Homogeneous Migration

Homogeneous migration is a database migration in which the source and target use the same database engine, such as MySQL to MySQL, PostgreSQL to PostgreSQL, or Oracle Database to Oracle Database. The infrastructure, operating environment, or database version can change without changing this classification. By contrast, moving Oracle Database to PostgreSQL is a heterogeneous migration because the database engine changes.

In the cloud, this approach commonly moves an on-premises database to a managed database service or to a database running on a virtual machine. For example, a company might migrate a self-managed PostgreSQL database to Amazon RDS for PostgreSQL. The application retains its PostgreSQL database interface, while responsibility for tasks such as infrastructure maintenance and automated backups shifts toward the managed service. Homogeneous migrations can also occur between cloud environments or between accounts and Regions.

The main benefit is reduced conversion effort. Tables, SQL statements, and application data-access logic are more likely to remain usable when the engine stays the same. However, same-engine does not mean identical behavior or complete compatibility. Engineers must check supported versions, extensions, character sets, collations, authentication methods, and database configuration. Managed services can restrict administrative privileges, filesystem access, or extensions that were available on the original server.

The transfer method depends on database size, acceptable downtime, and engine capabilities. A small database with a generous maintenance window might use a native logical export and import. Larger databases might use supported backup-and-restore procedures or an initial data load followed by change data capture. Change data capture copies ongoing source changes while applications continue using the original database, reducing the final interruption. It requires supported configurations and enough source log retention to avoid losing changes before they are applied.

For example, an online retailer migrating MySQL to Amazon RDS for MySQL could use AWS Database Migration Service to load existing data and replicate subsequent changes. Before cutover, engineers would test the application, compare source and target data, and monitor replication lag. They would then stop or carefully coordinate writes, wait for remaining changes to apply, switch application connections, and verify transactions against the target. A rollback plan must account for any writes accepted by the target after the switch.

A common misconception is that homogeneous migration guarantees zero downtime or automatically transfers every database object. Actual behavior depends on the migration tool and engine combination. Users, permissions, indexes, triggers, stored procedures, and scheduled jobs may require separate handling. Retaining the engine also does not guarantee the same performance: storage latency, instance sizing, network placement, and configuration can change query behavior.

For certification questions, identify the source and target engines first. Same-engine moves are homogeneous; different-engine moves are heterogeneous. AWS Database Migration Service supports both categories for supported endpoints. Schema conversion is generally associated with heterogeneous migration, rather than being the defining requirement for a homogeneous move. Choose the migration approach based on compatibility, downtime requirements, operational effort, and validation needs, not merely the shared engine name.