class ActiveRecord::ConnectionAdapters::ConnectionHandler

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