1. Redis is in-memory data store, cache.
2. Request is first sent to redis, then database.
3. Data(which is also stored in database) that is frequently used is stored in redis.
4. Data in redis is stored in memory, data in database is stored in disk. Accessing data from memory is much faster than from database.
原文：https://www.cnblogs.com/dark-rebel/p/9315996.html