1.mysql主从复制的作用：
（1）实时灾备，用于故障切换
（2) 读写分离，提供查询服务
(3) 备份，避免影响业务
2.主从部署必要条件：
(1) 主库开启binlog日志（设置log-bin参数）
(2) 主从server-id不同
(3)从库服务器能连通主库
3.主从复制实验：
实验环境：mysql-5.7.17-1.el6.x86_64.rpm-bundle.tar
server2:主数据库 master
server4:备数据库 slave
基本的主从复制原理实验
以下操作主、从数据库都需要进行
配置mysql实验环境：
tar xf mysql-5.7.17-1.el6.x86_64.rpm-bundle.tar
yum install mysql-community-client-5.7.17-1.el6.x86_64.rpm
mysql-community-common-5.7.17-1.el6.x86_64.rpm
mysql-community-libs-5.7.17-1.el6.x86_64.rpm
mysql-community-libs-compat-5.7.17-1.el6.x86_64.rpm
mysql-community-server-5.7.17-1.el6.x86_64.rpmvim /etc/my.cnf
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid
server-id=1 #和slave的id保持不同
log-bin=mysql-bin
/etc/init/mysqld start
[root@server2 ~]# grep password /var/log/mysqld.log
2018-08-08T08:43:04.408394Z 1 [Note] A temporary password is generated for root@localhost: yYaBEaJ9cC #这里是数据库的密码
2018-08-08T08:43:44.183933Z 0 [Note] Execution of init_file '/var/lib/mysql/install-validate-password-plugin.tvhQPf.sql' started.
[root@server2 ~]# mysql_secure_installation #数据库初始化
Securing the MySQL server deployment.
Enter password for user root:
The existing password for the user account root has expired. Please set a new password. #这里的密码必须由大小写字母、数字、特殊字符组成不小于8位的密码
New password:
Re-enter new password:
The 'validate_password' plugin is installed on the server.
The subsequent steps will run with the existing configuration
of the plugin.
Using existing password for root.
Estimated strength of the password: 100
Change the password for root ? ((Press y|Y for Yes, any other key for No) : n
... skipping.
By default, a MySQL installation has an anonymous user,
allowing anyone to log into MySQL without having to have
a user account created for them. This is intended only for
testing, and to make the installation go a bit smoother.
You should remove them before moving into a production
environment.
Remove anonymous users? (Press y|Y for Yes, any other key for No) : y
Success.
Normally, root should only be allowed to connect from
'localhost'. This ensures that someone cannot guess at
the root password from the network.
Disallow root login remotely? (Press y|Y for Yes, any other key for No) : y
Success.
By default, MySQL comes with a database named 'test' that
anyone can access. This is also intended only for testing,
and should be removed before moving into a production
environment.
Remove test database and access to it? (Press y|Y for Yes, any other key for No) : n
... skipping.
Reloading the privilege tables will ensure that all changes
made so far will take effect immediately.
Reload privilege tables now? (Press y|Y for Yes, any other key for No) : y
Success.
All done! master数据库的操作
mysql> grant replication slave on *.* to lily@'172.25.23.%' identified by 'WN123*westos';
Query OK, 0 rows affected, 1 warning (0.06 sec)
mysql> show master status;
+------------------+----------+--------------+------------------+-------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+-------------------+
| mysql-bin.000003 | 843 | | | |
+------------------+----------+--------------+------------------+-------------------+
1 row in set (0.00 sec)创建数据库
mysql> create database test;
Query OK, 1 row affected (0.36 sec)
mysql> use test;
Database changed
mysql> create table userlist(
-> username varchar(15) not null,
-> password varchar(25) not null);
Query OK, 0 rows affected (0.72 sec)
从数据库：
注意：这里必须指定日志和号码，master_log_file=’mysql-bin.000005’,master_log_pos=194，和gtid不同的是，gtid是动态查找，无需指定
change master to master_host='172.25.23.2',master_user='lily',master_password='WN123*westos',master_log_file='mysql-bin.000003',master_log_pos=843;
show slave status\G;#查看状态
mysql> show slave status\G;
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 172.25.23.2
Master_User: lily
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000005
Read_Master_Log_Pos: 194
Relay_Log_File: server4-relay-bin.000004
Relay_Log_Pos: 407
Relay_Master_Log_File: mysql-bin.000005
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: 194
use test;
select * from userlist;#和主数据库保持一致
基于Gtid的mysql主从复制
在之前的实验环境进行操作：
主、从 mysql 操作
vim /etc/my.conf
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid
server-id=1
log-bin=mysql-bin
gtid_mode=ON
enforce-gtid-consistency=true
/etc/init.d/mysql restart此时主服务器在test库的userlist表中已有三组数据，具体情况查看上方操作
从服务器：
mysql> stop slave;
Query OK, 0 rows affected (0.35 sec)
mysql>
mysql> change master to master_host='172.25.23.2',master_user='lily',master_password='WN123*westos',MASTER_AUTO_POSITION = 1;
Query OK, 0 rows affected, 2 warnings (0.51 sec)
mysql> start slave;
Query OK, 0 rows affected (0.33 sec)
mysql> show slave status\G;
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 172.25.23.2
Master_User: lily
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000005
Read_Master_Log_Pos: 194
Relay_Log_File: server4-relay-bin.000002
Relay_Log_Pos: 367
Relay_Master_Log_File: mysql-bin.000005
Slave_IO_Running: Yes #这里保证开启
Slave_SQL_Running: Yes # 这里保证开启
主数据库：对数据库信息进行更改，然后从数据库进行验证
mysql> use test;
Database changed
mysql> select * from userlist;
+----------+----------+
| username | password |
+----------+----------+
| user2 | 234 |
| user3 | 567 |
| user1 | 123 |
+----------+----------+
3 rows in set (0.00 sec)
#对数据进行删除，然后在从数据库看结果
mysql> delete from userlist where username='user1';
Query OK, 1 row affected (0.13 sec)
从数据库验证：
mysql> use test;
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 userlist;
+----------+----------+
| username | password |
+----------+----------+
| user2 | 234 |
| user3 | 567 |
+----------+----------+
2 rows in set (0.00 sec)
mysql>
mysql的半同步复制：
半同步复制简介
何为半同步复制模式呢？在此我们先了解异步复制模式，这是MySQL的默认复制选项。异步复制即是master数据库把binlog日志发送给slave数据库，然后就没有了然后了。在此暴露一个问题，当slave服务器发生故障了，那么肯定会导致主从数据库服务器的数据不一致。
为了解决上面的问题，MySQL5.5引入一种叫做半同步复制模式。开启这种模式，可以保证slave数据库接收完master数据库发送过来的binlog日志并写入自己的中继日志中，然后反馈给master数据库，告知已经复制完毕。
开启这种模式后，当出现超时，主数据库将会自动转为异步复制模式，直到至少有一台从服务器接受到主数据库的binlog，并且反馈给主数据库。这时主数据库才会切换回半同步复制模式。
主数据库
mysql> show variables like 'have_dynamic_loading';
+----------------------+-------+
| Variable_name | Value |
+----------------------+-------+
| have_dynamic_loading | YES |
+----------------------+-------+
1 row in set (0.00 sec)
mysql> install plugin rpl_semi_sync_master soname 'semisync_master.so';
Query OK, 0 rows affected (0.41 sec)
mysql> set global rpl_semi_sync_master_enabled=ON;
Query OK, 0 rows affected (0.00 sec)
mysql> show variables like '%semi%';
+-------------------------------------------+------------+
| Variable_name | Value |
+-------------------------------------------+------------+
| rpl_semi_sync_master_enabled | ON |
| rpl_semi_sync_master_timeout | 10000 |
| rpl_semi_sync_master_trace_level | 32 |
| rpl_semi_sync_master_wait_for_slave_count | 1 |
| rpl_semi_sync_master_wait_no_slave | ON |
| rpl_semi_sync_master_wait_point | AFTER_SYNC |
+-------------------------------------------+------------+
6 rows in set (0.00 sec)
这里是插件的所在位置，安装数据库5.7版本自带
从服务器：
mysql> install plugin rpl_semi_sync_slave soname 'semisync_slave.so';
Query OK, 0 rows affected (0.13 sec)
mysql> set global rpl_semi_sync_slave_enabled=ON;
Query OK, 0 rows affected (0.00 sec)
mysql> show variables like '%semi%';
+---------------------------------+-------+
| Variable_name | Value |
+---------------------------------+-------+
| rpl_semi_sync_slave_enabled | ON |
| rpl_semi_sync_slave_trace_level | 32 |
+---------------------------------+-------+
2 rows in set (0.00 sec)
测试：
从数据库关闭slave
mysql> stop slave;
Query OK, 0 rows affected (0.06 sec)主数据库进行数据库的操作，这里我们插入数据（此时会暂停大概10秒左右才会成功，因为从数据库关闭，主数据库没有等到响应，所以切换为异步模式，不再继续等待，并且参数也会有所改变）
mysql> insert into userlist values('user1','123');
Query OK, 1 row affected (10.40 sec)
mysql> show status like '%rpl_semi_sync%';
从数据库测试：当开启服务时，主数据库重新接受到返回数据,又切换到半同步模式
mysql> start slave;
Query OK, 0 rows affected (0.34 sec)
mysql> select * from userlist;
+----------+----------+
| username | password |
+----------+----------+
| user2 | 234 |
| user3 | 567 |
| user1 | 123 |
+----------+----------+
3 rows in set (0.00 sec)
mysql> select * from userlist;
+----------+----------+
| username | password |
+----------+----------+
| user2 | 234 |
| user3 | 567 |
+----------+----------+
2 rows in set (0.00 sec)
