DEA-C01 Data Ingestion and Transformation Practice Question
A company uses AWS DMS to migrate data from Oracle to Aurora MySQL. During the ongoing replication, the target table shows duplicate primary key errors. What is the most likely cause?
⚠ Common exam trap
The DEA-C01 exam often tests the misconception that duplicate key errors are caused by data type mismatches or LOB truncation, but the real trap is forgetting that auto-increment columns on the target can conflict with explicit primary key values from the source during ongoing replication.
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
✓
The target table has an auto-increment column, and DMS is inserting explicit values that conflict.
When DMS replicates into a target table with an auto-increment column, it attempts to insert explicit values from the source. If the target's auto-increment counter has already generated a value matching one of those explicit inserts, a duplicate primary key error occurs. This is the most likely cause because DMS does not automatically skip or re-map auto-increment columns unless explicitly configured.
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 is using 'Limited LOB mode' and truncating LOB data, causing row mismatches.
Why it's wrong here
LOB truncation does not cause PK duplicates.
- ✗
The source table has a trigger that inserts additional rows.
Why it's wrong here
Triggers on source are not replicated by DMS.
- ✓
The target table has an auto-increment column, and DMS is inserting explicit values that conflict.
Why this is correct
DMS inserts values for the PK, but auto-increment may also generate values, causing duplicates.
- ✗
The DMS task is configured with 'Parallel apply' threads that cause race conditions.
Why it's wrong here
Parallel apply should handle ordering; duplicates are more likely due to auto-increment.
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