MySQL5.7 OCP每日一题--Question: 3

You have a MySQL replication setup and you intentionally stop the SQL thread on the slave.
mysql> SHOW SLAVE STATUS\G
Slave_IO_Running: Yes
Slave_SQL_Running: No
What are two reasons that you may stop the SQL thread on the slave while keeping the I/ O thread running?
A. to allow the remaining events to be processed on the slave while not receiving new events from the master
B. to allow a backup to be created under reduced load
C. to allow for point-in-time recovery on the slave
D. to prevent schema changes from propagating to the slave before they are validated
E. to prevent any transaction experiencing a deadlock 

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解析： 什么情况下我们会主动停止salve节点上主从同步的SQL线程？SQL线程停止后，IO线程还在运行。从节点依然可以接受到主节点的binlog并且转存为relay log，只是停止将relay log应用到从节点，因此A错误；在从库负载比较高的情况下进行备份时，可以stop slave sql_thread停止sql线程，暂时降低负载加快备份；从库同步一般是同步的，无法做到恢复到某个时间点，只有在延迟的从库上，能进行延迟时间范围内的时间点恢复；。

答案：BC