class ActiveRecord::ConnectionAdapters::ConnectionHandler

Active Record Connection Handler

ConnectionHandler is a collection of ConnectionPool objects. It is used for keeping separate connection pools that connect to different databases.

For example, suppose that you have 5 models, with the following hierarchy:

class Author < ActiveRecord::Base
end

class BankAccount < ActiveRecord::Base
end

class Book < ActiveRecord::Base
  establish_connection :library_db
end

class ScaryBook < Book
end

class GoodBook < Book
end

And a database.yml that looked like this:

development:
  database: my_application
  host: localhost

library_db:
  database: library
  host: some.library.org

Your primary database in the development environment is “my_application” but the Book model connects to a separate database called “library_db” (this can even be a database on a different machine).

Book, ScaryBook, and GoodBook will all use the same connection pool to “library_db” while Author, BankAccount, and any other models you create will use the default connection pool to “my_application”.

The various connection pools are managed by a single instance of ConnectionHandler accessible via ActiveRecord::Base.connection_handler. All Active Record models use this handler to determine the connection pool that they should use.

The ConnectionHandler class is not coupled with the Active models, as it has no knowledge about the model. The model needs to pass a connection specification name to the handler, in order to look up the correct connection pool.

Attributes

connection_name_to_pool_manager[R]

Public Class Methods

new() click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 73
def initialize
  # These caches are keyed by pool_config.connection_name (PoolConfig#connection_name).
  @connection_name_to_pool_manager = Concurrent::Map.new(initial_capacity: 2)
end

Public Instance Methods

active_connections?(role = nil) click to toggle source

Returns true if there are any active connections among the connection pools that the ConnectionHandler is managing.

# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 154
def active_connections?(role = nil)
  each_connection_pool(role).any?(&:active_connection?)
end
clear_active_connections!(role = nil) click to toggle source

Returns any connections in use by the current thread back to the pool, and also returns connections to the pool cached by threads that are no longer alive.

# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 161
def clear_active_connections!(role = nil)
  each_connection_pool(role).each do |pool|
    pool.release_connection
    pool.disable_query_cache!
  end
end
clear_all_connections!(role = nil) click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 175
def clear_all_connections!(role = nil)
  each_connection_pool(role).each(&:disconnect!)
end
clear_reloadable_connections!(role = nil) click to toggle source

Clears the cache which maps classes.

See ConnectionPool#clear_reloadable_connections! for details.

# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 171
def clear_reloadable_connections!(role = nil)
  each_connection_pool(role).each(&:clear_reloadable_connections!)
end
connected?(connection_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard) click to toggle source

Returns true if a connection that’s accessible to this class has already been opened.

# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 197
def connected?(connection_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard)
  pool = retrieve_connection_pool(connection_name, role: role, shard: shard)
  pool && pool.connected?
end
connection_pool_list(role = nil) click to toggle source

Returns the pools for a connection handler and given role. If :all is passed, all pools belonging to the connection handler will be returned.

# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 92
def connection_pool_list(role = nil)
  if role.nil? || role == :all
    connection_name_to_pool_manager.values.flat_map { |m| m.pool_configs.map(&:pool) }
  else
    connection_name_to_pool_manager.values.flat_map { |m| m.pool_configs(role).map(&:pool) }
  end
end
Also aliased as: connection_pools
connection_pools(role = nil)
establish_connection(config, owner_name: Base, role: Base.current_role, shard: Base.current_shard, clobber: false) click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 112
def establish_connection(config, owner_name: Base, role: Base.current_role, shard: Base.current_shard, clobber: false)
  owner_name = determine_owner_name(owner_name, config)

  pool_config = resolve_pool_config(config, owner_name, role, shard)
  db_config = pool_config.db_config

  pool_manager = set_pool_manager(pool_config.connection_name)

  # If there is an existing pool with the same values as the pool_config
  # don't remove the connection. Connections should only be removed if we are
  # establishing a connection on a class that is already connected to a different
  # configuration.
  existing_pool_config = pool_manager.get_pool_config(role, shard)

  if !clobber && existing_pool_config && existing_pool_config.db_config == db_config
    # Update the pool_config's connection class if it differs. This is used
    # for ensuring that ActiveRecord::Base and the primary_abstract_class use
    # the same pool. Without this granular swapping will not work correctly.
    if owner_name.primary_class? && (existing_pool_config.connection_class != owner_name)
      existing_pool_config.connection_class = owner_name
    end

    existing_pool_config.pool
  else
    disconnect_pool_from_pool_manager(pool_manager, role, shard)
    pool_manager.set_pool_config(role, shard, pool_config)

    payload = {
      connection_name: pool_config.connection_name,
      role: role,
      shard: shard,
      config: db_config.configuration_hash
    }

    ActiveSupport::Notifications.instrumenter.instrument("!connection.active_record", payload) do
      pool_config.pool
    end
  end
end
flush_idle_connections!(role = nil) click to toggle source

Disconnects all currently idle connections.

See ConnectionPool#flush! for details.

# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 182
def flush_idle_connections!(role = nil)
  each_connection_pool(role).each(&:flush!)
end
remove_connection_pool(connection_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard) click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 202
def remove_connection_pool(connection_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard)
  if pool_manager = get_pool_manager(connection_name)
    disconnect_pool_from_pool_manager(pool_manager, role, shard)
  end
end
retrieve_connection_pool(connection_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard, strict: false) click to toggle source

Retrieving the connection pool happens a lot, so we cache it in @connection_name_to_pool_manager. This makes retrieving the connection pool O(1) once the process is warm. When a connection is established or removed, we invalidate the cache.

# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 211
def retrieve_connection_pool(connection_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard, strict: false)
  pool_manager = get_pool_manager(connection_name)
  pool = pool_manager&.get_pool_config(role, shard)&.pool

  if strict && !pool
    selector = [
      ("'#{shard}' shard" unless shard == ActiveRecord::Base.default_shard),
      ("'#{role}' role" unless role == ActiveRecord::Base.default_role),
    ].compact.join(" and ")

    selector = [
      (connection_name unless connection_name == "ActiveRecord::Base"),
      selector.presence,
    ].compact.join(" with ")

    selector = " for #{selector}" if selector.present?

    message = "No database connection defined#{selector}."

    raise ConnectionNotDefined.new(message, connection_name: connection_name, shard: shard, role: role)
  end

  pool
end

Private Instance Methods

determine_owner_name(owner_name, config) click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 279
def determine_owner_name(owner_name, config)
  if owner_name.is_a?(String) || owner_name.is_a?(Symbol)
    StringConnectionName.new(owner_name.to_s)
  elsif config.is_a?(Symbol)
    StringConnectionName.new(config.to_s)
  else
    owner_name
  end
end
disconnect_pool_from_pool_manager(pool_manager, role, shard) click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 253
def disconnect_pool_from_pool_manager(pool_manager, role, shard)
  pool_config = pool_manager.remove_pool_config(role, shard)

  if pool_config
    pool_config.disconnect!
    pool_config.db_config
  end
end
get_pool_manager(connection_name) click to toggle source

Returns the pool manager for a connection name / identifier.

# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 240
def get_pool_manager(connection_name)
  connection_name_to_pool_manager[connection_name]
end
pool_managers() click to toggle source
# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 249
def pool_managers
  connection_name_to_pool_manager.values
end
resolve_pool_config(config, connection_name, role, shard) click to toggle source

Returns an instance of PoolConfig for a given adapter. Accepts a hash one layer deep that contains all connection information.

Example

config = { "production" => { "host" => "localhost", "database" => "foo", "adapter" => "sqlite3" } }
pool_config = Base.configurations.resolve_pool_config(:production)
pool_config.db_config.configuration_hash
# => { host: "localhost", database: "foo", adapter: "sqlite3" }
# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 272
def resolve_pool_config(config, connection_name, role, shard)
  db_config = Base.configurations.resolve(config)
  db_config.validate!
  raise(AdapterNotSpecified, "database configuration does not specify adapter") unless db_config.adapter
  ConnectionAdapters::PoolConfig.new(connection_name, db_config, role, shard)
end
set_pool_manager(connection_name) click to toggle source

Get the existing pool manager or initialize and assign a new one.

# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 245
def set_pool_manager(connection_name)
  connection_name_to_pool_manager[connection_name] ||= PoolManager.new
end