Redis cache

redis As caching ：
Cache is not full , Caching should change with access

LFU： How many times

LRU： How long has it been

key The validity of the ： Will not extend with the visit

EXPIRE k1 50

Set expiration time  

key The validity of the ： Occurrence write , The expiration time will be excluded

Principle of expiration determination ：

（1） Passive access decision

（2） Periodic rotation judgment （ The incremental ）

Sacrifice memory a little , keep redis Performance of