More Advanced Database Features and Rails

Dr Nic Williams's Magic Multi-Connections gem (http://magicmodels.rubyforge.org/ magic_multi_connections/) allows you to connect to different databases concurrently from the same application. This is very useful when using one master and several read-only slaves serving the same models. The syntax is transparent; it uses module namespaces and imports the models (ActiveRecord::Base subclasses) into the namespaces.

For a single-master situation, you could define another database connection in database.yml for the read slave:

  read_slave:
    adapter: postgresql
    database: read_only_production
    username: user
    password: pass
    host: read_slave_host

This database is backed by a module, which mirrors the ActiveRecord classes using this database connection:

  require 'magic_multi_connections'
  module ReadSlave
    establish_connection :read_slave
  end

Now, all pre-existing models can be accessed through the read_slave connection by prefixing the model class with ReadSlave::.

  # use the read-only connection
  @user = ReadSlave::User.find(params[:id])

  # write to the master (can't use @user.update_attributes because it would
  # try to write to the read slave)
  User.update(@user.id, :login => "new_login")