, or transformation failures in CloudWatch Logs. These errors can cause specific transactions to be skipped during CDC. Reviewing the logs is the first step to identify why transactions are missing. The logs provide detailed messages that help pinpoint the root cause, such as a data type not supported by the target.
- ✗
Enable AWS DMS validation to compare source and target rows and identify discrepancies.
Why it's wrong here
Validation can identify discrepancies but does not prevent missing transactions. It is a monitoring tool, not a fix. While it could confirm that transactions are missing, it would not resolve the underlying cause. The engineer first needs to find why transactions are skipped, which is best done by examining logs for errors.
- ✗
Modify the DMS task to use 'Drop and create' target table preparation mode.
Why it's wrong here
The 'Drop and create' mode is used for full load and would drop existing tables, causing data loss. It does not help with CDC issues. Changing this setting during an ongoing migration could disrupt the process and is not a troubleshooting step for missing transactions. It is irrelevant to the problem of selective CDC failures.
- ✗
Increase the DMS replication instance size to handle the transaction volume.
Why it's wrong here
While insufficient resources can cause replication lag, the scenario states that some transactions are not replicated at all, not just delayed. Increasing instance size might improve performance but would not address selective transaction loss due to errors. The issue is more likely related to data compatibility or configuration, not raw capacity.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
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