1. 主从原理

1.1 主从介绍

所谓 mysql 主从就是建立两个完全一样的数据库，其中一个为主要使用的数据库，另一个为次要的数据库，一般在企业中，存放比较重要的数据的数据库服务器需要配置主从，这样可以防止因数据库服务器宕机导致数据丢失，还能保证业务量太多、数据太多和访问人数太多时服务的质量（服务器响应速度），还能提供故障切换、读写分离、和备份等等功能

1.2 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

1.3 主从形式

一主一从

主主复制：作为备份，当主服务器出现故障时，另一个主服务器会自动充值。

一主多从：实现读写分离，写操作少，读操作多，主服务器实现写操作，从服务器实现读操作。

多主一备：用于实现读写分离，在写操作多、读操作少的情况下，主服务器实现写操作，从服务器实现读操作。5.7启动支持

联级复制：是指从主场地复制过来的又从该场地再次复制到其他场地，即 A 场地把数据复制到 B 场地，B 场地又把这些数据或其中部分数据再复制到其他场地。

1.4 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

2. 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    192.168.23.4    Centos7.8 mysql-5.7 有数据
从数据库    192.168.23.5    Centos7.8 mysql-5.7 无数据

2.1 Mysql安装

注意：您需要将安装包上传到两台服务器上，并执行以下命令进行安装。

[root@localhost soft]# yum remove mysql-libs
[root@localhost soft]# rpm -qa | grep mariadb

进行安装

将下载好的mysql-5.7.22-1.el7.x86_64.rpm-bundle.tar上传

安装相应软件
[root@localhost soft]# yum install -y openssl-devel.x86_64 openssl.x86_64 yum install -y libaio.x86_64 libaio-devel.x86_64 yum install -y perl.x86_64 perl-devel.x86_64 yum install -y perl-JSON.noarch yum install -y autoconf yum install -y wget yum install -y net-tools

关闭防火墙
[root@localhost soft]# systemctl stop firewalld
[root@localhost soft]# systemctl disable firewalld

解压软件包：
[root@localhost soft]# tar -xvf mysql-5.7.22-1.el7.x86_64.rpm-bundle.tar

[root@localhost soft]# rpm -ivh mysql-community-common-5.7.22-1.el7.x86_64.rpm
[root@localhost soft]# rpm -ivh mysql-community-libs-5.7.22-1.el7.x86_64.rpm
[root@localhost soft]# rpm -ivh mysql-community-client-5.7.22-1.el7.x86_64.rpm
[root@localhost soft]# rpm -ivh mysql-community-server-5.7.22-1.el7.x86_64.rpm
[root@localhost soft]# rpm -ivh mysql-community-libs-compat-5.7.22-1.el7.x86_64.rpm
[root@localhostsoft]#rpm -ivh mysql-community-embedded-compat-5.7.22-1.el7.x86_64.rpm
[root@localhost soft]# rpm -ivh mysql-community-devel-5.7.22-1.el7.x86_64.rpm
[root@localhost soft]# rpm -ivh mysql-community-test-5.7.22-1.el7.x86_64.rpm
查看安装版本：
[root@localhost soft]# mysql -V

编辑配置文件

vim /etc/my.cnf

跳过登录验证 无需密码即可登录mysql

skip-grant-tables

设置默认字符集UTF-8

character_set_server=utf8

collation-server=utf8_general_ci

设置默认字符集UTF-8

init_connect=’SET NAMES utf8′

将数据库日志的过期天数设置为14天

server_id=1

expire_logs_days=14

[client]

default-character-set=utf8

##添加
skip-grant-tables
character_set_server=utf8
collation-server=utf8_general_ci
init_connect='SET NAMES utf8'
server_id=1
expire_logs_days=14
[client]
default-character-set=utf8

启动mysql
[root@localhost soft]# systemctl start mysqld.service
[root@localhost soft]# systemctl status mysqld

获取mysql的root用户的初始密码
[root@localhost soft]# grep 'temporary password' /var/log/mysqld.log

以获取mysql的root用户的初始密码登录数据库
[root@localhost soft]# mysql -u root -pAcqWlI64o:kG

修改root密码
mysql> flush privileges;
mysql> set password for root@localhost=password('123456');
使密码即时生效
mysql> flush privileges;
允许以root身份远程登录mysql
mysql> grant all privileges on *.* to root@'%' identified by "123456";
mysql> flush privileges;

2.2 mysql 主从配置

2.2.1 确保从数据库于主数据库的数据一样

为了确保备库与主库中的数据一致，需要充分准备好主库，并将其恢复到备库中

//主库为master
[root@localhost ~]# hostnamectl set-hostname master
[root@localhost ~]# bash
[root@master ~]#

//从库为slave
[root@localhost ~]# hostnamectl set-hostname slave
[root@localhost ~]# bash
[root@slave ~]#

//先查看主库有哪些库
[root@master soft]# mysql -uroot -p123456 -e‘show databases;'
mysql: [Warning] Using a password on the command line interface can be insecure.

+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| test               |
+--------------------+
//在查看从库
[root@slave soft]# mysql -uroot -p123456 -e‘show databases;'
mysql: [Warning] Using a password on the command line interface can be insecure.

+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+

//全备主库 //全备主库时需要另开一个终端，给数据库加上读锁，避免在备份期间有其他人在写入导致数据不一致

mysql> flush tables with read lock;
Query OK, 0 rows affected (0.00 sec)
//此锁表的终端必须在备份完成以后才能退出

//备份主库并将备份文件传送到从库
[root@master soft]# mysqldump -uroot -p123456 --all-databases > /opt/acc-2022.sql;
mysqldump: [Warning] Using a password on the command line interface can be insecure.

[root@master ~]# ls /opt/

[root@master soft]# scp /opt/acc-2022.sql root@192.168.23.5:/opt/

//解除主库的锁表状态，直接退出交互式界面即可
mysql> quit
Bye
[root@master ~]#

//在从库上恢复主库的备份并查看从库有哪些库，确保与主库一致
[root@slave ~]# mysql -uroot -p123456 < /opt/acc-2022.sql
mysql: [Warning] Using a password on the command line interface can be insecure.

[root@slave ~]# mysql -uroot -p123456 -e'show databases';
mysql: [Warning] Using a password on the command line interface can be insecure.

+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| test               |
+--------------------+
[root@slave ~]#

2.2.3 配置主数据库

[root@master soft]# vim /etc/my.cnf
//在[mysql]这段后面添加
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
log-bin=mysql-bin //添加 启用binlog日志
server-id=1  //添加 数据库服务器唯一标识符，主库的server-id值必须比从库的小
Disabling symbolic-links is recommended to prevent assorted security risks symbolic-links=0
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

//重启数主库的mysql服务
[root@master soft]# systemctl restart mysqld
[root@master soft]# ss -anlt
State      Recv-Q Send-Q                              Local Address:Port                                             Peer Address:Port
LISTEN     0      128                                             *:22                                                          *:*
LISTEN     0      128                                          [::]:22                                                       [::]:*
LISTEN     0      80                                           [::]:3306                                                     [::]:*
[root@master soft]#

//查看主库状态
[root@master soft]# mysql -uroot -p123456
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 2
Server version: 5.7.22-log MySQL Community Server (GPL)

Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.

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 master status;
+------------------+----------+--------------+------------------+-------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+-------------------+
| mysql-bin.000001 |      154 |              |                  |                   |
+------------------+----------+--------------+------------------+-------------------+
1 row in set (0.00 sec)

mysql>

2.2.4 配置从数据库

[root@slave ~]# vim /etc/my.cnf
//在[mysql]这段后面添加
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
server-id=2  //添加 从库的server-id比主库的大
relay-log=mysql-relay-bin  //添加
Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

//重启mysql服务
[root@slave ~]# systemctl restart mysqld
[root@slave ~]# ss -anlt
State      Recv-Q Send-Q                              Local Address:Port                                             Peer Address:Port
LISTEN     0      128                                             *:22                                                          *:*
LISTEN     0      128                                          [::]:22                                                       [::]:*
LISTEN     0      80                                           [::]:3306                                                     [::]:*
[root@slave ~]#

//配置并启动主从复制
[root@slave ~]# mysql -u root -p123456
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 2
Server version: 5.7.22 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.

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> change master to
    -> master_host='192.168.23.4',
    -> master_user='hqd',
    -> master_password='123456',
    -> master_log_file='mysql-bin.000001',
    -> master_log_pos=154;
Query OK, 0 rows affected, 2 warnings (0.03 sec)

mysql> start slave;
Query OK, 0 rows affected (0.00 sec)

mysql>
//查看服务器状态
mysql> show slave status \G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 192.168.23.4
                  Master_User: hqd
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000002
          Read_Master_Log_Pos: 154
               Relay_Log_File: mysql-relay-bin.000004
                Relay_Log_Pos: 367
        Relay_Master_Log_File: mysql-bin.000002
             Slave_IO_Running: Yes
            Slave_SQL_Running: Yes
              Replicate_Do_DB:
          Replicate_Ignore_DB:

3 测试验证

在主服务器创建‘hqd’名称的库 查看从服务器是否同步
mysql> create database hqd;
Query OK, 1 row affected (0.00 sec)

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| hqd                |
| mysql              |
| performance_schema |
| sys                |
| test               |
+--------------------+
6 rows in set (0.00 sec)
mysql>

在从数据库中查看数据是否同步
[root@slave ~]# mysql -uroot -p123456
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 5
Server version: 5.7.22 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.

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 |
| hqd                |
| mysql              |
| performance_schema |
| sys                |
| test               |
+--------------------+
6 rows in set (0.00 sec)

mysql>

Original: https://www.cnblogs.com/Jqazc/p/16618696.html
Author: 我真的兔了
Title: Mysql 一主一从