RDS Postgres reg data types and extensions

The reg* data types in PostgreSQL are used to represent regular expressions data types. These data types include retype, regclass etc. This is a PostgreSQL feature, refer pgsql documentation.

Before attempting a major version upgrade of your PostgreSQL database on Amazon RDS, you should remove  or migrate any data stored in the reg* data types that are not supported by the “pg_upgrade” utility. AWS documentation provides the sql statement which can be used to understand if any un-supported reg* data-types are being used.

Most of the Postgresql Extensions are generally not upgraded alongside the db engine major upgrade. Refer documentation It's essential that you ensure compatibility of the pg extensions with the new PostgreSQL version and your application code. It's recommended to schedule a maintenance window to upgrade the extensions and perform any necessary testing or application changes to ensure a smooth transition. Post upgrade, new sessions will automatically use the upgraded extension versions.