At present, the database setup guides do not adequately describe how to migrate Confluence from the embedded database to an external one as they are intended for users setting up a new database from scratch. However, the Migrating+to+a+Different+Database guide does not cover any database setup or database-specific steps.

Each guide should cover both new db setup and migration, possibly in separate docs, with the generic migration document removed once this is complete. This will reduce support load from uses who do not correctly configure their database permissions in particular.

http://confluence.atlassian.com/display/DOC/Database+Setup+Guides
http://confluence.atlassian.com/display/DOC/Migrating+to+a+Different+Database