set_pool_config

# File activerecord/lib/active_record/connection_adapters/pool_manager.rb, line 48
      def set_pool_config(role, shard, pool_config)
        if pool_config
          @role_to_shard_mapping[role][shard] = pool_config
        else
          raise ArgumentError, "The `pool_config` for the :#{role} role and :#{shard} shard was `nil`. Please check your configuration. If you want your writing role to be something other than `:writing` set `config.active_record.writing_role` in your application configuration. The same setting should be applied for the `reading_role` if applicable."
        end
      end