MySQL之主从复制

概述：

将主库的数据变更同步到从库，从而保证主库和从库数据一致。

它的作用是数据备份，失败迁移，读写分离，降低单库读写压力

原理：

主服务器上面的任何修改都会保存在二进制日志（ Bin-log日志）里面。从服务器上面启动一个I/O线程，连接到主服务器上面请求读取二进制（Bin-log）日志，然后把读取到的二进制日志写到本地的Realy-log（中继日志）里面。从服务器上面同时开启一个SQL线程，读取Realy-log（中继日志），如果发现有更新立即把更新的内容在本机的数据库上面执行一遍。

搭建：

1.准备服务器

2.配置主库

3.配置从库

4.测试主从复制

实践

1.首先准备俩台安装MySQL的纯净服务器

主库：192.168.231.153

从库：192.168.231.136

关闭防火墙与selinux

2.配置主库：

编辑主库服务器的配置文件 /etc/my.cnf

[mysqld]
log-bin=/var/log/mysql/mysql-bin       #启用二进制文件日志记录
server-id=1          # 服务id，保证整个集群环境唯一
read-only=0         #1是只读，0是读写

创建日志目录并赋予权限

# mkdir /var/log/mysql
# chown mysql.mysql /var/log/mysql

重启服务

# systemctl restart mysqld

在主库登录MySQL，创建用户

为了用户在从库中用来连接主库的账号

mysql>  create user '用户名'@'ip' identified with mysql_native_password by '密码'；mysql>  grant replication slave on *.* to '用户名'@'ip'  
这是为用户分配主从复制的权限

查看二进制日志坐标

mysql> show master status;
+------------------+----------+--------------+------------------+-------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+-------------------+
| mysql-bin.000001 |      313 |              |                  |                   |
+------------------+----------+--------------+------------------+-------------------+
1 row in set (0.00 sec)

3.配置从库

编辑从库服务器的配置文件my.cnf

[mysqld]
server-id=2
read-only=1     #普通用户一般只有只读

重启mysql服务

# systemctl restart mysqld

登录mysql

此处登录的是你从库mysql的root用户登录的账号与密码，不是在主库创建的用户

mysql>  change master to master_host='主库的ip'，master_user='连接主库用户名',master_password='连接主库用户的密码',master_log_file='日志文件名',mastre_log_pos='日志位置';日志位置就是在主库show master status查出来那个数字   ----313+------------------+----------+--------------+------------------+-------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+-------------------+
| mysql-bin.000001 |      313 |              |                  |                   |
+------------------+----------+--------------+------------------+-------------------+

启动：

mysql> start slave;

查看主从同步状态：

mysql> show slave status\G*************************** 1. row ***************************Slave_IO_State: Waiting for master to send eventMaster_Host: 192.168.231.153   -----主库的ipMaster_User: itcast     -----用来连接主库的用户名   Master_Port: 3306  ------端口Connect_Retry: 60Master_Log_File: mysql-bin.000001          -----二进制日志名字Read_Master_Log_Pos: 313Relay_Log_File: congku-relay-bin.000002   -----中继日志名字Relay_Log_Pos: 479Relay_Master_Log_File: mysql-bin.000001Slave_IO_Running: Yes         --------主要看俩个IO线程是否成功启动Slave_SQL_Running: Yes         --------看SQL线程是否成功启动Replicate_Do_DB: Replicate_Ignore_DB: Replicate_Do_Table: Replicate_Ignore_Table:

4.测试主从复制

主库！
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| company            |
| db1                |
| mysql              |
| performance_schema |
| school             |
| sys                |
| xian               |
+--------------------+
8 rows in set (0.00 sec)从库：
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| xian               |
+--------------------+
5 rows in set (0.00 sec)

这是因为配置主从复制是在主库已经存在这些库以后配置的

!!!!在主库创建库，创建表，写入数据
mysql> create database db2;
mysql> create table db2.zhucong(id int,name varchar(50),age int);mysql> insert into zhucong(id,name,age) values(1,'aaa',18),values(2,'bbb',19) ,(3,'ccc',20);mysql> select * from zhucong;
+------+------+------+
| id   | name | age  |
+------+------+------+
|    1 | aaa  |   18 |
|    2 | bbb  |   19 |
|    3 | ccc  |   20 |
+------+------+------+
3 rows in set (0.00 sec)!!!在从库查看
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| db2                |
| mysql              |
| performance_schema |
| sys                |
| xian               |
+--------------------+mysql> use db2;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -ADatabase changed
mysql> show tables;
+---------------+
| Tables_in_db2 |
+---------------+
| zhucong       |
+---------------+
1 row in set (0.00 sec)mysql> select * from zhucong;
+------+------+------+
| id   | name | age  |
+------+------+------+
|    1 | aaa  |   18 |
|    2 | bbb  |   19 |
|    3 | ccc  |   20 |
+------+------+------+

修改主库中的表数据，查看从库是否有变化

主库：
mysql> update zhucong set age=21;
Query OK, 3 rows affected (0.00 sec)
Rows matched: 3  Changed: 3  Warnings: 0mysql> select * from zhucong;
+------+------+------+
| id   | name | age  |
+------+------+------+
|    1 | aaa  |   21 |
|    2 | bbb  |   21 |
|    3 | ccc  |   21 |
+------+------+------+
3 rows in set (0.00 sec)查看从库：
mysql> select * from zhucong;
+------+------+------+
| id   | name | age  |
+------+------+------+
|    1 | aaa  |   21 |
|    2 | bbb  |   21 |
|    3 | ccc  |   21 |
+------+------+------+
3 rows in set (0.00 sec)