情景
有一個這樣的場景，某系統裏爲用戶開闢了一個空間，這個空間在有效期裏可以隨意使用。但是到期後要回收。我們可以通過定時任務對數據庫表中存在的空間信息進行檢查，如果截止時間到了，就進行對應的操作。也可以把這個定時的工程扔給系統以外。
我們可以嘗試另一種方案，例如創建空間的時候，將空間id作爲key的一部分存放在redis中，而ex設置爲有效時間。在redis將這個超時的key刪除的時候，通知我們系統，從而完成清除空間的操作。
實現
1.開啓事件
1.1,修改配置文件
默認的redis並沒有開啓這個功能，需要修改配置文件中的notify-keyspace-events配置
############################# Event notification ##############################
# Redis can notify Pub/Sub clients about events happening in the key space.
# This feature is documented at http://redis.io/topics/notifications
#
# For instance if keyspace events notification is enabled, and a client
# performs a DEL operation on key "foo" stored in the Database 0, two
# messages will be published via Pub/Sub:
#
# PUBLISH __keyspace@0__:foo del
# PUBLISH __keyevent@0__:del foo
#
# It is possible to select the events that Redis will notify among a set
# of classes. Every class is identified by a single character:
#
# K Keyspace events, published with __keyspace@<db>__ prefix.
# E Keyevent events, published with __keyevent@<db>__ 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.
#
# The "notify-keyspace-events" takes as argument a string that is composed
# by zero or multiple characters. The empty string means that notifications
# are disabled at all.
#
# Example: to enable list and generic events, from the point of view of the
# event name, use:
#
# notify-keyspace-events Elg
#
# Example 2: to get the stream of the expired keys subscribing to channel
# name __keyevent@0__:expired use:
#
# notify-keyspace-events Ex
#
# By default all notifications are disabled because most users don't need
# this feature and the feature has some overhead. Note that if you don't
# specify at least one of K or E, no events will be delivered.
notify-keyspace-events Ex
是的，重點就是：
notify-keyspace-events Ex
Ex代表：
# 以 “__keyevent@<db>__“ 爲前綴發佈Keyevent事件，<db>爲所使用的redis庫編號
1,E: Keyevent events, published with __keyevent@<db>__ prefix.
# 過期事件（每次鍵過期時生成的事件）
2,x: Expired events (events generated every time a key expires)、
1.2,運行時通過參數設置
#設置：
redis-cli: CONFIG SET notify-keyspace-events "Ex"
#查詢
redis-cli:CONFIG GET notify-keyspace-event
#redis: 指的是進入redis-cli後，並且執行成功的情況
但是這種重啓redis服務就沒了（恢復爲配置文件中的設置）。
2,運行時通過參數設置
psubscribe __keyevent@0__:expired