code: function initPool(dbConfig, alias, customizeConfig) {
    if (!alias) alias = DEFAULT_DB_NAME;
    if (!customizeConfig) customizeConfig = {};
  
    var initialedPool = dbName_pool_[alias];
    if (!initialedPool) {
      var pool = new pg.Pool(dbConfig);
      var dbName = dbConfig.database;
      dbNameList.push(dbName);
      pool.__db__ = dbName;
      dbName_pool_[alias] = pool;
      dbName_pool_[dbName] = pool;
  
      var startupConfig = { dbConfig, alias, customizeConfig };
      dbName_config_[alias] = startupConfig;
      dbName_config_[dbName] = startupConfig;
    } else {
      if (initialedPool.__db__ != dbConfig.database) {//不允许用一个别名初始化多个不同的数据库
        throw new Error(`alias [${alias}] has already been initialized to db ${initialedPool.__db__}`);
      } else {
        // do nothing, 保证只初始化一次
      }
    }
  }
docs: 初始化连接池对象,默认会使用config的database作为key映射pool，
  如果传入了dbName且dbName和database不相等，也会使用dbName作为key映射pool，
  此时dbName与database指向的是同一个pool
  @param {Object} otherConfig
  @param {Function} otherConfig.sqlWatcher