在Redis中，如果設定的maxmemory，那就要配置key的回收機制參數maxmemory-policy，預設volatile-lru，參閱Redis作者的原部落格：antirez weblog >> Redis as an LRU cache
原文中寫得很清楚：
複製代碼 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伺服器佔用記憶體達到maxmemory的情況下，當再想增加記憶體佔用時，會按maxmemory-policy機制將老的資料刪除。這裡簡單說一下volatile-lru，Redis會按LRU演算法刪除設定了到期時間但還沒有到期的key，而對於沒有設定到期時間的key，Redis是永遠保留的。當然，如果你不想刪除沒有到期的key，那可以使用noeviction機制
複製代碼 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
