案例：推进GTID解决MySQL主主不同步问题
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之前文章介绍过mysql修改lower_case_table_names参数，如果之前大写存储的表将无法识别，需要特殊处理。
最近遇到一例应用开发人员在修改这个参数之后，为了清除之前大写存储的表，做了误操作，导致主主不同步。
1.故障现象模拟
在lower_case_table_names=0时创建了测试库test和表TT：root@mysqldb 22:43: [(none)]> create database test;
Query OK, 1 row affected (0.01 sec)
root@mysqldb 22:43: [(none)]> use test;
Database changed
root@mysqldb 22:43: [test]> create table TT(id int);
Query OK, 0 rows affected (0.07 sec)
root@mysqldb 22:43: [test]> show tables;
+----------------+
| Tables_in_test |
+----------------+
| TT |
+----------------+
1 row in set (0.00 sec)
在修改lower_case_table_names=1时删除TT不成功：
root@mysqldb 22:27: [test]> drop table TT;
ERROR 1051 (42S02): Unknown table ‘test.tt‘
此时误操作来了。。据这样操作的人员反馈，是直接在网络搜索到这个错误就是要到OS层面去删除表的文件，然后就做了
我这里也按照这个误操作在测试环境来模拟下：
[root@test01 test]# rm TT.*
rm: remove regular file `TT.frm‘? y
rm: remove regular file `TT.ibd‘? y
而且后续根据故障现象推测：操作人员最初只在一个主节点做了这样的操作，随后在这个主节点执行了删除数据库的动作，最后又建立了新的数据库重新建表，最终才发现另一个主节点已经不同步了，尝试自己无法解决后，上报了故障给客户DBA。
此刻现象就是：Master1 删除数据库成功后，但Master2 同步报错1010，内容是删除数据库发生错误，具体如下：
root@mysqldb 23:04: [test]> show slave statusG
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.1.121
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mybinlog.000013
Read_Master_Log_Pos: 756
Relay_Log_File: test02-relay-bin.000034
Relay_Log_Pos: 532
Relay_Master_Log_File: mybinlog.000013
Slave_IO_Running: Yes
Slave_SQL_Running: No
Replicate_Do_DB:
Replicate_Ignore_DB:
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table:
Replicate_Wild_Ignore_Table:
Last_Errno: 1010
Last_Error: Error ‘Error dropping database (can‘t rmdir ‘./test‘, errno: 39)‘ on query. Default database: ‘test‘. Query: ‘drop database test‘
Skip_Counter: 0
Exec_Master_Log_Pos: 601
Relay_Log_Space: 1060
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: NULL
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 1010
Last_SQL_Error: Error ‘Error dropping database (can‘t rmdir ‘./test‘, errno: 39)‘ on query. Default database: ‘test‘. Query: ‘drop database test‘
Replicate_Ignore_Server_Ids:
Master_Server_Id: 1121
Master_UUID: 08c887bf-98ab-11ea-b70c-080027c2997a
Master_Info_File: mysql.slave_master_info
SQL_Delay: 0
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State:
Master_Retry_Count: 86400
Master_Bind:
Last_IO_Error_Timestamp:
Last_SQL_Error_Timestamp: 200702 23:04:11
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set: 08c887bf-98ab-11ea-b70c-080027c2997a:549-550
Executed_Gtid_Set: 08c887bf-98ab-11ea-b70c-080027c2997a:5-549,
5d3f3359-98ab-11ea-8101-080027763d24:1-13
Auto_Position: 0
Replicate_Rewrite_DB:
Channel_Name:
Master_TLS_Version:
1 row in set (0.00 sec)
root@mysqldb 23:04: [test]> q
2.推进GTID解决
这时就可以用一个空事物将当前执行报错的GTID（Global Transaction Identifier）给跳过去：set gtid_next=‘$Master_UUID:$gno‘;
begin;
commit;
set gtid_next=automatic;
start slave;
这里实际就是选取Master_UUID: 08c887bf-98ab-11ea-b70c-080027c2997a和gno：550（因为Executed_Gtid_Set最后是549，当前报错对应应该是549/550，期望用空事物代替跳过）
注意：这里的gno是连续的。第一次我尝试gtid_next=‘08c887bf-98ab-11ea-b70c-080027c2997a:549‘是不成功的，所以又尝试550:
set gtid_next=‘08c887bf-98ab-11ea-b70c-080027c2997a:550‘;
begin;
commit;
set gtid_next=automatic;
start slave;
这次执行后再次查看slave状态，确认已恢复正常：
root@mysqldb 23:11: [(none)]> set gtid_next=‘08c887bf-98ab-11ea-b70c-080027c2997a:550‘;
Query OK, 0 rows affected (0.00 sec)
root@mysqldb 23:11: [(none)]> begin;
Query OK, 0 rows affected (0.00 sec)
root@mysqldb 23:11: [(none)]> commit;
Query OK, 0 rows affected (0.00 sec)
root@mysqldb 23:11: [(none)]> set gtid_next=automatic;
Query OK, 0 rows affected (0.00 sec)
root@mysqldb 23:11: [(none)]> start slave;
Query OK, 0 rows affected (0.01 sec)
root@mysqldb 23:11: [(none)]> show slave statusG
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.1.121
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mybinlog.000013
Read_Master_Log_Pos: 951
Relay_Log_File: test02-relay-bin.000034
Relay_Log_Pos: 687
Relay_Master_Log_File: mybinlog.000013
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: 951
Relay_Log_Space: 1060
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: 1121
Master_UUID: 08c887bf-98ab-11ea-b70c-080027c2997a
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: 08c887bf-98ab-11ea-b70c-080027c2997a:549-550
Executed_Gtid_Set: 08c887bf-98ab-11ea-b70c-080027c2997a:5-550,
5d3f3359-98ab-11ea-8101-080027763d24:1-14
Auto_Position: 0
Replicate_Rewrite_DB:
Channel_Name:
Master_TLS_Version:
1 row in set (0.00 sec)
root@mysqldb 23:11: [(none)]>
当然Master2遗留的这个test库记得要处理掉，不然以后还会有问题隐患。
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