redis过期机制（官网文档总结）

官网地址：https://redis.io/commands/expire

redis过期定义如下：

Set a timeout on key. After the timeout has expired, the key will automatically be deleted. A key with an associated timeout is often said to be volatile in Redis terminology.

如下为 对 官网文档的总结，如有理解错误，请指正，不胜感激。