nosql - redis expire 疑問

Question

使用redis-cli 設定mykey, 並且設定其過期時間為40s, 然後, 我再重新設定mykey, 這時mykey 的值mykey, 我不明白的是被重置為啥

過期時間

也同時重置了?如果我僅僅想重置值, 不更改過期時間有沒辦法?

源碼🎜:🎜

SET mykey "Hello"

EXPIRE mykey 40

EXISTS mykey

SET mykey "Hello"

EXISTS mykey

EXISTS mykey

Answer 1

上官方網站看了一下expire的說明：
這樣解釋的：

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.

如果用DEL, SET, GETSET會將key對應儲存的值替換成新的，命令也會清除掉超時時間；如果list結構中新增一個資料或改變hset資料的一個欄位是不會清除逾時時間的；如果想要透過set去覆蓋值那就必須重新設定expire。

點擊連結

Answer 2

EXPIREAT和EXPIRE 更新value都會重置過期時間。

set之前透過ttl取得到key的過期時間
set之後再把ttl的值給設成過期時間

192.168.1.9:6379> set key value
OK
192.168.1.9:6379> expire key 100
(integer) 1
192.168.1.9:6379> ttl key
(integer) 98
192.168.1.9:6379> set key value1
OK
192.168.1.9:6379> expire key 98
(integer) 1
192.168.1.9:6379> ttl key
(integer) 96
192.168.1.9:6379>

但這樣子會有誤差，不知道其他人有沒有更好的方法。