http://redis.io/topics/notifications redis 在2.8版本新增的功能，鍵值可以發出事件通知，可以利用PUBSUB的功能 接受到相關的通知。

K Keyspace events, published with keyspace@ prefix.
E Keyevent events, published with keyevent@ prefix.
g Generic commands (non-type specific) like DEL, EXPIRE, RENAME, …
$ String commands
l List commands
s Set commands
h Hash commands
z Sorted set commands
x Expired events (events generated every time a key expires)
e Evicted events (events generated when a key is evicted for maxmemory)
A Alias for g$lshzxe, so that the “AKE” string means all the events.