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

3.1主从复制配置步骤：

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

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
[root@localhost ~]# 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 |

+--------------------+



//再查看从库有哪些库
[root@localhost ~]# 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 (0.14 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@localhost ~]# mysqldump -uroot -p123456 --all-databases > /opt/all-20191224.sql
mysqldump: [Warning] Using a password on the command line interface can be insecure.

[root@localhost ~]# ls /opt/

all-20191224.sql data

[root@localhost ~]# scp /opt/all-20191224.sql root@192.168.136.145:/opt/

root@192.168.136.145's password: 

all-20191224.sql 100% 782KB 2.7MB/s 00:00  



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



//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@localhost ~]# mysql -uroot -p123456 < /opt/all-20191224.sql 
mysql: [Warning] Using a password on the command line interface can be insecure.

[root@localhost ~]# 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 |

+--------------------+

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

mysql> CREATE USER 'repl'@'192.168.136.145' IDENTIFIED BY '123456';
Query OK, 0 rows affected (0.03 sec)

mysql> GRANT REPLICATION SLAVE ON *.* TO 'repl'@'192.168.136.145';
Query OK, 0 rows affected (0.00 sec)

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

3.2.3 配置主数据库

[root@localhost ~]# vim /etc/my.cnf

[mysqld]
basedir = /usr/local/mysql
datadir = /opt/data
socket = /tmp/mysql.sock
port = 3306
pid-file = /opt/data/mysql.pid
user = mysql
skip-name-resolve
log-bin=mysql-bin   
server-id=1 

//重启mysql服务
[root@localhost ~]# vim /etc/my.cnf
[root@localhost ~]# service mysqld restart
Shutting down MySQL.. SUCCESS! 
Starting MySQL.... SUCCESS! 
[root@localhost ~]# ss -antl
State Recv-Q Send-Q Local Address:Port Peer Address:Port              
LISTEN 0 128 *:22 *:*                  
LISTEN 0 100 127.0.0.1:25 *:*                  
LISTEN 0 128 :::22 :::*                  
LISTEN 0 100 ::1:25 :::*                  
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)

3.2.4 配置从数据库

[root@localhost ~]# vim /etc/my.cnf

[mysqld]
basedir = /usr/local/mysql
datadir = /opt/data
socket = /tmp/mysql.sock
port = 3306
pid-file = /opt/data/mysql.pid
user = mysql
skip-name-resolve
server-id=2     
relay-log=mysql-relay-bin

//重启从库的mysql服务
[root@localhost ~]# vim /etc/my.cnf
[root@localhost ~]# service mysqld restart
Shutting down MySQL.. SUCCESS! 
Starting MySQL........................... SUCCESS! 
[root@localhost ~]# ss -antl
State Recv-Q Send-Q Local Address:Port Peer Address:Port              
LISTEN 0 128 *:22 *:*                  
LISTEN 0 100 127.0.0.1:25 *:*                  
LISTEN 0 128 *:10050 *:*                  
LISTEN 0 25 *:514 *:*                  
LISTEN 0 128 :::22 :::*                  
LISTEN 0 100 ::1:25 :::*                  
LISTEN 0 25 :::514 :::*                  
LISTEN 0 80 :::3306 :::*      

//配置并启动主从复制
mysql> CHANGE MASTER TO
    -> MASTER_HOST='192.168.136.144',
    -> MASTER_USER='repl',
    -> MASTER_PASSWORD='123456',
    -> MASTER_LOG_FILE='mysql-bin.000001',
    -> MASTER_LOG_POS=154;
Query OK, 0 rows affected, 2 warnings (0.05 sec)

mysql> start slave;
Query OK, 0 rows affected (0.04 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: 192.168.136.144
                  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: 
          Replicate_Ignore_DB: 
           Replicate_Do_Table: 
       Replicate_Ignore_Table: 
      Replicate_Wild_Do_Table: 
  Replicate_Wild_Ignore_Table: 
                   Last_Errno: 0
                   Last_Error: 
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 154
              Relay_Log_Space: 527
              Until_Condition: None
               Until_Log_File:

3.2.5 测试验证

在主服务器的student库的student表中插入数据：

mysql> create database student;

Query OK, 1 row affected (0.03 sec)



mysql> use student;

Database changed

mysql> create table student (id int not null,name varchar(100) not null,age tinyint);

Query OK, 0 rows affected (0.09 sec)



mysql> insert into student (id,name,age) value (1,'tom',20);

Query OK, 1 row affected (0.16 sec)



mysql> select * from student;

+----+------+------+

| id | name | age |

+----+------+------+

| 1 | tom | 20 |

+----+------+------+

1 row 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 (0.00 sec)



mysql> use student;

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> show tables;

+-------------------+

| Tables_in_student |

+-------------------+

| student |

+-------------------+

1 row in set (0.00 sec)



mysql> select * from student;

+----+------+------+

| id | name | age |

+----+------+------+

| 1 | tom | 20 |

+----+------+------+

1 row in set (0.00 sec)