Initial commit.

.gitignore

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+/pkg

Gemfile

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+source 'http://rubygems.org/'
+
+gem 'activesupport', '>= 2.2'
+gem 'activerecord', '>= 2.2'

LICENSE

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+Copyright (c) 2011 [name of plugin creator]
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.markdown

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+Multidb
+=======
+
+A simple, no-nonsense ActiveRecord extension which allows the application to switch
+between multiple database connections, such as in a master/slave environment. For example:
+
+    Multidb.use(:slave) do
+      @posts = Post.all
+    end
+
+The extension was developed in order to support PostgreSQL 9.0's new hot standby
+support in a production environment.
+
+Randomized balancing of multiple connections within a group is supported. In the
+future, some kind of automatic balancing of read/write queries might be implemented.
+
+Testet with Rails 2.3.11. No guarantees about Rails 3.
+
+
+Comparison to other ActiveRecord extensions
+===========================================
+
+Unlike other, more full-featured extensions such as Octopus and Seamless Database Pool,
+Multidb strives to be:
+
+* Implemented using a minimal amount of
+monkeypatching magic. The only part of ActiveRecord that is overriden is
+`ActiveRecord::Base#connection`.
+
+* Non-invasive. Very small amounts of configuration and changes to the client 
+application are required.
+
+* Orthogonal. Unlike Octopus, for example, connections follow context:
+
+    Multidb.use(:master) do
+      @post = Post.find(1)
+      Multidb.use(:slave) do
+        @post.authors  # This will use the slave
+      end
+    end
+
+* Low-overhead. Since `connection` is called on every single
+database operation, it needs to be fast. Which it is: Multidb's implementation of
+`connection` incurs only a single hash lookup in `Thread.current`.
+
+However, Multidb also has fewer features. At the moment it will _not_ automatically 
+split reads and writes between database backends.
+
+
+Getting started
+===============
+
+In Rails 2.x applications without a `Gemfile`, add this to `environment.rb`:
+
+    config.gem 'ar-multidb'
+
+In Bundler-based on Rails apps, add this to your `Gemfile`:
+
+    gem 'ar-multidb', :require => 'multidb'
+
+You may also install it as a plugin:
+
+    script/plugin install git://github.com/alexstaubo/multidb.git
+
+All that is needed is to set up your `database.yml` file:
+
+    production:
+      adapter: postgresql
+      database: myapp_production
+      username: ohoh
+      password: mymy
+      host: db1
+      multidb:
+        databases:
+          slave:
+            host: db-slave
+
+Each database entry may be a hash or an array. So this also works:
+
+    production:
+      adapter: postgresql
+      database: myapp_production
+      username: ohoh
+      password: mymy
+      host: db1
+      multidb:
+        databases:
+          slave:
+            - host: db-slave1
+            - host: db-slave2
+            
+The database hashes follow the same format as the top-level adapter configuration. In
+other words, each database connection may override the adapter, database name, username
+and so on.
+
+To use the connection, modify your code by wrapping database access logic in blocks:
+
+    Multidb.use(:slave) do
+      @posts = Post.all
+    end
+
+To wrap entire controller requests, for example:
+
+    class PostsController < ApplicationController
+      around_filter :run_using_slave
+
+      def run_using_slave(&block)
+        Multidb.use(:slave, &block)
+      end
+    end
+
+You can also set the current connection for the remainder of the thread's execution:
+
+    Multidb.use(:slave)
+    # Do work
+    Multidb.use(:master)
+
+Note that the symbol `:default` will (unless you override it) refer to the default
+top-level ActiveRecord configuration.
+
+
+Legal
+=====
+
+Copyright (c) 2011 Alexander Staubo. Released under the MIT license. See the file LICENSE.

Rakefile

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+# encoding: utf-8
+
+require 'rubygems'
+require 'rake'
+require 'rake/rdoctask'
+
+begin
+  require 'jeweler'
+  Jeweler::Tasks.new do |gem|
+    gem.name = 'ar-multidb'
+    gem.summary = gem.description = %Q{Multidb is an ActiveRecord extension for switching between multiple database connections, such as master/slave setups.}
+    gem.email = "alex@bengler.no"
+    gem.homepage = "http://github.com/alexstaubo/multidb"
+    gem.authors = ["Alexander Staubo"]
+    gem.has_rdoc = true
+    gem.require_paths = ["lib"]
+    gem.files = FileList[%W(
+      README.markdown
+      VERSION
+      LICENSE*
+      lib/**/*
+    )]
+    gem.add_dependency 'activesupport', '>= 2.2'
+    gem.add_dependency 'activerecord', '>= 2.2'
+  end
+  Jeweler::GemcutterTasks.new
+rescue LoadError
+  $stderr << "Warning: Gem-building tasks are not included as Jeweler (or a dependency) not available. Install it with: `gem install jeweler`.\n"
+end
+
+Rake::RDocTask.new do |rdoc|
+  version = File.exist?('VERSION') ? File.read('VERSION') : ""
+
+  rdoc.rdoc_dir = 'rdoc'
+  rdoc.title = "ruby-hdfs #{version}"
+  rdoc.rdoc_files.include('README*')
+  rdoc.rdoc_files.include('lib/**/*.rb')
+end

VERSION

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+0.1.0

ar-multidb.gemspec

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+# Generated by jeweler
+# DO NOT EDIT THIS FILE DIRECTLY
+# Instead, edit Jeweler::Tasks in Rakefile, and run 'rake gemspec'
+# -*- encoding: utf-8 -*-
+
+Gem::Specification.new do |s|
+  s.name = %q{ar-multidb}
+  s.version = "0.1.0"
+
+  s.required_rubygems_version = Gem::Requirement.new(">= 0") if s.respond_to? :required_rubygems_version=
+  s.authors = ["Alexander Staubo"]
+  s.date = %q{2011-05-18}
+  s.description = %q{Multidb is an ActiveRecord extension for switching between multiple database connections, such as master/slave setups.}
+  s.email = %q{alex@bengler.no}
+  s.extra_rdoc_files = [
+    "LICENSE",
+    "README.markdown"
+  ]
+  s.files = [
+    "LICENSE",
+    "README.markdown",
+    "VERSION",
+    "lib/multidb.rb",
+    "lib/multidb/balancer.rb",
+    "lib/multidb/configuration.rb",
+    "lib/multidb/model_extensions.rb"
+  ]
+  s.homepage = %q{http://github.com/alexstaubo/multidb}
+  s.require_paths = ["lib"]
+  s.rubygems_version = %q{1.5.0}
+  s.summary = %q{Multidb is an ActiveRecord extension for switching between multiple database connections, such as master/slave setups.}
+
+  if s.respond_to? :specification_version then
+    s.specification_version = 3
+
+    if Gem::Version.new(Gem::VERSION) >= Gem::Version.new('1.2.0') then
+      s.add_runtime_dependency(%q<activesupport>, [">= 2.2"])
+      s.add_runtime_dependency(%q<activerecord>, [">= 2.2"])
+      s.add_runtime_dependency(%q<activesupport>, [">= 2.2"])
+      s.add_runtime_dependency(%q<activerecord>, [">= 2.2"])
+    else
+      s.add_dependency(%q<activesupport>, [">= 2.2"])
+      s.add_dependency(%q<activerecord>, [">= 2.2"])
+      s.add_dependency(%q<activesupport>, [">= 2.2"])
+      s.add_dependency(%q<activerecord>, [">= 2.2"])
+    end
+  else
+    s.add_dependency(%q<activesupport>, [">= 2.2"])
+    s.add_dependency(%q<activerecord>, [">= 2.2"])
+    s.add_dependency(%q<activesupport>, [">= 2.2"])
+    s.add_dependency(%q<activerecord>, [">= 2.2"])
+  end
+end
+

init.rb

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+# Init file for running as Rails plugin.
+require 'multidb'

lib/multidb.rb

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+require 'multidb/configuration'
+require 'multidb/model_extensions'
+require 'multidb/balancer'
+
+module Multidb
+  class << self
+
+    def install!
+      configure!
+      if @configuration and @configuration.raw_configuration[:databases].any?
+        ActiveRecord::Base.class_eval do
+          include Multidb::ModelExtensions
+        end
+        @balancer = Balancer.new(@configuration)
+      end
+    end
+
+    attr_reader :balancer
+
+    delegate :use, :get, :to => :balancer
+
+  end
+end
+
+Multidb.install!

lib/multidb/balancer.rb

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+module Multidb
+
+  class Candidate
+    def initialize(config)
+      adapter = config[:adapter]
+      begin
+        require "active_record/connection_adapters/#{adapter}_adapter"
+      rescue LoadError
+        raise "Please install the #{adapter} adapter: `gem install activerecord-#{adapter}-adapter` (#{$!})"
+      end
+      @connection_pool = ActiveRecord::ConnectionAdapters::ConnectionPool.new(
+        ActiveRecord::Base::ConnectionSpecification.new(config, "#{adapter}_connection"))
+    end
+
+    def connection
+      @connection_pool.connection
+    end
+  end
+
+  class Balancer
+
+    def initialize(configuration)
+      @candidates = {}.with_indifferent_access
+      @configuration = configuration
+      @configuration.raw_configuration[:databases].each_pair do |name, config|
+        configs = config.is_a?(Array) ? config : [config]
+        configs.each do |config|          
+          candidate = Candidate.new(@configuration.default_adapter.merge(config))
+          @candidates[name] ||= []
+          @candidates[name].push(candidate)
+        end
+      end
+      unless @candidates.include?(:default)
+        @candidates[:default] = [Candidate.new(@configuration.default_adapter)]
+      end
+    end
+
+    def get(name, &block)
+      candidates = @candidates[name] || []
+      raise ArgumentError, "No such database connection '#{name}'" if candidates.blank?
+      candidate = candidates.sample
+      block_given? ? yield(candidate) : candidate
+    end
+
+    def use(name, &block)
+      result = nil
+      get(name) do |candidate|
+        connection = candidate.connection
+        if block_given?
+          previous_connection, Thread.current[:multidb_connection] = 
+            Thread.current[:multidb_connection], connection
+          begin
+            result = yield
+          ensure
+            Thread.current[:multidb_connection] = previous_connection
+          end
+          result
+        else
+          result = Thread.current[:multidb_connection] = connection
+        end
+      end
+      result
+    end
+
+    def current_connection
+      Thread.current[:multidb_connection] ||= ActiveRecord::Base.connection_pool.connection
+    end
+
+    class << self
+      def use(name, &block)
+        Multidb.balancer.use(name, &block)
+      end
+
+      def current_connection
+        Multidb.balancer.current_connection
+      end
+    end
+
+  end
+
+end

lib/multidb/configuration.rb

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+module Multidb
+
+  class << self
+
+    def configure!
+      activerecord_config = ActiveRecord::Base.connection_pool.connection.instance_variable_get(:@config).dup.with_indifferent_access
+      default_adapter, configuration_hash = activerecord_config, activerecord_config.delete(:multidb)
+      @configuration = Configuration.new(default_adapter, configuration_hash)
+    end
+
+    attr_reader :configuration
+
+  end
+
+  class Configuration
+    def initialize(default_adapter, configuration_hash)
+      @default_adapter = default_adapter
+      @raw_configuration = configuration_hash
+    end
+
+    attr_reader :default_adapter
+    attr_reader :raw_configuration
+  end
+
+end