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

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