Storage and caching are two different problems so it's reasonable to assume two separate solutions. In this case, MongoDB is a leap ahead of MySQL; Redis is a

Storage and caching are two different problems so it's reasonable to assume two separate solutions. In this case, MongoDB is a leap ahead of MySQL; Redis is a leap ahead of Memcached. Both solve the core problems very well and include additional freebies (MongoDB's high-performance aggregate functions and Redis' atomic increments and set and list functions).