what happens if i remove username and password from database.yml with postgresql on rails

Question

Im making a web app with rails, using posgresql as my database. I was getting a weird error 'role my_app does not exist' everytime i tried to run rake db:create:all. but i found out that if you comment out or remove the username and password fields from the database.yml, then everything works fine. Is this bad? would this cause some problems later on?

here is my database.yml, as you see, ive commented out username and password:

    development:
  adapter: postgresql
  encoding: unicode
  database: db/website_test_development
  pool: 5
  #username: website_test
  #password:

  # Connect on a TCP socket. Omitted by default since the client uses a
  # domain socket that doesn't need configuration. Windows does not have
  # domain sockets, so uncomment these lines.
  #host: localhost

  # The TCP port the server listens on. Defaults to 5432.
  # If your server runs on a different port number, change accordingly.
  #port: 5432

  # Schema search path. The server defaults to $user,public
  #schema_search_path: myapp,sharedapp,public

  # Minimum log levels, in increasing order:
  #   debug5, debug4, debug3, debug2, debug1,
  #   log, notice, warning, error, fatal, and panic
  # Defaults to warning.
  #min_messages: notice

# Warning: The database defined as "test" will be erased and
# re-generated from your development database when you run "rake".
# Do not set this db to the same as development or production.
test:
  adapter: postgresql
  encoding: unicode
  database: db/website_test_test
  pool: 5
  #username: website_test
  #password:

production:
  adapter: postgresql
  encoding: unicode
  database: db/website_test_production
  pool: 5
  #username: website_test
  #password:

Answer 1

"role my_app does not exist" means it's complaining that the DB user doesn't exist:

http://www.postgresql.org/docs/current/static/sql-createuser.html

You'll want to refer to the heroku docs for your particular setup, as they likely have special scripts in place to do the same:

https://devcenter.heroku.com/articles/heroku-postgresql