The correct answer is that target tables lack unique constraints, causing AWS DMS to insert duplicate rows. When DMS performs ongoing replication using change data capture, it reads transaction logs and may re-apply the same change if the target table has no unique constraint to identify existing rows. Without a unique key, DMS cannot distinguish between a new insert and a replayed change, so it inserts a duplicate row instead of performing an update or skipping the record. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of how DMS handles CDC consistency and the critical role of primary keys or unique constraints on the target. A common trap is assuming the issue stems from case sensitivity or full-load settings, but the core concept is that DMS relies on unique constraints for idempotent replication. Memory tip: think "no key, double the rows" — if the target lacks a unique constraint, DMS will happily insert duplicates.
DEA-C01 Data Ingestion and Transformation Practice Question
This DEA-C01 practice question tests your understanding of data ingestion and transformation. 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 DMS to migrate an on-premises Oracle database to Amazon RDS for PostgreSQL. The migration completes, but the target table has more rows than the source. Which 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.
Option C is correct. DMS may re-apply changes from the transaction log if the target tables have no unique constraints, leading to duplicate rows. Option A is wrong because DMS uses CDC, not a full load. Option B is wrong because PostgreSQL is case-sensitive, but that would cause missing rows, not extras. Option D is wrong because binary replication is not relevant.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
DMS used binary replication which included extra metadata rows.
Why it's wrong here
Binary replication is not a standard DMS feature; it would not add rows.
✗
Oracle and PostgreSQL handle case sensitivity differently.
Why it's wrong here
Case sensitivity differences cause data mismatches, not extra rows.
✗
DMS performed a full load instead of ongoing replication.
Why it's wrong here
A full load would not create duplicates; it replaces data.
Without unique constraints, DMS may re-apply changes and create duplicates.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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. ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement. 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.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related DEA-C01 ACL questions on filtering logic and placement.
Data Ingestion and Transformation — This question tests Data Ingestion and Transformation — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Target tables lack unique constraints, causing DMS to insert duplicate rows. — Option C is correct. DMS may re-apply changes from the transaction log if the target tables have no unique constraints, leading to duplicate rows. Option A is wrong because DMS uses CDC, not a full load. Option B is wrong because PostgreSQL is case-sensitive, but that would cause missing rows, not extras. Option D is wrong because binary replication is not relevant.
What should I do if I get this DEA-C01 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related DEA-C01 ACL questions on filtering logic and placement.
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?
Standard ACLs match source addresses.
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Question Discussion
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