Why does Redis, a datastore, have Pub/Sub features? My first thought is that it's the wrong layer to implement such a thing. But maybe I need to think outside the box.
Redis is defined as data structure server. Redis provides multiple functionality like memcache, queue, pubsub etc. This is very useful for a cloudapp/webstack where 3 components RabbitMQ(queuing) + XMPP(pubsub) + Memcache can be currently replaced with redis. Queuing is not as feature rich as RabbitMQ though.
That would be true if it was about feeds for end users to subscribe to. Actually it's closer to the concept of events or database triggers - a process that knows the internals of the datastore keeps a connection open and does something when a change happens.
来源：https://stackoverflow.com/questions/4938520/why-does-redis-have-pub-sub-capabilities