MySQL主从复制

原理简介

主从复制过程存在三个线程，Master端的I/O线程，Slave的I/O线程与SQL线程。Master端需要开启binlog日志，Slave端需要开启relay日志。

1、Slave端的I/O读取master.info文件，获取binlog文件名和位置点，然后向Master端的I/O线程请求，该binlog文件名和位置点的binlog信息。

（master.info文件在配置主从复制时使用change master命令来指定生成）

2、Master端的I/O线程会根据Slave端的I/O线程请求的信息来读取Master的binlog日志信息与及读取到最新的binlog文件名和位置点一同返回给Slave的I/O线程。

3、Slave端的I/O线程会把获取到的binlog日志写入relay日志（中继日志）文件中，并且更新master.info文件信息。（把读取到Master最新的binlog日志文件名和位置点更新到master.info文件中，下一次当前位置去读取Master的binlog日志）

4、Slave端的SQL线程会定期读取relay日志，把二进制的日志解析成SQL语句，并执行这些SQL语句，同步数据到从库中。

环境准备

软件及系统: CentOS 7.5 — 2台、MySQL 5.7 --- Yum安装

系统环境准备:

##关闭防火墙及SElinux安全机制
[root@mysql ~]# systemctl disable firewalld
Removed symlink /etc/systemd/system/multi-user.target.wants/firewalld.service.
Removed symlink /etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service.
[root@mysql ~]# sed -ri s/SELINUX=enforcing/SELINUX=disabled/g /etc/selinux/config
[root@mysql ~]# reboot
​
##必要的软件环境准备
[root@mysql ~]# yum -y install wget vim net-tools
[root@mysql ~]# yum -y groupinstall "Development Tools"
[root@mysql ~]# wget https://dev.mysql.com/get/mysql80-community-release-el7-1.noarch.rpm
[root@mysql ~]# rpm -ivh mysql80-community-release-el7-1.noarch.rpm

⚠️需要修改MySQL的安装仓库的设置, 开启5.7的安装源, 关闭8.0的安装源

###安装构建

要求: master-slave架构

构建过程:

##安装配置过程
[root@mysql ~]# yum -y install mysql-community-server
[root@mysql ~]# systemctl enable mysqld && systemctl start mysqld
##主从配置过程
 ##------------------------------------主库设置------------------------------------##
[root@master ~]# vi /etc/my.cnf //开启二进制日志并设置服务ID
[mysqld]
server-id=21 

log-bin=mysql-bin
​
[root@master ~]# systemctl start mysqld && systemctl enable mysqld
[root@master ~]# grep 'password' /var/log/mysqld.log
2019-06-22T01:53:04.173732Z 1 [Note] A temporary password is generated for root@localhost: ied,1qj(y/gH //注意修改密码
​
[root@master ~]# mysql -uroot -p'(Cyy..123)'
​
mysql> CREATE USER 'replication'@'192.168.233.22' IDENTIFIED BY "#Cyy..123#";
Query OK, 0 rows affected (0.01 sec)
​
mysql> GRANT REPLICATION SLAVE ON *.* TO 'replication'@'192.168.233.22';
Query OK, 0 rows affected (0.00 sec)
​
mysql> SHOW MASTER STATUS;
+------------------+----------+--------------+------------------+-------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+-------------------+
| mysql-bin.000002 | 877 | | | |
+------------------+----------+--------------+------------------+-------------------+
1 row in set (0.00 sec)
​
 ##------------------------------------主库设置------------------------------------##
​
 ##------------------------------------从库设置------------------------------------##
[root@slave ~]# vi /etc/my.cnf
[mysqld]
server_id=22
​
[root@slave ~]# systemctl start mysqld && systemctl enable mysqld
[root@slave ~]# grep 'password' /var/log/mysqld.log
2019-06-22T02:07:33.890742Z 1 [Note] A temporary password is generated for root@localhost: dFS:z5DQ/
[root@slave ~]# mysql -uroot -p'(Cyy..123)'
​
mysql> CHANGE MASTER TO
 -> MASTER_HOST='192.168.233.21',
 -> MASTER_USER='replication',
 -> MASTER_PASSWORD='#Cyy..123#',
 -> MASTER_LOG_FILE='mysql-bin.000001',
 -> MASTER_LOG_POS=877;
​
mysql> start slave;
mysql> show slave status\\G;
*************************** 1. row ***************************
 Slave_IO_State: Waiting for master to send event
 Master_Host: 192.168.233.21
 Master_User: replication
 Master_Port: 3306
 Connect_Retry: 60 

 Master_Log_File: mysql-bin.000001
 Read_Master_Log_Pos: 1206
 Relay_Log_File: slave-relay-bin.000002
 Relay_Log_Pos: 649
 Relay_Master_Log_File: mysql-bin.000001
 Slave_IO_Running: Yes
 Slave_SQL_Running: Yes
 ##------------------------------------从库设置------------------------------------##