Class: ActiveRecord::ConnectionAdapters::ConnectionHandler
- Inherits:
-
Object
- Object
- ActiveRecord::ConnectionAdapters::ConnectionHandler
- Defined in:
- lib/active_record/connection_adapters/abstract/connection_pool.rb
Overview
ConnectionHandler is a collection of ConnectionPool objects. It is used for keeping separate connection pools for Active Record models 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.
Instance Method Summary collapse
-
#active_connections? ⇒ Boolean
Returns true if there are any active connections among the connection pools that the ConnectionHandler is managing.
-
#clear_active_connections! ⇒ Object
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.
- #clear_all_connections! ⇒ Object
-
#clear_reloadable_connections! ⇒ Object
Clears the cache which maps classes.
-
#connected?(klass) ⇒ Boolean
Returns true if a connection that’s accessible to this class has already been opened.
- #connection_pool_list ⇒ Object
- #connection_pools ⇒ Object
- #establish_connection(owner, spec) ⇒ Object
-
#initialize ⇒ ConnectionHandler
constructor
A new instance of ConnectionHandler.
-
#remove_connection(owner) ⇒ Object
Remove the connection for this class.
-
#retrieve_connection(klass) ⇒ Object
Locate the connection of the nearest super class.
-
#retrieve_connection_pool(klass) ⇒ Object
Retrieving the connection pool happens a lot so we cache it in @class_to_pool.
Constructor Details
#initialize ⇒ ConnectionHandler
Returns a new instance of ConnectionHandler.
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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 505 def initialize # These caches are keyed by klass.name, NOT klass. Keying them by klass # alone would lead to memory leaks in development mode as all previous # instances of the class would stay in memory. @owner_to_pool = ThreadSafe::Cache.new(:initial_capacity => 2) do |h,k| h[k] = ThreadSafe::Cache.new(:initial_capacity => 2) end @class_to_pool = ThreadSafe::Cache.new(:initial_capacity => 2) do |h,k| h[k] = ThreadSafe::Cache.new end end |
Instance Method Details
#active_connections? ⇒ Boolean
Returns true if there are any active connections among the connection pools that the ConnectionHandler is managing.
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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 538 def active_connections? connection_pool_list.any?(&:active_connection?) end |
#clear_active_connections! ⇒ Object
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.
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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 545 def clear_active_connections! connection_pool_list.each(&:release_connection) end |
#clear_all_connections! ⇒ Object
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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 554 def clear_all_connections! connection_pool_list.each(&:disconnect!) end |
#clear_reloadable_connections! ⇒ Object
Clears the cache which maps classes.
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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 550 def clear_reloadable_connections! connection_pool_list.each(&:clear_reloadable_connections!) end |
#connected?(klass) ⇒ Boolean
Returns true if a connection that’s accessible to this class has already been opened.
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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 572 def connected?(klass) conn = retrieve_connection_pool(klass) conn && conn.connected? end |
#connection_pool_list ⇒ Object
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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 517 def connection_pool_list owner_to_pool.values.compact end |
#connection_pools ⇒ Object
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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 521 def connection_pools ActiveSupport::Deprecation.warn(<<-MSG.squish) In the next release, this will return the same as `#connection_pool_list`. (An array of pools, rather than a hash mapping specs to pools.) MSG Hash[connection_pool_list.map { |pool| [pool.spec, pool] }] end |
#establish_connection(owner, spec) ⇒ Object
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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 530 def establish_connection(owner, spec) @class_to_pool.clear raise RuntimeError, "Anonymous class is not allowed." unless owner.name owner_to_pool[owner.name] = ConnectionAdapters::ConnectionPool.new(spec) end |
#remove_connection(owner) ⇒ Object
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.
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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 581 def remove_connection(owner) if pool = owner_to_pool.delete(owner.name) @class_to_pool.clear pool.automatic_reconnect = false pool.disconnect! pool.spec.config end end |
#retrieve_connection(klass) ⇒ Object
Locate the connection of the nearest super class. This can be an active or defined connection: if it is the latter, it will be opened and set as the active connection for the class it was defined for (not necessarily the current class).
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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 562 def retrieve_connection(klass) #:nodoc: pool = retrieve_connection_pool(klass) raise ConnectionNotEstablished, "No connection pool for #{klass}" unless pool conn = pool.connection raise ConnectionNotEstablished, "No connection for #{klass} in connection pool" unless conn conn end |
#retrieve_connection_pool(klass) ⇒ Object
Retrieving the connection pool happens a lot so we cache it in @class_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.
Ideally we would use #fetch here, as class_to_pool may sometimes be nil. However, benchmarking (gist.github.com/jonleighton/3552829) showed that #fetch is significantly slower than #[]. So in the nil case, no caching will take place, but that’s ok since the nil case is not the common one that we wish to optimise for.
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# File 'lib/active_record/connection_adapters/abstract/connection_pool.rb', line 599 def retrieve_connection_pool(klass) class_to_pool[klass.name] ||= begin until pool = pool_for(klass) klass = klass.superclass break unless klass <= Base end class_to_pool[klass.name] = pool end end |