redis中使用set更新一个有有效时间的key，会使有效时间变成永久有效

最近在开发中遇到一个问题，使用redis中的set更新一个含有有效时间的key时，会时这个key的有效时间变成永久有效
用客户端尝试：

127.0.0.1:6379> set test test
OK
127.0.0.1:6379> expire test 1000
(integer) 1
127.0.0.1:6379> set test test
OK
127.0.0.1:6379> ttl test
(integer) -1
127.0.0.1:6379>

查阅redis官方文档是这样介绍的
The timeout will only be cleared by commands that delete or overwrite the contents of the key, including DEL, SET, GETSET and all the *STORE commands. This means that all the operations that conceptually alter the value stored at the key without replacing it with a new one will leave the timeout untouched. For instance, incrementing the value of a key with INCR, pushing a new value into a list with LPUSH, or altering the field value of a hash with HSET are all operations that will leave the timeout untouched.

翻译:

如果用DEL, SET, GETSET会将key对应存储的值替换成新的，命令也会清除掉超时时间；如果list结构中添加一个数据或者改变hset数据的一个字段是不会清除超时时间的；如果想要通过set去覆盖值那就必须重新设置expire。