photo by ArtWerk
The masochism plugin provides an easy solution for Ruby on Rails applications to work in a
replicated database environment. It works by replacing the
connection object accessed by
ActiveRecord models by ConnectionProxy that chooses between master and slave when
executing queries. Generally all writes go to master.
First, setup your database.yml:
# default configuration (slave) production: &defaults adapter: mysql database: app_production username: webapp password: ******** host: localhost # setup for masochism (master) master_database: <<: *defaults host: master.example.com
To enable masochism, this is required:
# enable masochism ActiveReload::ConnectionProxy.setup!
# in environment.rb config.after_initialize do if Rails.env.production? ActiveReload::ConnectionProxy::setup! end end
Thinking Sphinx inspects the
connection object to determine the database adapter.
Because masochism works by putting the connection proxy in its place, TS will be confused
ActiveReload::ConnectionProxy and abort. A possible workaround is to monkeypatch TS right to hardcode our adapter after masochism has been enabled:
# ConnectionProxy from masochism confuses TS ThinkingSphinx::Index.class_eval do def adapter() :mysql end end ThinkingSphinx::AbstractAdapter.class_eval do def self.detect(model) ThinkingSphinx::MysqlAdapter end end
Litespeed web server or Phusion Passenger (mod_rails)
If you are using the Litespeed web server or Passenger (mod_rails), child processes are initialized on creation, which means any setup done in an environment file will be effectively ignored. A brief discussion of the problem is posted here.
One solution for Litespeed/Passenger users is to check the connection at your first request and do
setup! call if your connection hasn't been initialized, like:
# in ApplicationController prepend_before_filter do |controller| unless ActiveRecord::Base.connection.is_a? ActiveReload::ConnectionProxy ActiveReload::ConnectionProxy.setup! end end
The ActiveReload::MasterDatabase model uses a 'master_database' setting that can either be defined for all of your environments, or for each environment as a nested declaration.
The ActiveReload::SlaveDatabase model uses a 'slave_database' setting that can only be defined per environment.
login: &login adapter: postgresql host: localhost port: 5432 production: database: production_slave_database_name <<: *login master_database: database: production_master_database_name <<: *login staging: database: staging_database_name host: slave-db-pool.local <<: *login master_database: database: staging_database_name host: master-db-server.local <<: *login qa: database: qa_master_database_name host: qa-master <<: *login slave_database: database: qa_slave_database_name host: qa-slave <<: *login development: # Does not use masochism database: development_database_name <<: *login
If you want a model to always use the Master database, you can inherit
ActiveReload::MasterDatabase. Any models with their own database connection will not be
More control at setup
By default, masochism
setup! is a shorthand for this:
ActiveReload::ConnectionProxy.setup_for ActiveReload::MasterDatabase, ActiveRecord::Base
The first argument is the model that has the master database connection established; the
second argument is the model whose
connection gets hijacked by ConnectionProxy. But we
don't have to touch
ActiveRecord::Base at all:
# set up MyMaster's connection as the master database connection for User: ActiveReload::ConnectionProxy.setup_for MyMaster, User
The controller filter
If you have any actions you know require the master database for both reads and writes, simply do the following:
# in a controller: around_filter ActiveReload::MasterFilter, :only => [:show, :edit, :update]