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.
Methods
- active_connections?
- clear_active_connections!
- clear_all_connections!
- clear_reloadable_connections!
- connected?
- connection_pool_list
- connection_pools
- establish_connection
- flush_idle_connections!
- new
- remove_connection
- retrieve_connection_pool
Class Public methods
new()
Source:
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 959
def initialize
# These caches are keyed by spec.name (ConnectionSpecification#name).
@owner_to_pool = ConnectionHandler.create_owner_to_pool
# Backup finalizer: if the forked child never needed a pool, the above
# early discard has not occurred
ObjectSpace.define_finalizer self, ConnectionHandler.unowned_pool_finalizer(@owner_to_pool)
end
Instance Public methods
active_connections?()
Returns true if there are any active connections among the connection pools that the ConnectionHandler
is managing.
Source:
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 997
def active_connections?
connection_pool_list.any?(&:active_connection?)
end
clear_active_connections!()
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 activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 1004
def clear_active_connections!
connection_pool_list.each(&:release_connection)
end
clear_all_connections!()
Source:
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 1015
def clear_all_connections!
connection_pool_list.each(&:disconnect!)
end
clear_reloadable_connections!()
Clears the cache which maps classes.
See ConnectionPool#clear_reloadable_connections!
for details.
Source:
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 1011
def clear_reloadable_connections!
connection_pool_list.each(&:clear_reloadable_connections!)
end
connected?(spec_name)
Returns true if a connection that's accessible to this class has already been opened.
Source:
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 1038
def connected?(spec_name)
conn = retrieve_connection_pool(spec_name)
conn && conn.connected?
end
connection_pool_list()
Source:
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 968
def connection_pool_list
owner_to_pool.values.compact
end
establish_connection(config)
Source:
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 973
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
flush_idle_connections!()
Disconnects all currently idle connections.
See ConnectionPool#flush!
for details.
Source:
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 1022
def flush_idle_connections!
connection_pool_list.each(&:flush!)
end
remove_connection(spec_name)
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.
Source:
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 1047
def remove_connection(spec_name)
if pool = owner_to_pool.delete(spec_name)
pool.automatic_reconnect = false
pool.disconnect!
pool.spec.config
end
end
retrieve_connection_pool(spec_name)
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.
Source:
# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 1058
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