I want to use redis cache on my custom PHP sites, I know that it allows storing key and valuing pairs and offers data replication but what more advantage can it give me for my cloud server as I've install php redis for this same stuff.
Redis is a NoSQL database, a storage backend which indeed stores data in key-value pairs. To be clear, it is not some sort of transparent cache solution.
Like with any database, you need client software to talk to it. That link suggests using predis as a client library for PHP, which you can use to talk to the database.
Fuel however already comes with a built-in Redis client, and if the PHP PECL extension for Redis is installed, fuel will use that. The fuel data cache system can use several backends, and Redis is one of them. It uses the built-in client.
Nobody is stopping you from using any other client, but then you'll need to write your own cache library.
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