You can select Target table preparation mode when you choose to a create data migration task under the Advanced Settings tab in the AWS DMS console for PostgreSQL, MongoDB, and Amazon DocumentDB migrations.
Drop tables on target
In Drop tables on target mode, AWS DMS homogeneous migration drops the target tables and recreates them before starting the migration. This approach ensures that the target tables are empty at the start of the migration. During homogeneous migrations, AWS DMS creates all secondary objects, including indexes defined in the source table metadata, before loading the data to ensure efficient data migration.
When using the Drop tables on target mode, you might need to configure the target database. For example, with a PostgreSQL target, AWS DMS cannot create a schema user for security reasons. In this case, you must pre-create the schema user to match the source, allowing AWS DMS to create the tables and assign them to a similar role as the source when the migration begins.
Truncate
In Truncate mode, AWS DMS homogeneous migration truncates all existing target tables before the migration begins. This preserves the table structure. This mode is suitable for full load or full load plus CDC migrations where the target schema is pre-created. For an Amazon DocumentDB target, if the collection does not exist, AWS DMS creates the collection without indexes during the migration.
Do nothing
In Do nothing mode, AWS DMS homogeneous migration assumes that the target tables are pre-created. If the target tables are not empty, data conflicts may occur during migration, potentially causing a DMS task error. In this mode, the table structure remains unchanged, and any existing data is preserved. Do nothing mode is suitable for CDC-only tasks when the target tables have been backfilled from the source, and ongoing replication is used to synchronize the source and target. For an Amazon DocumentDB target, if the collection does not exist, AWS DMS creates the collection without secondary indexes. Additionally, Do nothing mode can be used during the Full Load phase when migrating data from a MongoDB sharded collection to Amazon DocumentDB.
