how-does-mysql-replication-really-work/ what-causes-replication-lag
https://www.cnblogs.com/kevingrace/p/6274073.html
https://www.cnblogs.com/kevingrace/p/6261091.html
https://dba.stackexchange.com/questions/18433/trying-to-understand-show-slave-status-g
https://dev.mysql.com/doc/refman/5.7/en/show-slave-status.html
https://www.percona.com/blog/2013/01/09/how-does-mysql-replication-really-work/
https://dev.mysql.com/doc/refman/8.0/en/replication-gtids-lifecycle.html
https://www.percona.com/blog/2013/01/09/how-does-mysql-replication-really-work/
https://blogs.oracle.com/jsmyth/what-causes-replication-lag
https://www.percona.com/blog/2014/05/02/how-to-identify-and-cure-mysql-replication-slave-lag/