配置方法如下：

config/config.php

$config['sess_driver'] = 'redis';
$config['sess_save_path'] = 'tcp://localhost:6379?auth=yourpassword&persistent=1&weight=1&timeout=12&database=3&prefix=cnfood_';
//auth:授权密码; persistent:持久化链接0跟1; weight=1 权重为1; timeout: 12秒超时; 
 database: 需数字id, 数据库3; prefix: 会话前缀