mysql主从

1. 主从简介

为了解决以下典型两个问题，我们导入主从学习

• 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： 搭建三台MySQL服务器，一台作为主服务器，其它两台作为从服务器（其中一项主从为主库中存有数据，另一项主库中没有数据），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	192.168.56.20	centos7/redhat7 mysql-5.7	先没有数据，后面创建数据
从数据库	192.168.56.22	centos7/redhat7 mysql-5.7	无数据
从数据库	192.168.56.23	centos7/redhat7 mysql-5.7	无数据

3.1 mysql安装

分别在主从三台服务器上安装mysql-5.7版本

安装主服务器（192.168.56.20）

//解压安装包至/usr/local下
[root@20liuzhenchao ~]# tar xf mysql-5.7.22-linux-glibc2.12-x86_64.tar.gz -C /usr/local/

//创建用户和组
[root@20liuzhenchao ~]# groupadd -r mysql
[root@20liuzhenchao ~]# useradd -M -s /sbin/nologin -g mysql mysql

//创建软链接并修改/usr/local/mysql目录属组
[root@20liuzhenchao local]# ln -sv mysql-5.7.22-linux-glibc2.12-x86_64/ mysql
"mysql" -> "mysql-5.7.22-linux-glibc2.12-x86_64/"
[root@20liuzhenchao local]# chown -R mysql.mysql mysql*
[root@20liuzhenchao local]# ll |grep mysql
lrwxrwxrwx   1 mysql mysql       36 5月  15 22:55 mysql -> mysql-5.7.22-linux-glibc2.12-x86_64/
drwxr-xr-x   9 mysql mysql      129 5月  15 22:46 mysql-5.7.22-linux-glibc2.12-x86_64

//添加环境变量
[root@20liuzhenchao local]# echo 'export PATH=/usr/local/mysql/bin:$PATH' > /etc/profile.d/mysql.sh
[root@20liuzhenchao local]# . /etc/profile.d/mysql.sh

//建立数据存放目录
[root@20liuzhenchao ~]# mkdir /opt/data
[root@20liuzhenchao ~]# chown -R mysql.mysql /opt/data
[root@20liuzhenchao ~]# ll /opt/data -d
drwxr-xr-x 2 mysql mysql 6 5月  15 23:02 /opt/data

//初始化数据库
[root@20liuzhenchao ~]# mysqld --initialize --user=mysql --datadir=/opt/data
2019-05-15T15:04:16.463631Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2019-05-15T15:04:16.837927Z 0 [Warning] InnoDB: New log files created, LSN=45790
2019-05-15T15:04:16.899304Z 0 [Warning] InnoDB: Creating foreign key constraint system tables.
2019-05-15T15:04:17.011781Z 0 [Warning] No existing UUID has been found, so we assume that this is the first time that this server has been started. Generating a new UUID: b58e7a1c-7722-11e9-b5d5-000c29fc116c.
2019-05-15T15:04:17.012413Z 0 [Warning] Gtid table is not ready to be used. Table 'mysql.gtid_executed' cannot be opened.
2019-05-15T15:04:17.013201Z 1 [Note] A temporary password is generated for root@localhost: e88-hL,1?YRT//此处临时密码为:e88-hL,1?YRT

//修改配置文件
[root@20liuzhenchao ~]# vim /etc/my.cnf
[mysqld]
datadir=/opt/data
socket=/tmp/mysql.sock


//配置服务启动脚本
[root@20liuzhenchao ~]# cp -a /usr/local/mysql/support-files/mysql.server /etc/init.d/mysqld
[root@20liuzhenchao ~]# sed -ri 's#^(basedir=).*#1/usr/local/mysql#g' /etc/init.d/mysqld
[root@20liuzhenchao ~]# sed -ri 's#^(datadir=).*#1/opt/data#g' /etc/init.d/mysqld

//启动mysql
[root@20liuzhenchao ~]# service mysqld start
Starting MySQL. SUCCESS! 
[root@20liuzhenchao ~]# ss -antl|grep 3306
LISTEN     0      80          :::3306                    :::* 

//修改密码
[root@20liuzhenchao ~]# mysql -uroot -p'e88-hL,1?YRT' -e 'set password=password("liu123!");' --connect-expired-password
mysql: [Warning] Using a password on the command line interface can be insecure.

从服务器（192.168.56.22 和 192.168.56.23）的安装和上类似，此处略

3.2 mysql主从配置之主、从数据库均为初始化，没有数据

主数据没有数据——从数据库（192.168.56.22）与主数据库（192.168.56.20）均为初始化状态

3.2.1 在主数据库里创建一个同步账号授权给从数据库使用

mysql> create user 'repl'@'192.168.56.22' identified by 'liu123!';
Query OK, 0 rows affected (0.00 sec)

mysql> grant replication slave on *.* to 'repl'@'192.168.56.22';
Query OK, 0 rows affected (0.00 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

3.2.2 配置主数据库

[root@20liuzhenchao ~]# vim /etc/my.cnf
[mysqld]
datadir=/opt/data
socket=/tmp/mysql.sock
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
//添加下面两行
log-bin=mysql-bin //启用binlog日志
server-id=1 //数据库服务器唯一标识符，主库的server-id值必须比从库的小

//重启mysql服务
[root@20liuzhenchao ~]# service mysqld restart
Shutting down MySQL.. SUCCESS! 
Starting MySQL. SUCCESS! 
[root@20liuzhenchao ~]# ss -antl |grep 3306
LISTEN     0      80          :::3306                    :::* 

//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 |      154 |              |                  |                   |
+------------------+----------+--------------+------------------+-------------------+
1 row in set (0.00 sec)

mysql>

3.2.3 配置从数据库

[root@22liuzhenchao ~]# vim /etc/my.cnf
[mysqld]
datadir=/opt/data
socket=/tmp/mysql.sock
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
//添加下面两行
server-id=2 //设置从库的唯一标识符，从库的server-id值必须大于主库的该值
relay-log=mysql-relay-bin //启用中继日志relay-log

//重启从库的mysql服务
[root@22liuzhenchao ~]# service mysqld restart
Shutting down MySQL.. SUCCESS! 
Starting MySQL. SUCCESS!
[root@22liuzhenchao ~]# ss -antl|grep 3306
LISTEN     0      80          :::3306                    :::* 

//配置并启动主从复制
mysql> change master to master_host='192.168.56.20',master_user='repl',master_password='liu123!',master_log_file='mysql-bin.000001',master_log_pos=154;
Query OK, 0 rows affected, 2 warnings (0.01 sec)

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

//查看从服务器状态
mysql> show slave status G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 192.168.56.20
                  Master_User: repl
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000001
          Read_Master_Log_Pos: 154
               Relay_Log_File: mysql-relay-bin.000002
                Relay_Log_Pos: 320
        Relay_Master_Log_File: mysql-bin.000001
             Slave_IO_Running: Yes //此处必须为Yes
            Slave_SQL_Running: Yes //此处必须为Yes
              Replicate_Do_DB:

3.2.4 测试验证

在主服务器中创建库liuzhenchao,并插入表student

mysql> create database liuzhenchao;
Query OK, 1 row affected (0.00 sec)

mysql> use liuzhenchao;
Database changed
mysql> create table student(id int(10) not null,name varchar(50) not null);
Query OK, 0 rows affected (0.01 sec)

mysql> insert student values(1,'zhangshan'),(2,'lisi'),(3,'wangwu');
Query OK, 3 rows affected (0.03 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from student;
+----+-----------+
| id | name      |
+----+-----------+
|  1 | zhangshan |
|  2 | lisi      |
|  3 | wangwu    |
+----+-----------+
3 rows in set (0.00 sec)

在从数据库中查看数据是否同步：

mysql> select * from liuzhenchao.student;
+----+-----------+
| id | name      |
+----+-----------+
|  1 | zhangshan |
|  2 | lisi      |
|  3 | wangwu    |
+----+-----------+
3 rows in set (0.00 sec)

3.3 mysql主从配置之主数据库有数据

主数据库中有数据——从数据库（192.168.56.23）为初始化状态；主数据库（192.168.56.20）中有创建的数据

3.3.1 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
[root@20liuzhenchao ~]# mysql -uroot -p'liu123!' -e 'show databases;'
mysql: [Warning] Using a password on the command line interface can be insecure.
+--------------------+
| Database           |
+--------------------+
| information_schema |
| liuzhenchao        |
| mysql              |
| performance_schema |
| sys                |
+--------------------+


//再查看从库有哪些库
[root@23liuzhenchao ~]# mysql -uroot -p'liu123!' -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@20liuzhenchao ~]# mysqldump -uroot -p'liu123!' --all-databases > /opt/all-201905151640.sql
mysqldump: [Warning] Using a password on the command line interface can be insecure.
[root@20liuzhenchao ~]# ls /opt |grep all
all-201905151640.sql
[root@20liuzhenchao ~]# scp /opt/all-201905151640.sql root@192.168.56.23:/opt/
root@192.168.56.23's password: 
all-201905151640.sql                                                                                                   100%  784KB  13.2MB/s   00:00 

//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@23liuzhenchao ~]# mysql -uroot -p'liu123!' < /opt/all-201905151640.sql 
mysql: [Warning] Using a password on the command line interface can be insecure.
[root@23liuzhenchao ~]# mysql -uroot -p'liu123!' -e 'show databases;'
mysql: [Warning] Using a password on the command line interface can be insecure.
+--------------------+
| Database           |
+--------------------+
| information_schema |
| liuzhenchao        |
| mysql              |
| performance_schema |
| sys                |
+--------------------+

//解除主库的锁表状态，直接退出交互式界面即可
mysql> quit
Bye

3.3.2 在主数据库里创建一个同步账号授权给从数据库使用

mysql> grant replication slave on *.* to 'repl'@'192.168.56.23' identified by 'liu123!';
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

3.3.3 配置主数据库

//重启mysql服务
[root@20liuzhenchao ~]# service mysqld restart
Shutting down MySQL............ SUCCESS! 
Starting MySQL. SUCCESS! 
[root@20liuzhenchao ~]# ss -antl|grep 3306
LISTEN     0      80          :::3306                    :::*  

//查看主库的状态
mysql> show master status;
+------------------+----------+--------------+------------------+-------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+-------------------+
| mysql-bin.000002 |      154 |              |                  |                   |
+------------------+----------+--------------+------------------+-------------------+
1 row in set (0.00 sec)

3.3.4 配置从数据库

[root@23liuzhenchao ~]# vim /etc/my.cnf
[mysqld]
datadir=/opt/data
socket=/tmp/mysql.sock
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
//添加如下内容
relay-log=mysql-relay-bin
server-id=3

//重启从库的mysql服务
[root@23liuzhenchao ~]# service mysqld restart
Shutting down MySQL.. SUCCESS! 
Starting MySQL. SUCCESS! 
[root@23liuzhenchao ~]# ss -antl|grep 3306
LISTEN     0      80          :::3306                    :::*  

//配置并启动主从复制
mysql> change master to master_host='192.168.56.20',master_user='repl',master_password='liu123!',master_log_file='mysql-bin.000002',master_log_pos=154;
Query OK, 0 rows affected, 2 warnings (0.30 sec)

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

//查看从服务器状态
mysql> show slave statusG
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 192.168.56.20
                  Master_User: repl
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000002
          Read_Master_Log_Pos: 154
               Relay_Log_File: mysql-relay-bin.000002
                Relay_Log_Pos: 320
        Relay_Master_Log_File: mysql-bin.000002
             Slave_IO_Running: Yes //此处必须为yes
            Slave_SQL_Running: Yes //此处必须为yes

3.3.5 测试验证

在主服务器的liuzhenchao.student表中插入数据：

mysql> use liuzhenchao;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> insert student values(4,'liu'),(5,'zhen'),(6,'chao');
Query OK, 3 rows affected (0.01 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from student;
+----+-----------+
| id | name      |
+----+-----------+
|  1 | zhangshan |
|  2 | lisi      |
|  3 | wangwu    |
|  4 | liu       |
|  5 | zhen      |
|  6 | chao      |
+----+-----------+
6 rows in set (0.00 sec)

在从数据库中查看数据是否同步：

mysql> select * from liuzhenchao.student;
+----+-----------+
| id | name      |
+----+-----------+
|  1 | zhangshan |
|  2 | lisi      |
|  3 | wangwu    |
|  4 | liu       |
|  5 | zhen      |
|  6 | chao      |
+----+-----------+
6 rows in set (0.00 sec)