在Redis中，如果設置的maxmemory，那就要配置key的回收機制參數maxmemory-policy，默認volatile-lru，參閱Redis作者的原博客：antirez weblog >> Redis as an LRU cache
原文中寫得很清楚：
復制代碼代碼如下:
Another way to use Redis as a cache is the maxmemory directive, a feature that allows specifying a maximum amount of memory to use. When new data is added to the server, and the memory limit was already reached, the server will remove some old data deleting a volatile key, that is, a key with an EXPIRE (a timeout) set, even if the key is still far from expiring automatically.
在Redis服務器占用內存達到maxmemory的情況下，當再想增加內存占用時，會按maxmemory-policy機制將老的數據刪除。這里簡單說一下volatile-lru，Redis會按LRU算法刪除設置了過期時間但還沒有過期的key，而對于沒有設置過期時間的key，Redis是永遠保留的。當然，如果你不想刪除沒有過期的key，那可以使用noeviction機制
復制代碼代碼如下:
# MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
# is reached? You can select among five behavior:
#
# volatile-lru -> remove the key with an expire set using an LRU algorithm
# allkeys-lru -> remove any key accordingly to the LRU algorithm
# volatile-random -> remove a random key with an expire set
# allkeys-random -> remove a random key, any key
# volatile-ttl -> remove the key with the nearest expire time (minor TTL)
# noeviction -> don't expire at all, just return an error on write operations
