Class: ActiveRecord::ConnectionAdapters::ConnectionHandler

Inherits:
Object
  • Object
show all
Defined in:
lib/active_record/connection_adapters/abstract/connection_handler.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 connection specification name to the handler, in order to look up the correct connection pool.

Defined Under Namespace

Classes: StringConnectionOwner

Instance Method Summary collapse

Constructor Details

#initialize ⇒ ConnectionHandler

Returns a new instance of ConnectionHandler.



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# File 'lib/active_record/connection_adapters/abstract/connection_handler.rb', line 75

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?(role = ActiveRecord::Base.current_role) ⇒ 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 'lib/active_record/connection_adapters/abstract/connection_handler.rb', line 161

def active_connections?(role = ActiveRecord::Base.current_role)
  connection_pool_list(role).any?(&:active_connection?)
end

#all_connection_pools ⇒ Object 



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# File 'lib/active_record/connection_adapters/abstract/connection_handler.rb', line 117

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

#clear_active_connections!(role = ActiveRecord::Base.current_role) ⇒ 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_handler.rb', line 168

def clear_active_connections!(role = ActiveRecord::Base.current_role)
  connection_pool_list(role).each(&:release_connection)
end

#clear_all_connections!(role = ActiveRecord::Base.current_role) ⇒ Object 



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# File 'lib/active_record/connection_adapters/abstract/connection_handler.rb', line 179

def clear_all_connections!(role = ActiveRecord::Base.current_role)
  connection_pool_list(role).each(&:disconnect!)
end

#clear_reloadable_connections!(role = ActiveRecord::Base.current_role) ⇒ Object

Clears the cache which maps classes.

See ConnectionPool#clear_reloadable_connections! for details.



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# File 'lib/active_record/connection_adapters/abstract/connection_handler.rb', line 175

def clear_reloadable_connections!(role = ActiveRecord::Base.current_role)
  connection_pool_list(role).each(&:clear_reloadable_connections!)
end

#connected?(spec_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard) ⇒ Boolean

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

Returns:

  • (Boolean) 


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# File 'lib/active_record/connection_adapters/abstract/connection_handler.rb', line 216

def connected?(spec_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard)
  pool = retrieve_connection_pool(spec_name, role: role, shard: shard)
  pool && pool.connected?
end

#connection_pool_list(role = ActiveRecord::Base.current_role) ⇒ Object Also known as: connection_pools 



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# File 'lib/active_record/connection_adapters/abstract/connection_handler.rb', line 121

def connection_pool_list(role = ActiveRecord::Base.current_role)
  owner_to_pool_manager.values.flat_map { |m| m.pool_configs(role).map(&:pool) }
end

#connection_pool_names ⇒ Object

:nodoc:



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# File 'lib/active_record/connection_adapters/abstract/connection_handler.rb', line 113

def connection_pool_names # :nodoc:
  owner_to_pool_manager.keys
end

#establish_connection(config, owner_name: Base, role: ActiveRecord::Base.current_role, shard: Base.current_shard) ⇒ Object 



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# File 'lib/active_record/connection_adapters/abstract/connection_handler.rb', line 126

def establish_connection(config, owner_name: Base, role: ActiveRecord::Base.current_role, shard: Base.current_shard)
  owner_name = StringConnectionOwner.new(config.to_s) if config.is_a?(Symbol)

  pool_config = resolve_pool_config(config, owner_name, role, shard)
  db_config = pool_config.db_config

  # Protects the connection named `ActiveRecord::Base` from being removed
  # if the user calls `establish_connection :primary`.
  if owner_to_pool_manager.key?(pool_config.connection_specification_name)
    remove_connection_pool(pool_config.connection_specification_name, role: role, shard: shard)
  end

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

  if ActiveRecord.legacy_connection_handling
    owner_to_pool_manager[pool_config.connection_specification_name] ||= LegacyPoolManager.new
  else
    owner_to_pool_manager[pool_config.connection_specification_name] ||= PoolManager.new
  end
  pool_manager = get_pool_manager(pool_config.connection_specification_name)
  pool_manager.set_pool_config(role, shard, pool_config)

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

#flush_idle_connections!(role = ActiveRecord::Base.current_role) ⇒ Object

Disconnects all currently idle connections.

See ConnectionPool#flush! for details.



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# File 'lib/active_record/connection_adapters/abstract/connection_handler.rb', line 186

def flush_idle_connections!(role = ActiveRecord::Base.current_role)
  connection_pool_list(role).each(&:flush!)
end

#prevent_writes ⇒ Object

:nodoc:



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# File 'lib/active_record/connection_adapters/abstract/connection_handler.rb', line 83

def prevent_writes # :nodoc:
  ActiveSupport::IsolatedExecutionState[:active_record_prevent_writes]
end

#prevent_writes=(prevent_writes) ⇒ Object

:nodoc:



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# File 'lib/active_record/connection_adapters/abstract/connection_handler.rb', line 87

def prevent_writes=(prevent_writes) # :nodoc:
  ActiveSupport::IsolatedExecutionState[:active_record_prevent_writes] = prevent_writes
end

#remove_connection_pool(owner, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard) ⇒ Object 



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# File 'lib/active_record/connection_adapters/abstract/connection_handler.rb', line 221

def remove_connection_pool(owner, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard)
  if pool_manager = get_pool_manager(owner)
    pool_config = pool_manager.remove_pool_config(role, shard)

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

#retrieve_connection(spec_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard) ⇒ 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_handler.rb', line 194

def retrieve_connection(spec_name, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard) # :nodoc:
  pool = retrieve_connection_pool(spec_name, role: role, shard: shard)

  unless pool
    if shard != ActiveRecord::Base.default_shard
      message = "No connection pool for '#{spec_name}' found for the '#{shard}' shard."
    elsif ActiveRecord::Base.connection_handler != ActiveRecord::Base.default_connection_handler
      message = "No connection pool for '#{spec_name}' found for the '#{ActiveRecord::Base.current_role}' role."
    elsif role != ActiveRecord::Base.default_role
      message = "No connection pool for '#{spec_name}' found for the '#{role}' role."
    else
      message = "No connection pool for '#{spec_name}' found."
    end

    raise ConnectionNotEstablished, message
  end

  pool.connection
end

#retrieve_connection_pool(owner, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard) ⇒ 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 'lib/active_record/connection_adapters/abstract/connection_handler.rb', line 235

def retrieve_connection_pool(owner, role: ActiveRecord::Base.current_role, shard: ActiveRecord::Base.current_shard)
  pool_config = get_pool_manager(owner)&.get_pool_config(role, shard)
  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.

This method does not provide the same protection as a readonly user and is meant to be a safeguard against accidental writes.

See READ_QUERY for the queries that are blocked by this method.



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# File 'lib/active_record/connection_adapters/abstract/connection_handler.rb', line 102

def while_preventing_writes(enabled = true)
  unless ActiveRecord.legacy_connection_handling
    raise NotImplementedError, "`while_preventing_writes` is only available on the connection_handler with legacy_connection_handling"
  end

  original, self.prevent_writes = self.prevent_writes, enabled
  yield
ensure
  self.prevent_writes = original
end