MySQL主从的介绍与应用

mysql主从

1. 主从简介

在现代企业中，数据显得尤为重要，而存储数据的数据库选择又五花八门，但无论是何种数据库，均存在着一种隐患。

想几个问题：

• 用一台数据库存放数据，若此数据库服务器宕机了导致数据丢失怎么办？
• 业务量大了，数据多了，访问的人多了，一台数据库无法保证服务质量了怎么办？

1.1 主从作用

• 实时灾备，用于故障切换
• 读写分离，提供查询服务
• 备份，避免影响业务

1.2 主从形式

• 一主一从
• 主主复制
• 一主多从—扩展系统读取的性能，因为读是在从库读取的
• 多主一从—5.7开始支持
• 联级复制

2. 主从复制原理

主从复制步骤：

• 主库将所有的写操作记录到binlog日志中并生成一个log dump线程，将binlog日志传给从库的I/O线程
• 从库生成两个线程，一个I/O线程，一个SQL线程
  • I/O线程去请求主库的binlog，并将得到的binlog日志写到relay log（中继日志） 文件中
  • SQL线程，会读取relay log文件中的日志，并解析成具体操作，来实现主从的操作一致，达到最终数据一致的目的

3. 主从复制配置

主从复制配置步骤：

1. 确保从数据库与主数据库里的数据一样
2. 在主数据库里创建一个同步账号授权给从数据库使用
3. 配置主数据库（修改配置文件）
4. 配置从数据库（修改配置文件）

需求：
搭建两台MySQL服务器，一台作为主服务器，一台作为从服务器，主服务器进行写操作，从服务器进行读操作

环境说明：

数据库角色	IP	应用与系统版本	有无数据
主数据库	192.168.116.140	rockylinux9	无数据
从数据库	192.168.116.143	rockylinux9	无数据

3.1 mysql安装（两台主机安装一致，下面只演示一台主机操作）

分别在主从两台服务器上安装mysql8.0.35版本，此处略过安装步骤，若有疑问请参考《mysql基础》与《mysql进阶》两篇文章。

1.修改主机名
[root@localhost ~]# hostnamectl set-hostname master
[root@localhost ~]# bash
[root@master ~]# [root@localhost ~]# hostnamectl set-hostname slave
[root@localhost ~]# bash
[root@slave ~]# 2.关闭防火墙
[root@master ~]# systemctl disable --now firewalld
Removed "/etc/systemd/system/multi-user.target.wants/firewalld.service".
Removed "/etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service".
[root@master ~]# vi /etc/selinux/config
[root@master ~]# cat /etc/selinux/config|grep '^SELINUX'
SELINUX=disabled
SELINUXTYPE=targeted
[root@master ~]# setenforce 0
[root@master ~]# getenforce
Permissive[root@slave ~]# systemctl disable --now firewalld
Removed "/etc/systemd/system/multi-user.target.wants/firewalld.service".
Removed "/etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service".
[root@slave ~]# vi /etc/selinux/config
[root@slave ~]# cat /etc/selinux/config|grep '^SELINUX'
SELINUX=disabled
SELINUXTYPE=targeted
[root@slave ~]# setenforce 0
[root@slave ~]# getenforce
Permissive3.下载软件包
[root@master ~]# ls
anaconda-ks.cfg  mysql-8.0.35-linux-glibc2.28-x86_64.tar.xz4.压缩软件包
[root@master ~]# tar xf mysql-8.0.35-linux-glibc2.28-x86_64.tar.xz  -C /usr/local
[root@master ~]# cd /usr/local
[root@master local]# ls
bin  etc  games  include  lib  lib64  libexec  mysql-8.0.35-linux-glibc2.28-x86_64  sbin  share  src
[root@master local]# mv mysql-8.0.35-linux-glibc2.28-x86_64 mysql
[root@master local]# ls
bin  etc  games  include  lib  lib64  libexec  mysql  sbin  share  src
[root@master local]# 5.配置环境变量
[root@master local]# ls
bin  etc  games  include  lib  lib64  libexec  mysql  sbin  share  src
[root@master local]# echo 'export PATH=/usr/local/mysql/bin:$PATH' > /etc/profile.d/mysql.sh
[root@master local]# source /etc/profile.d/mysql.sh 6.做软连接
[root@master local]# ls
bin  etc  games  include  lib  lib64  libexec  mysql  sbin  share  src
[root@master local]# ln -s /usr/local/mysql/include/ /usr/include/mysql7.告知lib在哪
[root@master local]# vim /etc/ld.so.conf.d/mysql.conf
[root@master local]# ldconfig -v8.添加帮助文档
[root@master local]# ls
bin  etc  games  include  lib  lib64  libexec  mysql  sbin  share  src
[root@master local]# vim /etc/man_db.conf 
#
MANDATORY_MANPATH                       /usr/man
MANDATORY_MANPATH                       /usr/share/man
MANDATORY_MANPATH                       /usr/local/share/man
MANDATORY_MANPATH                       /usr/local/mysql/man
#---------------------------------------------------------9.创建用户并修改/usr/local/mysql/的所有者和所属组为mysql
[root@master ~]# useradd -r -M -s /sbin/nologin mysql
[root@master ~]# id mysql
uid=991(mysql) gid=991(mysql) groups=991(mysql)
[root@master ~]# chown -R mysql.mysql /usr/local/mysql 
[root@master ~]# ll -d /usr/local/mysql
drwxr-xr-x. 9 mysql mysql 129 Dec 26 16:40 /usr/local/mysql10.创建数据库存放数据的目录并修改属组
[root@master ~]# mkdir /opt/data
[root@master ~]# chown -R mysql.mysql /opt/data
[root@master ~]# ll -d /opt/data
drwxr-xr-x. 2 mysql mysql 6 Dec 26 16:48 /opt/data11.初始化
[root@master ~]# mysqld --initialize --user mysql --datadir /opt/data
2023-12-26T08:49:43.219451Z 0 [System] [MY-013169] [Server] /usr/local/mysql/bin/mysqld (mysqld 8.0.35) initializing of server in progress as process 57766
2023-12-26T08:49:43.231426Z 1 [System] [MY-013576] [InnoDB] InnoDB initialization has started.
2023-12-26T08:49:43.579789Z 1 [System] [MY-013577] [InnoDB] InnoDB initialization has ended.
2023-12-26T08:49:45.083767Z 6 [Note] [MY-010454] [Server] A temporary password is generated for root@localhost: otVyge;=q7eY
[root@master ~]# echo 'otVyge;=q7eY' > pass
[root@master ~]# cat pass
otVyge;=q7eY12.向配置文件添加内容
[root@master ~]# vim /etc/my.cnf
[root@master ~]# cat /etc/my.cnf
[mysqld]
basedir = /usr/local/mysql
datadir = /opt/data
port = 3306
socket = /tmp/mysql.sock
pid-file = /opt/data/mysql.pid
user = mysql
skip-name-resolve13.给mysql服务指定位置
[root@master ~]# cd /usr/local/mysql
[root@master mysql]# ls
bin  docs  include  lib  LICENSE  man  README  share  support-files
[root@master mysql]# cd support-files/
[root@master support-files]# ls
mysqld_multi.server  mysql-log-rotate  mysql.server
[root@master support-files]# vim mysql.server 
[root@master support-files]# cat mysql.server | grep '^datadir'
datadir=/opt/data
datadir_set=
[root@master support-files]# cat mysql.server | grep '^basedir'
basedir=/usr/local/mysql
[root@master support-files]# systemctl daemon-reload14.启动服务
[root@master support-files]# service mysqld start
Starting MySQL.Logging to '/opt/data/master.err'.SUCCESS! 
[root@master support-files]# ss -antl
State              Recv-Q             Send-Q                          Local Address:Port                            Peer Address:Port             Process             
LISTEN             0                  128                                   0.0.0.0:22                                   0.0.0.0:*                                    
LISTEN             0                  70                                          *:33060                                      *:*                                    
LISTEN             0                  151                                         *:3306                                       *:*                                    
LISTEN             0                  128                                      [::]:22                                      [::]:*                                    15.设置开机自启
[root@master ~]# cd /usr/lib/systemd/system
[root@master system]# cp sshd.service mysql.service
[root@master system]# vim mysql.service
[root@master system]# cat mysql.service 
[Unit]
Description=mysql server daemon
After=network.target sshd-keygen.target[Service]
Type=forking
ExecStart=service mysqld start
ExecStop=service mysqld stop
ExecReload=/bin/kill -HUP $MAINPID[Install]
WantedBy=multi-user.target
[root@master system]# service mysqld stop
Shutting down MySQL.ss. SUCCESS! 
[root@master system]# systemctl daemon-reload
[root@master system]# systemctl status mysql
○ mysql.service - mysql server daemonLoaded: loaded (/usr/lib/systemd/system/mysql.service; disabled; preset: disabled)Active: inactive (dead)
[root@master system]# systemctl enable --now mysql
Created symlink /etc/systemd/system/multi-user.target.wants/mysql.service → /usr/lib/systemd/system/mysql.service.
[root@master system]# systemctl status mysql
● mysql.service - mysql server daemonLoaded: loaded (/usr/lib/systemd/system/mysql.service; enabled; preset: disabled)Active: active (running) since Tue 2023-12-26 17:06:55 CST; 7s agoProcess: 99845 ExecStart=service mysqld start (code=exited, status=0/SUCCESS)Main PID: 99862 (mysqld_safe)Tasks: 39 (limit: 10820)Memory: 371.5MCPU: 829msCGroup: /system.slice/mysql.service├─ 99862 /bin/sh /usr/local/mysql/bin/mysqld_safe --datadir=/opt/data --pid-file=/opt/data/mysql.pid└─100052 /usr/local/mysql/bin/mysqld --basedir=/usr/local/mysql --datadir=/opt/data --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=ma>Dec 26 17:06:53 master systemd[1]: Starting mysql server daemon...
Dec 26 17:06:55 master service[99849]: Starting MySQL. SUCCESS!
Dec 26 17:06:55 master systemd[1]: Started mysql server daemon.16.修改数据库密码
[root@master ~]# cat pass
otVyge;=q7eY
[root@master ~]# mysql -uroot -p'otVyge;=q7eY'
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 8.0.35Copyright (c) 2000, 2023, Oracle and/or its affiliates.Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql> alter user root@localhost identified with mysql_native_password by 'Passw0rd@_~';
Query OK, 0 rows affected (0.00 sec)
mysql> quit
Bye
[root@master ~]# mysql -uroot -p'Passw0rd@_~'
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 11
Server version: 8.0.35 MySQL Community Server - GPLCopyright (c) 2000, 2023, Oracle and/or its affiliates.Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.01 sec)

3.2 mysql主从配置

3.2.1 确保从数据库与主数据库里的数据一样

为确保从数据库与主数据库里的数据一样，先全备主数据库并还原到从数据库中

//先查看主库有哪些库
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.00 sec)//再查看从库有哪些库
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.00 sec)

3.2.2 在主数据库里创建一个同步账号授权给从数据库使用

[root@master ~]# mysql -uroot -pPassw0rd@_~
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 12
Server version: 8.0.35 MySQL Community Server - GPLCopyright (c) 2000, 2023, Oracle and/or its affiliates.Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql> create user repl@192.168.116.143 identified with mysql_native_password by 'Passw0rd@_~';
Query OK, 0 rows affected (0.01 sec)mysql> grant replication slave on *.* to repl@192.168.116.143-> ;
Query OK, 0 rows affected (0.00 sec)mysql> flush privileges-> ;
Query OK, 0 rows affected (0.01 sec)//到slave主机登入
[root@slave ~]# mysql -urepl -pPassw0rd@_~ -h192.168.116.140
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 11
Server version: 8.0.35 MySQL Community Server - GPLCopyright (c) 2000, 2023, Oracle and/or its affiliates.Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql> 

3.2.3 配置主数据库

[root@master ~]# vim /etc/my.cnf
[root@master ~]# cat /etc/my.cnf
[mysqld]
basedir = /usr/local/mysql
datadir = /opt/data
port = 3306
socket = /tmp/mysql.sock
pid-file = /opt/data/mysql.pid
user = mysql
skip-name-resolvelog-bin = mysql_bin
server-id = 10
[root@master ~]# systemctl restart mysql
[root@master ~]# ss -antl
State              Recv-Q             Send-Q                          Local Address:Port                            Peer Address:Port             Process             
LISTEN             0                  128                                   0.0.0.0:22                                   0.0.0.0:*                                    
LISTEN             0                  70                                          *:33060                                      *:*                                    
LISTEN             0                  151                                         *:3306                                       *:*                                    
LISTEN             0                  128                                      [::]:22                                      [::]:*               //查看主库的状态
mysql> show master status;
+------------------+----------+--------------+------------------+-------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+-------------------+
| mysql_bin.000001 |      157 |              |                  |                   |
+------------------+----------+--------------+------------------+-------------------+
1 row in set (0.00 sec)

3.2.4 配置从数据库

[root@slave ~]# vim /etc/my.cnf
[root@slave ~]# cat /etc/my.cnf
[mysqld]
basedir = /usr/local/mysql
datadir = /opt/data
port = 3306
socket = /tmp/mysql.sock
pid-file = /opt/data/mysql.pid
user = mysql
skip-name-resolverelay-log = mysql_relay_bin
server-id = 20
[root@slave ~]# systemctl restart mysql
[root@slave ~]# ss -antl
State              Recv-Q             Send-Q                          Local Address:Port                            Peer Address:Port             Process             
LISTEN             0                  128                                   0.0.0.0:22                                   0.0.0.0:*                                    
LISTEN             0                  128                                      [::]:22                                      [::]:*                                    
LISTEN             0                  151                                         *:3306                                       *:*                                    
LISTEN             0                  70                                          *:33060                                      *:*                                    //配置并启动主从复制
mysql> change master to-> master_host='192.168.116.140',-> master_user='repl',-> master_password='Passw0rd@_~',-> master_port=3306,-> master_log_file='mysql_bin.000001',-> master_log_pos=157;
Query OK, 0 rows affected, 9 warnings (0.02 sec)mysql> start slave-> ;
Query OK, 0 rows affected, 1 warning (0.01 sec)//查看从服务器状态
mysql> show slave status\G
*************************** 1. row ***************************Slave_IO_State: Waiting for source to send eventMaster_Host: 192.168.116.140Master_User: replMaster_Port: 3306Connect_Retry: 60Master_Log_File: mysql_bin.000001Read_Master_Log_Pos: 157Relay_Log_File: mysql_relay_bin.000002Relay_Log_Pos: 326Relay_Master_Log_File: mysql_bin.000001Slave_IO_Running: YesSlave_SQL_Running: YesReplicate_Do_DB: Replicate_Ignore_DB: Replicate_Do_Table: Replicate_Ignore_Table: Replicate_Wild_Do_Table: Replicate_Wild_Ignore_Table: Last_Errno: 0Last_Error: Skip_Counter: 0Exec_Master_Log_Pos: 157Relay_Log_Space: 536Until_Condition: NoneUntil_Log_File: Until_Log_Pos: 0Master_SSL_Allowed: NoMaster_SSL_CA_File: Master_SSL_CA_Path: Master_SSL_Cert: Master_SSL_Cipher: Master_SSL_Key: Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: NoLast_IO_Errno: 0Last_IO_Error: Last_SQL_Errno: 0Last_SQL_Error: Replicate_Ignore_Server_Ids: Master_Server_Id: 10Master_UUID: b6998aa8-a3cb-11ee-900f-000c29ed2b10Master_Info_File: mysql.slave_master_infoSQL_Delay: 0SQL_Remaining_Delay: NULLSlave_SQL_Running_State: Replica has read all relay log; waiting for more updatesMaster_Retry_Count: 86400Master_Bind: Last_IO_Error_Timestamp: Last_SQL_Error_Timestamp: Master_SSL_Crl: Master_SSL_Crlpath: Retrieved_Gtid_Set: Executed_Gtid_Set: Auto_Position: 0Replicate_Rewrite_DB: Channel_Name: Master_TLS_Version: Master_public_key_path: Get_master_public_key: 0Network_Namespace: 
1 row in set, 1 warning (0.00 sec)

3.2.5 测试验证

在主服务器创建库并创建表，向表中插入数据：

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
4 rows in set (0.01 sec)mysql> create database student;
Query OK, 1 row affected (0.01 sec)mysql> use student;
Database changed
mysql> create table hl(id int not null,name varchar(20));
Query OK, 0 rows affected (0.02 sec)mysql> desc hl;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int         | NO   |     | NULL    |       |
| name  | varchar(20) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.01 sec)
mysql> insert hl(id,name) value(1,'tom'),(2,'jerry');
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0mysql> select * from hl;
+----+-------+
| id | name  |
+----+-------+
|  1 | tom   |
|  2 | jerry |
+----+-------+
2 rows in set (0.00 sec)

在从数据库中查看数据是否同步：

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| student            |
| sys                |
+--------------------+
5 rows in set (0.01 sec)mysql> select * from student.hl;
+----+-------+
| id | name  |
+----+-------+
|  1 | tom   |
|  2 | jerry |
+----+-------+
2 rows in set (0.00 sec)