一 GTID的介绍
GTID是一个基于原始mysql服务器生成的一个已经被成功执行的全局事务ID，它由服务器ID以及事务ID组合而成。这个全局事务ID不仅仅在原始服务器器上唯一，在所有存在主从关系 的mysql服务器上也是唯一的。正是因为这样一个特性使得mysql的主从复制变得更加简单，以及数据库一致性更可靠。
二 GTID工作原理
1、当一个事务在主库端执行并提交时，产生GTID，一同记录到binlog日志中。
2、binlog传输到slave,并存储到slave的relaylog后，读取这个GTID的这个值设置gtid_next变量，即告诉Slave，下一个要执行的GTID值。
3、sql线程从relay log中获取GTID，然后对比slave端的binlog是否有该GTID。
4、如果有记录，说明该GTID的事务已经执行，slave会忽略。
5、如果没有记录，slave就会执行该GTID事务，并记录该GTID到自身的binlog，
在读取执行事务前会先检查其他session持有该GTID，确保不被重复执行。
6、在解析过程中会判断是否有主键，如果没有就用二级索引，如果没有就用全部扫描。
三 配置实验
主服务器 server3 172.25.55.3
副服务器 server4 172.25.55.4
解压mysql软件包
server3 和 server4 做同样的配置
[root@server3 ~]# yum install -y *.rpm
编写配置文件 vim my.conf
在主服务器server3中
# For advice on how to change settings please see
# http://dev.mysql.com/doc/refman/5.7/en/server-configuration-defaults.html
[mysqld]
#
# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
# innodb_buffer_pool_size = 128M
#
# Remove leading # to turn on a very important data integrity option: logging
# changes to the binary log between backups.
# log_bin
#
# Remove leading # to set options mainly useful for reporting servers.
# The server defaults are faster for transactions and fast SELECTs.
# Adjust sizes as needed, experiment to find the optimal values.
# join_buffer_size = 128M
# sort_buffer_size = 2M
# read_rnd_buffer_size = 2M
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
user=mysql
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
#server-id
server-id=199
#binary log
log-bin=mysql-bin
#statement row mixed
binlog-format=mixed
[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid
在主服务器server4中
# For advice on how to change settings please see
# http://dev.mysql.com/doc/refman/5.7/en/server-configuration-defaults.html
[mysqld]
#
# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
# innodb_buffer_pool_size = 128M
#
# Remove leading # to turn on a very important data integrity option: logging
# changes to the binary log between backups.
# log_bin
#
# Remove leading # to set options mainly useful for reporting servers.
# The server defaults are faster for transactions and fast SELECTs.
# Adjust sizes as needed, experiment to find the optimal values.
# join_buffer_size = 128M
# sort_buffer_size = 2M
# read_rnd_buffer_size = 2M
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
user=mysql
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
#server-id
server-id=200
#relay-log
relay-log=mysql-relay
[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid
一起重启mysql数据库
/etc/init.d/mysqld restart
1.数据库的配置
安装数据库
/etc/init.d/mysqld start
修改密码：
grep password /var/log/mysqld.log
查看那数据库的临时密码
mysql -p 登陆数据库的修改密码
Enter password:
mysql> show databases;
mysql> ALTER USER root@localhost identified by ‘Redhat+007’;
添加本地数据库用户
mysql> show databases;
mysql> select * from mysql.user\G;
检查数据库
[root@server3 ~]# mysql -p
mysql> show databases;可以在从数据库端进行测试:
mysql -uwax -pRedhat+007 -h 172.25.55.1
mysql> show master status;+------------------+----------+--------------+------------------+-------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+-------------------+
| mysql-bin.000001 | 833 | test | mysql | |
+------------------+----------+--------------+------------------+-------------------+mysql-bin.000001 是二进制日志文件
833 是结束的位置
扫描二维码关注公众号，回复：
2720892 查看本文章
在从数据库上
[root@server3 ~]# mysql -p
Enter password:
mysql> show slave status;
mysql> change master to master_host=’172.25.55.1’,master_user=’wax’, master_password=’Redhat+007’, master_log_file=’mysql-bin.000001’, master_log_pos=833;
mysql> start slave;
mysql> show slave status;
mysql> show slave status\G; Relay_Log_Pos: 638
Relay_Master_Log_File: mysql-bin.000001
Slave_IO_Running: Yes
Slave_SQL_Running: Yes测试：
在主数据库上
mysql> create database test;
mysql> use test;
Database changed
mysql> create table usertb (
-> username varchar(15) not null ,
-> password varchar(25) not null );
mysql> insert into usertb values (“user1”,”123”);
mysql> insert into usertb values (“user2”,”123”);
mysql> select * from usertb ;
mysql> update usertb set password=’333’ where username=’user2’;
mysql> select * from usertb ;
从数据库
[root@server3 ~]# mysql -p
mysql> show databases;
mysql> use test;
mysql> select * from usertb;
mysql> quit四、半同步复制
修改配置文件：/etc/my.cnf
## 主（server4）：
[mysqld]
server-id=4
log-bin=mysql-bin
gtid_mode=ON
enforce-gtid-consistency=true
## 从（server5）：
[mysqld]
server-id=5
gtid_mode=ON
enforce-gtid-consistency=true连接成功（即基于gtid的主从复制搭建成功）后关闭slave
mysql> show slave status\G;
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 172.25.55.4
Master_User: server4
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000006
Read_Master_Log_Pos: 860
Relay_Log_File: server5-relay-bin.0000011
Relay_Log_Pos: 320
Relay_Master_Log_File: mysql-bin.000006
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: 860
Relay_Log_Space: 529
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: 4
Master_UUID: 38eaae01-7ec6-11e8-8ddb-525400cbb7a9
Master_Info_File: /var/lib/mysql/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)
mysql> stop slave;
Query OK, 0 rows affected (0.07 sec)主库端加载mater模块：
mysql> install plugin rpl_semi_sync_slave soname 'semisync_slave.so';
Query OK, 0 rows affected (0.05 sec)
mysql> set global rpl_semi_sync_master_enabled=1;
Query OK, 0 rows affected (0.00 sec)从库端配置
mysql> install plugin rpl_semi_sync_slave soname 'semisync_slave.so';
Query OK, 0 rows affected (0.04 sec)
## 启动半同步复制,也可写到配置文件中
mysql> set global rpl_semi_sync_slave_enabled=1;
Query OK, 0 rows affected (0.00 sec)
## 重启从上的IO线程,如果没有重启，则默认还是异步复制，重启后，slave会在master上注册为半同步复制的slave角色。
mysql> stop slave io_thread;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> start slave io_thread;
Query OK, 0 rows affected (0.00 sec)主库端查看配置情况
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 |
| rpl_semi_sync_slave_enabled | OFF |
| rpl_semi_sync_slave_trace_level | 32 |
+-------------------------------------------+------------+
8 rows in set (0.00 sec)
rpl_semi_sync_master_wait_for_slave_count
MySQL 5.7.3引入的，该变量设置主需要等待多少个slave应答，才能返回给客户端，默认为1。
rpl_semi_sync_master_wait_no_slave
ON
默认值，当状态变量Rpl_semi_sync_master_clients中的值小于rpl_semi_sync_master_wait_for_slave_count时，Rpl_semi_sync_master_status依旧显示为ON。
OFF
当状态变量Rpl_semi_sync_master_clients中的值于rpl_semi_sync_master_wait_for_slave_count时，Rpl_semi_sync_master_status立即显示为OFF，即异步复制。mysql> show status like '%semi%';
+--------------------------------------------+-------+
| Variable_name | Value |
+--------------------------------------------+-------+
| Rpl_semi_sync_master_clients | 1 |
| Rpl_semi_sync_master_net_avg_wait_time | 0 |
| Rpl_semi_sync_master_net_wait_time | 0 |
| Rpl_semi_sync_master_net_waits | 1 |
| Rpl_semi_sync_master_no_times | 0 |
| Rpl_semi_sync_master_no_tx | 0 |
| Rpl_semi_sync_master_status | ON |
| Rpl_semi_sync_master_timefunc_failures | 0 |
| Rpl_semi_sync_master_tx_avg_wait_time | 277 |
| Rpl_semi_sync_master_tx_wait_time | 277 |
| Rpl_semi_sync_master_tx_waits | 1 |
| Rpl_semi_sync_master_wait_pos_backtraverse | 0 |
| Rpl_semi_sync_master_wait_sessions | 0 |
| Rpl_semi_sync_master_yes_tx | 1 |
| Rpl_semi_sync_slave_status | OFF |
+--------------------------------------------+-------+
15 rows in set (0.00 sec)
Rpl_semi_sync_master_clients
当前半同步复制从的个数，如果是一主多从的架构，并不包含异步复制从的个数。
查看半同步是否在运行
## 主：
mysql> show status like 'Rpl_semi_sync_master_status';
+-----------------------------+-------+
| Variable_name | Value |
+-----------------------------+-------+
| Rpl_semi_sync_master_status | ON |
+-----------------------------+-------+
1 row in set (0.00 sec)
## 从：
mysql> show status like 'Rpl_semi_sync_slave_status';
+----------------------------+-------+
| Variable_name | Value |
+----------------------------+-------+
| Rpl_semi_sync_slave_status | ON |
+----------------------------+-------+
1 row in set (0.00 sec)
这两个变量常用来监控主从是否运行在半同步复制模式下。value为ON，
至此，MySQL半同步复制搭建完毕~从根本上来说，半同步复制并不是严格意义上的半同步复制
当半同步复制发生超时时（由rpl_semi_sync_master_timeout参数控制，单位是毫秒，默认为10000，即10s），会暂时关闭半同步复制，转而使用异步复制。当master dump线程发送完一个事务的所有事件之后，如果在rpl_semi_sync_master_timeout内，收到了从库的响应，则主从又重新恢复为半同步复制。