分享程序员开发的那些事...
更新时间：2022-09-27 14:09:50
一、简介
在实际生产中，数据的重要性不言而喻，因此考虑到数据的重要性比如单点故障导致后端数据库奔溃，或者后端数据库访问压力过大等，mysql数据库做主从非常有必要，减轻后端数据库压力，主服务器负责读写，从服务器只负责读，这样一来即保证了数据的可靠性，同时提高服务器的高可用。
MySQL主从复制架构如图：
MySQL主从复制原理：master服务器将数据的改变记录二进制日志，当master上的数据发生改变时，则将其改变写入二进制日志中，salve服务器会在一定时间间隔内对master二进制日志进行探测其是否发生改变，如果发生改变，则开始一个I/OThread请求master二进制事件，同时主节点为每个I/O线程启动一个dump线程，用于向其发送二进制事件，并保存至从节点本地的中继日志中，从节点将启动SQL线程从中继日志中读取二进制日志，在本地重放，使得其数据和主节点的保持一致，最后I/OThread和SQLThread将进入睡眠状态，等待下一次被唤醒。
二、主从复制配置实现
要求：
1、双方mysql版本需一致，如不一致，只要主节点低于从节点
2、两节点间时间需同步
配置：
主服务器配置如下：
1、修改/etc/my.cnf配置文件
log-bin=/mydata/data/binlogs/master-bin
2、创建此目录并修改属组属主为mysql
mkdir /mydata/binlogs/
chown -R mysql.mysql /mydata/binlogs/
3、授权用户
grant replication slave,replication client on *.* to 'repluser'@'10.1.10.%' identified by 'pass';
flush privileges;
从服务器配置如下：
1、修改/etc/my.cnf配置文件，注释二进制日志，开启中继日志，修改server-id和主节点不一致
server-id=11
relay-log=/mydata/relaylogs/relay-bin
2、创建其目录并授予此目录的属主、属组为mysql
mkdir /mydata/relaylogs/
chown -R mysql.mysql /mydata/relaylogs/
3、连接主服务器
change master to master_host='10.1.10.1',master_user='repluser',master_password='pass';
完成上诉配置过程即可各自启动mysql服务器，且在从服务器上启动I/O,SQL线程，例如：start slave
测试两数据可数据是否能同步，则可在主库上插入数据在从库上查看是否存在，注意：从库只能读，而不能写
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[root@centos6 ~]# mysql
Welcome to the MariaDB monitor. Commands end with ; or \g.Your MariaDB connection id is 13
Server version: 5.5.32-MariaDB MariaDB ServerCopyright (c) 2000, 2013, Oracle, Monty Program Ab and others.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]> show slave status\G;*************************** 1. row *************************** Slave_IO_State: Waiting for master to send event
Master_Host: 10.1.10.1
Master_User: repluser
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: master-bin.000003
Read_Master_Log_Pos: 326
Relay_Log_File: relay-bin.000007
Relay_Log_Pos: 611
Relay_Master_Log_File: master-bin.000003
Slave_IO_Running: Yes #确保I/O和SQL线程开启，即可实现数据同步
Slave_SQL_Running: Yes #确保I/O和SQL线程开启，即可实现数据同步
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: 326
Relay_Log_Space: 1184
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
1 row in set (0.00 sec)
ERROR: No query specifiedMariaDB [(none)]> #测试在主库上删除dbs,验证从库是否存在dbs数据库，结果如下：
MariaDB [(none)]> show databases;+--------------------+| Database |+--------------------+| information_schema || dbs || hellodb || mydbs || mysql || performance_schema || test |
+--------------------+7 rows in set (0.01 sec)
MariaDB [(none)]> show databases;+--------------------+| Database |+--------------------+| information_schema || hellodb || mydbs || mysql || performance_schema || test |
+--------------------+6 rows in set (0.00 sec)
MariaDB [(none)]>[root@centos6 ~]# mysql
Welcome to the MariaDB monitor. Commands end with ; or \g.Your MariaDB connection id is 14
Server version: 5.5.32-MariaDB-log MariaDB ServerCopyright (c) 2000, 2013, Oracle, Monty Program Ab and others.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]>MariaDB [(none)]> show databases;+--------------------+| Database |+--------------------+| information_schema || dbs || hellodb || mydbs || mysql || performance_schema || test |
+--------------------+7 rows in set (0.02 sec)
MariaDB [(none)]> drop database dbs;Query OK, 0 rows affected (0.04 sec)MariaDB [(none)]> |
三、实战：主从不同步时，如何进行数据同步至一致
描述：当主服务器已经运行一段时间，并且存在不小的数据时，则需把主服务器备份，然后在从服务器恢复，从备份时所在的位置开始复制。
1、将主服务器上的数据做完全备份
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[root@centos6 ~]# mysqldump --lock-all-tables --all-databases --flush-logs --master-data=2 >/root/all.sql
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2、在从服务器上导入主服务上的完全备份，在导入时关闭I/O和SQL线程
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[root@centos6 ~]# mysql
Welcome to the MariaDB monitor. Commands end with ; or \g.Your MariaDB connection id is 34
Server version: 5.5.32-MariaDB MariaDB ServerCopyright (c) 2000, 2013, Oracle, Monty Program Ab and others.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]> source /root/alren.sql
MariaDB [testdbs]> change master to master_host='10.1.10.1',master_user='repluser',master_password='pass',MASTER_LOG_FILE='master-bin.000007',MASTER_LOG_POS=245;
Query OK, 0 rows affected (0.02 sec)MariaDB [testdbs]> start slave;Query OK, 0 rows affected (0.02 sec)MariaDB [testdbs]> show slave status\G*************************** 1. row *************************** Slave_IO_State: Waiting for master to send event
Master_Host: 10.1.10.1
Master_User: repluser
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: master-bin.000007 #已经恢复到主节点的二进制的位置
Read_Master_Log_Pos: 245
Relay_Log_File: relay-bin.000002
Relay_Log_Pos: 530
Relay_Master_Log_File: master-bin.000007
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: 245
Relay_Log_Space: 818
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
1 row in set (0.00 sec)
MariaDB [testdbs]> show tables;+-------------------+| Tables_in_testdbs |+-------------------+| tbl |+-------------------+1 row in set (0.00 sec)
MariaDB [testdbs]> select * from tbl;
+-------+| name |+-------+| tom || jerry || lucy |+-------+3 rows in set (0.00 sec)
MariaDB [testdbs]> use mydbs;Database changedMariaDB [mydbs]> show tables; #测试数据是否和主节点一致
+-----------------+| Tables_in_mydbs |+-----------------+| students |+-----------------+1 row in set (0.00 sec)
MariaDB [mydbs]> select * from students;
+------+-------+| id | name |
+------+-------+| 1 | tom || 2 | jerry |+------+-------+2 rows in set (0.00 sec)
MariaDB [mydbs]> |
总结：此实战中最为关键主要有两步①主服务器上锁表做完全备份，并滚动日志，②从服务器上进行半道恢复.
本文转自chengong1013 51CTO博客，原文链接：http://blog.51cto.com/purify/1876048，如需转载请自行联系原作者
