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gtid一般又server_uuid+gno组成
/*
函数位置:mysqld.cc
*/
init_server_auto_options() //mysql启动的时候会调用该函数读取auto.cnf文件获取server_uuid
generate_server_uuid() //如果auto.cnf文件不存在，则会调用该函数生成一个新的server_uuid
/*
这部分代码是server_uuid的主要初始化过程，该函数首先会分配一个临时的变量thd，来进行过程中的计算
为了保证在新启动mysqld时uuid的不重复，我们可以看到uuid和以下三个方面有关
1.数据库的启动时间
2.轻量级现成的id
3.随机内存地址
*/
sql_print_information("Salting uuid generator variables, current_pid: %lu, "
"server_start_time: %lu, bytes_sent: %llu, ",
current_pid,
(ulong)server_start_time, thd->status_var.bytes_sent);
const time_t save_server_start_time= server_start_time;
server_start_time+= ((ulonglong)current_pid << 48) + current_pid;
thd->status_var.bytes_sent= (ulonglong)thd;
lex_start(thd);
func_uuid= new (thd->mem_root) Item_func_uuid();
func_uuid->fixed= 1;
func_uuid->val_str(&uuid);
sql_print_information("Generated uuid: '%s', "
"server_start_time: %lu, bytes_sent: %llu",
uuid.c_ptr(),
(ulong)server_start_time, thd->status_var.bytes_sent);
// Restore global variables used for salting
server_start_time = save_server_start_time;
/*
函数位置：rpl_gtid_state.cc
*/
rpl_gno Gtid_state::get_automatic_gno()//gno生成以及gtid的生成
