Redis is advanced key-value cache and store, under BSD license. It is very fast, has many data types(String, Hash, List, Set, Sorted Set …), uses RDB or AOF persistence and replication to guarantee data security, and supplies many language client libraries. Most of all, market chooses Redis. There are many companies using Redis and it has proved its worth. Although redis is greate, it still has some disadvantages, and the biggest one is memory limitation. Redis keeps all data in memory, which limits the whole dataset size and lets us save more data impossibly.