tobowers/mb-octopus

Database Sharding for ActiveRecord

Octopus - Easy Database Sharding for ActiveRecord

Octopus is a better way to do Database Sharding in ActiveRecord. Sharding allows multiple databases in the same rails application. While there are several projects that implement Sharding (e.g. DbCharmer, DataFabric, MultiDb), each project has its own limitations. The main goal of octopus project is to provide a better way of doing Database Sharding.

Feature list:

The api is designed to be simple as possible. Octopus focuses on the end user, giving the power of multiple databases but with reliable code and flexibility. Octopus is focused on Rails 3, but is compatible with Rails 2.x.

Octopus supports:

• Sharding (with multiple shards, and grouped shards).
• Replication (Master/slave support, with multiple slaves).
• Moving data between shards with migrations.
• Tools to manage database configurations. (soon)

Replication

When using replication, all writes queries will be sent to master, and read queries to slaves. More info could be found at: Wiki

Sharding

When using sharding, you need to specify which shard to send the query. Octopus supports selecting the shard inside a controller, or manually in each object. More could be found at Wiki

Replication + Sharding

Replication + Sharding isn't supported yet. This is on our TODO list and will be done ASAP. If you need, feel free to fork and implement it.

Install

Rails 2.x

Install the octopus gem:

 sudo gem install ar-octopus 

Add this line to enviroment.rb:

config.gem 'ar-octopus', :lib => "octopus"

Rails 3.x

Add this line to Gemfile:

gem 'ar-octopus', :require => "octopus"

Runs a bundle install:

bundle install

How to use Octopus?

First, you need to create a config file, shards.yml, inside your config/ directory. to see the syntax and how this file should look, please checkout this page on wiki.

Syntax

Octopus adds a method to each AR Class and object: the using method is used to select the shard like this:

User.where(:name => "Thiago").limit(3).using(:slave_one) 

Octopus also supports queries within a block. When you pass a block to the using method, all queries inside the block will be sent to the specified shard.

Octopus.using(:slave_two) do 
  User.create(:name => "Mike")
end

Each model instance knows which shard it came from so this will work automatically:

 
# This will find the user in the shard1
@user = User.using(:shard1).find_by_name("Joao")

# This will find the user in the master database
@user2 = User.find_by_name("Jose")

#Sets the name
@user.name = "Mike"

# Save the user in the correct shard, shard1. 
@user.save

Migrations

In migrations, you also have access to the using method. The syntax is basically the same. This migration will run in the brazil and canada shards.

  class CreateUsersOnBothShards < ActiveRecord::Migration
    using(:brazil, :canada)

    def self.up
      User.create!(:name => "Both")
    end

    def self.down
      User.delete_all
    end
  end

You also could send a migration to a group of shards. This migration will be sent to all shards that belongs to history_shards group, specified in shards.yml:

  class CreateUsersOnMultiplesGroups < ActiveRecord::Migration
    using_group(:history_shards)

    def self.up
      User.create!(:name => "MultipleGroup")
    end

    def self.down
      User.delete_all
    end
  end

Rails Controllers

If you want to send a specified action, or all actions from a controller, to a specific shard, use this syntax:

  class ApplicationController < ActionController::Base
    around_filter :select_shard      
    
    def select_shard(&block)
      Octopus.using(:brazil, &block)
    end    
  end

To see the complete list of features and syntax, please check out our Wiki Want to see sample rails applications using octopus features? please check it out: Sharding Example and Replication Example. Also, we have an example that shows how to use Octopus without Rails: Octopus + Sinatra Example.

Important!

Sometimes, when a connection isn't used for much time, this will makes ActiveRecord raising an exception. if you have this kind of applications, please, add the following line to your configuration:

verify_connection: true

This will tell Octopus to verify the connection before sending the query.

Contributing with Octopus

Contributors are welcome! To run the test suite, you need mysql, postgresql and sqlite3 installed. This is what you need to setup your Octopus development environment:

  git clone http://github.com/tchandy/octopus.git
  cd octopus
  bundle install
  rake db:prepare
  rake

To run our integrations tests inside sample_app, you need to following commands:

  cd sample_app
  bundle install
  cucumber

If you are having issues running the octopus spec suite, verify your database users and passwords match those inside the config files and your permissions are correct.

Thanks

This project is sponsored by the Ruby Summer of Code, and my mentors Mike Perham and Amit Agarwal.

Copyright

Copyright (c) 2010 Thiago Pradi, released under the MIT license.