How people build software ! " Multiple Connections in AR 

How people build software ! @arthurnn 2 ! 

How people build software ! ! Open source 3 • Rails commiter team • rubygems.org • memcached gem CONTRIBUTORS.RUBYONRAILS.ORG 

How people build software ! Agenda 4 • Before Rails 5 • What is new in Rails 5 • Future work in Rails 5.1 # 

How people build software ! Why? 5 ! 

How people build software ! ! Use cases for different connections 6 • Data partitioning • Read only database • Sharding 

How people build software ! How does it work right now? 7 ! 

How people build software ! ! 8 1 # user.rb 2 class User < ActiveRecord::Base 3 establish_connection :user_db 4 end 5 6 # database.yml 7 development: 8 database: foo_db 9 user_db: 10 database: user_db 

How people build software ! 9 What is the problem? 

How people build software ! ! Architecture 10 

How people build software ! ! 11 1 def establish_connection(owner, spec) 2 @class_to_pool.clear 3 raise RuntimeError, "Anonymous class is not allowed." unless owner.name 4 owner_to_pool[owner.name] = ConnectionAdapters::ConnectionPool.new(spec) 5 end 

How people build software ! ! 12 1 def retrieve_connection_pool(klass) 2 class_to_pool[klass.name] ||= begin 3 until pool = pool_for(klass) 4 klass = klass.superclass 5 break unless klass <= Base 6 end 7 8 class_to_pool[klass.name] = pool 9 end 10 end 

How people build software ! ! Solutions 13 • Install a gem. • db_charmer • octopus • apartment • Do your own • Inline extend models • multiple connection handlers 

How people build software ! ! 14 Multiple connection handlers 

How people build software ! ! 15 Multiple connection handlers 

How people build software ! ! Multiple connection handlers 16 1 class ConnectionSwitcher 2 def initialize 3 self.handlers = {readonly: ConnectionHandler.new} 4 end 5 6 def with_readonly(&block) 7 before = ActiveRecord::Base.connection_handler 8 ActiveRecord::Base.connection_handler = handlers[:readonly] 9 yield 10 ensure 11 ActiveRecord::Base.connection_handler = before 12 end 13 end 

How people build software ! ! Multiple connection handlers 17 1 class User < ActiveRecord::Base 2 establish_connection :user_db 3 switcher.with_readonly do 4 establish_connection :user_db_readonly 5 end 6 end 7 8 switcher.with_readonly do 9 user = User.find 10 end 

How people build software ! 18 So what is the actual problem? 

How people build software ! What is next? 19 ! 

How people build software ! ! Rails 5 20 • Decouple Active Record model and connection pool • Model.establish_connection() method • Use a new key for the connection pools list • Fix all the things around it 

How people build software ! ! Handler establish_connection code 21 1 def establish_connection(config) 2 resolver = ConnectionSpecification::Resolver.new(Base.configurations) 3 spec = resolver.spec(config) 4 5 remove_connection(spec.name) 6 owner_to_pool[spec.name] = ConnectionAdapters::ConnectionPool.new(spec) 7 end 

How people build software ! ! Data partitioning use case 22 1 # initializer 2 ActiveRecord::Base.connection_handler.establish_connection :user_db 3 4 # user.rb 5 class User < ActiveRecord::Base 6 self.connection_specification_name = :user_db 7 end 

How people build software ! ! Readonly use case 23 1 class User < ActiveRecord::Base 2 attr_writer :readonly_mode 3 4 def self.connection_specification_name 5 if readonly_mode 6 "readonly" 7 else 8 "primary" 9 end 10 end 11 end 12 13 User.readonly_mode = true 14 user = User.find(1) 

How people build software ! ! 24 

How people build software ! ! Backwards compatible 25 1 class User < ActiveRecord::Base 2 establish_connection :user_db 3 end Model.establish_connection still works: ⚠ Don’t use it ⚠ 

How people build software ! Future work 26 ! 

How people build software ! ! Rails 5.1 27 • Better database.yml • Improve db: tasks • establish all connections during boot 

How people build software ! ! Better database.yml 28 1 # database.yml 2 development: 3 primary: 4 database: foo_development 5 adapter: mysql2 6 shard1: 7 database: foo2_development 8 adapter: mysql2 9 readonly: 10 database: foo_development 11 user: readonly_user 12 adapter: mysql2 13 test: 14 primary: 15 production: 16 primary: 

How people build software ! ! Rails 5.1 29 • Better database.yml • Improve db: tasks • establish all connections during boot • Migrations • Fixtures 

How people build software ! ! Summary 30 • Rails < 5 • Lot of code necessary + Patches in AR • Rails 5 • Ground work is done for ease connection handling • Rails 5.1 • Will have even more improvements 

How people build software ! " THANKS