MYSQL主从

一、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、 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

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

3、 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

4、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）

二、配置从数据库

1、环境

两台虚拟机版本为 rocky Linux mysql-5.7，主数据库有数据，从数据库无数据，使用 Xshell 进行连接

mysql搭建：http://t.csdnimg.cn/4dlmU

主数据库：

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| shiqian            |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

mysql> show tables;
+-------------------+
| Tables_in_shiqian |
+-------------------+
| sq                |
+-------------------+
1 row in set (0.00 sec)

mysql> select * from sq;
+----+-------+------+
| id | name  | age  |
+----+-------+------+
|  1 | tom   |   18 |
|  2 | marry |   19 |
|  3 | rose  |   20 |
|  4 | mike  |   19 |
+----+-------+------+
4 rows in set (0.00 sec)

从数据库：

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

2、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 (0.01 sec)

新开一个终端连接到主数据库

[root@mysql ~]# mysqldump -uroot -predhat --all-databases > /opt/all-202408061001.sql
mysqldump: [Warning] Using a password on the command line interface can be insecure.
[root@mysql ~]# ls /opt/
all-202408061001.sql  data  software

//将文件传输到从数据库端
[root@mysql ~]# scp /opt/all-202408061001.sql root@192.168.100.112:/opt/
The authenticity of host '192.168.100.112 (192.168.100.112)' can't be established.
ED25519 key fingerprint is SHA256:qoGezja/t9Hid/DD5+L7baEr1jkiPvJqhdXfVXaJjBo.
This key is not known by any other names
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '192.168.100.112' (ED25519) to the list of known hosts.
root@192.168.100.112's password: 
all-202408061001.sql                                                            100%  856KB  48.0MB/s   00:00    

在这些都做完后，解除主库的锁表状态，直接exit退出数据库即可

mysql> exit
Bye
[root@mysql ~]# 

3、从库恢复主库数据

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@client ~]# mysql -uroot -predhat < /opt/all-202408061001.sql 
mysql: [Warning] Using a password on the command line interface can be insecure.
[root@client ~]# mysql -uroot -predhat
mysql: [Warning] Using a password on the command line interface can be insecure.

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| shiqian            |
| sys                |
+--------------------+
5 rows in set (0.00 sec)
mysql> use shiqian;
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_shiqian |
+-------------------+
| sq                |
+-------------------+
1 row in set (0.00 sec)

mysql> select * from sq;
+----+-------+------+
| id | name  | age  |
+----+-------+------+
|  1 | tom   |   18 |
|  2 | marry |   19 |
|  3 | rose  |   20 |
|  4 | mike  |   19 |
+----+-------+------+
4 rows in set (0.00 sec)

4、配置主库

创建同步用户

主库创建一个同步账号给从库使用

//创建同步用户
mysql> create user 'repl'@'192.168.100.112' identified by 'redhat';
Query OK, 0 rows affected (0.00 sec)

//给同步用户授权
mysql> grant replication slave on *.* to 'repl'@'192.168.100.112';
Query OK, 0 rows affected (0.00 sec)

//刷新权限
mysql> flush privileges;
Query OK, 0 rows affected (0.01 sec)

修改主库配置文件

[root@mysql ~]# vim /etc/my.cnf
//在末尾写入以下内容
log-bin=mysql-bin
server-id=1
symbolic-links=0
log-error=/var/log/mysqld.log
//第一个是启用binlog日志
//第二个是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@mysql ~]# systemctl restart mysqld
[root@mysql ~]# ss -antl
//查看端口情况
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            80                             *:3306                        *:*                        
[root@mysql ~]# mysql -uroot -predhat
mysql: [Warning] Using a password on the command line interface can be insecure.

//查看主库状态
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)

5、配置从库

修改从库配置文件

[root@client ~]# vim /etc/my.cnf
//在末尾写入
server-id=2
relay-log=mysql-relay-bin
symbolic-links=0symbolic-links=0
log-error = /var/log/mysqld.log

重启mysql服务

[root@client ~]# systemctl restart mysqld
[root@client ~]# ss -anlt
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            80                             *:3306                        *:*                       

6、启动主从配置

从库配置

[root@client ~]# mysql -uroot -predhat
mysql: [Warning] Using a password on the command line interface can be insecure.

mysql> change master to master_host='192.168.100.111',
    -> master_user='repl',
    -> master_password='redhat',
    -> master_log_file='mysql-bin.000002',
    -> 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)

mysql> show slave status \G;
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 192.168.100.111
                  Master_User: repl
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000002
          Read_Master_Log_Pos: 364
               Relay_Log_File: mysql-relay-bin.000003
                Relay_Log_Pos: 320
        Relay_Master_Log_File: mysql-bin.000002
             Slave_IO_Running: Yes
            Slave_SQL_Running: 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: 364
              Relay_Log_Space: 527
              Until_Condition: None
               Until_Log_File: 
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_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: No
                Last_IO_Errno: 0
                Last_IO_Error: 
               Last_SQL_Errno: 0
               Last_SQL_Error: 
  Replicate_Ignore_Server_Ids: 
             Master_Server_Id: 1
                  Master_UUID: dcf64bad-4e4d-11ef-a5b1-000c29d1dcca
             Master_Info_File: /opt/data/master.info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: Slave has read all relay log; waiting for more updates
           Master_Retry_Count: 86400
                  Master_Bind: 
      Last_IO_Error_Timestamp: 
     Last_SQL_Error_Timestamp: 
               Master_SSL_Crl: 
           Master_SSL_Crlpath: 
           Retrieved_Gtid_Set: 
            Executed_Gtid_Set: 
                Auto_Position: 0
         Replicate_Rewrite_DB: 
                 Channel_Name: 
           Master_TLS_Version: 
1 row in set (0.00 sec)

ERROR: 
No query specified

一定要确保 Slave_IO_Running: Yes
Slave_SQL_Running: Yes
全部为yes，这样主从才配置完成

7、验证

在主库添加信息

mysql> select * from sq;
+----+-------+------+
| id | name  | age  |
+----+-------+------+
|  1 | tom   |   18 |
|  2 | marry |   19 |
|  3 | rose  |   20 |
|  4 | mike  |   19 |
+----+-------+------+
4 rows in set (0.00 sec)

mysql> insert into sq values(5,'zhangsan',18),(6,'lisi',20),(7,'wangwu',18);
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from sq;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  1 | tom      |   18 |
|  2 | marry    |   19 |
|  3 | rose     |   20 |
|  4 | mike     |   19 |
|  5 | zhangsan |   18 |
|  6 | lisi     |   20 |
|  7 | wangwu   |   18 |
+----+----------+------+
7 rows in set (0.00 sec)

查看从库信息

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| shiqian            |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

mysql> use shiqian;
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> select * from sq;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  1 | tom      |   18 |
|  2 | marry    |   19 |
|  3 | rose     |   20 |
|  4 | mike     |   19 |
|  5 | zhangsan |   18 |
|  6 | lisi     |   20 |
|  7 | wangwu   |   18 |
+----+----------+------+
7 rows in set (0.00 sec)