class ActiveRecord::ConnectionAdapters::ConnectionHandler
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 specification name to the handler, in order to look up the correct connection pool.
Public Class Methods
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 869 def initialize # These caches are keyed by spec.name (ConnectionSpecification#name). @owner_to_pool = Concurrent::Map.new(initial_capacity: 2) do |h, k| h[k] = Concurrent::Map.new(initial_capacity: 2) end end
Public Instance Methods
Returns true if there are any active connections among the connection pools that the ConnectionHandler
is managing.
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 905 def active_connections? connection_pool_list.any?(&:active_connection?) 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.
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 912 def clear_active_connections! connection_pool_list.each(&:release_connection) end
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 923 def clear_all_connections! connection_pool_list.each(&:disconnect!) end
Clears the cache which maps classes.
See ConnectionPool#clear_reloadable_connections!
for details.
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 919 def clear_reloadable_connections! connection_pool_list.each(&:clear_reloadable_connections!) end
Returns true if a connection that's accessible to this class has already been opened.
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 941 def connected?(spec_name) conn = retrieve_connection_pool(spec_name) conn && conn.connected? end
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 876 def connection_pool_list owner_to_pool.values.compact end
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 881 def establish_connection(config) resolver = ConnectionSpecification::Resolver.new(Base.configurations) spec = resolver.spec(config) remove_connection(spec.name) message_bus = ActiveSupport::Notifications.instrumenter payload = { connection_id: object_id } if spec payload[:spec_name] = spec.name payload[:config] = spec.config end message_bus.instrument("!connection.active_record", payload) do owner_to_pool[spec.name] = ConnectionAdapters::ConnectionPool.new(spec) end owner_to_pool[spec.name] end
Remove the connection for this class. This will close the active connection and the defined connection (if they exist). The result can be used as an argument for establish_connection
, for easily re-establishing the connection.
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 950 def remove_connection(spec_name) if pool = owner_to_pool.delete(spec_name) pool.automatic_reconnect = false pool.disconnect! pool.spec.config end end
Retrieving the connection pool happens a lot, so we cache it in @owner_to_pool. 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 activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 961 def retrieve_connection_pool(spec_name) owner_to_pool.fetch(spec_name) do # Check if a connection was previously established in an ancestor process, # which may have been forked. if ancestor_pool = pool_from_any_process_for(spec_name) # A connection was established in an ancestor process that must have # subsequently forked. We can't reuse the connection, but we can copy # the specification and establish a new connection with it. establish_connection(ancestor_pool.spec.to_hash).tap do |pool| pool.schema_cache = ancestor_pool.schema_cache if ancestor_pool.schema_cache end else owner_to_pool[spec_name] = nil end end end
Private Instance Methods
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 980 def owner_to_pool @owner_to_pool[Process.pid] end
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 984 def pool_from_any_process_for(spec_name) owner_to_pool = @owner_to_pool.values.reverse.find { |v| v[spec_name] } owner_to_pool && owner_to_pool[spec_name] end