Redis(REmote DIctionary Server) is a key-value storage system written by Salvatore Sanfilippo. Redis provides a wealth of data structures and operations on these data structures. Because Redis's data is stored in memory, accessing it can be very fast, so Redis is used extensively in the cache system to store hotspot data, which can greatly improve the responsiveness of the website. Redis is often referred to as a data structure server. Redis's key values include strings, hashes, sets, sorted sets and other data types. For these data types, you can perform atomic operations, such as: append the string (append); increment the value in the hash; add elements to the list; calculate the intersection, the union and difference of sets, and so on.