ActiveRecord::Sharding

Simple Database Sharding in ActiveRecord.

ActiveRecord object distributed multiple databases by modulo. Modulo target is id, generated by sequencer database.

Support database

• MySQL

Installation

Add this line to your application's Gemfile:

gem 'activerecord-sharding'

And then execute:

$ bundle

Or install it yourself as:

$ gem install activerecord-sharding

Usage

Add database connections to your application's config/database.yml:

default: &default
  adapter: mysql2
  encoding: utf8
  pool: 5
  username: root
  password:
  host: localhost

user_sequencer:
  <<: *default
  database: user_001
  host: localhost

user_001:
  <<: *default
  database: user_001
  host: localhost

user_002:
  <<: *default
  database: user_002
  host: localhost

user_003:
  <<: *default
  database: user_003
  host: localhost

Add this example your application's config/initializers/active_record_sharding.rb:

ActiveRecord::Sharding.configure do |config|
  config.define_sequencer(:user) do |sequencer|
    sequencer.register_connection(:user_sequencer)
    sequencer.register_table_name('user_id')
  end

  config.define_cluster(:user) do |cluster|
    cluster.register_connection(:user_001)
    cluster.register_connection(:user_002)
    cluster.register_connection(:user_003)
  end
end

• define user cluster config
• define user sequencer config

Model

app/model/user.rb

class User < ActiveRecord::Base
  include ActiveRecord::Sharding::Model
  use_sharding :user, :modulo # shard name, algorithm
  define_sharding_key :id

  include ActiveRecord::Sharding::Sequencer
  use_sequencer :user

  before_put do |attributes|
    attributes[:id] = next_sequence_id unless attributes[:id]
  end
end

Create sequencer databases

$ rake active_record:sharding:sequencer:setup

Create cluster dtabases

$ rake active_record:sharding:setup

and, migrations all cluster databases.

in applications

Create

using #put! method.

user = User.put! name: 'foobar'

if transaction to shard database and nest other database transactions.

User.put!(name: 'foobar') do |new_user| # transaction for user shard database
  OTHER_MODEL.transaction do
    OTHER_MODEL.create!(user_id: new_user.id)
  end
end

returns User new object.

Select Query

sharding_key = user.id
User.shard_for(sharding_key).where(name: 'foorbar')

sharding_key is your define_syarding_key.(example is User Object id)

#shard_for is returns User class.

for all shards query

User.all_shards.flat_map { |model| model.find_by(name: 'foorbar') }.compact

for all shards query in parallel

User.parallel.flat_map { |model| model.find_by(name: 'foorbar') }.compact

Association/Relation

if use database association/relation in sharding databases.

Please, don't use ActiveRecord standard associations/relation features(has_may, has_one, belongs_to... etc).because, it using ActiveRecord::Base.connection(not sharding databases conneciton).

Please, manually add association/relation methods.

Bad sample

class User < ActiveRecord::Base
  has_many :items # connect to not sharding databases(default database)

  include ActiveRecord::Sharding::Model
  use_sharding :user, :modulo
  define_sharding_key :id
  # (snip)
end

Manually add method

class User < ActiveRecord::Base
  def items
    return [] unless id
    Item.shard_for(id).where(user_id: id).all
  end

  include ActiveRecord::Sharding::Model
  use_sharding :user, :modulo
  define_sharding_key :id
  # (snip)
end

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/hirocaster/activerecord-sharding.