CI3提供了使用Redis的配置，不过需要通过PHP的Redis扩展phpredis来使用链接Redis

官网这样说：

Redis is an in-memory key-value store which can operate in LRU cache mode. To use it, you need Redis server and phpredis PHP extension.

phpredis是用C语言编写的PHP扩展，效率比较高。

既然是PHP扩展，那就得先安装了，之前有写过安装扩展的办法，PHP安装pdo_mysql扩展，PHP安装mysqli扩展

这里说下安装过程

1，下载phpredis源码，解压放到PHP源码的扩展目录/home/php-5.6.8/ext

2，进入phpredis的解压目录编译安装

# /usr/local/php/bin/phpize
# ./configure --with-php-config=/usr/local/php/bin/php-config 
# make & make install

3，修改php.ini，添加redis.so，并重启php-fpm和nginx

4，打开phpinfo，可以看到redis扩展了

下面介绍CodeIgniter3中配置Redis

1，在application/config添加配置文件redis.php，内容如下：

<?php
defined('BASEPATH') OR exit('No direct script access allowed');

$config['socket_type'] = 'tcp'; //`tcp` or `unix`
$config['socket'] = '/var/run/redis.sock'; // in case of `unix` socket type
$config['host'] = '127.0.0.1';
$config['password'] = NULL;
$config['port'] = 6379;
$config['timeout'] = 0;

2，在控制器中使用Redis

        public function set()
        {
                $username = $this->input->post('username',TRUE);
                $this->load->driver('cache');
                // 数据保存到Redis
                $this->cache->redis->save('username', $username, 300);
        
        }

        public function get()
        {
                $this->load->driver('cache');
                // 获取Redis数据
                $username = $this->cache->redis->get('username');
                $data = array('username' => $username);

        }

更多用法，请查看官网:https://www.codeigniter.com/userguide3/libraries/caching.html#redis-caching