MongoDB深究之ObjectId - 信客 - 博客园 https://www.cnblogs.com/xjk15082/archive/2011/09/18/2180792.html
从MongoDB的ObjectId中获取时间信息 - Jaxu - 博客园 https://www.cnblogs.com/jaxu/p/6605283.html
ObjectId — MongoDB Manual https://docs.mongodb.com/manual/reference/method/ObjectId/
Returns a new ObjectId value. The 12-byte ObjectId value consists of:
- a 4-byte timestamp value, representing the ObjectId's creation, measured in seconds since the Unix epoch
- a 5-byte random value
- a 3-byte incrementing counter, initialized to a random value