DBS-C01 Management and Operations Practice Question
A company is migrating an on-premises Oracle database to Amazon RDS for Oracle using AWS DMS. The source database is 2 TB and has high transaction volume. The migration needs minimal downtime. Currently, full load completes but CDC task fails with 'ORA-1555: snapshot too old' errors. What should the DBA do to resolve this?
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
✓
Increase the undo retention period and undo tablespace size on the source Oracle database.
The 'ORA-1555: snapshot too old' error occurs when Oracle's undo data for a read-consistent view is overwritten before DMS can read it. Increasing the undo retention period and undo tablespace size on the source database ensures that undo data is preserved longer, allowing DMS's CDC task to read consistent data without errors. Option B is correct because it directly addresses the root cause. Option A would restart the full load but not fix the CDC failure. Option C (supplemental logging and larger DMS instance) does not resolve undo retention issues. Option D (reducing transactions) is not practical and may cause data loss. Therefore, the correct solution is to increase undo retention and tablespace size.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Restart the migration with a new full load and use a smaller task.
Why it's wrong here
Does not address the root cause.
- ✓
Increase the undo retention period and undo tablespace size on the source Oracle database.
Why this is correct
Larger undo retention prevents snapshot too old errors.
- ✗
Enable supplemental logging on the source and use a larger DMS instance.
Why it's wrong here
Supplemental logging does not affect undo.
- ✗
Reduce the transaction volume by pausing non-essential transactions during CDC.
Why it's wrong here
Not feasible in production.
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