【示例】
如果数据复制的慢的话，就会导致主从数据不一致性；
有的企业需要数据保持强一致性；比如银行等；
日志回放默认是单线程；
mysql> show processlist;
+----+-------------+-----------+------+---------+--------+--------------------------------------------------------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+-------------+-----------+------+---------+--------+--------------------------------------------------------+------------------+
| 6 | system user | | NULL | Connect | 170990 | Waiting for master to send event | NULL |
| 7 | system user | | NULL | Connect | 23369 | Slave has read all relay log; waiting for more updates | NULL |
| 12 | root | localhost | NULL | Sleep | 24065 | | NULL |
| 13 | root | localhost | NULL | Query | 0 | starting | show processlist |
+----+-------------+-----------+------+---------+--------+--------------------------------------------------------+------------------+
4 rows in set (0.00 sec)
#做日志的多线程回放；加快回访速度；
#上一个实验我们在slave2上做了延迟；这一个实验就不要在设定了SQL_Delay: 60延迟的slave上做，这样毫无意义！
master slave1
slave1上：编辑主配置文件：
多线程上需要把gtid打开
root@mysql2 \~\]# vim /etc/my.cnf \[root@mysql2 \~\]# cat /etc/my.cnf \[mysqld
datadir=/data/mysql
socket=/data/mysql/mysql.sock
symbolic-links=0
server-id=2
super_read_only=on
gtid_mode=on
enforce-gtid-consistency=onslave-parallel-type=LOGICAL_CLOCK #基于组提交
slave-parallel-workers=16 #开启线程数量
master_info_repository=TABLE #master信息在表中记录，默认记录在/data/mysql//master.info
relay_log_info_repository=TABLE #回放日志信息在表中记录，默认记录在/data/mysql/relay-log.info #多线程回放，日志会成为瓶颈，设置这两条将日志记录在数据表里，而不是文件里
relay_log_recovery=ON #日志回放恢复功能开启root@mysql2 \~\]# cd /data/mysql/ \[root@mysql2 mysql\]# ls auto.cnf folian ibtmp1 mysql2.pid mysql.sock relay-log.info ca-key.pem ib_buffer_pool master.info mysql2-relay-bin.000002 mysql.sock.lock server-cert.pem ca.pem ibdata1 mysql mysql2-relay-bin.000003 performance_schema server-key.pem client-cert.pem ib_logfile0 mysql1.err mysql2-relay-bin.index private_key.pem sys client-key.pem ib_logfile1 mysql2.err mysql-bin.index public_key.pem #重启数据库 \[root@mysql2 \~\]# /etc/init.d/mysqld start Starting MySQL SUCCESS! #查看进程：这里刚开始出现了问题 \[root@mysql2 \~\]# /etc/init.d/mysqld start Starting MySQL SUCCESS! \[root@mysql2 \~\]# 2024-08-27T02:41:31.233896Z mysqld_safe A mysqld process already exists #这里出错了我们并没有查看到应有的效果 \[root@mysql2 \~\]# mysql -uroot -predhat mysql\> show processlist; +----+-------------+-----------+------+---------+--------+--------------------------------------------------------+------------------+ \| Id \| User \| Host \| db \| Command \| Time \| State \| Info \| +----+-------------+-----------+------+---------+--------+--------------------------------------------------------+------------------+ \| 6 \| system user \| \| NULL \| Connect \| 172796 \| Waiting for master to send event \| NULL \| \| 7 \| system user \| \| NULL \| Connect \| 25175 \| Slave has read all relay log; waiting for more updates \| NULL \| \| 12 \| root \| localhost \| NULL \| Sleep \| 25871 \| \| NULL \| \| 14 \| root \| localhost \| NULL \| Query \| 0 \| starting \| show processlist \| +----+-------------+-----------+------+---------+--------+--------------------------------------------------------+------------------+ 4 rows in set (0.01 sec) mysql\> exit; Bye \[root@mysql2 \~\]# ps aux \| grep mysql avahi 793 0.0 0.1 62268 2276 ? Ss Aug26 0:11 avahi-daemon: running \[mysql1.local
root 17093 0.0 0.0 113412 1608 ? S 00:47 0:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --datadir=/data/mysql --pid-file=/data/mysql/mysql2.pid
mysql 17234 0.6 10.6 1603764 198588 ? Sl 00:47 3:45 /usr/local/mysql/bin/mysqld --basedir=/usr/local/mysql --datadir=/data/mysql --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=mysql2.err --pid-file=/data/mysql/mysql2.pid --socket=/data/mysql/mysql.sock
root 22394 0.0 0.2 163396 4172 pts/3 S+ 09:01 0:00 mysql -px xxxx
root 23902 0.0 0.0 112812 968 pts/1 S+ 10:53 0:00 grep --color=auto mysql
root@mysql2 \~\]# kill 17093 \[root@mysql2 \~\]# kill 17234 \[root@mysql2 \~\]# kill 22394 \[root@mysql2 \~\]# ps aux \| grep mysql avahi 793 0.0 0.1 62268 2276 ? Ss Aug26 0:11 avahi-daemon: running \[mysql1.local
root 23918 0.0 0.0 112812 968 pts/1 S+ 10:54 0:00 grep --color=auto mysql
root@mysql2 \~\]# /etc/init.d/mysqld start Starting MySQL...... SUCCESS! #成功解决并查看 \[root@mysql2 \~\]# mysql -uroot -predhat mysql\> show processlist; +----+-------------+-----------+------+---------+------+--------------------------------------------------------+------------------+ \| Id \| User \| Host \| db \| Command \| Time \| State \| Info \| +----+-------------+-----------+------+---------+------+--------------------------------------------------------+------------------+ \| 1 \| system user \| \| NULL \| Connect \| 9 \| Slave has read all relay log; waiting for more updates \| NULL \| \| 3 \| system user \| \| NULL \| Connect \| 11 \| Waiting for an event from Coordinator \| NULL \| \| 4 \| system user \| \| NULL \| Connect \| 11 \| Waiting for an event from Coordinator \| NULL \| \| 5 \| system user \| \| NULL \| Connect \| 11 \| Waiting for an event from Coordinator \| NULL \| \| 6 \| system user \| \| NULL \| Connect \| 11 \| Waiting for an event from Coordinator \| NULL \| \| 7 \| system user \| \| NULL \| Connect \| 11 \| Waiting for an event from Coordinator \| NULL \| \| 8 \| system user \| \| NULL \| Connect \| 11 \| Waiting for an event from Coordinator \| NULL \| \| 9 \| system user \| \| NULL \| Connect \| 11 \| Waiting for an event from Coordinator \| NULL \| \| 10 \| system user \| \| NULL \| Connect \| 11 \| Waiting for an event from Coordinator \| NULL \| \| 11 \| system user \| \| NULL \| Connect \| 11 \| Waiting for an event from Coordinator \| NULL \| \| 12 \| system user \| \| NULL \| Connect \| 11 \| Waiting for an event from Coordinator \| NULL \| \| 13 \| system user \| \| NULL \| Connect \| 10 \| Waiting for an event from Coordinator \| NULL \| \| 14 \| system user \| \| NULL \| Connect \| 10 \| Waiting for an event from Coordinator \| NULL \| \| 15 \| system user \| \| NULL \| Connect \| 10 \| Waiting for an event from Coordinator \| NULL \| \| 16 \| system user \| \| NULL \| Connect \| 10 \| Waiting for an event from Coordinator \| NULL \| \| 18 \| system user \| \| NULL \| Connect \| 9 \| Waiting for an event from Coordinator \| NULL \| \| 19 \| system user \| \| NULL \| Connect \| 9 \| Waiting for an event from Coordinator \| NULL \| \| 20 \| root \| localhost \| NULL \| Query \| 0 \| starting \| show processlist \| +----+-------------+-----------+------+---------+------+--------------------------------------------------------+------------------+ 18 rows in set (0.00 sec) #从上我们可以看出有16个SQL进程来做日志回放，但是最终还是要落到CPU性能上。 #多线程：使主从的数据差异尽可能减小，（数据库优化）