UUID means Universally Unique Identifier, which refers to a number generated on a machine, and it is guaranteed to be unique to all machines in the same time and space. Usually the platform will provide the generated API. According to the standard calculation formulated by the Open Software Foundation (OSF), the Ethernet card address, nanosecond time, chip ID code and many possible digital UUIDs are composed of the following parts: (1) Current date and time, the first part of UUID is related to time. If you generate a UUID after a few seconds, the first part is different and the rest are the same. (2) clock sequence. (3) The globally unique IEEE machine identification number. If there is a network card, it is obtained from the MAC address of the network card. If there is no network card, it is obtained by other means.