主从架构介绍
mysql自带的副本机制允许从一个mysql数据库（称之为主或者源库）复制一个或多个mysql数据库（称之为从或者副本库）。副本机制默认情况下是异步进行的，不需要永久连接从源库接收更新。副本机制作用的范围可以为所有数据库，选定的数据库或者选定的表。
MySQL 8.0支持不同的两种复制方法：
1）基于从源库的二进制日志（binary log）复制事件实现，并要求在源库和副本库之间同步日志文件和日志文件中的位置，异步实现，不具有事务性。
mysql-replication-based-on-binary-log.png
2）基于全局事务标识符(GTIDs)实现，具有事务性，因此不需要处理日志文件及其位置，这极大地简化了许多常见的复制任务。只要在源库上提交的所有事务也应用于副本库上，使用GTIDs的复制就可以保证源和副本之间的一致性。
主从架构优点
- 可以实现读写分离架构，对主库进行写，对从库进行读，可以工作负载到副本库进而提高整体性能。
- 可以保障数据安全，因为副本可以暂停复制过程，所以可以在副本上运行备份服务，而不会损坏相应的源数据。
- 可以实现数据的备份，实现容灾
基于binary log的主从架构实践
主库设置
首先在在 MySQL 中增加一个可以进行主从复制权限的用户。在 mysql 交互环境中执行如下命令
# mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 14
Server version: 8.0.13 MySQL Community Server - GPL
Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> create user 'repl'@'10.20.131.38' identified by 'Inspur123!@#';
Query OK, 0 rows affected (0.07 sec)
mysql> grant replication slave on *.* to 'repl'@'10.20.131.38';
Query OK, 0 rows affected (0.05 sec)
mysql> show master status;
+---------------+----------+--------------+------------------+-------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+---------------+----------+--------------+------------------+-------------------+
| binlog.000001 | 2324 | | | |
+---------------+----------+--------------+------------------+-------------------+
1 row in set (0.00 sec)
mysql>
命令**show master status **获取到当前归档日志的名字和位置，后面从服务器设置主从复制的时候需要从这个位置开始。
从库设置
# mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 11
Server version: 8.0.13 MySQL Community Server - GPL
Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> change master to
-> master_host='10.20.131.37',
-> master_port=3306,
-> master_user='repl',
-> master_password='Test123!@#',
-> master_log_file='binlog.000001',
-> master_log_pos=2324;
Query OK, 0 rows affected, 2 warnings (0.07 sec)
mysql> start slave;
Query OK, 0 rows affected (0.01 sec)
mysql> show slave status\G;
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 10.20.131.37
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: binlog.000001
Read_Master_Log_Pos: 2324
Relay_Log_File: h10p20p131p38-relay-bin.000002
Relay_Log_Pos: 319
Relay_Master_Log_File: binlog.000001
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: 2324
Relay_Log_Space: 535
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: 37
Master_UUID: 109ae7ea-1d7c-11eb-980d-48f97cff3ddf
Master_Info_File: mysql.slave_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:
Master_public_key_path:
Get_master_public_key: 0
1 row in set (0.00 sec)
ERROR:
No query specified
Slave_IO_State 的值为 Waiting for master to send event ，表示已经准备好接受主库发送过来的归档日志进行处理了。
测试主从复制
主库建立名字为test的database，如下：
mysql> create database test default character set utf8;
Query OK, 1 row affected, 1 warning (0.03 sec)
从库确认是否已经同步备份，如下：
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
| test |
+--------------------+
5 rows in set (0.00 sec)
mysql>
根据以上输出，可以确认主从复制已经生效。
参照
- Chapter 17 Replication