Redis Vs MongoDB
Redis and MongoDB can be used together with good results. A company well-known for running MongoDB and Redis (along with MySQL and Sphinx) is Craiglist. See this presentation from Jeremy Zawodny. MongoDB is interesting for persistent, document oriented, data indexed in various ways. Redis is more interesting for volatile data, or latency sensitive semi-persistent data. Here are a few examples of concrete usage of Redis on top of MongoDB. MongoDB does not have yet an expiration mechanism. Capped collections cannot really be used to implement a real TTL. Redis has a TTL-based expiration mechanism, making it convenient to store volatile data. For instance, user sessions are commonly stored in Redis, while user data will be stored and indexed in MongoDB. Redis provides a convenient set datatype and its associated operations (union, intersection, difference on multiple sets, etc ...). It is quite easy to implement a basic faceted search or tagging engine on top of this featur
