(PECL memcached >= 2.0.0)
Memcached::decrementByKey — Decrement numeric item's value, stored on a specific server
$server_key,$key,$offset = 1,$initial_value = 0,$expiry = 0
Memcached::decrementByKey() decrements a numeric item's
value by the specified offset. If the item's value
is not numeric, an error will result. If the operation
would decrease the value below 0, the new value will be 0.
Memcached::decrementByKey() will set the item to the
initial_value parameter if the key doesn't exist.
server_key本鍵名用于識別儲存和讀取值的服務(wù)器。沒(méi)有將實(shí)際的鍵名散列到具體的項目，而是在決定與哪一個(gè) memcached 服務(wù)器通信時(shí)將其散列為服務(wù)器鍵名。這使得關(guān)聯(lián)的項目在單一的服務(wù)上被組合起來(lái)以提高多重操作的效率。
keyThe key of the item to decrement.
offsetThe amount by which to decrement the item's value.
initial_valueThe value to set the item to if it doesn't currently exist.
expiryThe expiry time to set on the item.
Returns item's new value on success 或者在失敗時(shí)返回 false.