What is Redis
Redis Cache is a NoSQL key-value database that runs entirely in memory. As a database that runs in memory its very fast,faster than typical database systems
Why use Redis Cache
The speed advantage of Redis means that there is much less performance overhead when reading and writing data. If you have an application that needs to store/cache lots of data and you have memory to spare then Redis might be exactly what you are looking for.
License and Cost
Its free to use for both non-commercial and commercial uses under the BSD license
Why not caching
Redis has great advantages over traditional memory caching,it persists to disk and its data is available across applications rather than a single process.