The simplest way to backup the Mingle database would be to use the pgadmin . Its graphical interface supports all PostgreSQL features and makes administration easy. The attached PDF describes the steps in detail to dump and restore the database via pgadmin.
If you are comfortable with command-line, you could use the following commands:
1) Backup db ( run the command as the Postgres user)
pg_dump db_name > db_name.dump
2) Restore db:
Create a database using the command : createdb db_name
psql db_name < db_name.dump ( where db_name.dump is the dump obtained from the previous step)