Minimal Downtime Oracle Migration using AWS DMS CDC
A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. The database is 2 TB in size and has a high transaction rate. The migration must have minimal downtime and support ongoing replication. Which AWS service should be used for the migration?
Quick Answer
The answer is AWS Database Migration Service (DMS). This is the correct choice because DMS supports ongoing change data capture (CDC) replication, which allows you to migrate an Oracle database to Amazon RDS for Oracle with minimal downtime by continuously syncing transactions from the source to the target during the migration window. For a 2 TB database with a high transaction rate, DMS’s CDC capability ensures that only a brief cutover pause is needed, rather than a full outage. On the AWS Certified Database Specialty DBS-C01 exam, this question tests your understanding of migration strategies under the “Migration and Management” domain; a common trap is confusing AWS Schema Conversion Tool (SCT) with DMS—SCT handles schema conversion but not data replication, while DMS handles the actual ongoing sync. Another trap is selecting Snowball, which is for offline bulk transfers and cannot achieve minimal downtime. Memory tip: think “DMS = Data Moves Sync” for ongoing replication, while SCT = Schema Conversion Tool only.
⚠ Common exam trap
Watch out — candidates often confuse AWS DMS with AWS SCT, thinking SCT handles data migration, but SCT only converts schema objects and does not perform any data transfer or 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
✓
AWS Database Migration Service (AWS DMS)
AWS DMS is the correct service because it supports ongoing replication (change data capture) from an on-premises Oracle source to Amazon RDS for Oracle, enabling a migration with minimal downtime. It can handle a 2 TB database by using a full load followed by continuous replication of transactions, and it supports Oracle-specific features like supplemental logging and LogMiner for CDC.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
AWS Schema Conversion Tool (AWS SCT)
Why it's wrong here
AWS SCT is used for schema conversion, not for data replication or migration with minimal downtime.
- ✓
AWS Database Migration Service (AWS DMS)
Why this is correct
AWS DMS supports ongoing replication from on-premises to RDS, enabling minimal downtime migrations.
- ✗
AWS Direct Connect
Why it's wrong here
Direct Connect provides a dedicated network connection but does not perform data migration.
- ✗
Amazon RDS Read Replica
Why it's wrong here
Read Replicas are for RDS instances, not for on-premises databases.
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Same concept, more angles
3 more ways this is tested on DBS-C01
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Variation 1. A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. The database uses Oracle Data Pump for export/import. The migration must be completed within a short maintenance window. Which migration approach should they use?
medium- A.Use AWS Snowball to transfer the database files to AWS and then restore to RDS.
- ✓ B.Use AWS Database Migration Service with full load and change data capture (CDC).
- C.Use Oracle Data Pump to export the database and import into RDS.
- D.Use AWS Schema Conversion Tool (SCT) to convert the schema and then use DMS for data migration.
Why B: AWS Database Migration Service (DMS) with full load and change data capture (CDC) is the correct approach because it minimizes downtime by performing an initial full load of the Oracle database and then continuously replicating ongoing changes until the cutover, allowing the migration to complete within a short maintenance window. Unlike Oracle Data Pump, which requires the source database to be offline during export/import, DMS with CDC keeps the source operational and only requires a brief outage at final cutover.
Variation 2. A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. The database is 5 TB in size and has a daily change rate of 2%. The migration must have minimal downtime. Which migration strategy should be used?
medium- A.Use AWS Schema Conversion Tool (SCT) to convert the schema, then use AWS DMS for full load only.
- B.Create an RDS read replica in the same region and promote it.
- ✓ C.Use AWS Database Migration Service (DMS) with ongoing replication from the source database.
- D.Export the database to a dump file using Oracle Data Pump, upload to S3, and restore to RDS.
Why C: AWS DMS with ongoing replication (change data capture, CDC) allows a full load of the 5 TB database followed by continuous replication of the 2% daily changes, minimizing downtime by keeping the target RDS instance nearly synchronized until cutover. This approach handles large databases and high change rates without requiring a lengthy final export/import window.
Variation 3. A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. The database is 1 TB and has a large number of stored procedures and triggers. The migration must minimize application changes. Which migration approach should be used?
medium- A.Use AWS Schema Conversion Tool (AWS SCT) to convert the schema and AWS DMS for data migration
- ✓ B.Use AWS Database Migration Service (AWS DMS) with full load and ongoing replication
- C.Use Oracle Data Pump (expdp/impdp) to export and import the database
- D.Use AWS S3 to store the data and AWS Glue to transform and load into RDS
Why B: AWS DMS with full load and ongoing replication minimizes application changes by supporting heterogeneous migrations with minimal downtime, and it can handle stored procedures and triggers by replicating data changes in near real-time without requiring schema conversion. AWS DMS directly supports Oracle as a source and Amazon RDS for Oracle as a target, preserving the existing schema and procedural logic, which avoids the need for application rewrites.
JA
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Senior Network & Security Engineer · founder of Courseiva
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