def set_driver_connection_pool(driver_class, driver_config)
      conf = {
          size:     driver_config[:pool_size],
          timeout:  driver_config[:timeout_sec]
      }
      pool = ConnectionPool.new(conf) { driver_class.connect(driver_config) }

      RailsKvsDriver::KVS_CONNECTION_POOL[driver_class.name] ||= Array.new
      RailsKvsDriver::KVS_CONNECTION_POOL[driver_class.name].push({config: driver_config, pool: pool})

      return pool
    end
def set_driver_connection_pool(driver_class, driver_config)
      conf = {
          size:     driver_config[:pool_size],
          timeout:  driver_config[:timeout_sec]
      }
      pool = ConnectionPool.new(conf) { driver_class.connect(driver_config) }

      RailsKvsDriver::KVS_CONNECTION_POOL[driver_class.name] ||= Array.new
      RailsKvsDriver::KVS_CONNECTION_POOL[driver_class.name].push({config: driver_config, pool: pool})

      return pool
    end
set driver connection pool

 @param driver_class   [RailsKvsDriver::Base]  driver_class
 @param driver_config  [Hash]                  driver_config
 @return [ConnectionPool] connection pool of driver