The answer is that the target table has an identity column not set to allow insert of explicit values, which is the most likely cause when you troubleshoot DMS duplicate key error cutover scenarios. This occurs because AWS DMS attempts to replicate the exact source data, including identity column values, but the target SQL Server table’s identity property is configured to auto-generate new values, rejecting the incoming explicit inserts and raising the duplicate key conflict. On the AWS Certified Database Specialty DBS-C01 exam, this question tests your understanding of how DMS handles schema differences during ongoing replication cutovers, often appearing as a trap where candidates mistakenly blame primary key conflicts or transaction log issues. The key insight is that identity columns on the target must have IDENTITY_INSERT set to ON for DMS to succeed, a detail frequently overlooked in migration planning. Memory tip: think “IDENTITY = INSERT OFF” to recall that explicit inserts are blocked by default.
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 3 TB SQL Server database to Amazon RDS for SQL Server. The migration must be completed with less than 15 minutes of downtime. The company has set up AWS DMS with ongoing replication. During the final cutover, the DMS task fails with a 'Target error: Cannot insert duplicate key' error. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The target table has an identity column that is not set to allow insert of explicit values.
Option D is correct because duplicate key errors in DMS often occur when there are identity columns or triggers on the target that generate values conflicting with the source. Option A is wrong because DMS handles primary key conflicts by default. Option B is wrong because DMS usually handles this if configured, but the error suggests target-side uniqueness. Option C is wrong because transaction log size does not cause duplicate key errors.
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 target table has an identity column that is not set to allow insert of explicit values.
Why this is correct
If identity insert is off, DMS cannot insert source values, causing duplicate key errors.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The DMS task is not set to truncate the target before loading.
Why it's wrong here
Truncate option is for full load, not ongoing replication.
✗
The source database transaction log is full.
Why it's wrong here
Transaction log full would cause DMS to fail, but not with duplicate key error.
✗
The source database has a primary key violation.
Why it's wrong here
Primary key violations on source would be unlikely to cause target duplicate key error during ongoing replication.
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
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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: The target table has an identity column that is not set to allow insert of explicit values. — Option D is correct because duplicate key errors in DMS often occur when there are identity columns or triggers on the target that generate values conflicting with the source. Option A is wrong because DMS handles primary key conflicts by default. Option B is wrong because DMS usually handles this if configured, but the error suggests target-side uniqueness. Option C is wrong because transaction log size does not cause duplicate key errors.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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