Class: ActiveRecord::ConnectionAdapters::ConnectionHandler

Inherits:
Object
  • Object
show all
Defined in:
activerecord/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 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.

Instance Method Summary collapse

Constructor Details

#initializeConnectionHandler

Returns a new instance of ConnectionHandler.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1005

def initialize
  # These caches are keyed by pool_config.connection_specification_name (PoolConfig#connection_specification_name).
  @owner_to_pool_manager = Concurrent::Map.new(initial_capacity: 2)

  # Backup finalizer: if the forked child skipped Kernel#fork the early discard has not occurred
  ObjectSpace.define_finalizer self, FINALIZER
end

Instance Method Details

#active_connections?Boolean

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

Returns:

  • (Boolean)

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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1066

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 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1073

def clear_active_connections!
  connection_pool_list.each(&:release_connection)
end

#clear_all_connections!Object


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1084

def clear_all_connections!
  connection_pool_list.each(&:disconnect!)
end

#clear_reloadable_connections!Object

Clears the cache which maps classes.

See ConnectionPool#clear_reloadable_connections! for details.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1080

def clear_reloadable_connections!
  connection_pool_list.each(&:clear_reloadable_connections!)
end

#connected?(spec_name, pool_key = :default) ⇒ Boolean

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

Returns:

  • (Boolean)

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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1116

def connected?(spec_name, pool_key = :default)
  pool = retrieve_connection_pool(spec_name, pool_key)
  pool && pool.connected?
end

#connection_pool_listObject Also known as: connection_pools


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1037

def connection_pool_list
  owner_to_pool_manager.values.compact.flat_map { |m| m.pool_configs.map(&:pool) }
end

#connection_pool_namesObject

:nodoc:


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1033

def connection_pool_names # :nodoc:
  owner_to_pool_manager.keys
end

#establish_connection(config, pool_key = :default) ⇒ Object


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1042

def establish_connection(config, pool_key = :default)
  pool_config = resolve_pool_config(config)
  db_config = pool_config.db_config

  remove_connection(pool_config.connection_specification_name, pool_key)

  message_bus = ActiveSupport::Notifications.instrumenter
  payload = {}
  if pool_config
    payload[:spec_name] = pool_config.connection_specification_name
    payload[:config] = db_config.configuration_hash
  end

  owner_to_pool_manager[pool_config.connection_specification_name] ||= PoolManager.new
  pool_manager = owner_to_pool_manager[pool_config.connection_specification_name]
  pool_manager.set_pool_config(pool_key, pool_config)

  message_bus.instrument("!connection.active_record", payload) do
    pool_config.pool
  end
end

#flush_idle_connections!Object

Disconnects all currently idle connections.

See ConnectionPool#flush! for details.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1091

def flush_idle_connections!
  connection_pool_list.each(&:flush!)
end

#prevent_writesObject

:nodoc:


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1013

def prevent_writes # :nodoc:
  Thread.current[:prevent_writes]
end

#prevent_writes=(prevent_writes) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1017

def prevent_writes=(prevent_writes) # :nodoc:
  Thread.current[:prevent_writes] = prevent_writes
end

#remove_connection(spec_name, pool_key = :default) ⇒ 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 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1125

def remove_connection(spec_name, pool_key = :default)
  if pool_manager = owner_to_pool_manager[spec_name]
    pool_config = pool_manager.remove_pool_config(pool_key)

    if pool_config
      pool_config.disconnect!
      pool_config.db_config.configuration_hash
    end
  end
end

#retrieve_connection(spec_name) ⇒ 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 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1099

def retrieve_connection(spec_name) #:nodoc:
  pool = retrieve_connection_pool(spec_name)

  unless pool
    # multiple database application
    if ActiveRecord::Base.connection_handler != ActiveRecord::Base.default_connection_handler
      raise ConnectionNotEstablished, "No connection pool with '#{spec_name}' found for the '#{ActiveRecord::Base.current_role}' role."
    else
      raise ConnectionNotEstablished, "No connection pool with '#{spec_name}' found."
    end
  end

  pool.connection
end

#retrieve_connection_pool(spec_name, pool_key = :default) ⇒ Object

Retrieving the connection pool happens a lot, so we cache it in @owner_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.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1139

def retrieve_connection_pool(spec_name, pool_key = :default)
  pool_config = owner_to_pool_manager[spec_name]&.get_pool_config(pool_key)
  pool_config&.pool
end

#while_preventing_writes(enabled = true) ⇒ Object

Prevent writing to the database regardless of role.

In some cases you may want to prevent writes to the database even if you are on a database that can write. `while_preventing_writes` will prevent writes to the database for the duration of the block.


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# File 'activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb', line 1026

def while_preventing_writes(enabled = true)
  original, self.prevent_writes = self.prevent_writes, enabled
  yield
ensure
  self.prevent_writes = original
end