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1. Uuid () function

Mysql > select uuid (), uuid () +-+-+ | uuid () | uuid () | +-- -+ | 50120c25-d75c-11e7-9484-000c29c9278a | 50120c53-d75c-11e7-9484-000c29c9278a | +-- +- -+ 1 row in set (0.00 sec) String * Item_func_uuid::val_str (String * str) {. Mac\ rand get...uint32 time_low= (uint32) (tv & 0xFFFFFFFF) Uint16 time_mid= (uint16) ((tv > > 32) & 0xFFFF); uint16 time_hi_and_version= (uint16) ((tv > 48) | UUID_VERSION); s [8] = s [13] ='-'; tohex (s, time_low, 8); tohex (swarm 9, time_mid, 4); tohex (swarm 14, time_hi_and_version, 4); strmov (swarm 18, clock_seq_and_node_str) .} detailed generation of uuid process, refer to the above function for analysis.

Time_low, time_mid and time_high_and_version correspond to paragraph 123 respectively when they are converted to hexadecimal.

This time is the 100ns value from 1582-10-1500 to the current time. (in fact, the system can only get the exact us and multiply it by 10). So if you execute continuously for a short period of time, it is more likely that only the first value is changing, in fact, 1 / 2 / 3 may change. Paragraph 4 is the random number when you execute select uuid () for the first time after you start the MySQL, which will change each time you restart. Paragraph 5 is the Mac value turned around, and multiple instances of the same machine are generally the same. If the Mac value is not available, it is a random value. So this value can be thought of as different for each execution. And there is only a very small probability of repetition between different instances.

2. Uuid_short () function

Mysql > select uuid_short (), uuid_short () +-+ | uuid_short () | uuid_short () | +-+ | 818004335832072194 | 818004335832072195 | +- -+ 1 row in set (0.00 sec) function call procedure:

Main- > init_common_variables ()-> server_start_time= flush_status_time= my_time (0); / / obtain the timestamp of server startup ulonglong uuid_value;main- > init_common_variables- > item_init- > void uuid_short_init () {uuid_value= (ulonglong) server_id))

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