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Difficulty: MediumDatabase Migration and Schema Conversion using DMS and SCT

A solutions architect is planning the migration of an on-premises Oracle database to an Amazon Aurora PostgreSQL-Compatible Edition DB cluster. The database contains tables with Large Objects (LOBs) and requires continuous replication to minimize downtime. The schema has already been converted using the AWS Schema Conversion Tool (SCT). The architect is now configuring AWS Database Migration Service (AWS DMS) for the full load and Change Data Capture (CDC) replication phases.

Which two configurations are required to ensure the replication succeeds and performs optimally? (Select two.)

  1. Enable supplemental logging at the Oracle database level and add supplemental logging for primary keys on all tables selected for replication.Answer
  2. Configure the AWS DMS task using Limited LOB mode and set a Max LOB size parameter that accommodates the maximum size of LOBs in the migrated tables.Answer
  3. C
    Rely on default Oracle configurations by executing the replication task without enabling supplemental logging, as AWS DMS reads the active redo logs directly to capture changes automatically.
  4. D
    Execute the database migration as a simple Replatforming path by utilizing the AWS SCT to automatically deploy unchanged Oracle PL/SQL stored procedures directly into the Aurora PostgreSQL target database.
  5. E
    Configure the AWS DMS target endpoint to use Aurora PostgreSQL read replicas to scale the database write performance and parallelize the data load during the CDC phase.

Answer

To perform a successful and optimal migration, you must enable supplemental logging at both the database and primary key table levels on the source Oracle database, and configure the AWS DMS task to use Limited LOB mode with an appropriate maximum LOB size.
Enabling supplemental logging at the database level and on the tables ensures that Oracle writes full row changes to its redo logs, which is a hard prerequisite for AWS DMS CDC. Configuring Limited LOB mode with a correct Max LOB size optimizes data transfer speeds during full load and replication because DMS pre-allocates memory buffers, avoiding the performance degradation associated with Full LOB mode.

Step-by-Step Solution

1
Configure the source database for Change Data Capture (CDC).
Supplemental logging is enabled at the database level and for primary keys on target tables, ensuring changed data details are captured in the redo logs.
Without supplemental logging, Oracle does not write the necessary columns to the redo logs for updates and deletes, preventing DMS from replicating transactions.
2
Determine the optimal LOB handling strategy.
Limited LOB mode is selected, and the Max LOB size parameter is configured based on the largest LOB in the source tables.
Limited LOB mode pre-allocates memory buffers, making replication much faster than Full LOB mode, which queries LOB columns line-by-line.
3
Establish target connections and migration types.
The target endpoint is pointed to the primary writer instance, and the migration strategy is treated as a Refactoring project.
AWS DMS must write to the writer node, and heterogeneous database migrations require code conversions that go beyond simple replatforming.

Key Concept

Heterogeneous database migration requirements including source database CDC prerequisites and LOB optimization settings in AWS DMS.
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Topics

Database Migration and Schema Conversion using DMS and SCT

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