Problem description ： hold max_connections and max_user_connections Parameters for analysis and test , seeing the name of a thing one thinks of its function ,max_connections Is the number of connections that are responsible for the global database ,max_user_connections You can limit the maximum number of connections for a single user .
1. Temporary modification max_user_connections Global parameter , When max_user_connections by 0 when , There are no restrictions on all parameters under the database , However, it does not mean that the user under the database has not enabled this parameter
mysql> set global max_user_connections=1;
Query OK, 0 rows affected (0.00 sec)
Open multiple windows to test the connection , The connection fails
[[email protected] ~]# /usr/local/mysql8/bin/mysql -utest01 -p123 -h192.168.163.21 -P33306
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1203 (42000): User test01 already has more than 'max_user_connections' active connections
2. Restrict the connection of a single user
Restart to release the temporarily set parameters
mysql> restart
-> ;
Query OK, 0 rows affected (0.01 sec)
mysql> show variables like '%max_user_conn%';
+----------------------+-------+
| Variable_name | Value |
+----------------------+-------+
| max_user_connections | 0 |
+----------------------+-------+
1 row in set (0.01 sec)
Set connection limits for a single user , The statement given by the official document ,
mysql> CREATE USER 'francis'@'localhost' IDENTIFIED BY 'frank'
-> WITH MAX_QUERIES_PER_HOUR 20
-> MAX_UPDATES_PER_HOUR 10
-> MAX_CONNECTIONS_PER_HOUR 5
-> MAX_USER_CONNECTIONS 2;
Conduct user connection test , You will see the prompt that the maximum number of connections is 3 when , The connection fails
[[email protected] ~]# /usr/local/mysql8/bin/mysql -ufrancis -pfrank -S /data/mysql8/db_dxpt08/mysql.sock
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1226 (42000): User 'francis' has exceeded the 'max_user_connections' resource (current value: 3)
Users who successfully test view the current connection information , The maximum number of user connections that can be seen by connected users here is 2, however root Observed global max_user_connections still 0
mysql> show variables like '%max_user_connections%';
+----------------------+-------+
| Variable_name | Value |
+----------------------+-------+
| max_user_connections | 2 |
+----------------------+-------+
1 row in set (0.00 sec)
3. If you want to see where the modified parameters are set , Need user See these in the table
mysql> select * from user where user='francis'\G
*************************** 1. row ***************************
Host: localhost
User: francis
Select_priv: N
Insert_priv: N
Update_priv: N
Delete_priv: N
Create_priv: N
Drop_priv: N
Reload_priv: N
Shutdown_priv: N
Process_priv: N
File_priv: N
Grant_priv: N
References_priv: N
Index_priv: N
Alter_priv: N
Show_db_priv: N
Super_priv: N
Create_tmp_table_priv: N
Lock_tables_priv: N
Execute_priv: N
Repl_slave_priv: N
Repl_client_priv: N
Create_view_priv: N
Show_view_priv: N
Create_routine_priv: N
Alter_routine_priv: N
Create_user_priv: N
Event_priv: N
Trigger_priv: N
Create_tablespace_priv: N
ssl_type:
ssl_cipher: 0x
x509_issuer: 0x
x509_subject: 0x
max_questions: 20
max_updates: 10
max_connections: 5
max_user_connections: 2
plugin: mysql_native_password
authentication_string: *63DAA25989C7E01EB96570FA4DBE154711BEB361
password_expired: N
password_last_changed: 2022-06-13 10:46:16
password_lifetime: NULL
account_locked: N
Create_role_priv: N
Drop_role_priv: N
Password_reuse_history: NULL
Password_reuse_time: NULL
Password_require_current: NULL
User_attributes: NULL
1 row in set (0.01 sec)
4. Two official amendments are attached max_user_connections The way
mysql> CREATE USER 'francis'@'localhost' IDENTIFIED BY 'frank'
-> WITH MAX_QUERIES_PER_HOUR 20
-> MAX_UPDATES_PER_HOUR 10
-> MAX_CONNECTIONS_PER_HOUR 5
-> MAX_USER_CONNECTIONS 2; mysql> ALTER USER 'francis'@'localhost' WITH MAX_QUERIES_PER_HOUR 100;
mysql> ALTER USER 'francis'@'localhost' WITH MAX_QUERIES_PER_HOUR 100;
5. Conclusion
1.max_connections You can manage the global maximum number of connections .
2.max_user_connections Responsible for limiting the maximum number of connections per user , The number of settings cannot exceed max_connections.max_user_connections When opening global variables , Will affect all users , Except that... Is set separately max_user_connections All users of the parameter .
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