Technology sharing | gtid that needs to be configured carefully_ mode

author ： Wang Yarong

DBA, be responsible for MySQL Daily problem handling and DMP Product maintenance .

In this paper, the source ： Original contribution

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Background information ：

This article is related to the problems found in a daily operation and maintenance process . Questions as follows ：

The customer takes over the database for backup , An error has occurred ：

 error : manual backup error: rpc error: code = Unknown desc = task(manual_backup_manual_mysql-2db0mi_2022_07_09_22_30_33_mysql-2db0mi_2022_07_09_22_30_33) is failed,
 reason is parse last gtid from file(/dmp/mysql/backup/3306/backup-616678719/tmp/backup.log) failed\n\n Rollback log :\n\t

analysis ：

Because the error is caused by parsing the last one from the file gtid Failure , So check first gtid Parameters

In the database gtid Parameters ：gtid_mode=OFF_PERMISSIVE（ The database was restarted after taking over ）

Check the configuration file gtid_mode The relevant information is

Inquire relevant information through the official website , hear gtid_mode Yes 4 It's worth ：OFF;OFF_PERMISSIVE;ON_PERMISSIVE;ON

In this configuration , The platform cannot start the slave high availability configuration , Copying from the library will report an error ：

            Slave_IO_Running: No
            Slave_SQL_Running: Yes
......
                Last_IO_Errno: 1593
                Last_IO_Error: The replication receiver thread cannot start in AUTO_POSITION mode: the master has GTID_MODE = OFF_PERMISSIVE instead of ON.
               Last_SQL_Errno: 0
               Last_SQL_Error:

And the database at this time cannot be backed up

Local testing ：

1） Set the database configuration file's gtid_mode It is amended as follows =1, And restart the database

2） After restart, log in to the database to view gtid_mode Parameter values , Found after restart gtid_mode=OFF_PERMISSIVE

3） Set the database configuration file's gtid_mode It is amended as follows =ON, And restart the database

4) After restart, log in to the database to view gtid_mode Parameter values , Found after restart gtid_mode=ON

It can be concluded that ：gtid_mode = 1 The effect is not equal to gtid_mode = ON, It's equal to gtid_mode = OFF_PERMISSIVE

because gtid_mode The type of parameter is Enumeration, So variables have aliases of multiple values

gtid_mode Variable	The configuration file can write values
OFF	0
OFF_PERMISSIVE	1
ON_PERMISSIVE	2
ON	3

mysql> show variables like "gtid_mode";
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| gtid_mode     | OFF   |
+---------------+-------+
1 row in set (0.01 sec)
 
mysql> set global gtid_mode=0;
Query OK, 0 rows affected (0.00 sec)
 
mysql> show variables like "gtid_mode";
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| gtid_mode     | OFF   |
+---------------+-------+
1 row in set (0.00 sec)
 
mysql> set global gtid_mode=1;
Query OK, 0 rows affected (0.00 sec)
 
mysql> show variables like "gtid_mode";
+---------------+----------------+
| Variable_name | Value          |
+---------------+----------------+
| gtid_mode     | OFF_PERMISSIVE |
+---------------+----------------+
1 row in set (0.01 sec)
 
mysql> set global gtid_mode=2;
Query OK, 0 rows affected (0.01 sec)
 
mysql> show variables like "gtid_mode";
+---------------+---------------+
| Variable_name | Value         |
+---------------+---------------+
| gtid_mode     | ON_PERMISSIVE |
+---------------+---------------+
1 row in set (0.00 sec)
 
mysql> set global gtid_mode=3;
Query OK, 0 rows affected (0.01 sec)
 
mysql> show variables like "gtid_mode";
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| gtid_mode     | ON    |
+---------------+-------+
1 row in set (0.00 sec)

resolvent :

In the configuration file gtid_mode = 1 Change it to gtid_mode = ON

Enter... In the database

mysql> set global GTID_MODE = ON_PERMISSIVE;
Query OK, 0 rows affected (0.02 sec)
  
// Execute the following commands on the master and slave nodes , Check whether anonymous transactions are consumed , It's best to check more times , To confirm that the value of this parameter is 0
mysql> SHOW STATUS LIKE 'ONGOING_ANONYMOUS_TRANSACTION_COUNT';
+-------------------------------------+-------+
| Variable_name                       | Value |
+-------------------------------------+-------+
| Ongoing_anonymous_transaction_count | 0     |
+-------------------------------------+-------+
1 row in set (0.00 sec)
 
 
mysql> set global GTID_MODE = ON;
Query OK, 0 rows affected (0.02 sec)

After modification, the database can be successfully backed up

summary ：

In daily operation and maintenance , We are used to setting it to ON The parameter of is written as =1, however gtid_mode=1 But not will gtid_mode Set to ON

So be sure to write gtid_mode=ON, perhaps gtid_mode=3

Reference resources ：

https://dev.mysql.com/doc/mysql-replication-excerpt/8.0/en/replication-options-gtids.html#sysvar_gtid_mode

https://dev.mysql.com/doc/mysql-replication-excerpt/8.0/en/replication-mode-change-online-enable-gtids.html