关于 MySQL GTID 复制
MySQL5.7以后都基本用GTID方式复制了，相对于binlog和position号方式，在failover时候减少很多人工切换操作
GTID，global transaction identitifiers，基于全局事务的复制方式，由server_uuid:transaction_id组成,server_uuid在数据库启动过程生成,在/data/auto.cnf中
复制过程：master事务提交时GTID，记录到binlog；然后master的binlog传送到slave的relaylog,slave读取GTID生成gtid_next系统参数;slave校验GTID是否在binlog并进一步应用事务（5.7后是存放在gtid_executed系统表，这样不用开启log_slave_updates参数，从而不用把relaylog记录再记录到binlog，减少slave压力）
下面操作下：
首先主从都配置gtid_mode、enforce_gtid_consistency参数,其中备库多加个log_slave_updates=1
[root@localhost /usr/local/mysql/data]$ cat /etc/my.cnf
[mysqld]
datadir=/usr/local/mysql/data
log_bin=mysql-bin
server_id=1
gtid_mode=on
enforce_gtid_consistency=on
[root@localhost /usr/local/mysql/data]$
mysql> show variables like '%gtid%';
+----------------------------------+-----------+
| Variable_name | Value |
+----------------------------------+-----------+
| binlog_gtid_simple_recovery | ON |
| enforce_gtid_consistency | ON |
| gtid_executed_compression_period | 1000 |
| gtid_mode | ON |
| gtid_next | AUTOMATIC |
| gtid_owned | |
| gtid_purged | |
| session_track_gtids | OFF |
+----------------------------------+-----------+
8 rows in set (0.00 sec)
mysql>
然后将之前异步复制的配置去掉，重新配置slave中主库信息即可
mysql> show variables like '%log_slave_updates%';
+-------------------+-------+
| Variable_name | Value |
+-------------------+-------+
| log_slave_updates | ON |
+-------------------+-------+
1 row in set (0.00 sec)
mysql> stop slave;
Query OK, 0 rows affected (0.01 sec)
mysql> reset slave all;
Query OK, 0 rows affected (0.02 sec)
mysql> change master to
-> master_host='192.0.1.10',
-> master_user='scott',
-> master_password='tiger',
-> master_port=3306,
-> master_auto_position=1;
Query OK, 0 rows affected, 2 warnings (0.02 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: 192.0.1.10
Master_User: scott
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000004
Read_Master_Log_Pos: 573
Relay_Log_File: localhost-relay-bin.000002
Relay_Log_Pos: 786
Relay_Master_Log_File: mysql-bin.000004
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: 573
Relay_Log_Space: 997
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: 531fa6d1-627f-11e9-8dc7-000c297887a1
Master_Info_File: /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: 531fa6d1-627f-11e9-8dc7-000c297887a1:1-2
Executed_Gtid_Set: 531fa6d1-627f-11e9-8dc7-000c297887a1:1-2
Auto_Position: 1
Replicate_Rewrite_DB:
Channel_Name:
Master_TLS_Version:
1 row in set (0.00 sec)
mysql>
测试一下，ok的，主库状态可以看到
mysql> show master status;
+------------------+----------+--------------+------------------+------------------------------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set |
+------------------+----------+--------------+------------------+------------------------------------------+
| mysql-bin.000004 | 573 | | | 531fa6d1-627f-11e9-8dc7-000c297887a1:1-2 |
+------------------+----------+--------------+------------------+------------------------------------------+
1 row in set (0.00 sec)
mysql>
将slave中log_slave_updates关掉，就能看到mysql.gtid_executed表中记录已执行gtid信息了
mysql> select * from mysql.gtid_executed;
+--------------------------------------+----------------+--------------+
| source_uuid | interval_start | interval_end |
+--------------------------------------+----------------+--------------+
| 531fa6d1-627f-11e9-8dc7-000c297887a1 | 1 | 2 |
| 531fa6d1-627f-11e9-8dc7-000c297887a1 | 3 | 3 |
+--------------------------------------+----------------+--------------+
2 rows in set (0.00 sec)
由于是基于事务的，所以就有了限制条件： create table select的方式在基于行复制的情况下会被拆分为创建表和insert数据两个事件，某些情况下这两个事件会被分配相同GTID导致后面insert数据部分被忽略而产生错误； 一个事务中既包含InnoDB表又包含MyISAM表会导致可能产生多个gtid，或者表在主从库中存储引擎不一致都会产生gtid复制异常