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
Public Class Methods
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
Source
# 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
Returns true if there are any active connections among the connection pools that the ConnectionHandler
is managing.
Source
# 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
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.
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
Source
# 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
Clears the cache which maps classes.
See ConnectionPool#clear_reloadable_connections!
for details.
Source
# 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
Returns true if a connection that’s accessible to this class has already been opened.
Source
# 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
Returns the pools for a connection handler and given role. If :all
is passed, all pools belonging to the connection handler will be returned.
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
Source
# 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
Disconnects all currently idle connections.
See ConnectionPool#flush!
for details.
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
Source
# 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
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.
Private Instance Methods
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
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
Source
# 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
Returns the pool manager for a connection name / identifier.
Source
# File lib/active_record/connection_adapters/abstract/connection_handler.rb, line 249 def pool_managers connection_name_to_pool_manager.values end
Source
# 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
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" }
Source
# 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
Get the existing pool manager or initialize and assign a new one.