Redis is a very popular fast in-memory data structure storage engine, which is typically used as a database server, cache, and message broker. It is written in the C programming language. It also provides official PHP modules for communication between PHP scripts and the Redis server. With redis, all data is stored in memory. That is what makes it totally different from other No-SQL storage engines. Usually, when you access and read some data from the database, you don???t know if the data is in memory(cache) or not, but that is not the case when it comes to Redis.