MySQL：半同步（三）从库端初始化和回调函数
作者简介：高鹏，笔名八怪。《深入理解MySQL主从原理》图书作者，同时运营个人公众号“MySQL学习”，持续分享遇到的有趣case以及代码解析！
源码版本5.7.29
一、全局变量
semisync_slave_plugin.cc
ReplSemiSyncSlave repl_semisync;
/*
indicate whether or not the slave should send a reply to the master.
This is set to true in repl_semi_slave_read_event if the current
event read is the last event of a transaction. And the value is
checked in repl_semi_slave_queue_event.
*/
bool semi_sync_need_reply= false;
