Correct Answer:
Use the AWS Schema Conversion Tool with AWS Database Migration Service (AWS DMS) using a memory optimized replication instance. Create a full load plus change data capture (CDC) replication task and a table mapping to select all tables.

Explanation:
The AWS Schema Conversion Tool is used to convert the Oracle schema to a PostgreSQL-compatible format. AWS DMS supports a full load plus change data capture (CDC) mode, which performs an initial full load and then keeps the target database synchronized by capturing ongoing changes. A memory-optimized replication instance is ideal for environments with high write throughput, ensuring replication performance during the hybrid phase where both databases remain in use.

Why the other options are incorrect:

Using AWS DataSync for the initial migration: DataSync is not designed for live, ongoing database replication. It is optimized for file-based transfers, not transactional databases.
Using a compute-optimized replication instance: Compute-optimized instances may not provide sufficient memory buffering and I/O performance for write-heavy CDC operations.
Selecting only the largest tables: This would risk leaving important changes unsynchronized. All tables must be kept in sync for consistency during phased application migration.

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