Octoshark is a simple ActiveRecord connection manager. It provides connection switching mechanisms that can be used in various scenarios like master-slave, sharding or multi-tenant architecture.

Add this line to your application's Gemfile:

gem 'octoshark'

And then execute:

$ bundle

Or install it yourself as:

$ gem install octoshark

Octoshark has two connection managers: ConnectionPoolsManager for managing connection pools using persistent connections and ConnectionManager for managing non-persistent connections. It depends on your application performance and scaling requirements which one to use.

• If you have a limited number of consumers (application and worker servers), ConnectionPoolsManager would be the preferred option. Standard Rails application has a single connection pool, and ConnectionPoolsManager just makes it possible for application models to work with multiple connection pools.

• If you have a very big infrastructure with lots of consumers (application and worker servers) and you are hitting max connections limit on database servers, i.e. you need to scale horizontally, ConnectionManager is the option to use. Because it uses non-persistent connections it comes up with a performance penalty because connections are re-established over and over again. Some ActiveRecord plugins that depend on having an active database connection all the time might need a change in order to work with non-persistent connections.

ConnectionPoolsManager and ConnectionManager can be combined together and many of them can be used at the same time.

Here is how to create connection pools manager:

CONN_MANAGER = Octoshark::ConnectionPoolsManager.new({ c1: config1, c2: config2 })

config1 and config2 are standard ActiveRecord database configs:

config = {
  adapter:  'mysql2',
  host:     'localhost',
  port:     3306,
  database: 'database',
  username: 'root',
  password: 'pass',
  pool:     1,
  encoding: 'utf8',
}

To switch a connection using a specific pool:

CONN_MANAGER.with_connection(:c1) do |connection|
  connection.execute("SELECT 1")
end

Multiple with_connection blocks can be nested:

CONN_MANAGER.with_connection(config1) do
  # run queries on connection specified with config1

  CONN_MANAGER.with_connection(config2) do
    # run queries on connection specified with config2
  end

  # run queries on connection specified with config1
end

If you establish a connection to database server instead of to database, then you can use the second optional argument database_name to tell the connection manager to switch the connection to that database within the same connection. This is useful when you want to have fewer connection pools and keep number of active connection per database server under control. This option is only MySQL specific for now, it uses USE database_name statement to switch the connection.

CONN_MANAGER.with_connection(:c1, database_name) do |connection|
  connection.execute("SELECT 1")
end

Using non-persistent connections with Octoshark::ConnectionManager has the same API:

CONN_MANAGER = Octoshark::ConnectionManager.new

Opening a new connection, executing query and closing the connection:

CONN_MANAGER.with_connection(config) do |connection|
  connection.execute("SELECT 1")
end

To tell an ActiveRecord model to use the Octoshark connection we can override the Model.connection method.

class Post < ActiveRecord::Base
  class << self
    def connection
      CONN_MANAGER.current_connection
    end

    # For Rails 7.2+ we need to override the following methods too:

    def lease_connection
      connection
    end

    def with_connection
      yield connection
    end

    def schema_cache
      connection.schema_cache
    end
  end
end

To use a specific database connection:

CONN_MANAGER.with_connection(:c1) do
  # run queries on c1
  Post.first
end

This connection switching in Rails applications is usually done from within an around_filter for controllers and in a similar way for other application "entry-points" like background jobs:

around_filter :select_shard

def select_shard(&block)
  CONN_MANAGER.with_connection(current_user.shard, &block)
end

CONN_MANAGER.current_connection returns the active connection while the execution is in the with_connection block or raises Octoshark::Error::NoCurrentConnection outside of the with_connection block. In some cases, falling back to the default database connection for the Rails app might be preferable which can be done using CONN_MANAGER.current_or_default_connection.

When using Octoshark::ConnectionPoolsManager, whenever ActiveRecord::Base calls establish_connection (usually by an ancestor process that must have subsequently forked), Octoshark.reset_connection_managers! is automatically called to re-establish the Octoshark connections. It prevents ActiveRecord::ConnectionNotEstablished in the scenarios like:

• Unicorn before/after fork
• Spring prefork/serve
• Some rake tasks like rake db:test:prepare

For Octoshark::ConnectionPoolsManager, we can use DatabaseCleaner and RSpec like:

config.before(:suite) do
  setup_database_cleaner
  DatabaseCleaner.clean_with(:truncation)
end

config.before(:each) do
  setup_database_cleaner
  DatabaseCleaner.start
end

config.after(:each) do
  DatabaseCleaner.clean_with(:transaction)
end

def setup_database_cleaner
  DatabaseCleaner[:active_record, {connection: ActiveRecord::Base.connection_pool}]
  Octoshark::ConnectionPoolsManager.connection_managers.each do |manager|
    manager.connection_pools.each_pair do |connection_name, connection_pool|
      DatabaseCleaner[:active_record, {connection: connection_pool}]
    end
  end
end

For Octoshark::ConnectionManager where connections and databases are dynamically created and cannot be configured in the test setup, we can write a custom database cleaner inspired by DatabaseRewinder. The example below is for a multi-tenant test setup with a main (core) database and a tenant database for the CURRENT_USER in the test suite. CustomDatabaseCleaner.clean_all cleans all core database tables before test suite and CustomDatabaseCleaner.clean cleans used tables in both core and tenant databases after each test.

module CustomDatabaseCleaner
  INSERT_REGEX = /\AINSERT(?:\s+IGNORE)?\s+INTO\s+(?:\.*[`"]?(?<table>[^.\s`"]+)[`"]?)*/i

  @@tables_with_inserts = []

  class << self
    def record_inserted_table(connection, sql)
      match = sql.match(INSERT_REGEX)

      if match && match[:table] && tables_with_inserts.exclude?(match[:table])
        tables_with_inserts << match[:table]
      end
    end

    def clean_all
      with_core_db_connection do |connection|
        clean_tables(connection)
      end

      reset_tables_with_inserts
    end

    def clean
      with_core_db_connection do |connection|
        clean_tables(connection, { 'users' => [CURRENT_USER.id] })
      end

      CURRENT_USER.with_tenant do |connection|
        clean_tables(connection)
      end

      reset_tables_with_inserts
    end

    private
    def with_core_db_connection(&block)
      CoreDBManager.with_connection(ActiveRecord::Base.configurations[Rails.env].symbolize_keys, &block)
    end

    def clean_tables(connection, keep_data = {})
      tables_to_clean = connection.tables.reject { |t| t == ActiveRecord::Migrator.schema_migrations_table_name }
      tables_to_clean = tables_to_clean & tables_with_inserts if tables_with_inserts.present?

      tables_to_clean.each do |table|
        connection.disable_referential_integrity do
          table_name = connection.quote_table_name(table)
          keep_ids   = keep_data[table]

          if keep_ids
            connection.execute("DELETE FROM #{table_name} WHERE id NOT IN (#{keep_ids.join(',')});")
          else
            connection.execute("DELETE FROM #{table_name};")
          end
        end
      end
    end

    def reset_tables_with_inserts
      @@tables_with_inserts = []
    end

    def tables_with_inserts
      @@tables_with_inserts
    end
  end
end

module CustomDatabaseCleaner
  module InsertRecorder
    def execute(sql, *)
      CustomDatabaseCleaner.record_inserted_table(self, sql)
      super
    end

    def exec_query(sql, *)
      CustomDatabaseCleaner.record_inserted_table(self, sql)
      super
    end
  end
end

require 'active_record/connection_adapters/abstract_mysql_adapter'
ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter.send(:prepend, CustomDatabaseCleaner::InsertRecorder)

Setup database config and create databases:

cp spec/support/config.yml.template spec/support/config.yml
rake db:create

Run specs:

bundle exec rspec spec

Install different active record versions defined in Appraisals and run specs for all of them:

bundle exec appraisal
bundle exec appraisal rspec spec

Thanks to @saschamt for Octoshark logo design. :)

1. Fork it ( http://github.com/dalibor/octoshark/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request